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Introduction to Dental Research

• First Online: 10 April 2022

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• Fahimeh Tabatabaei 3 &
• Lobat Tayebi 3  

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Research in dentistry includes a wide range of laboratory or clinical studies, animal studies, clinical trials, materials manufacturing, prevention, and more. To select a research topic, you should be aware of the meaning of key concepts in the research literature, be familiar with the different types of research , determine the field of interest, and review the literature. Following the special rules of scientific research would allow you to achieve the research objectives, which are not just optimizing/developing treatments, materials, tools, and techniques but also improving the living conditions.

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Tabatabaei, F., Tayebi, L. (2022). Introduction to Dental Research. In: Research Methods in Dentistry. Springer, Cham. https://doi.org/10.1007/978-3-030-98028-3_1

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by Mary Beth Versaci

June 12, 2022

Original Article

Pathways to dentistry: Researchers move dental profession forward

Contributions have lasting impact on oral health care.

Editor's note: This is the third article in a series that celebrates the diversity of career paths in dentistry and the Association's efforts in supporting dentists' career choices in the profession.

From examining the connections between oral and overall health to evaluating the behavior of materials used in dentistry, researchers ask the questions and do the work to inform how dentists care for their patients every day.

"Dentistry is an amazing profession that has offered so many of us the opportunity to improve patients' lives. It is critical that we continue to evolve and expand our understanding of the diseases and conditions that affect our patients and continue to work to optimize the treatments that they receive," said Mia Geisinger, D.D.S., professor and director of the Advanced Education Program in Periodontology at the University of Alabama at Birmingham School of Dentistry. "My goal in research is always to change the way that we treat patients for the better, and while the pace of scientific discovery may be incremental, we continually strive to improve oral and overall health for all."

The American Dental Association recognizes the importance of research — like Dr. Geisinger's on the impact of periodontal disease and treatment on overall health — to the practice of dentistry. One of its core values is to be a science- and evidence-based organization, a goal that is supported by the ADA Science & Research Institute, which conducts research and produces evidence-based resources for dentists.

"Scientific research is so important to the health and advancement of the dental profession. That's why I'm really proud of the work ADASRI does," said Marcelo Araujo, D.D.S., Ph.D., chief science officer of the ADA and CEO of ADASRI. "At ADASRI, our work runs the gamut of scientific research — everything from basic science, like the creation of novel dental materials, to applied science that tests and refines dental materials, to clinical and translational research that communicates that basic and applied science in a way that is easy to implement chairside. As a whole, the work of ADASRI’s researchers, and really the work of all dental researchers, has a profound impact on improving dentistry."

The ADA also has two scientific journals: The Journal of the American Dental Association and JADA Foundational Science.

"The ADA continues to demonstrate its strong commitment to the health sciences through many avenues, including the dissemination of basic, translational and clinical research through its journals and other media offerings," said Jack L. Ferracane, Ph.D., editor-in-chief of JADA Foundational Science. "It all boils down to creating new and better pathways to oral health, and we all find it exciting and gratifying to play our different roles in the process that links discovery to successful clinical care."

A New Day for Dentistry, a campaign launched by ADA President Cesar R. Sabates, D.D.S., celebrates the ADA’s diverse community of dentists by recognizing their personal differences and the varied career paths they have chosen within the profession.

"Researchers are essential members of the dental workforce," Dr. Sabates said. "Clinicians strive to provide the best care they can to their patients, and researchers provide the evidence they need to make informed decisions. Their work also helps to expand dentistry’s knowledge base, driving innovation and advancement in our profession. The contributions of researchers have a lasting impact on all facets of oral health care."

For dentists who choose to pursue research as part of their career, a natural curiosity is key.

"I was exposed to research and science when I was in high school, and ever since, I was always interested in learning the underlying mechanisms of diseases," said Hatice Hasturk, D.D.S., Ph.D., director of the Center for Clinical and Translational Research and senior member of the staff at the Forsyth Institute. "I believe that without knowing what is really involved in tissues or structures we are working with, we cannot provide an effective and long-lasting solution."

Dr. Hasturk, who won the ADA’s 2020-21 Norton M. Ross Award for Excellence in Clinical Research and serves on the ADA Council on Scientific Affairs, teaches at the Boston University Henry M. Goldman School of Dental Medicine and Harvard School of Dental Medicine and practices once a week as a staff dentist/periodontist at the Forsyth Faculty Associates Clinic. Her research focuses on periodontology and immunology.

Dr. Hasturk's studies have shown that changing the body's response to infections and diseases can reduce the oral disease it is experiencing, provide better stability and lead the body to produce more beneficial molecules that can help improve its defense system against other infections and diseases.

"As a dentist/periodontist, my goal is to provide the best prevention and best treatment to my patients," Dr. Hasturk said. "As a researcher, this goal drives me to better understand health and disease, not only to improve oral health, but also overall health."

For Rajesh Lalla, B.D.S., Ph.D., professor of oral medicine and associate dean for research at the University of Connecticut School of Dental Medicine, his favorite part of being a researcher is the ability to create new knowledge.

"It is extremely satisfying to be able to go through the process of having an idea, designing a study to test that hypothesis and determining what the truth really is," said Dr. Lalla, who studies the oral side effects of radiation therapy and chemotherapy used in the treatment of cancer.

His research team is working to publish results from a multicenter clinical study that enrolled more than 500 patients undergoing radiation therapy for head and neck cancer.

"One of the novel findings is that the radiation treatment led to a striking increase in gingival recession," said Dr. Lalla, who is the immediate past president of the Multinational Association of Supportive Care in Cancer — the first dentist to hold the role. "It was known that these patients tend to get cervical caries after radiation therapy, but the reasons were not clear. Our finding indicates that exposure of the cervical areas of teeth due to gingival recession may explain the increased risk for cervical caries."

At the University of Connecticut, Dr. Lalla developed the dental school’s course on evidence-based decision making, which emphasizes the importance of evidence to the practice of dentistry.

"Dentistry is a scientific profession. The care we provide for our patients must be evidence based," said Dr. Lalla, who won the ADA’s 2020 Evidence-Based Dentistry Accomplished Faculty Award. "Research provides that evidence, so research is the very foundation of our profession."

With a background in engineering, Nathaniel Lawson, D.M.D., Ph.D., performs applied dental materials research at the University of Alabama at Birmingham School of Dentistry, where he is an associate professor, director of the biomaterials residency program and director of the division of biomaterials. He and his team devise testing equipment and protocols to evaluate dental materials to best predict their clinical performance, and they are perhaps most well known for performing wear testing. His lab is currently testing the wear of new 3D-printed materials being developed for dentures, crowns and occlusal guards.

"There are many different types of dental research. Many dentists may think of the incredible scientific work conducted by basic and translational scientists who are working to develop new treatments, materials and drugs to treat dental and oral conditions," said Dr. Lawson, who won the ADA's 2016 John W. Stanford New Investigator Award. "However, there is still research needed to evaluate the materials that are already in clinical use in order to determine the best uses of these materials. This information can help the clinician better perform work in their office."

Dr. Lawson began conducting research when he was applying to dental school at the University of Alabama. After a brief stint in clinical practice following graduation, his dental school research adviser asked if he would be interested in returning to his alma mater for an academic position performing research and teaching.

"Within a couple years of working in the position, I realized that I really loved what I was doing," Dr. Lawson said. "I really enjoy thinking of clinical problems, performing a study to try to better understand the best clinical treatment, trying what I learned in practice and then sharing that information through teaching."

Dr. Geisinger, too, was initially unsure of her career path and thought she would go into private practice until she began volunteering as a faculty member at a dental school.

"When I thought about the opportunity to make an exponential impact on our profession through education, research and service, I knew that I had to try to make the biggest impact I could on the oral health of patients and communities," she said. "And it is the research part of that mission that allows me to have the widest reach — impacting the global delivery of dental care through incremental discovery."

Dr. Geisinger, who is a member of the ADASRI Board of Directors and secretary-treasurer of the American Academy of Periodontology, is currently involved in a project examining best practices for delivering oral hygiene care to people with dementia in skilled nursing facilities, as well as the impact of periodontal health on the development and progression of dementia.

The research dentists perform has a lasting impact on not only the profession but public health as well.

"Dentists are an integral part of health care, and as an important health care provider, we need to base what we do on science and biology in order to offer evidence-based, scientifically proven and solid approaches to our patients," Dr. Hasturk said. "They are hungry to learn from us to do better at home and in their lives and to be examples to their children and young generations. We can only be better prepared for the future with proper education, and proper education is a result of research."

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The research mission of UTHealth Houston School of Dentistry is to conduct basic, clinical and translational research on the orofacial complex and related aspects of systemic health in order to improve the well-being of our patients and the community.

To be leaders in understanding the etiology and pathogenesis of common and complex oral conditions that impact the quality of life of our patients.

Research at UTHealth Houston School of Dentistry (UTSD) advances the dental profession. Our investigators perform innovative and cutting-edge basic, translational and clinical research that offers the opportunity to improve patient care and clinical practice. Participation in research provides dental students, residents, graduate students and postdoctoral fellows with the knowledge they need to deliver evidence-based best practices.

Three research centers at UTSD allow faculty and trainees to collaborate on research studies that require multidisciplinary approaches. UTSD’s Center for Craniofacial Research (CCR) houses faculty scientists and their lab members whose research focuses on craniofacial tissues including normal and abnormal development, oral cancer, mucosal immunity, pathogenesis of oral diseases, biomaterials, biomarker discovery and tissue regeneration/engineering. The Center for Oral Health Quality and Research emphasizes informatic approaches to improve the quality and safety of treatments promoting oral health. The Powers Center for Biomaterials and Biomimetics hosts faculty seeking to advance the restoration and maintenance of oral health with a focus on dental materials.

The UTSD is committed to fostering and disseminating research and scholarship by promoting intra- and inter-institutional relationships among all stakeholders. UTSD’s location in the Texas Medical Center, the largest in the world, offers unrivaled opportunities for collaboration with local, national and international partners. Integration with the Center for Clinical and Translational Sciences (CCTS) provides exceptional resources for planning clinical trials, bioethics and epidemiology. UTSD’s state-of-the-art biomedical research laboratories are supported by the Center for Craniofacial Research Instrumentation Core (CCRIC). UTSD faculty can participate as members of the Graduate School for Biomedical Sciences (GSBS) that offers both MS and PhD programs.

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UTHealth Houston School of Dentistry at Houston houses a research department that performs innovative and cutting-edge basic, clinical and educational research.

The School of Dentistry houses the Center for Craniofacial Research (CCR), the Houston Center for Biomaterials and Biomimetics (HCBB), and the Texas Center for Oral Healthcare Quality and Safety (TXOHQS).

The Student Research Group (SRG) promotes, supports, and nurtures the interests of dental student researchers during their time at the school.

Faculty Research Areas of Interest

Dr. Farach-Carson’s  laboratory uses three dimensional models to study the behavior of both cancer cells and normal cells. The Farach-Carson laboratory uses our understanding of extracellular matrix to create “smart” biomaterials that can mimic the native tissue to provide an environment in which to study cell and tissue behavior under physiologically relevant conditions. We partner with the Houston Center for Biomaterials and Biomimetics (HCBB) to create and study these biologically based materials.

Dr. Frey’s   research focuses on biomaterials, especially durability and esthetic qualities of dental prosthetics and bonding materials. He has emphasized Pedodontic crowns and various wear, fracture, and cementation studies. He also researches in the study of wear on different enamels (primary and permanent) upon itself and various crown materials. His most recent studies involve gloss, roughness, and their interdependence.

Dr. Harrington has an interest in using biomaterials as tools to expand our knowledge of cellular processes, and improve our ability to impact human health. His projects have spanned applications of soft, biocompatible hydrogels, degradable lactide/glycolide polymeric scaffolds, and self-assembling peptide nanostructures for regenerative medicine. His laboratory’s recent projects involve tissue engineering of the salivary gland as a post-radiotherapy treatment for xerostomia, and “tumor engineering” to study mechanisms of oral cancer and prostate cancer in unique 3D models, adapted to high-throughput screening. By customizing matrices and manufacturing techniques, we design biomimetic solutions that address needs at the cell, tissue, and organ level.

Dr. Kasper’s  research applies fundamentals of engineering, materials science, and the biosciences toward the development and evaluation of biomaterial-based technologies to meet clinical needs. Current research interests include the application of engineered culture conditions for the development of bioactive constructs for craniofacial and orthopedic tissue regeneration. Additional research focuses on applications of 3D printing and digital technologies in dentistry.

Dr. Kiat-amnuay's  research focuses on the areas of maxillofacial prosthetic and prosthodontics. Her team has investigated color stability and mechanical properties of pigmented maxillofacial prosthetic elastomers subjected to artificial/natural weathering and microwave energy. The goal is to find the best combinations of silicone/pigment/opacifier used to make facial prostheses last longer. Several in vivo studies were also performed on adhesive retention of maxillofacial prostheses. In addition, randomized controlled crossover clinical trials related to maxillofacial prosthetic and implant dentistry were conducted to improve patients’ quality of lives. Her group has also studied cement bond strengths of implant-supported ceramic crowns on custom ceramic abutments.

Dr. Ontiveros’  research focuses on in vitro mechanical properties of dental materials; light polymerization; adhesion; ceramic; resin composite; color/optical properties and esthetics. Clinical investigations focus around current techniques related to tooth whitening and other appearance related studies. 

Dr. Young's  research efforts focuses on the treatment of craniomaxillofacial trauma and pathology. This includes the synthesis and characterization of implantable biomaterials designed to elicit in situ cell recruitment and programming. This work includes the use of materials able to simultaneously deliver multiple bioactive factors with distinct release profiles. These constructs have been used in a diverse set of applications such as the promotion of craniofacial tissue regeneration and cancer immunotherapy. His lab has broad experience in the fields of polymer synthesis and characterization, growth factor delivery, in vivo models, characterization of bone and neovascularization, cancer immunotherapy, and implantable therapeutic cancer vaccines. Several NIH-funded collaborations with Rice University and the University of Texas Arlington include the use of multi-domain peptide hydrogels for nerve regeneration and the use of semiconductor-based coatings to impart enhanced bioactivity and bone regeneration around titanium implants, respectively.

Dr. Adibi’s research consists of biomedical studies including devices to solve diagnostic challenges and treatment options for Temporomandibular Disorders (TMD), Orofacial Pain and Nocturnal Bruxism (night time grinding of teeth).

Dr. Chiquet’s  research focuses on studying the genetics of craniofacial development, with emphasis on cleft lip and palate.  He has shown that the CRISPLD2 gene has been shown to be associated with nonsyndromic cleft lip and palate and critical for normal palate and jaw formation in zebrafish.  Pathway analysis is underway testing for association with differentially regulated genes in the presence or absence of CRISPLD2 in zebrafish. Additionally, his lab is looking at a known pathway of development, the β-catenin mediated WNT pathway, to determine if these genes are involved in clefting etiology.  Other ongoing projects include (1) studying genetic modifiers of cleft lip and palate phenotype, (2) evaluating the microbiome of patients born with cleft lip and palate, (3) analyzing dental materials used in presurgical appliance therapy for children born with cleft lip and palate, and (4) minimizing exposure of general anesthesia for children undergoing dental rehabilitation under general anesthesia.

Dr. Fakhouri’s   research interests focus on identifying epigenetic and genetic factors that cause and contribute to increase the risk of craniofacial disorders including cleft lip and palate, craniosynostosis and micrognathia. His lab uses mouse models and organ cultures to delineate the molecular mechanism of a novel genetic interaction between two transcription factors, IRF6 and TWIST1, that plays a critical role in regulating the epithelial-mesenchymal interaction during oral, facial and skull development. Using biochemical and genetic approaches, his lab investigates how mutations in TWIST1 phospho-sites disrupt formation of craniofacial tissues derived from mesenchymal cells. Integration of experimental data and bioinformatics for developing computational models are also utilized in Fakhouri’s lab to identify etiologic non-coding DNA variants associated with cancer diseases including head and neck squamous carcinoma. The overall goal of his lab research is to translate their bench findings into the clinic to improve risk assessment and pave the way to personalized medicine.

Dr. Hecht  has two research focuses. Genes contributing to nonsyndromic cleft lip and palate are identified using next generation sequencing in a family-based approach, and then functionally tested in zebrafish. This approach has successfully identified genes that are now being modeled in mice. In our cartilage biology studies, a DOX-inducible mouse (MT-COMP) with the common COMP mutation was used to delineate the chondrocyte-specific mechanisms causing the dwarfing condition, pseudoachondroplasia. We have successfully tested different treatments in the MT-COMP mouse, which partially rescued the short limb phenotype.

Dr. Iwata’s   research focuses on understanding mechanisms that cause craniofacial birth defects and oral diseases. His group is trying to determine the roles of 1) exocytosis and autophagy, 2) non-coding RNAs, 3) cellular cholesterol metabolism, and 4) WNT signaling pathway in craniofacial development and homeostasis. They have generated new genetic mouse models and has been characterizing the molecular mechanism using multidisciplinary approaches including genetics, genomics, proteomics, and bioinformatics. His group seek to identify novel targets for new therapeutics and new diagnostic tools for identifying defects and diseases in at risk populations.

Dr. Noriaki Ono’s  research focuses on the fundamental biology of skeletal stem cells, with a further scope on understanding pathophysiology of dental, craniofacial and skeletal deformities and diseases that affect millions of children and adults.

Dr. Wanida Ono’s  research focuses on the fundamental biology of dental development and tooth eruption, with a further scope on understanding signaling pathways and molecular mechanism involving in these processes.

Dr. Wong  has two major research interests. Within the AFIRM consortium, his project focuses on the management of severe maxillofacial injuries through a series of therapeutic interventions. First, preservation of skeletal space is accomplished with a drug-eluting methylmethacrylate polymer. This is followed by the generation of customized vascularized bone grafts formed in a distant site and subsequently transferred into the traumatic defect. His second research focus involves the characterization of TMJ disease and the regeneration of the disc and condyle using tissue engineering principles.

Dr. Walji's  research interests are focused on using informatics approaches to improve the safety and quality of oral healthcare, with a particular focus on electronic health records. He currently serves as a Principal Investigator of two NIH/NIDCR funded studies 1) “Developing a Patient Safety System for Dentistry” and 2) Implementing Dental Quality Measures in Practice. He also serves as a PI on an AHRQ funded study titled “Measuring Occurrence of and Disparities in Dental Clinic Adverse Events”. He has provided informatics expertise in the development and maintenance of the Dental Diagnostic System (DDS) which serves as a collection of specific dental terms that is designed for the purposes of dental diagnosis documentation. He also leads a multi-institutional team that has developed the BigMouth Dental Data Repository, which currently contains data on over 2 million patients derived from EHRs from 6 dental institutions.

Dr. Adibi's  research includes studies of policies with integration of care. Understanding of the oral and systemic disorders including Orofacial Pain condition connections by means of radiographic images, salivary components and the new and innovative technologies in clinical research.

Dr. Myers  is interested in gathering more scientific data on the consumption of addictive and carcinogenic areca nut preparations (e.g. betel quid, supari, paan, gutka) in the Houston metropolis. Specifically his research employs a mystery shopper study design to better understand the availability, buying experience, package labeling, costs, and marketing information of these oral toxins. Furthermore, Dr. Myers’ research aims to characterize the chemical diversity of these areca nut products.

Dr. Neumann's   research interest is on the improvement of oral health at a population level. She currently serves as Co-Investigator on two funded NIH/NIDCR projects: a) “CATCH Healthy Smiles: Planning and feasibility of an elementary school-based child oral health RCT” in collaboration with the School of Public Health and the CATCH study team (PI: S. Sharma) and b) “Implementing Dental Quality Measures in Practice” (PI: M. Walji). She is also actively involved in the various applications of Caries Management by Risk Assessment (CAMBRA) and interprofessional initiatives.

Dr. Chun-Teh Lee’s  research interests focus on understanding inflammation resolution and host-microbiome interactions in periodontitis. Specialized pro-resolving lipid mediators (SPMs), including lipoxins, resolvins, protectins, and maresins, induce resolution of inflammation in inflammatory diseases. Treatment of experimental periodontitis with SPMs results in disease reversal and periodontal regeneration. Currently, his research project aims to determine the clinical SPM profile and associated microbiota in periodontitis.

Dr. Klein’s  has two primary areas of research. The first is aimed at understanding the involvement of a novel immune system derived splice variant of thyroid stimulating hormone in the development and/or perpetuation of autoimmune thyroiditis, and as a regulator of host metabolic activity.  Various targeted knockdown systems are being applied in these studies.  In a second area of research, Dr. Klein is exploring factors that regulate the adaptive and innate immune responses in mucosal sites, particularly in the intestine and the oral cavity.  

Dr. Lou’s  research related to roles of immune cells and molecules in autoimmune diseases and tissue aging. His group developed a unique rat model and discovered a novel immune cell called antigen-presenting NK cell. They are current examining how this novel cell controls autoimmune disease.  His team is also examining how immune molecules such as cytokines regulate physiological process such as aging and tissue remodeling.  They have identified a cytokine interleukin33 to be critical in rejuvenation of aged neurons in brains in a special mouse model; deficiency of this molecule causes neurodegeneration in the old animals. Currently, they are investigating whether interleukin33 deficiency is a causes of human elderly dementias such as Alzheimer’s disease.    

Dr. Ransome van der Hoeven’s  research focuses on understanding the mechanisms of host-pathogen interactions. The major areas of our current research are: 1) To elucidate innate immune defense mechanisms in response to oral and systemic pathogens using a simple invertebrate model Caenorhabditis elegans, and 2) To determine how Enterococcus faecalis an opportunistic pathogen is able to persist and cause secondary endodontic infections.

Dr. Farach-Carson’s  research relates to the role of extracellular matrix in progression of cancer following metastasis from primary sites, such as prostate or oral cavity, to bone. Primary tumors are slow growing and are not life-threatening until they form tumors in bone. Factors sequestered in bone matrix provide a rich environment to promote growth of invading cancer cells. Many factors are bound to proteoglycans, including perlecan/HSPG2, that contain heparan sulfate that regulate their bioactivity. We seek to identify factors responsible for cancer growth and progression with the long term aim of developing "molecular drugs" to combat cancer metastasis.

Dr. Myers'  pharmacological-based research focuses on acquiring greater insight towards the biodisposition of chemical compounds (e.g. drugs, drug metabolites, natural products) in the human body. His major areas of current research are: (1) Clarifying the enzyme-mediated mechanisms of activation and detoxification of arecoline, an oral toxicant contained in the areca (betel) nut, in human liver; (2) Elucidating the untoward effects of EdAG and several natural compounds on the glutathione, specifically the thioredoxin enzyme system which is a promising druggable target for oral malignancies; (3) Defining the pre-clinical and clinical pharmacokinetics of novel anti-cancer medications.

Dr. Ogbureke’s  research involves investigating the role of the family of glycophosphoproteins comprising osteopontin (OPN), bone sialoprotein (BSP), dentin matrix protein 1 (DMP1), dentin sialophosphoprotein (DSPP) and matrix extracellular phosphoglycoprotein (MEPE) - small integrin-binding ligand N-linked glycoproteins (SIBLINGs)- in biology of oral cancer and other head and neck cancers. These proteins have key functional roles during malignant transformation, invasion and metastasis, and may potentially be used as diagnostic and prognostic tools, as well as targets for therapeutic intervention. Some of the SIBLING family of proteins may therefore identify patients who could benefit from more extensive surgical resection, or from adjunct treatments such as radiotherapy for primary OSCCs. Dissecting the functional and mechanistic pathways of SIBLING activity in oral cancer as well as investigating the interaction of BSP and DSPP with the HPV16 oncoproteins (E6/E7) in the biology of HPV-associated oral cancers are ongoing projects.

Dr. Parikh's  research interests encompass molecular mechanisms involved in cancer signaling and aging. In collaboration with faculty in the Department of Endodontics and Diagnostic and Biomedical Sciences, Dr. Parikh is currently assessing a poorly characterized brown precipitate formed in the dentinal tubules with the consecutive usage of common irrigant solutions. Using eukaryotic model systems, she is addressing the toxic effects of the brown precipitate and an alternative irrigation protocol to avoid forming this potentially toxic brown precipitate.

Dr. Dharini van der Hoeven’s  research focuses on identification of novel anti-cancer therapeutics for the treatment of oral squamous cell carcinomas. Our studies target the EGFR-Ras signaling pathway which is overactive in most oral squamous cell carcinomas. Current research interests include identification of novel, indirect inhibitors of EGFR and Ras which perturb their function through altering plasma membrane topology, extensive characterization of such compounds in cellular signaling and functional studies, pre-clinical development and chemical optimization of compounds with the overall aim of identifying advanced drug candidates.

Dr. Vigneswaran’s   group focus on clinical and laboratory-based research related to oral cancer and its precursors. His clinical research focuses on the use non-invasive optical imaging and quantitative cytology for monitoring of the progression of oral premalignant lesions. His basic research involves the development of experimental animal models of oral cancer for pre-clinical testing of molecular targeted diagnostic imaging and therapy.

Dr. Young’s   research involves the development and characterization of biomaterials-based platform technologies focused in two areas: immunotherapy and craniofacial tissue regeneration. With respect to the treatment of oral cancer, our lab has been working on injectable cancer vaccine systems which act as sites for in situ dendritic cell programming. By leveraging our knowledge of bioengineering technologies for cell recruitment and differentiation, we have been able to translate these fundamental strategies to the cancer immunotherapy setting. Our goal is to examine the efficacy of these vaccine systems in the context of oral squamous cell carcinoma, and explore any synergies that may arise from the use of cancer vaccines and other forms of immunotherapy. The concept of in situ cell programming is also utilized in our tissue regeneration projects where we are exploring the use of various hydrogels and layer-by-layer polymer coating technologies to promote nerve and bone regeneration in several challenging preclinical models.

Dr. Angelov’s  research focus encompasses basic, clinical and translational studies, mainly in the area of oral mucosal wound healing, periodontal microbiology and dental implants. More recently, a focus of the collaborative research efforts of our department and Baylor’s College of Medicine has been the role of oral bacteria in blood pressure regulation via the Nitrate-Nitrite-Nitric Oxide Pathway. The goal is to understand the role of human microbial communities in the host’s NO homeostasis, to allow the development of new diagnostics and other approaches to manipulate these microbial communities to promote human health and prevent disease.

Dr. Tribble’s  research focuses on two groups of anaerobic bacteria associated with periodontitis, Porphyromonas gingivalis and Prevotella spp. In particular, she investigates the molecular mechanisms of horizontal DNA transfer in oral microbial communities, and the biological consequences of gene exchange. Her research objectives are to improve our understanding of the role of DNA exchange as it contributes to bacterial survival and persistence in the host, and adaptive evolution transitioning microbiome- host interactions from commensal to pathogenic.

Dr. Wang  has focused her research on oral infectious diseases such as periodontal diseases and dental caries. Using molecular genetics approach, we are deciphering the mechanisms of interferences of Streptococcus mutans quorum sensing by other oral bacteria. We are also investigating the role of bacterial interspecies interactions in racial discrepancies in periodontitis. We, in collaboration with Dr. Hua Xie, have demonstrated that Streptococcus cristatus (an oral commensal) inhibited the colonization of Porphyromonas gingivalis (a periodontal pathogen) in vitro and in vivo. The long-term goal of our research is to target certain pathogens specifically for prevention of common oral infectious diseases.

Dr. Eswaran’s  primary research focus is hard and soft tissue regeneration. He is also involved in educational and health outcomes research pertaining to the field of periodontology and implant dentistry. His current study involves utilizing Platelet Rich Fibrin (PRF) in extraction sockets and evaluating its efficacy in bone regeneration and maintenance of alveolar ridge width for implant placement. His educational research focuses on faculty calibration. In particular, he investigates the variations in periodontal diagnosis and calculus detection among faculties in the clinic. The study also involves problem centered calibration techniques to enhance the reliability and consistency among faculties in teaching students.

Dr. Farach-Carson’s   laboratory uses proteoglycans, particularly those bearing heparan sulfate chains such as perlecan, in engineering of complex tissues such as bone, cartilage or salivary gland. Cell and molecular engineering strategies are being developed that facilitate controlled tissue growth and differentiation. Growth factor binding and delivery by engineered proteoglycans are used in oral surgery and orthopaedic applications. Engineering partnerships support these studies. We use a variety of techniques including 3D hydrogel cell culture, recombinant and natural protein purification and analysis, cloning and molecular biology, immunodetection, 3D printing, confocal imaging and pre-clinical models.

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How an increase in income affects the use of dental care services among a low-income population: evidence from the Finnish basic income experiment

• Miska Simanainen 1 , 2  

BMC Health Services Research volume  24 , Article number:  499 ( 2024 ) Cite this article

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Previous research has shown that the use of dental care services has a significant socioeconomic gradient. Lower income groups tend to use dental care services less, and they often have poorer dental health than higher income groups. The purpose of this study is to evaluate how an increase in income affects the use of dental care services among a low-income population.

The study examines the causal effect of increasing cash transfers on the use of dental care services by utilizing unique register-based data from a randomized field experiment conducted in Finland in 2017–2018. The Finnish basic income experiment introduced an exogenous increase in the income of persons who previously received basic unemployment benefits. Register-based data on the study population’s use of public and private dental care services were collected both for the treatment group ( N  = 2,000) and the control group ( N  = 173,222) of the experiment over a five-year period 2015–2019: two years before, two years during, and one year after the experiment. The experiment’s average treatment effect on the use of dental care services was estimated with OLS regressions.

The Finnish basic income experiment had no detectable effect on the overall use of dental care services. However, it decreased the probability of visiting public dental care (-2.7% points, -4.7%, p  =.017) and increased the average amount of out-of-pocket spending on private care (12.1 euros, 29.8%, p  =.032). The results suggest that, even in a country with a universal public dental care coverage, changes in cash transfers do affect the dental care patterns of low-income populations.

Peer Review reports

Introduction

Oral diseases create a significant health burden for many people around the world by lowering the quality of life and causing pain, discomfort, and even death [ 1 , 2 ]. In addition, oral diseases share common risk factors, and they are associated with many other major diseases [ 3 , 4 , 5 , 6 , 7 , 8 ]. Most oral health conditions are largely preventable and can be treated in their early stages. However, for individuals, treatments for oral health conditions are often expensive even in countries with universal health care coverage. In high income countries, dental treatments comprise as much as 20% of out-of-pocket health expenditure, on average [ 9 ].

Oral diseases affect individuals within societies unequally. Earlier research has indicated a strong and consistent association between socioeconomic status, measured as income, occupation, and educational level, and the prevalence and severity of oral diseases [ 10 , 11 , 12 , 13 ]. Lifestyle factors and quality of nutrition obviously contiribute to dental health. Part of the socioeconomic inequality in dental health may, however, result from differences in the use of dental health care services. Previous research has shown that despite having poorer dental health, lower socioeconomic groups utilize less dental care services [ 14 , 15 , 16 , 17 , 18 ]. Sosioeconomic status predicts the use of dental care even in countries with publicly subsidized universal health care, such as Finland [ 19 , 20 ].

This study examines the effect of a cash transfer reform on the use of dental care services. Although the socioeconomic gradient in the use of dental services is well documented, we lack experimental evidence on the effects of income on dental care usage. The study contributes to the topic by analyzing the use of dental care services in the Finnish basic income experiment. The experiment introduced an exogenous increase in the income of previous basic unemployment benefit recipients for a period of two years in 2017–2018. The probability of visiting, number of visits, and out-of-pocket costs of dental care services are analyzed with data collected from administrative registers. If dental care costs create a barrier to meet the needs of dental care among low-income groups, as documented in other contexts [ 21 , 22 , 23 , 24 ], increasing cash transfers should lead to an increase in the overall use of dental care services.

In a broad perspective, the study contributes to the research on the relationship between income and health by examining one specific causal pathway, i.e., the effect of an income change on the use of health services. From a policy perspective, the study aims to increase our understanding on the role of cash transfers in meeting the dental care needs of low-income populations in a universal and publicly subsidized health care system.

Dental care usage in previous policy experiments

Previous studies have indicated that persons with lower income tend to use less dental care services than persons with higher income, even though the needs of the former may be greater than those of the latter [ 14 , 15 , 16 , 17 , 18 , 19 , 25 , 26 ]. However, only a few studies have examined the causal effect of changes in individuals’ economic conditions on dental care usage in a controlled setting.

Experimental studies in low-income and middle-income countries have found that the introduction of a cash transfer program that improves individuals’ economic resources may increase the use of preventive health care [ 27 ]. However, evidence on the comparable effectiveness of different types of cash transfer reforms remain weak [ 28 ]. Moreover, dental care usage spesifically has not been measured in the studies.

Most of the experimental research conducted in high-income countries on the effects of policies on health care usage focus on different types of insurance schemes. For example, in the RAND Health Insurance Experiment, reducing the patient’s part in cost-sharing increased the demand for dental services during the first year of the policy change [ 29 ]. In the Oregon Health Insurance Experiment, Medicaid insurance coverage significantly reduced the share of respondents reporting unmet dental care needs and doubled the share of people visiting the emergency departments for dental care, but it had no detectable effect on out-of-pocket spending [ 30 ]. In another study, extending dental coverage provided through a health insurance program for children in Western Pennsylvania increased their access to both dental care and preventive dental services [ 31 ].

Only a few studies conducted in high-income countries have assessed the dental care effects of direct cash transfers. In the Family Rewards Experiment, introducing a cash transfer program conditional to using health services led to a consistent and large increase in the use of preventive dental care [ 32 ]. On the effects of unconditional cash transfers, the evidence base is less clear [ 33 ]. In the Iowa and North Carolina Rural Income Maintenance Experiment (RIME), small but inconsistent effects on the use of health services, including dental care consumption, were found [ 34 ]. Relatively recently, a study that interviewed program participants in the Ontario Basic Income Pilot (OBIP) indicated that some low-income participants used their additional income on health services, including dental treatments [ 35 ].

To sum up, experimental studies on the dental care effects of cash transfer programs that are not conditional to using health services are rare. Available studies are based on uncontrolled study designs or report inconsistent findings. In addition, studies on cash transfer reforms in the context of universal health care systems are basically non-existent. Studying dental care usage in the Finnish basic income experiment provides a unique opportunity to contribute to the knowledge gap– with register-based data from a randomized field experiment that introduced an exogenous increase in the income of previous basic unemployment benefit recipients for a period of two years.

Institutional context and the policy experiment

The finnish dental care system.

In Finland, dental care is organized through both public and private health care schemes. Dental care provided by the public sector is universally covered for all residents. Until 2023, municipalities provided basic dental care including dental checks and follow-up checks. Specialized dental care was provided by both the municipalities and the hospital districts. Public services are mainly financed through taxation. However, co-payments are usually required for dental appointments and procedures. In 2018, the maximum basic co-payment for an adult for a visit to a public dentist was 13.10 euros [ 36 ]. The out-of-pocket costs for different dental procedures varied between 8.40 euros and 183.50 euros. The annual ceiling for co-payments of public health care services was 683 euros. In addition, low-income households may receive basic social assistance to cover the costs of public oral and dental care services.

Dental care provided by the private sector is based on a free-market principle [ 37 ]. The average price for a basic oral examination in the private sector was 63 euros in 2018 [ 38 ]. The use of private dental care is partly subsidized through the National Health Insurance scheme. It covers dental checks, treatments, and laboratory and X-ray examinations but excludes cosmetic procedures and prosthodontics. In addition, procedures conducted by a dental hygienist may be covered. In 2018, the total reimbursement rate for dental care was 14.2% [ 39 ]. The National Health Insurance coverage and reimbursement rate have decreased over the years. Since 2016, dental examinations have been reimbursed under the National Health Insurance scheme only every other year, unless the patient’s health status, as verified by a dentist, requires more frequent examinations.

In Finland, dental care provided by the public sector has been associated with long waiting times. In October 2018, 45% of the patients with non-urgent appointments in public dental care had waited longer than three weeks [ 40 ]. Waiting times are typically shorter in the private sector, and the patient can choose the dentist freely. It is typical for private dentists to offer their patients annual or biannual recalls. Due to lack of resources, public dentists mostly use regular recalls for children [ 41 ].

Limited availability of public care, especially in non-urgent cases, may channel service demand to the private market.

In addition, previous research has shown that socioeconomic background predicts the dental care provider in Finland. Those with the lowest income use public services more frequently than private services. The higher the income and the higher the education, the more likely a person is to use private services [ 20 ]. To account for the specificities of the Finnish dental care system, this study collects register data on the use of both public and private dental care services and examines both the overall use and use by service provider.

The basic income experiment

During 2017–2018, the Government of Finland conducted a field experiment that tested an unconditional cash transfer policy in practice. The experiment was targeted at 25–58 year-old persons who received basic unemployment benefits from the Social Insurance Institution in November 2016 ( N  = 175,222). The intervention in the experiment was a specific change in the social benefit legislation: The persons chosen to participate in the experiment received an unconditional cash transfer (a basic income) of 560 euros per month without an obligation to search for a job, make benefit claims, or report earnings. In addition to replacing a part of the existing social benefit schemes with an unconditional cash transfer, the intervention increased monetary incentives of finding a job during the experiment because basic income payments were paid also for the employed. The experiment was designed as a randomized field experiment. From the target population, 2,000 persons were randomly chosen to be in the basic income group for the duration of two years. The rest of the target population formed the control group.

The primary objective of the experiment was to evaluate the effect of an unconditional cash transfer policy on the recipients’ labor market behavior. According to the main evaluation study, the experiment had no effect on employment during the first year. During the second year, persons in the basic income group had slightly more days in employment (6.6) than persons in the control group [ 42 ]. As a result of the experiment, however, the average annual income increased significantly in the basic income group. In the average annual income, including taxable market income, taxable social benefits, basic income, and housing benefits, there was an increase of 9.2% (1,330.1 euros) during the first year and 11.0% (1,734.7 euros) during the second year [ 42 ]. The increase in income was mostly due to structural changes attributable to the intervention: First, unemployment benefits from December 2016 and the first basic income payments were received in January 2017, doubling the benefit income for most of the participants in the beginning of the experiment. Second, persons who found a job before or during the experiment received basic income payments in addition to their earnings. Part of the increase during the second year (15.6%) was also due to behavioral changes in the labor market, i.e., the slight employment effect contributing to higher earnings in the basic income group compared to the control group during the second year [ 42 ].

Study design

To enable causal inference about the average treatment effect of the Finnish basic income experiment on the use of dental care services, the original experimental design of the experiment is exploited by comparing the study outcomes of the marginally randomized basic income group and control group. Because persons were randomly allocated to the basic income group and to the control group, the groups are similar both in their observed and unobserved characteristics. Thus, any differences in the use of dental care services are attributable to the policy intervention. Being in the basic income system versus being in the existing tax-benefit system is the only characteristic that differs systematically between the study groups.

Data sources

For the target population of the Finnish basic income experiment, the data were collected from administrative registers for the years 2015–2019 and linked together using pseudonymized individual identifiers. Demographic data, including information on gender, age, having children, having a partner, native language, and place of residence, were derived from the Benefit Register of the Social Insurance Institution. Information about the treatment status in the experiment and previous unemployment benefit type were collected from the Social Insurance Institution’s Basic Income Experiment Register. Annual-level information on taxable income was gathered from the Personal Income Tax Register. Register data on the utilization of public dental care services were obtained from the Register of Primary Health Care Visits (municipal health care centers) and from the Care Register for Health Care (units of hospital districts) maintained by the Finnish Institute of Health and Welfare. The registers contain information on the dates of visits and received treatments. Information on the use of private dental care services was collected from the Benefit Register of the Social Insurance Institution. This information covers the dates and costs of health care visits and treatments reimbursed by the National Health Insurance scheme. Reimbursed procedures include dental checks, treatments, and examinations but exclude cosmetic procedures and prosthodontics. Data on the use of public and private care was restricted to visits containing oral-health-related procedures defined in the national classification of oral health care procedures [ 43 ].

Outcome variables

In the main analysis, the individual-level outcome variables were defined as (1) having one or more visits to dental care services, (2) the total number of visits to dental care services, and (3) the out-of-pocket expenditure on dental care services during the experimentation period (2017–2018). The large range of outcome variables was chosen in order to capture and differentiate between changes in access (yes/no), volume (number of visits), and consumption patterns (out-of-pocket spending). In addition, the study outcomes were separately defined for public (including primary care and hospital care) and private dental care services to take into account the institutional specificities of the Finnish dental care system.

A visit to dental care may contain several procedures. For this study, a visit was further defined as a single date with oral-health-related procedures, i.e., each person was set to have a maximum of one visit per day and per service provider (primary care, hospital care, private care). Concerning primary care services, the data were limited to contacts that were actual visits by using information on the contact type and excluded, for example, remote contacts by phone or email.

Data on dental care expenses were available only for the private service use. Out-of-pocket expenditure was defined as costs of dental procedures after National Health Insurance reimbursements. The expenses were operationalized as out-of-pocket costs in order to directly measure how much money the participants spend on private care services. In the main analysis, total private dental care expenditure is also reported to evaluate the impact on the National Health Insurance system.

For the outcome variables of the main analysis, a two-year period (2017–2018) was chosen for two reasons. First, it is typical for dentists to recommend booking a visit for regular checkups for every other year only. Second, in 2016, the National Health Insurance scheme was changed to cover visits in the private sector only every other calendar year unless the patient’s health status, verified by a dentist, requires otherwise.

For descriptive purposes, all outcome variables were calculated also for the two-year period preceding the experiment (2015–2016). For further analyses (see Supplement ), annual and monthly outcome variables were calculated for the whole data period of 2015–2019. In addition, outcomes during the experiment (2017–2018) were calculated separately for selected dental procedure categories and for different service providers (private care, primary care, hospital care) to gain information on different types of services, such as preventive, specialized and emergency care.

Visits to private dental care services are not recorded in the data if a person does not apply for National Health Insurance reimbursements. However, the number of unreimbursed cases is likely very small because reimbursements are usually handled automatically when paying for the service. In addition, the use of dental care services provided by the employers is not measured in the data. On the other hand, dental care is rarely included in the health care service contracts of the employers, and thus the employer-provided visits are expected to be very few in the study population.

Statistical approach

The study utilizes the following statististical approach: First, basic descriptives of the background variables of the basic income group and control group are reported in order to describe the study population and to evaluate the success of the randomization procedure in balancing the study groups in relation to characteristics that may predict the later use of dental care services. Second, the average treatment effects on different outcome variables are analysed by estimating the following Ordinary Least Squares (OLS) regression model:

In the equation, \( {Y}_{i}\) represents the examined dental care usage outcomes (one or more visits, number of visits, out-of-pocket costs) measured for the two-year experimentation period 2017–2018. \( {Tr}_{i}\) is the treatment status indicator (basic income groups vs. control group), \( {X}_{i}\) includes the control variables for different background characteristics observed before the experiment, and \( {\epsilon }_{i}\) is the individual-level error term in the model.

The average treatment effect is estimated both with a simple (1) and a multiple (2) OLS regression model with heteroskedasticity-robust standard errors. In a marginally randomized experiment, a simple regression model (1) suffices for estimating the average treatment effect. However, adding baseline variables with predictive power as covariates in the model may increase the statistical power of the estimation [ 44 ]. Covariates in the multiple model (2) include previous unemployment benefit type, gender, age group, having children, having a partner, native language, urbanization level of the place of residence, and previous use of public and private dental care services.

In the multiple model (2), age is categorized into three brackets: 25-34, 35-44, and 45-59. Gender is included as a binary covariate, and native language is coded as official domestic language (Finnish or Swedish) or foreign language. Family structure is measured with the number of dependent children, recoded into a binary variable having or not having children, and with marital status and with information on cohabitation, together recoded into a binary variable having a partner (= married or cohabiting) or not having a partner. Data on the place of residence (municipality) is categorized to urban, semi-urban, and rural municipalities according to Statistics Finland’s classification for year 2016 [ 45 ]. For age, children, partner, and place of residence, information from the end of 2016 is used.

The estimation is complemented with an analysis of effect heterogeneity withing selected subgroups. The analysis is conducted by estimating the simple model (1) separately for each of the subgroups. In addition, regression analyses are conducted separately for visits with surgical and non-surgical dental care procedures and for visits with different types of non-surgical procedures (e.g., examinations, preventive procedures, and restorative treatments) (see Supplement ).

Study population descriptives

The target population of the Finnish basic income experiment composed of low-income individuals. Accoding to the main evaluation study, persons in the study population had 24 days in employment and 286 days in unemployment during year 2016, on average [ 42 ]. Average earnings from employment were 1,900 euros in 2016.

Table  1 describes the socioeconomic and demographic background characteristics of the study groups. The mean annual taxable income, including earnings and taxable social benefits, was around 10,800 euros in the basic income group and in the control group in 2016. The gender ratio was quite equal between the study groups, 48% of the persons being women. The mean age in the basic income group was 40.8 years and 40.4 years in the control group, and 25% of the persons in the groups had other than Finnish or Swedish (official domestic languages) registered as their native language. There are no statistically significant differences between the study groups regarding the listed background characteristics at 5% significance level indicating a successful randomization procedure in balancing the study groups.

In order to further describe the study population, Table  2 summarizes the pre-experimental use of dental care services in the study groups (a two-year period 2015–2016). In both groups, 63% of the persons had a visit in dental care services. About 56% visited primary care, while 6% in the basic income group and 5% in the control group had visits in hospital care. Approximately 11% in both groups used private dental care services.

Number of visits to dental care services during the two-year period was 5.9 in the basic income group and 5.8 in the control group, on average. In the basic income and control groups, the number of visits in primary care was 5.0 and 5.1, in hospital care 0.1 and 0.2, and in private care 0.7 and 0.6, respectively. Persons in the basic income group spent, on average, 44 euros in private dental care services during the two years before the experiment, while the average expenditure in the control group was 41 euros. The differences between the study groups are not statistically significant at 5% significance level indicating balanced study groups needed for a design-based causal inference.

Results: effects on the use of dental care services

Table  3 reports the estimated average treatment effects on the selected outcome variables measuring the use of dental care, i.e., the probability of visiting, total number of visits, and the out-of-pocket expenditure on dental care services. The estimation period covers the whole two years of the experiment (2017–2018), and the effect estimates are provided separately for using any care, public care (including primary care and hospital care), or private care. Table  3 reports the estimates from a simple OLS regression with only the treatment status indicator as a predictor.

Based on the estimation, we do not find statistically significant effects (at 5% level) on the overall use of dental care services, measured both in probability of visiting and total number of visits. However, we do find a statistically significant negative effect of -2.7% points (-4.7% in relative terms) on the probability of visiting public care ( p  =.017). The estimated effect on the number of visits to public care is also negative, -0.2 (-4.2%), although the estimate is not statistically significant ( p  =.212).

The estimated effect on the probability of visiting private care is positive, 1.3% points (11.9%), as is the estimated effect on the number of visits to private care, 0.1 (20.4%), but neither of the estimates is statistically significant ( p  =.072 and p  =.066, respectively). However, we find a statistically significant positive effect of 12.1 euros (29.8%) on the out-of-pocket expenditure on private care (p.=0.032). The effect estimate on total expenditure (before National Health Insurance reimbursements) indicates a proportional effect on the National Health Insurance expenditure. Adjusting for the selected background characteristic in the regression produces effect estimates and standard errors of similar sizes as found in Table  3 (see Table S1 in Supplement).

In sum, we do not find a statistically significant effect on the use of dental care services overall. However, the estimation indicates a negative effect on the use of public dental care and a positive effect on the use of private care. Further graphical examinations and statistical estimations provided in Supplement support the findings of the main analysis.

The results of the study indicate that the patterns of using dental care services among low-income populations may be affected by changes in the policies that directly impact individuals’ economic circumstances, even in a country with a universal public dental care coverage. The found positive effect on the use of private care fits the hypothesis that increasing economic resources should lower the cost barrier for using dental care services among low-income populations [ 21 , 22 , 23 , 24 ]. However, the lack of evidence about a positive effect on the overall use and the found negative effect on the use of public care suggest that, instead of overall use, an increase in income may be affecting the individuals’ choice over the service provider. For example, given the potentially long waiting times in the public care, choosing private care may be an attractive choice when there are additional economic resources available [ 46 ].

The reported effect estimates on private dental care usage would be biased if the persons in the basic income group, having higher income than the control group, were less likely to apply for National Health Insurance reimbursements than the persons in the control group. In such case, the true effect of being in the basic income group on the use of private dental care would be underestimated. In addition, if the persons in the basic income group were more likely to use dental care services provided by the employers than the persons in the control group, then the effects on the overall use of dental care would be underestimated. The latter source of bias could partly result from the slight positive employment effect found during the second year of the experiment [ 42 ]. Increased use of employer-provided dental care services in the basic income group could also partly explain the reduction in the use of public services. However, asymmetric changes in the claiming of reimbursements and in the use of employer-provided dental services are unlikely, as, in Finland, National Health Insurance reimbursements are basically automatically provided when paying for private services, and employers only rarely have dental care services included in their occupational health care contracts.

In principle, instead of being direct effects of income the changes in the use of dental care services could partly be explained by changes in the participants’ dental health. Increasing income could lead to nutritional choices that are beneficial for the overall health, but the effect could also be detrimental [ 35 , 47 , 48 , 49 ]. A survey study conducted near the end of the Finnish basic income experiment suggests that the experiment may have had positive effects on the participants’ self-evaluated state of health [ 50 ]. However, the short timespan (one year) between the policy change and the observed effects on the service-use makes it plausible that the changes in care-seeking behavior are a direct result of higher income rather than a result mediated by a genuine change in dental health.

Conclusions

The study assessed the effect of cash transfers on the use of dental care services among a low-income population by utilizing register-based data from the Finnish basic income experiment (2017–2018). The experiment exogenously increased the annual income of the participants by 9.2–11.0% [ 42 ]. The study found no effects on the overall use of dental care services during the two-year experiment, but the results indicate that the experiment decreased the use of public care and increased the use of private care slightly. The probability of visiting public care decreased by 2.7% points (-4.7%, p  =.017), the probability of visiting private care increased by 1.3% points (11.9%, p  =.072), and the out-of-pocket expenditure on private care increased by 12.1 euros (29.8%, p  =.032), on average. When comparing the change in expenditure to the increase in income caused by the intervention, private dental care consumption was more than proportionally affected.

The results of the study indicate that in a country with publicly provided universal dental care, increasing cash transfers does not necessarily increase the overall use of dental services among low-income populations. However, additional economic resources may affect an individual’s choice over the service provider. From the policy perspective, the findings encourage putting attention to the availability of services in meeting the needs of dental care among low-income populations: For example, lowering co-payments of public services may not be the most effective policy action to increase access if the availability of public care remains limited [ 20 ]. On the other hand, if the public services are under-resourced, then improving the economic resources of a low-income population or reducing the patient’s part in cost-sharing of private services could serve as an immediate policy action to direct service demand from the public sector to the private providers. Obviously, the findings are likely highly context-specific, and the overall conclusions about the relative importance of individuals’ economic resources, cost of services, and the service supply in meeting the dental care needs of low-income populations may differ in other countries [ 51 ].

Regarding the potential unmet dental care needs of low-income populations, more money does not necessarily lead to more use overall, but it may give more freedom in choosing the service provider. If changing service providers means getting the needed dental care earlier, then at least some pain and discomfort may be avoided leading to higher quality of life and, in the best case, improved overall health.

Data availability

Access to data that support the findings of this study was authorized by permissions from the officials that administer the registers. As a general rule, legal restrictions prevent the public sharing of sensitive pseudonymized data [ 54 , 55 ]. In addition, the researchers’ permissions from the data providers do not allow data sharing. In principle, the data are available from the Social Insurance Institution of Finland, Finnish Tax Administration, and Finnish Institute of Health and Welfare, but restrictions apply to the availability of these data, which were used under license for the current study.

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Acknowledgements

Grateful thanks to Sven Drefahl, Kari Hämäläinen, Markus Jäntti, Emilia Norlamo, Hanna Rättö, Jouko Verho, and the Reviewers for providing valuable comments and suggestions for improving the study and its reporting.

The study has received funding from the Social Insurance Institution of Finland, Kone Foundation, and Finnish Cultural Foundation. Conclusions expressed in the article are solely those of the author and do not represent the views of the funders.

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Simanainen, M. How an increase in income affects the use of dental care services among a low-income population: evidence from the Finnish basic income experiment. BMC Health Serv Res 24 , 499 (2024). https://doi.org/10.1186/s12913-024-10933-0

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Perceptions and attitudes of dental students and dentists in South Korea toward artificial intelligence: a subgroup analysis based on professional seniority

• Hui Jeong 1   na1 ,
• Sang-Sun Han 1   na1 ,
• Hoi-In Jung 2 ,
• Wan Lee 3 &
• Kug Jin Jeon 1  

BMC Medical Education volume  24 , Article number:  430 ( 2024 ) Cite this article

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This study explored dental students’ and dentists’ perceptions and attitudes toward artificial intelligence (AI) and analyzed differences according to professional seniority.

In September to November 2022, online surveys using Google Forms were conducted at 2 dental colleges and on 2 dental websites. The questionnaire consisted of general information (8 or 10 items) and participants’ perceptions, confidence, predictions, and perceived future prospects regarding AI (17 items). A multivariate logistic regression analysis was performed on 4 questions representing perceptions and attitudes toward AI to identify highly influential factors according to position, age, sex, residence, and self-reported knowledge level about AI of respondents. Participants were reclassified into 2 subgroups based on students’ years in school and 4 subgroups based on dentists’ years of experience. The chi-square test or Fisher’s exact test was used to determine differences between dental students and dentists and between subgroups for all 17 questions.

The study included 120 dental students and 96 dentists. Participants with high level of AI knowledge were more likely to be interested in AI compared to those with moderate or low level (adjusted OR 24.345, p  < 0.001). Most dental students (60.8%) and dentists (67.7%) predicted that dental AI would complement human limitations. Dental students responded that they would actively use AI in almost all cases (40.8%), while dentists responded that they would use AI only when necessary (44.8%). Dentists with 11–20 years of experience were the most likely to disagree that AI could outperform skilled dentists (50.0%), and respondents with longer careers had higher response rates regarding the need for AI education in schools.

Conclusions

Knowledge level about AI emerged as the factor influencing perceptions and attitudes toward AI, with both dental students and dentists showing similar views on recognizing the potential of AI as an auxiliary tool. However, students’ and dentists’ willingness to use AI differed. Although dentists differed in their confidence in the abilities of AI, all dentists recognized the need for education on AI. AI adoption is becoming a reality in dentistry, which requires proper awareness, proper use, and comprehensive AI education.

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Artificial intelligence (AI) enables machines to perform tasks with a level of intelligence comparable to that of humans. It has been approximately 10 years since AI passed through 2 periods of stagnation, often referred to as “winters,” and it has now entered its third heyday. AI is currently advancing faster than ever before, and commercialization has begun to occur in various fields. Translation, voice recognition, and navigation services have already been commercialized and are extensively used. Autonomous driving vehicles can be seen on the roads, and ChatGPT, a large language model, has recently come into the spotlight and is gaining worldwide popularity.

In dentistry, AI is applied to various image data, such as panoramic, periapical, bitewing, cephalometric, cone-beam computed tomography, and magnetic resonance images. AI has been studied extensively and can now be used across the entire process of dental care, from patient diagnosis to treatment plan establishment and prognosis evaluation. Dental AI is capable of diagnosing dental caries [ 1 ] and periodontal disease [ 2 ], identifying orthodontic landmarks [ 3 , 4 ], predicting the difficulty of extracting wisdom teeth [ 5 ], and even accurately assessing patients’ facial asymmetry before and after orthognathic surgery [ 6 ]. As a report published in 2020 suggests [ 7 ], dental AI enables quick completion of tasks, accurate diagnosis through rational decision-making, and standardization of procedures. It is expected to become more customized to meet user needs and provide convenience.

School programs have begun to implement education on AI, and it is likely that dental students and seasoned dentists will become users of AI in the near future. The key will be individual choices about appropriate AI utilization and the technology’s reliability. To ensure the correct development and practical use of dental AI, a survey to understand the perceptions and attitudes of all generations of dentists must occur first. This approach makes it possible to identify whether students, with only theoretical knowledge, and dentists, with practical experience, align or differ in their opinions on dental AI based on their respective backgrounds. Some studies have been conducted in Brazil [ 8 ], Saudi Arabia [ 9 ], Turkey [ 10 ], and multinational institutions [ 11 ]. However, there has been no such attempt in South Korea; although some previous studies have analyzed the responses of dental students by their year of study [ 10 ], no studies have accounted for dentists’ length of professional experience.

Therefore, the aim of this study was to investigate and compare the current perceptions, confidence, predictions, and perceived future prospects of AI among dental students and dentists in South Korea. In addition, we categorized participants into subgroups to investigate whether their perceptions differed by their school year or length of professional experience.

Participant recruitment

This study was approved by the Institutional Review Board of the College of Dentistry, Yonsei University (No. 2–2022-0035). The sample size was calculated using G*Power software (ver. 3.1.9.7; Universität Kiel, Germany) with an effect size of 0.2, significance level of 0.05, and power of 0.85. An online survey using Google Forms was distributed from September to November 2022. Dental students were recruited from two randomly selected colleges (one in a metropolitan city and another in a rural area) out of a total of 11 dental colleges in South Korea. Dentists were recruited from the two most actively used dental social websites in South Korea: Dentphoto ( http://www.dentphoto.com ) and moreDEN ( http://www.moreden.co.kr ). Anyone enrolled in a Korean dental college or had a Korean dentist’s license could participate in the study. However, given that the major dental courses and clinical training begin in the third year in the 6-year Korean dental curriculum, recruitment was limited to students who were in their third year or higher. All participants confirmed their understanding and agreement to participate in the study by reading a research statement that was prepared in advance and completing the questionnaire.

Questionnaire

The study used a comprehensive questionnaire developed by Jeong et al. [ 12 ] to survey all dental providers’ (dentists, dental hygienists, dental technicians, and students majoring in these fields, etc.) perceptions and attitudes toward AI. The reliability of the questionnaire was shown by a Cronbach’s alpha coefficient of 0.695 in the previous study, and minor details were modified to target dentists and dental students. The survey was distributed in their native language, Korean. It contained a basic section to investigate participants’ general information (8 questions for students, 10 for dentists), followed by a main section with 4 subsections to evaluate participants’ perceptions (5 questions), confidence (3 questions), predictions (4 questions), and perceived future prospects (5 questions) regarding AI. In the main section, participants could choose only one answer for each question, except in 3 multiple-response questions (items 9, 10, and 12). For the multiple-response questions, the number of possible responses was limited to determine priorities, with 2 for question 9 (“Which role will AI play in dental healthcare?”), 2 for question 10 (“Which field of dentistry will benefit most from AI?”), and 3 for question 12 (“Which branch of dentistry will be the first to commercialize AI?”). Participants were allowed to provide personalized responses if their opinion differed from the options presented, excluding questions on the ordinal scale.

Data analysis

All responses were thoroughly anonymized before analysis. Frequency analysis was performed for all questions, and the questionnaire’s 5-point Likert scale was simplified to a 3-point scale to assess participants’ responses as a positive or negative tendency. The results of the frequency analysis are presented as percentages relative to the total number of participants (not the total number of responses). A logistic regression analysis was conducted to investigate the impact of multivariable factors (position, age, sex, residence, and self-reported knowledge level about AI of respondents) on perceptions and attitudes towards AI. One representative question was selected for each subsection of the main section, and all variables were classified into two categories for analysis. The two-tailed chi-square test was performed to analyze the statistical significance between dental students and dentists, and within the respective subgroups of dental students and dentists for the 17 main questions. Dental students were divided into lower years (third and fourth) and upper years (fifth and sixth), and dentists were divided into 4 groups according to how long ago they had received their dentist license: 5 years or less, 6–10 years, 11–20 years, and 21 years or more. The Fisher’s exact test was applied for questions where the chi-square test was not possible due to an expected frequency of fewer than 5 (exceeding 20% of the total). The statistical analysis was performed using SPSS version 26 (IBM Corp., Armonk, NY, USA), with a statistical significance threshold of p <  0.05.

A total of 264 responses were collected, including 120 dental students (55.6%) and 96 dentists (44.4%). Data from 48 participants were excluded because they disagreed to participate in the survey or selected more responses than allowed (for instance, choosing 3 or more options when only 2 were allowed). General information about the participants is shown in Table 1 . Among dental students, fourth-year students accounted for the most responses (35.0%). Dentists with more than 21 years of experience accounted for 31.3, and 81.3% of dentists worked in dental clinics. A total of 60.8% of dental students and 43.8% of dentists accessed the latest dental news through their schools or academic conferences. Approximately one-quarter of respondents (24.2% of dental students and 25.0% of dentists) stated that they well known or very well known about AI.

Questionnaire analysis

The results of the main section to evaluate participants’ perceptions, confidence, predictions, and perceived future prospects regarding AI are shown in Table 2 .

Perceptions toward AI

A total of 63.3% of dental students and 58.3% of dentists expressed an interest in AI. Only 8.3% of dental students and 11.5% of dentists responded that they had obtained information about AI from schools or academic conferences, and 42.5 and 49.0% of them, respectively, agreed that dental schools should provide educational programs on AI.

Confidence in AI

A total of 25.0% of both groups agreed or strongly agreed on the diagnostic superiority of AI over a skilled dentist. Only 9.2% of dental students and 7.3% of dentists answered that they would follow the AI’s judgment if it differed from their own. In cases when AI misdiagnosed a patient, 68.3% of dental students and 76.0% of dentists responded that the dentist should be responsible.

Predictions about the applications of AI

Both dental students (60.8%) and dentists (67.7%) selected “complementing the limits of human intelligence” as one of the top roles for AI in future dental healthcare, with some personalized responses such as “revenue analysis” or “patient attraction.” They predicted that dental AI would be useful in diagnosing diseases (74.2% of dental students and 85.4% of dentists). The majority of participants (70.0% of dental students and 70.8% of dentists) responded that oral and maxillofacial radiology would be the branch where AI would be commercialized first, followed by orthodontics (52.5% of dental students and 49.0% of dentists).

Perceived future prospects for the application of dental AI

A total of 75.0% of dental students and 70.8% of dentists answered positively to its potential utility. Many respondents predicted the commercialization of dental AI within 8 to 11 years (41.6% of dental students and 43.7% of dentists). Regarding the possibility that dental AI could replace their job in the future, 64.2% of dental students and 71.9% of dentists disagreed.

Multivariate factor analysis influencing perceptions and attitudes toward AI

The respondents who self-reported high level of knowledge about AI were more likely to show interest in AI than those with moderate and low level of knowledge (aOR = 24.345, p  < 0.001) in multivariate factor analysis of perceptions and attitudes. There were no statistical significance depending on position, age, sex, and residence (Table 3 ).

Difference analysis in perceptions and attitudes between dental students and dentists

Statistically significant differences were found between dental students and dentists for 3 questions in the questionnaire’s main section. In question 3, which asks about the greatest advantage of AI, dental students (52.6%) most often chose the integration of extensive data, while dentists (32.3%) most often responded that it is fast and objective. In question 15, dental students (40.8%) said they would use dental AI in all or most cases in the future, and dentists (44.8%) said they would use it only seldom or when necessary. Question 17 showed that a higher proportion of dental students (87.5%) than dentists (80.2%) anticipated that dental AI will develop and reduce misdiagnosis rates in the future (Table 2 ).

Difference analysis within subgroups according to seniority of dental students and dentists

The subgroup analysis according to the seniority of dental students indicated that only the responses to question 11 exhibited a statistically significant difference (Fig. 1 ). Dental students in the lower years (third and fourth) believed (64.7%) that university hospitals would be the first to commercialize AI, while 42.0% of students in the upper years (fifth and sixth) thought that specialty clinics would be the first to do so.

Responses of the student subgroups (lower and upper years) to Question 11. Fisher’s exact test showed a statistically significant difference in the responses of the 2 subgroups ( p  = 0.003). AI artificial intelligence

In the subgroup analysis according to dentists’ seniority, 3 questions exhibited statistically significant differences. The most frequently mentioned strength of AI in question 3 was its fast and objective nature among the subgroup with 21 years or more of experience (43.3%), followed by the subgroup with less than 5 years of experience (37.0%). The subgroup with 6–10 years of experience chose “reduction of misdiagnosis rates” (66.7%), and the subgroup with 11–20 years chose “integration of extensive data” (37.5%). None of the dentists selected “no constraints of time and space” (Fig. 2 ). Question 5 indicated that the longer the dentists’ careers, the more they agreed that AI-related information should be provided in schools: 25.9% for 5 years or less, 40.0% for 6–10 years, 50.0% for 11–20 years, and 73.3% for 21 years or more (Fig. 3 ). In question 6, 50.0% of dentists with 11–20 years of experience disagreed that AI’s diagnostic ability could outperform that of a skilled dentist (Fig. 4 ).

Responses to Question 3 according to dentists’ years of experience. Fisher’s exact test showed a statistically significant difference in the responses of the subgroups ( p  = 0.029). AI artificial intelligence

Responses to Question 5 according to dentists’ years of experience. Fisher’s exact test showed a statistically significant difference in the responses of the subgroups ( p  = 0.020). AI artificial intelligence

Responses to Question 6 according to dentists’ years of experience. The chi-square test showed a statistically significant difference in the responses of the subgroups ( p  = 0.043). AI artificial intelligence

The field of dentistry is undergoing significant changes through extensive research and development in dental AI, and its use is becoming a consideration across the dental profession, not only for a select few. This study aimed to investigate the perceptions and attitudes of dental students and dentists toward AI in South Korea. Some studies have been previously conducted, but this is the first attempt in South Korea. The novelty of this research lies in not only comparing the results between dental students and dentists but also analyzing differences based on their seniority. Furthermore, it is expected that the rapid development of AI will lead to changes in perception, so it would be interesting to compare the results of our study with the perceptions described in previous studies.

This study included 216 participants, consisting of 120 dental students and 96 dentists. The response rate for students was 20.7%, but an accurate calculation was not possible for dentists because the number of subscribers was not disclosed on the websites. Several strategies suggested by Phillips et al. [ 13 ] were implemented to collect as many responses as possible, but the possibility of non-response bias due to the small number of participants must be considered. The findings revealed no significant differences among dental students and dentists in most of their perceptions, confidence, predictions, and perceived future prospects of AI. Interestingly, despite the rapid advancement of AI technology, the overall trend observed in this study remains consistent with previous studies [ 8 , 9 , 10 , 11 ] conducted 2 to 3 years earlier.

In a previous survey of medical and dental students in 63 countries [ 11 ], only 15.3% of participants responded that they were interested in the use of AI in daily life, but our study observed a significant increase, with 63.3 and 58.3% of dental students and dentists, respectively. Nevertheless, it appeared that AI-related education is not yet sufficiently provided in schools. Only a small number of dental students and dentists answered that they obtained information on AI from schools or academic conferences (8.3 and 11.5%, respectively), and almost half of the participants (42.5 and 49%, respectively) responded that school programs should provide education on AI. Since several dental colleges have begun offering AI-related school programs, the proportion of participants who stated that schools should provide education on AI was somewhat lower than that in previous studies [ 8 , 10 , 11 ], and our results showed that related educational support is still lacking.

The findings in this study highlight the ethical challenges facing AI. Respondents said they would rely on the judgment of humans, such as themselves or other dentists, when their opinions and those of AI differed (83.4% of students and 89.6% of dentists). Although there was a prevalent belief that dentists should bear responsibility for AI misdiagnoses (68.3% of students and 76.0% of dentists), others pointed toward the companies that developed the algorithms (20.0% of students and 18.8% of dentists). AI algorithms have a blind spot, referred to as the “black box” problem, wherein they do not reveal the patterns they analyze and apply when learning from training data [ 14 ]. The opacity of AI decision-making processes and the potential inconsistency in judgments call into question the validity of AI, sparking debates on responsibility attribution [ 15 ]. Therefore, indiscriminate use of AI should be avoided in high-risk healthcare settings where accurate decisions and appropriate actions based on evidence are important.

Both students and dentists were aware of the role and limitations of AI. They expected AI to serve primarily as an adjuvant in diagnosing oral diseases (74.2 and 85.4%, respectively) and recognized that it could compensate for deficiencies in human intellectual limits (60.8 and 67.7%, respectively). More than 70% of participants identified oral and maxillofacial radiology as the field with the highest potential for dental AI to be commercialized first, followed by orthodontics. AI technologies, including machine learning and deep learning, are being utilized to accurately detect [ 16 , 17 , 18 , 19 , 20 ] or segment [ 21 , 22 , 23 ] oral lesions on dental radiographs. Several commercial software applications in orthodontics automatically recognize landmarks in this way.

Most students and dentists participating in our study had a positive outlook on the potential and utility of dental AI but did not believe it would replace their jobs (64.2 and 71.9%, respectively). Most agreed that AI cannot replace all jobs but expected that it will first replace simple jobs that do not require much skill. However, recent generative AI tools can create text, photos, and videos, and the idea that white-collar jobs based on professional knowledge will be replaced by AI is growing.

Respondents who considered themselves to have a high level of knowledge about AI were approximately 24 times more likely to be highly interested in everyday AI applications. There were differences in perceptions and attitudes toward AI depending on position, age, sex, and residence, but these were not statistically significant. It is thought that further research on this is needed in the future.

Contrasting opinions were observed between dental students and dentists on certain topics. First, dental students (52.6%) highly rated AI’s capability to integrate extensive datasets, but dentists (32.3%) prioritized AI’s fast and objective ability to identify abnormalities or diseases that are difficult to detect with the naked eye in real-world clinical settings. Second, students (40.8%) expressed an inclination to use dental AI actively, whereas dentists (44.8%) indicated a more selective approach to its usage. This discrepancy likely reflects differences between students who lack clinical experience and take theoretical classes and dentists who have substantial clinical experience; furthermore, most of the students were younger than 30 years old (92.5%), suggesting a greater ability to accept new concepts and the accompanying social changes.

When the results of the survey were compared between the upper- and lower-year subgroups of dental students, the differences in responses to all but 1 question were not statistically significant. Regarding the dental facilities where AI is anticipated to be commercialized first, lower-year students (64.7%) opted for university hospitals, while upper-year students (42.0%) chose specialty clinics such as orthodontics and aesthetic prosthetics. This difference may have been influenced by the students’ respective educational levels in dentistry.

The differences in perceptions and attitudes according to dentists’ seniority were more noteworthy. Dentists with more experience were more likely to agree that schools should provide AI-related education. This indicates that even older dentists unfamiliar with digital advancements now recognize the need for AI in the field. Now that the need for AI-related school programs is no longer a controversial issue, it is time to develop appropriate educational programs, including programs that can provide AI-related information to dentists in the field. Another difference was found in the responses to whether participants thought that AI’s diagnostic ability could outperform that of a skilled dentist. Dentists with less than 5 years of experience showed the same response rates (33.3% each) for agreement and disagreement, and 50.0% of dentists with 11–20 years of experience disagreed. Half of the dentists with more than 21 years of experience expressed neither agreement nor disagreement. Dentists with 11–20 years of experience are usually considered to be in their prime regarding their knowledge and diverse clinical experience, and they seemed to trust skilled dentists more than AI.

This study is significant in that it is the first study in South Korea to investigate overall perceptions and attitudes toward AI among dental students and dentists and the first in the world to analyze differences according to participants’ years of professional experience. The findings provide valuable insights into the challenges that AI researchers must address and directions for the application of AI to dentistry. Moreover, it may help with understanding the requirements of future and current dentists to use dental AI effectively in their practice. However, this study has some limitations. The sample size was small, and the data may have been biased since the participants were recruited from a limited number of dental colleges and social websites in South Korea. Additionally, this study did not include specific questions about dental AI, making it difficult to fully understand participants’ in-depth perceptions or attitudes. Lastly, the emergence of highly trained AI systems such as ChatGPT using large-scale data is significantly changing the paradigm and becoming increasingly integrated into healthcare, but this study was conducted prior to these developments. Given the rapid development of AI, there is a need for future surveys to track changes in perceptions over time and provide detailed analysis results.

This survey showed that the greatest influential factor on perceptions and attitudes toward AI was the level of knowledge about AI, but the general view was found to be largely similar among dental students and dentists. Both dental students and dentists responded that they would follow their own judgment if it differed from that of an AI application and that dentists were responsible for AI-based diagnostic errors. This suggests that there is a growing tendency to perceive AI as an aid rather than to use it with blind faith. However, educational programs on AI are still lacking, and dentists with more experience showed the highest response rate regarding the need for AI-related education in schools. Students showed more active intention to use AI, and dentists expressed their intention to use it more selectively. These results showed that although some differences in perception still separate dental students and dentists by background and generation, the use of dental AI has become a reality for all dental students and dentists, and AI training for all generations is necessary.

Availability of data and materials

All data generated or analysed during this study are included in this published article.

Abbreviations

• Artificial intelligence

Reference category

Adjusted odds ratio

Confidence interval

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This work was supported by a grant from the National Research Foundation of Korea, funded by the Korean government (NRF-2022R1A2B5B01002517).

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Hui Jeong, and Sang-Sun Han contributed equally as the first authors.

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Department of Oral and Maxillofacial Radiology, Yonsei University College of Dentistry, Seoul, South Korea

Hui Jeong, Sang-Sun Han & Kug Jin Jeon

Department of Preventive Dentistry & Public Oral Health, Yonsei University College of Dentistry, Seoul, South Korea

Hoi-In Jung

Department of Oral and Maxillofacial Radiology, Wonkwang University College of Dentistry, Iksan, South Korea

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All authors made substantial contributions to the conception and design of the work. Wan Lee contributed to data acquisition and analysis, and Hoi-In Jung analyzed and interpreted of data for the work. Hui Jeong, Sang-Sun Han and Kug Jin Jeon drafted of this study as well as acquiring, analyzing, and interpreting the data. All authors collaborated on revising the manuscript and gave final approval for the version to be published and agreed to be accountable for all aspects of work, ensuring its integrity and accuracy.

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Jeong, H., Han, SS., Jung, HI. et al. Perceptions and attitudes of dental students and dentists in South Korea toward artificial intelligence: a subgroup analysis based on professional seniority. BMC Med Educ 24 , 430 (2024). https://doi.org/10.1186/s12909-024-05441-y

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Quantum mechanical analysis of yttrium-stabilized zirconia and alumina: implications for mechanical performance of esthetic crowns

• Ravinder S. Saini 1 ,
• Abdulkhaliq Ali F. Alshadidi 1 ,
• Vishwanath Gurumurthy 1 ,
• Abdulmajeed Okshah 1 ,
• Sunil Kumar Vaddamanu 1 ,
• Rayan Ibrahim H. Binduhayyim 1 ,
• Saurabh Chaturvedi 2 ,
• Shashit Shetty Bavabeedu 3 &
• Artak Heboyan 4 , 5 , 6  

European Journal of Medical Research volume  29 , Article number:  254 ( 2024 ) Cite this article

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Metrics details

Yttrium-stabilized zirconia (YSZ) and alumina are the most commonly used dental esthetic crown materials. This study aimed to provide detailed information on the comparison between yttrium-stabilized zirconia (YSZ) and alumina, the two materials most often used for esthetic crowns in dentistry.

Methodology

The ground-state energy of the materials was calculated using the Cambridge Serial Total Energy Package (CASTEP) code, which employs a first-principles method based on density functional theory (DFT). The electronic exchange–correlation energy was evaluated using the generalized gradient approximation (GGA) within the Perdew (Burke) Ernzerhof scheme.

Optimization of the geometries and investigation of the optical properties, dynamic stability, band structures, refractive indices, and mechanical properties of these materials contribute to a holistic understanding of these materials. Geometric optimization of YSZ provides important insights into its dynamic stability based on observations of its crystal structure and polyhedral geometry, which show stable configurations. Alumina exhibits a distinctive charge, kinetic, and potential (CKP) geometry, which contributes to its interesting structural framework and molecular-level stability. The optical properties of alumina were evaluated using pseudo-atomic computations, demonstrating its responsiveness to external stimuli. The refractive indices, reflectance, and dielectric functions indicate that the transmission of light by alumina depends on numerous factors that are essential for the optical performance of alumina as a material for esthetic crowns. The band structures of both the materials were explored, and the band gap of alumina was determined to be 5.853 eV. In addition, the band structure describes electronic transitions that influence the conductivity and optical properties of a material. The stability of alumina can be deduced from its bandgap, an essential property that determines its use as a dental material. Refractive indices are vital optical properties of esthetic crown materials. Therefore, the ability to understand their refractive-index graphs explains their transparency and color distortion through how the material responds to light..The regulated absorption characteristics exhibited by YSZ render it a highly attractive option for the development of esthetic crowns, as it guarantees minimal color distortion.

The acceptability of materials for esthetic crowns is strongly determined by mechanical properties such as elastic stiffness constants, Young's modulus, and shear modulus. YSZ is a highly durable material for dental applications, owing to its superior mechanical strength.

Introduction

An esthetic dental crown is an esthetic restoration used to replace the original shape, color, size, and thickness of teeth that are damaged or weakened [ 1 ]. This dental procedure is routinely used when a tooth has extensive decay coupled with structural damage, or when the tooth lacks a cosmetically acceptable appearance [ 2 ]. The principal aim of an esthetic crown is to safeguard the damaged tooth while simultaneously improving its function and esthetics [ 3 ].

The materials used to make esthetic crowns are different, and the choice depends on the location of the tooth, chewing needs, and patient preference [ 4 , 5 ]. Porcelain or ceramic crowns are natural-looking teeth that are especially suitable for the front teeth or areas of the mouth where the teeth are visible [ 6 ]. Porcelain-fused-to-metal crowns combine the esthetic appeal of porcelain with the added strength derived from a metal substructure. Zirconia crowns have become increasingly popular because of their strength and appearance. Zirconia ceramics can withstand chipping and cracking. It can be used in anterior and posterior crowns [ 7 , 8 ]. For cases in which both esthetics and strength are important, the solution is porcelain-fused-to-zirconia crowns, which combine the esthetics of porcelain with the strength of zirconia and can also be used for posterior teeth [ 9 ].

The advantages of metal crowns (made from gold or metal alloys) are their strength and durability [ 10 ]. However, because of their metallic appearance, these crowns are less commonly used in visible areas of the mouth. Composite resin crowns are made of tooth-colored filling materials that can be used to create temporary crowns [ 11 ]. Although less durable compared to some materials, composite resin crowns offer an esthetically pleasing alternative [ 12 , 13 ].

The choice of crown material is based on a concerted decision between the dentist and patient, considering oral health, specific tooth requirements, and personal esthetic preferences [ 14 ]. This approach allows the operator to customize the treatment for each individual patient so that the selected crown material is tailored to their own individual requirements and contributes to the functional and esthetic requirements [ 4 ]. Yttrium-stabilized zirconia (YSZ) and alumina are two types of ceramics that are frequently used to make ceramic dental crowns, with their own advantages for application in dentistry [ 15 , 16 ].

The main component of YSZ is zirconium oxide (ZrO2), which is used with yttrium oxide (Y2O3) as the stabilizing agent [ 17 ]. Yttrium is added to prevent the transformation from a tetragonal to monoclinic crystal structure, thus improving its mechanical properties [ 18 ]. YSZ has excellent strength, toughness, and hardness and is a viable material for dental crowns. Its high fracture resistance protects the crown from chipping or cracking and is biocompatible with the oral environment [ 19 ]. In terms of esthetics, YSZ can be matched in color to more natural teeth, and additional translucency adds to the more natural appearance of restorations. It is suitable for both anterior and posterior teeth [ 20 ].

Alumina crowns, in contrast, are largely made of aluminum oxide (aluminum trioxide or Al 6 2O 3 ), which is a ceramic that is well known for its hardness and resistance to wear [ 21 ]. Alumina exhibits notable hardness and wear resistance that contribute to its durability [ 22 , 23 ]. It has excellent biocompatibility with oral tissues and can be made to match the color of natural teeth; while it is less translucent than YSZ, the esthetics of alumina crowns are continuously improved through material processing [ 24 ]. Alumina crowns are commonly used for anterior teeth where esthetics are a primary concern, and they may be chosen for cases where wear resistance is a key consideration [ 25 , 26 ]. Yttrium-stabilized zirconia and alumina are suitable options for the production of esthetic dental crowns. The choice between the two materials depends on the location of the tooth, type of clinical requirement, and patient’s choice [ 27 ]. These ceramics continue to evolve as new advancements in material science become available to the dental profession, which ultimately allows dentists to provide optimized functional and esthetic outcomes in restorative dentistry [ 28 , 29 ].

In this study, we comprehensively analyzed the mechanical properties, Density of states (DOS), integrated DOS, band structures, optical properties, and stress properties of yttrium-stabilized zirconia (YSZ) and alumina, specifically in the context of their application in esthetic dental crowns. The calculations were based on the computational approach of the CASTEP (Cambridge Serial Total Energy Package) code. The results were verified to provide ideas regarding the structural, electronic, and optical parameters of these materials and to identify their potential usefulness in esthetic crown applications.

Material and methodology

The Cambridge Serial Total Energy Package (CASTEP) code [ 30 , 31 ], utilizing a first-principles approach grounded in density functional theory (DFT), was employed to calculate the ground-state energy of the materials. The generalized gradient approximation (GGA) within the Perdew (Burke) Ernzerhof scheme was used to evaluate the electronic exchange–correlation energy. Vanderbilt-type norm-conserving pseudopotentials, along with a Koelling–Harmon relativistic treatment, were applied to represent the interaction between the valence electrons and ion cores. This pseudopotential selection balances the computational efficiency with the accuracy [ 32 , 33 ]. The valence electron configurations considered were 1s 2 2s 2 2p 4 for 0, 1s 2 2s 2 2p 6 3s 2 3p 1 for Al in alumina, and 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 1 5s 2 for Y and 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 2 5s 2 for zirconia in YSZ.

Geometry optimization for yttrium-stabilized zirconia and alumina was performed using the limited-memory Broyden–Fletcher–Goldfarb–Shanno (LBFGS) minimization scheme to achieve the lowest energy structure. A plane-wave cutoff energy of 500 eV for alumina and 625 eV for YSZ was used for the expansion. Brillouin zone (BZ) integration was conducted using the Monkhorst–Pack method, employing the k-point for alumina (3 × 3 × 1) and YSZ (2 × 2 × 2). The geometry optimization employed convergence tolerances of 10 -4  eV/atom for total energy, 10 -2  Å for maximum lattice point displacement, 0.03 eV Å -1 for maximum ionic Hellmann–Feynman force, and 0.05 GPa for maximum stress tolerance. To guarantee accurate structural, elastic, and electronic band structure property estimates while preserving the computational efficiency, finite basis set modifications were used.

Results and discussion

Structural properties.

The structural properties of alumina were determined through a geometry optimization process employing the LBFGS (limited-memory Broyden–Fletcher–Goldfarb–Shanno) minimization scheme [ 34 ]. The optimization involved an unbounded number of LBFGS updates with a preconditioned LBFGS activated using an exponential (EXP) stabilization constant of 0.1000 and a parameter A value of 3.0000. The real lattice parameters were a  = 4.759 Å, b  = 4.759 Å, and c  = 12.991 Å, with corresponding cell angles of α  = 90.000°, β  = 90.000°, and γ  = 120.000°. The current volume of the unit cell was calculated as 254.803051 A 3 , resulting in a density of 2.400943 AMU/A 3 or 3.986860 g/cm 3 . The crystal system was identified as trigonal with a hexagonal geometry. The rhombohedral centers were determined to be at coordinates (0, 0, 0), (2/3, 1/3, 1/3), and (1/3, 2/3, 2/3), corresponding to crystal class – 3 m. Additionally, the LBFGS optimization results indicated a final enthalpy of − 9.29467617 × 10 3  eV, a final frequency of 543.62876 cm -1 , and a final bulk modulus of 220.64766 GPa. These optimization parameters, including the estimated bulk modulus and frequency, are crucial for obtaining the lowest-energy structure of alumina, providing insights into its stable geometric configuration and overall structural characteristics.

The structural properties of yttrium-stabilized zirconia (YSZ) were also investigated through geometry optimization using the LBFGS (limited-memory Broyden–Fletcher–Goldfarb–Shanno) minimization scheme. The optimization process utilized an unbounded number of LBFGS updates with an activated preconditioned LBFGS, employing an exponential (EXP) stabilization constant of 0.1000 and a parameter A value of 3.0000. The nearest-neighbor distance, cutoff distance, and parameter mu were determined automatically, whereas the variable cell method with a fixed basis quality was employed. The optimization comprised a maximum of 2 steps, with an estimated bulk modulus of 500.0 GPa and frequency of 1668 cm -1 . The real lattice parameters for the unit cell were identified as a  = 5.154630 Å, b  = 5.154630 Å, and c  = 5.154630 Å, resulting in a cubic geometry with cell angles of α  = 90.000°, β  = 90.000°, and γ  = 90.000°. The current cell volume was calculated as 136.959604 A 3 , resulting in a density of 30.452467 AMU/A 3 or 50.567510 g/cm 3 . The crystal system was characterized as cubic, the geometry was cubic, and the rhombohedral centers were specified at the coordinates (0,0,0). The crystal class was identified as 1, and the space group as P 1 with space number 1. The LBFGS optimization results indicated a final enthalpy of 4.89620241 × 10 5  eV, an unchanged final frequency value from the initial value, and a final bulk modulus of 117.20470 GPa. These findings offer insight into the stable geometric configuration, crystal structure, and overall structural properties of yttrium-stabilized zirconia.

Figure  1 data offer insights into the geometry (Fig.  1 (a)), polyhedron (Fig.  1 (b)), and charge, kinetic, and potential (CKP) (Fig.  1 (c)) energy of alumina (Al 6 2O 3 ) having aluminum (Al) in the + 3 oxidation state and oxygen (O) in the − 2 oxidation state. In Fig.  1 (a), the unit cell of alumina exhibits the following lattice parameters: a  = 4.759 Å, b  = 4.759 Å, c  = 12.991 Å, with angles α  =  β  = 90° and γ  = 120°. The current cell volume was 254.803051 Å 3 and the density was 2.400943 AMU/A 3 or 3.986860 g/cm 3 . The crystal structure was characterized as a supercell containing three primitive cells.

a Coordination environment, b polyhedron, and c charge, kinetics, and potential (CKP) of alumina

In crystallography, a polyhedron is a three-dimensional geometric shape formed by connecting neighboring atoms around a central atom. As shown in Fig.  1 (b), the crystal structures of alumina and aluminum atoms are typically surrounded by oxygen atoms, forming a coordination polyhedron around each aluminum center. In the polyhedron (Fig.  1 (b)), alumina comprises 30 ions distributed between two species, oxygen (O) and aluminum (Al). The highest number of species was 18. The fractional coordinates of the atoms were specified by detailing their positions within a unit cell. As shown in Fig.  1 (c), the potential energy density is influenced by the arrangement of the charged particles (nuclei and electrons). In alumina, the potential energy density is shaped by electrostatic interactions between the positively charged aluminum ions and negatively charged oxygen ions. The ionic character of Al–O bonds contributes to the potential energy landscape.

The crystal structure of yttrium-stabilized zirconia (YSZ) is described in terms of its unit cell parameters ( a  = 5.154630 Å, b  = 5.154630 Å, c  = 5.154630 Å), as shown in Fig.  2 (a). The angles between the lattice vectors were all 90°( α  =  β  =  γ  = 90°) with the same cubic crystal system geometry. The unit cells contained oxygen (O), yttrium (Y), and zirconium (Zr). In Fig.  2 (b), the polyhedron, in the context of crystallography, typically refers to a coordination polyhedron around a specific atom. In YSZ, the coordination polyhedra around Y, Zr, and O atoms depend on the crystal structure. For YSZ, the central atoms could be zirconium (Zr), yttrium (Y), or oxygen (O). The zirconium and yttrium atoms may exhibit polyhedral coordination with the surrounding oxygen atoms. Oxygen atoms typically form polyhedra around cationic species, such as Zr and Y. Ellipsoids are often associated with the electron density distribution around an atom. In the context of electronic structure calculations, an ellipsoidal representation of the charge density or electron cloud is used to describe the spatial distribution of the electrons. In Fig.  2 (c), the zirconium and yttrium atoms in yttrium-stabilized zirconia (YSZ) have associated ellipsoids that describe their thermal vibrations. These ellipsoids were centered at the average positions of the Zr and Y atoms.

a coordination environment, b polyhedron, and c ellipsoid geometry of Yttrium-Stabilized Zirconia (YSZ)

Optical properties and dynamic stability of alumina and yttrium-stabilized zirconia

Band structure.

Figure  3 shows the band structure of alumina, which provides details of its electronic properties. The X-axis of the graph shows the high-symmetry points in the Brillouin zone. In this case, they are labeled as G, A, H, K, M, and L. These points correspond to definite crystallographic directions in the reciprocal lattice of the material. The broadening at the G and A points on the axis shown in Fig.  3 suggests the fanning out (dispersion) of the electronic states at the high-symmetry points. Therefore, this can indicate electronic transitions or electronic interactions occurring at G and A. The Y-axis gives the energy in electron volt (eV) units, which encompasses—− 20 to 20 eV, the energy level associated with the electronic states of the material.

Band structure of alumina

The band gap of alumina was 5.853 eV. The bandgap represents the energy difference between the top of the valence band and bottom of the conduction band. The band structure of alumina is crucial for understanding its electronic behavior. The wide bandgap of 5.853 eV [ 35 ] indicates that alumina is an insulating material, implying that it does not conduct electricity well. This property is desirable for applications such as esthetic crowns in dentistry. The insulating nature of alumina ensures that it does not interfere with electrical signals in the surrounding biological environment, making it suitable for use in dental crowns where electrical conductivity could be problematic. Overall, the band structure of alumina, with a significant band gap and specific broadening at high-symmetry points, supports its feasibility as a material for esthetic crowns, ensuring both electrical insulation and potentially favorable optical characteristics.

Moreover, the bandgap of alumina is a key factor in determining its stability. In general, materials with larger bandgaps are more stable. The bandgap represents the energy required to transition electrons from the valence to the conduction band. Alumina, which has a bandgap of 5.853 eV, is considered to have a relatively wide bandgap. A wide band gap indicates a large energy difference between the filled valence band and the empty conduction band. This large energy separation suggests that alumina is less prone to electron excitation and conductivity, making it an insulator. As an insulator, alumina is less likely to undergo spontaneous electron transitions, which contribute to its overall stability.

In contrast, in Fig.  4 , the Y-axis represents the energy values of the electronic bands in electron volts (eV). The range was—-15 to 15 eV. In any case, the x-axis is almost the same as the previous one. The bandgap of yttrium-stabilized zirconia was 7.631 eV [ 36 ]. The bandgap represents the energy difference between the valence and conduction bands. A larger bandgap indicates a better insulation. Moreover, materials with larger bandgaps are more stable. Yttrium-stabilized zirconia (YSZ) is known for its high strength and resistance to fracture, making it a popular choice for dental ceramics, especially for esthetic crowns.

Band structure graph of Yttrium-Stabilized Zirconia

Refractive index

The refractive index ( n ) of a material is a dimensionless quantity that provides a quantitative description of the bending or refraction of light as it enters a material from a different medium. The refractive index is often represented as (n + i k), where ( n ) is the real part and ( k ) is the imaginary part. The real part of the refractive index (n) describes how much the speed of light in the material is lowered with respect to the speed of light in vacuum. The positive values of ( n ) imply that the material is one in which the speed of light is attenuated. The imaginary part of the refractive index ( k ) is part of the optical index, which is directly related to the absorption or attenuation of light in the material.

The real part of the refractive index, the upward trend at 9 eV in Fig.  5 , suggests an increase in the refractive index, indicating increased slowing of light at this point. The downward trend at 24 Hz indicated a decrease in the refractive index, suggesting a reduction in the slowing of light. The imaginary part of the refractive index, the broadening from to the 6–24 frequency in the ( k ) values, indicates increased absorption or attenuation of light in this frequency range.

Refractive index of alumina

The refractive index is an important parameter in optical materials used for esthetic crown applications [ 37 ]. The positive values of ( n ) suggest that alumina can influence the speed of light, which is relevant for optical applications. The absorption indicated by ( k ) values may need to be considered, especially in esthetic applications where light transmission and appearance are crucial. Controlling the absorption properties is vital in esthetic crowns to prevent unwanted color distortions and to ensure that the crown appears natural.

The refractive index is directly associated with the dispersion of light. Achieving a harmonious color match with natural teeth requires careful control of the refractive index, particularly in the context of the broadening observed in the given frequency range. Figure  5 presents an overview of the optical behavior of alumina. The consistency of the refractive index and its response to light is critical for ensuring the optical clarity and esthetically pleasing appearance of an esthetic crown.

On the other hand, the refractive-index graph in Fig.  6 for yttrium-stabilized zirconia (YSZ) provides essential information about its optical properties, shedding light on its suitability for esthetic crown. The constant value of the refractive index ( n ) in the range of 6–18 frequency indicates that YSZ maintains a consistent optical behavior within this frequency range. This consistency is beneficial for achieving uniform optical properties in esthetic crowns. The sharp decrease from 5 to 1 on the y-axis suggests a substantial change in the refractive index, which may have implications for light transmission and color perception. The subsequent upward trend to 1.5 indicates a recovery in the refractive index. The sharp downward trend in the imaginary part of the refractive index ( k ) up to 10 eV indicates low light absorption within this frequency range. This is advantageous for esthetic crowns, as it suggests minimal color distortion due to absorption. The subsequent stabilization and slight upward trend of ( k ) beyond 10 eV indicate controlled absorption properties, contributing to the stability and color accuracy of the material. A constant refractive index within certain frequency ranges is desirable for achieving optical clarity and maintaining a natural appearance in esthetic crowns. The controlled absorption properties indicated by ( k ) contribute to the prevention of unwanted color distortions, ensuring that the crown closely matches natural teeth. The consistent refractive index values and controlled absorption properties suggest the stability of the optical performance of the YSZ. This is crucial for long-term durability and esthetic success of crown restorations.

Refractive index graph of Yttrium-Stabilized Zirconia

In comparison, alumina exhibits varying refractive index trends with absorption ( k ) in the observed frequency range. YSZ maintains a constant refractive index, indicating consistent optical behavior. YSZ exhibits better-controlled absorption, suggesting improved stability and color accuracy. The optical characteristics of YSZ make it a promising material for esthetic crown applications. In conclusion, yttrium-stabilized zirconia exhibits more desirable optical characteristics than alumina, making it a potentially superior material for esthetic crown applications, owing to its stable refractive index and controlled absorption properties.

• Mechanical properties

Stiffness matrix of alumina and yttrium-stabilized zirconia

The elastic stiffness constants (Cij) [ 38 ] of alumina, represented in GPa, provide crucial information regarding the response of the material to the applied stress and deformation, as shown in Table  1 . The data in Table  1 for the elastic stiffness constants of alumina are presented for a 6 × 6 matrix.

The high elastic stiffness constants, particularly those of the diagonal elements (C11, C22, C33, C44, C55, and C66), suggest that alumina is mechanically stable and can withstand stress and deformation. Stability is a crucial factor in dental restorations because it ensures that the crown material can endure forces exerted during mastication without undergoing significant deformation. The off-diagonal terms (C12, C13, C23, C14, C15, C16, C24, C25, and C26) indicate the anisotropic nature of alumina. Anisotropy implies that the mechanical properties of a material vary with the direction. Anisotropic behavior is important in esthetic crowns, as it allows for tailored mechanical properties depending on the orientation of the crown and its interaction with surrounding teeth.

The elastic stiffness constants allow the material to resist wear and deformation, thereby enhancing the long-term durability of the dental restorations. The values in the matrix that contribute to the mechanical integrity of the alumina crown would permit its use for esthetic crowns that need to withstand a variety of mechanical stresses, and knowing the elastic stiffness constants becomes important when we consider the proper design and fabrication of an esthetic crown because these values will need to be able to predict how the material under study will deform to the ideal loading conditions in such a way that its performance will be optimized; on the other hand, the elastic stiffness constants (Cij) of yttrium-stabilized zirconia (YSZ), also represented in GPa, are given in a 6 × 6 matrix in Table  2 .

The high values of the elastic stiffness constants, particularly those of the diagonal elements (C11, C22, C33, C44, C55, and C66), indicate that YSZ is mechanically stiff and exhibits excellent resistance to deformation under stress. High stiffness is advantageous in dental restorations because it contributes to the ability of the material to withstand forces exerted during biting and chewing. The diagonal terms of the matrix are identical, indicating isotropic behavior. Isotropy implies that the mechanical properties of the material are consistent in all the directions. Isotropic behavior simplifies the design and fabrication process for esthetic crowns, as the material responds uniformly to applied stress, ensuring predictable and reliable performance. The elastic stiffness constants influence the durability and resistance of the material to wear. YSZ’s stiffness of YSZ contributes to its ability to maintain its structural integrity over time, ensuring its long-term success as a dental restoration material. Understanding the elastic stiffness constants is crucial for designing esthetic crowns with precise mechanical properties. This enables dental professionals to tailor the material response to specific loading conditions and optimize the crown performance. While elastic stiffness is critical for mechanical performance, other factors, such as biocompatibility and esthetics, also play a role in the feasibility of YSZ for esthetic crowns. YSZ is known for its biocompatibility, and its natural color can contribute to visually appealing esthetic outcomes.

Comparing these values, YSZ has relatively higher values in its matrix than alumina, which means that YSZ is stiffer. In terms of the isotropic properties, the diagonal terms are the same for both values, indicating that they are isotropic. YSZ, which is stiffer, is more likely to have higher durability and resistance to deformation than alumina. Both materials offer precision in crown design owing to their isotropic behavior. The choice between them may depend on specific design requirements. This comparison indicates that YSZ generally has higher stiffness values, which may be advantageous in certain applications.

Average properties of alumina and yttrium-stabilized zirconia

The feasibility of alumina for esthetic crown applications is supported by its mechanical and optical properties derived from the average properties obtained through the Voigt, Reuss, and Hill averaging schemes listed in Table  3 .

The mechanical strength of a material is often characterized by parameters such as Young’s modulus ( E ), bulk modulus ( K ), and shear modulus ( G ). The Young’s modulus measures a material's stiffness, indicating how much it will deform under a given load. High values of the Young’s modulus imply that the material is stiff and resistant to deformation. A high Young’s modulus indicates that alumina can maintain its shape and resist bending or flexing, which is crucial for dental crowns subjected to biting and chewing forces. The bulk modulus is a measure of the resistance of a material to volume change under pressure. The high bulk modulus values indicate that the material was resistant to compression. In dental crowns that experience pressure from biting forces, a high bulk modulus is essential for maintaining the structural integrity of the crown and preventing undesirable changes in volume. The shear modulus measures the resistance of a material to deformation caused by shear stress. This represents the ability of a material to withstand the forces that act parallel to its surface. High shear modulus values imply that the material can resist shear forces, making it mechanically robust. In dental applications, resistance to shear force is crucial for the longevity and stability of crowns during mastication. The combination of the high Young's modulus and shear modulus values indicates that alumina can provide precise and stable crown fabrication. This is important for achieving an accurate fit and long-term durability of the dental crowns.

On the other hand, the average properties of yttrium-stabilized zirconia (YSZ) provide insights into its mechanical behavior in Table  4 , and these properties play a significant role in determining its feasibility as a material for esthetic crowns.

This averaging scheme provides an upper bound for the material properties. The high values of the bulk modulus (KV = 360.61 GPa), Young’s modulus (EV = 850.86 GPa), and shear modulus (GV = 384.39 GPa) indicate that YSZ is a stiff material with excellent resistance to deformation. This is advantageous for dental crowns because it suggests that YSZ can withstand forces associated with biting and chewing. This scheme provides a lower bound for the material properties. The values of the bulk modulus (KR = 360.61 GPa), Young's modulus (ER = 832.4 GPa), and shear modulus (GR = 373.18 GPa) obtained through Reuss averaging confirmed the stiffness and mechanical robustness of YSZ. The values of bulk modulus (KH = 360.61 GPa), Young’s modulus (EH = 841.66 GPa), and shear modulus (GH = 378.79 GPa) suggest that YSZ maintains a consistently high level of stiffness across the different averaging schemes.

The values of Poisson’s ratio obtained through different averaging schemes (νV = 0.10675, νR = 0.11528, νH = 0.111) suggest that YSZ has a relatively low Poisson’s ratio. A lower Poisson’s ratio is favorable for dental crowns because it indicates a lower susceptibility to deformation and better ability to maintain shape under stress. In general, the high stiffness, resistance to deformation, and low Poisson's ratio of YSZ, as indicated by its averaged properties, make it a feasible material for esthetic crowns.

In comparison, yttrium-stabilized zirconia (YSZ) exhibits a higher bulk modulus, Young's modulus, and shear modulus, along with a lower Poisson's ratio than alumina. These mechanical properties collectively suggest that YSZ is a stiffer and more resistant material, making it potentially more suitable for applications such as esthetic crowns, where mechanical strength and durability are crucial.

The eigenvalues of the stiffness matrix represent the natural frequencies at which a material vibrates when it is subjected to mechanical stimuli. In the context of alumina in Table  5 , the eigenvalues of its stiffness matrix (represented by λ1 to λ6) correspond to different modes of vibration and provide insights into its mechanical behavior.

The eigenvalues represent the stiffness or rigidity of alumina in different directions. Higher eigenvalues suggest higher stiffness in these specific directions, contributing to the overall stability of the material. The eigenvalues are associated with the natural frequencies of vibrations. Understanding these frequencies is crucial in applications where the material may be subjected to mechanical vibrations, ensuring that the material does not resonate or deform undesirably under specific loads.

In the context of esthetic crowns, the eigenvalues provide insights into how alumina responds to forces and stresses. Higher eigenvalues indicate a greater resistance to deformation, which is essential for maintaining the structural integrity of dental restorations.

On the other hand, in the context of yttrium-stabilized zirconia (YSZ), the eigenvalues (λ1 to λ6) provide insights into its mechanical behavior and structural characteristics in Table  6 . Equal values of the first three eigenvalues (λ1, λ2, and λ3) indicate isotropic or uniform stiffness in those directions. This property is beneficial in dental applications where consistent material behavior is desired. The last three eigenvalues (λ4, λ5, and λ6) were higher, indicating an increased stiffness in specific directions. This anisotropic stiffness provides YSZ with tailored mechanical properties, making it suitable for applications in which strength and resistance to deformation are crucial.

Moreover, the higher eigenvalues in certain directions suggest that YSZ can effectively resist deformations and stresses. This durability is essential for esthetic crowns to ensure long-term performance without mechanical failure.

In contrast, the eigenvalues of the stiffness matrix highlight the mechanical differences between yttrium-stabilized zirconia and alumina. YSZ exhibits a more isotropic stiffness profile with a higher overall stiffness, making it suitable for applications that require enhanced mechanical properties, such as esthetic crowns in dentistry.

Elastic moduli of yttrium-stabilized zirconia and alumina

Table 7 provides information about the variations in the elastic moduli of alumina, including the Young's modulus (Fig.  7 and (Additional file 1 : Figure S1 for 2D representation), linear compressibility, shear modulus, and Poisson's ratio. These variations are crucial for understanding the response of the material to mechanical stress and play a significant role in the suitability of alumina for esthetic crown applications.

3D representation of Young’s modulus of alumina

The range from E min (266.16 GPa) to E max (399.71 GPa) represents the variation in Young's modulus. This variation describes the stiffness of the material and its ability to withstand deformation under an applied stress. An anisotropy value of 1.502 indicates that the stiffness of the material varied in different crystallographic directions.

The variation from β min (1.5841 TPa^–1) to β max (1.8125 TPa^–1) represents the linear compressibility of alumina (Fig.  8 and (Additional file 1 : Figure S2 for 2D representation). This property indicates that the material responds to compressive stress. Furthermore, the range from G min (103.75 GPa) to G max (173.38 GPa) represents the variation in the shear modulus (Fig.  9 and (Additional file 1 : Figure S3 for 2D representation). The shear modulus reflects the resistance of a material to deformation under shear stress. Moreover, the range from ν min (0.053073) to ν max (0.3787) represents the variation in Poisson’s ratio (Fig.  10 and (Additional file 1 : Figure S4 for 2D representation). This ratio describes the tendency of the material to contract laterally when longitudinally compressed.

3D representation of linear alumina compressibility

3D representation of the shear modulus of alumina

3D representation of Poisson’s ratio of alumina

The anisotropy values for each property indicate the extent to which the material varies in different crystallographic directions, and the axis values indicate the orientation of the crystallographic axes with respect to the measurement axes. Nonetheless, this anisotropy allows the stiffness of alumina to be tailored in different directions. For dental applications, crown materials must closely resemble the mechanical properties of the natural teeth. The anisotropy values and axis information are helpful during fabrication to orient the crown with respect to the optimized mechanical properties of the material for the given directions.

In conclusion, variations in the elastic moduli of alumina are vital for tailoring the mechanical properties of materials to meet the specific requirements of esthetic crown applications. These properties ensure that the crown exhibits appropriate stiffness, deformation response, and dimensional stability, thereby contributing to the overall success of the dental restorations.

However, variations in the elastic moduli of yttrium-stabilized zirconia (YSZ) are important for esthetic crown applications for several reasons.

Young’s modulus ( E ) represents the stiffness of the material (Table  8 , Fig.  11 , and (Figure S5 for the 2D representation). The variation from E min (716.92 GPa) to E max (932.53 GPa) allows for controlled stiffness in different directions. This is crucial for mimicking the mechanical behavior of natural teeth and ensuring that the esthetic crown exhibits an appropriate level of rigidity.

3D representation of Young’s modulus of Yttrium-Stabilized Zirconia

The constant values of linear compressibility ( β min and β max at 0.92437 TPa^–1) indicate a consistent response to compressive stress (Fig.  12 and (Additional file 1 : Figure S6 for 2D representation). In esthetic crown applications, where the material may experience compressive forces during biting and chewing, predictable linear compressibility is essential for stability and reliability.

3D representation of the linear compressibility of Yttrium-Stabilized Zirconia

The variation in shear modulus ( G min to G max from 306.73 GPa to 436.17 GPa) reflects YSZ's ability to resist deformation under shear stress (Fig.  13 and (Additional file 1 : Figure S7 for 2D representation). This property is critical for ensuring that the esthetic crown maintains its structural integrity, especially in areas where shear forces are applied during mastication.

3D representation of the shear modulus of Yttrium-Stabilized Zirconia

The range of Poisson's ratio values ( ν min to ν max from − 0.0057521 to 0.20403) provides insights into the response of YSZ to longitudinal compression (Fig.  14 and (Additional file 1 : Figure S8 for 2D representation). Understanding the lateral contraction behavior is vital for preventing dimensional changes and maintaining the stability of the esthetic crown. The anisotropy values and axis information help align the crown orientation with the optimal mechanical properties of YSZ in specific directions. This enables manufacturers to customize crown structures based on the anisotropic nature of materials.

3D representation of Poisson’s ratio of Yttrium-Stabilized Zirconia

Overall, these variations in elastic moduli allow tailoring of the mechanical properties of YSZ to meet the specific demands of esthetic crown applications. This material can be designed to provide the right balance between stiffness, compressibility, shear resistance, and dimensional stability, thereby ensuring the long-term success and functionality of dental restorations. YSZ generally exhibits higher Young’s modulus, shear modulus, and anisotropy values than alumina.

Overall, YSZ and alumina possess different strengths and advantages when used in esthetic crowns, and the former seems to be a promising material with high mechanical strength, stable optical properties, and geometries. Alumina, on the other hand, shows a unique CKP geometry, as well as stable band structures and esthetically desirable optical properties, making it suitable for use in esthetic crown designs. In conclusion, dental practitioners should have knowledge of the scientific basis for material selection; however, the best choice may ultimately be specific to individual cases, requiring a delicate balancing act.

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Acknowledgements

1. All the authors are thankfull to the King Khalid University , Saudi Arabia for the financial Support. 2. All the authors would like to thank Mr Wahid Hussain for his assistance with Quantum Analysis.

The authors extend their appreciation to the Deanship of Scientific Research at King Khalid University for funding this work through the Small Group Research Project under Grant Number RGP1/331/44.

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Ravinder S. Saini, Abdulkhaliq Ali F. Alshadidi, Vishwanath Gurumurthy, Abdulmajeed Okshah, Sunil Kumar Vaddamanu & Rayan Ibrahim H. Binduhayyim

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Conceptualization and methodology: Ravinder Saini, Abdulkhaliq Shadidi. Data curation and formal analysis: Vishwanath Gurumurthy, Sunil Vaddamanu. Investigation and resources: Abdulmajeed Okshah, Rayan Binduhayyim. Original draft preparation: Ravinder S Saini, and Artak Heboyan. Writing, reviewing and editing: Saurabh Chaturvedi, Shashit Bavabeedu. Supervision and project administration: Ravinder Saini, Artak Heboyan. Funding acquisition: Ravinder Saini.

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Additional file1 : fig. s1..

2D representation of Young's modulus of Alumina in xy, xz and yz plane. Fig. S2. 2D representation of linear compressibility of Alumina in xy, xz and yz plane. Fig. S3. 2D representation of Shear modulus of Alumina in xy, xz and yz plane. Fig. S4. 2D representation of Poisson's ratio of Alumina in xy, xz and yz plane. Fig. S5. 2D representation of Youngs’s modulus of Yttrium-Stabilized Zirconia in xy, xz and yz plane. Fig. S6. 2D representation of linear compressibility of Yttrium-Stabilized Zirconia in xy, xz and yz plane. Fig. S7. 2D representation of Shear modulus of Yttrium-Stabilized Zirconia in xy, xz and yz plane. Fig. S8. 2D representation of Poisson’s ratio of Yttrium-Stabilized Zirconia in xy, xz and yz plane.

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Saini, R.S., Alshadidi, A.A.F., Gurumurthy, V. et al. Quantum mechanical analysis of yttrium-stabilized zirconia and alumina: implications for mechanical performance of esthetic crowns. Eur J Med Res 29 , 254 (2024). https://doi.org/10.1186/s40001-024-01851-2

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The potential use of nanozymes as an antibacterial agents in oral infection, periodontitis, and peri-implantitis

• Mohammad Hosseini Hooshiar 1 ,
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Several studies suggest that oral pathogenic biofilms cause persistent oral infections. Among these is periodontitis, a prevalent condition brought on by plaque biofilm. It can even result in tooth loss. Furthermore, the accumulation of germs around a dental implant may lead to peri-implantitis, which damages the surrounding bone and gum tissue. Furthermore, bacterial biofilm contamination on the implant causes soft tissue irritation and adjacent bone resorption, severely compromising dental health. On decontaminated implant surfaces, however, re-osseointegration cannot be induced by standard biofilm removal techniques such as mechanical cleaning and antiseptic treatment. A family of nanoparticles known as nanozymes (NZs) comprise highly catalytically active multivalent metal components. The most often employed NZs with antibacterial activity are those that have peroxidase (POD) activity, among other types of NZs. Since NZs are less expensive, more easily produced, and more stable than natural enzymes, they hold great promise for use in various applications, including treating microbial infections. NZs have significantly contributed to studying implant success rates and periodontal health maintenance in periodontics and implantology. An extensive analysis of the research on various NZs and their applications in managing oral health conditions, including dental caries, dental pulp disorders, oral ulcers, peri-implantitis, and bacterial infections of the mouth. To combat bacteria, this review concentrates on NZs that imitate the activity of enzymes in implantology and periodontology. With a view to the future, there are several ways that NZs might be used to treat dental disorders antibacterially.

Graphical Abstract

Introduction

Globally, bacterial infections pose a significant risk to public health. Antibiotics continue to be the most comprehensive form of medical intervention for bacterial infections. Nevertheless, antibiotic abuse and neglect have significantly contributed to the development of antibiotic-resistant strains, most notably in the context of the COVID-19 pandemic. Moreover, antibiotic management strategies are dramatically impacted by the improper and excessive application of disinfectants and biocides. As a result, alternative antibacterial remedies are required immediately to alleviate this crisis. Nanozymes (NZs) have emerged as highly prospective novel antibacterial agents in recent times due to their broad-spectrum antibacterial activity, reduced drug resistance, and exceptional stability [ 1 , 2 ]. Nanotechnology presents an innovative solution to the most urgent problems of the present day. Nanotechnology applications provide a flawless and accurate alternative in dentistry and appear to have solutions to issues that arise in conventional dental practices. These novel nanoparticles (NPs) can imitate the surface and contact characteristics of tooth tissues. Since the inception and application of NPs and nanocarriers, nanotechnology has been applied extensively in various fields. NPCs may readily breach the defenses of biological organisms due to their diminutive size. The potential applications of nanobiomedical knowledge have also been investigated, encompassing imaging, early-stage disease diagnostics, and the targeted and efficient transportation of pharmaceuticals, DNA, and therapeutic compounds to particular organs or cells [ 3 , 4 , 5 , 6 ].

Furthermore, there are numerous conventional therapies available to address periodontitis, each of which focuses on a distinct facet of the condition’s etiology and pathogenesis. The use of antibiotics and antimicrobial drugs is prevalent in treatment. Nevertheless, conventional methods are rendered ineffective as a result of drug resistance and the development of adverse effects. Because of their biocompatibility, extended shelf life, and high specific surface area to volume ratio, metal NPs exhibit the most significant potential as antibacterial agents. Many scientists are becoming intrigued by metal NPs due to the development of drug-resistant strains and the enhancement of microbial resistance to antibiotics. The biofilm can be inhibited due to the NPs’ miniature size allowing them to penetrate the biofilm matrix and establish direct contact with the bacterial cells. It is anticipated that antibacterial research will advance further as we approach practical applications. Metal NPs exhibit potent antibacterial properties [ 7 ]. Because silver-based biomaterials (AgBMs) have the potential to be very effective antibacterial agents with relatively low toxicity, a great deal of study has been done on them. AgBMs display various antimicrobial properties, including bacterial cell membrane disruption, disruption of bacterial proteins and enzymes, bacterial contact death, and damage to genetic material. More specifically, AgBMs are now more helpful because of improvements in nanotechnology. Consequently, AgBMs have been investigated and used in a wide range of dental subspecialties, such as implant coating, denture additives, periodontal plaque suppression, caries prevention or arrest, root canal sterilization, and anti-inflammatory material in oral and maxillofacial surgery [ 8 ].

Since magnetite NPs were shown to have horseradish peroxidase (POD)-like activity in 2007, other researchers have looked into various NP forms that exhibit enzyme-like activities, notably NZs [ 9 ]. NZs exhibit superior efficacy, stability, and cost-effectiveness compared to their natural counterparts [ 10 ]. As a result, NZs have already been thoroughly investigated in several fields, such as chemical engineering, agriculture, the food industry, dentistry, and medical research [ 11 ]. Natural enzymes have been applied extensively in various sectors, such as industry, medicine, biology, and more, owing to their potent catalytic capabilities and substrate specificity. While showing potential, these materials frequently encounter inherent deficiencies, including exorbitant expenses, precarious operational stability, and recycling complexities [ 12 , 13 ]. For a very long time, researchers have been exploring artificial enzyme mimics as a means of overcoming these inadequacies. One class of nanomaterials having enzyme catalytic characteristics is NZs. Since NZs are less expensive, more stable, and more durable than natural enzymes, they are often used in the biological, medicinal, and industrial domains [ 14 ]. A comprehensive understanding of the potential catalytic mechanisms will significantly aid in advancing innovative and highly effective NZs, while the logical control of their activities holds immense importance [ 15 , 16 ]. Present a comprehensive analysis of the categorization, catalytic process, and regulation of activity, along with recent advancements in research concerning NZs utilized in biosensing, environmental protection, and disease treatment, among other applications, over the last few years [ 17 ]. While antibiotic therapy is the most commonly accepted paradigm for treating these kinds of illnesses, long-term overuse, abuse, and misuse of antibiotic-based medications have led to the emergence of super-bacteria that are resistant to several antibiotics [ 18 ].

However, due to the numerous limitations of natural enzymes, engineered NZs are increasingly being utilized as viable substitutes in antibacterial therapy that does not involve antibiotics [ 19 ]. Because of their high membrane permeability and biocompatibility, NZs are also less prone to acquire bacterial resistance. More significantly, bacterial biofilms may be eliminated by using NZs capable of catalysis [ 20 , 21 ].

NZs are composed of various materials, including iron-based nanomaterials, carbon dots (CDs), carbon nanotubes (CNTs), graphene oxide, carbon nitride, fullerene, polymer-based substances, noble and non-noble metals, and their derivatives. Their efficacy has been demonstrated across multiple catalytic activity categories, including those of superoxide dismutase (SOD)-like, POD-like, and oxidase (OXD)-like enzymes [ 22 ].

An estimated billion people worldwide are impacted by oral disorders, such as dental caries, periodontal disease, and oral cancer, according to a series of articles on oral health published in The Lancet in 2019. As biomaterials evolve quickly, stomatology also advances, significantly advancing the prevention and treatment of oral diseases [ 23 ]. Nevertheless, conventional dental materials, including Ag amalgam, possess certain drawbacks that can result in associated complications and ultimately unsuccessful treatments [ 24 , 25 ]. The development of nanomaterials has opened up a wide range of options for improving oral function, maintaining dental health, and improving overall quality of life. Numerous naturally occurring enzymes, including amylase and proteolytic enzymes, have been proven to have antibacterial, anti-inflammatory, and immunity-boosting properties in oral studies and applications. These enzymes may be utilized to treat dental caries and mouth ulcers [ 26 ]. Oral cancer arises from a multitude of factors, including genetic modifications, interactions within the tumor microenvironment (TME), lifestyle choices, and microbial infections that are associated with the disease [ 27 ]. Oral cancer is treated and diagnosed using a variety of techniques. Artificial enzymes called NZs have significant promise for the treatment and diagnosis of cancers. Compared to natural enzymes, they are much more advantageous and have unique biological and physical characteristics [ 19 , 28 ].

Pathogenic biofilm-induced oral diseases, such as periodontitis caused by the accumulation of bacterial biofilm on the gums and teeth, have presented a substantial risk to human health [ 29 ]. Conventional therapeutic approaches, including mechanical debridement and antibiotic therapy, demonstrate limited efficacy in treating the condition. In treating oral diseases, numerous NZs with exceptional antibacterial activity have been utilized extensively in recent years [ 30 ]. Natural enzymes do, however, have several drawbacks, including poor stability in severe environments (such as heat and extreme pH), high production costs, time-consuming separation and purification, and long-term storage difficulties, among others [ 31 , 32 ].

The development of dentistry is parallel to that of material science. Oral NZ research and application is emerging as a new subfield of nanocatalytic medicine [ 33 ]. To underscore the significant impact of NZs on dental health, an initial examination was conducted of the overall research advancements in multifunctional NZs for the treatment of oral diseases such as dental caries, pulp diseases, ulcers, and peri-implantitis; surveillance of oral cancer, oral bacteria, and ions; and regeneration of both soft and hard tissue [ 34 ]. Oral maladies induced by biofilm are treated with a variety of conventional techniques, including mechanical scaling and root planing; however, both of these methods necessitate considerable effort and manual skill [ 35 ]. The adjunctive use of regional antibiotics may present an alternative therapeutic approach for oral infectious diseases. However, bacterial biofilm is difficult to eradicate in vivo with minimal antibiotic concentrations [ 36 ].

Furthermore, excessive antibiotic dosages may promote bacterial drug resistance and increase biofilm tolerance to antibiotics. Because of these limitations, developing new alternative strategies is urgent [ 37 ]. A novel approach that has emerged in recent years is the utilization of nanomaterials possessing enzyme-like characteristics to generate reactive oxygen species (ROS) in situ eliminating microorganisms [ 38 ]. The NZs utilized in dentistry research and application primarily catalyze POD, OXD, SOD, and catalase (CAT)-like activities. These activities have the potential to induce irreversible bacterial and biofilm destruction. Because DNA or ions can substantially increase the enzymatic activity of NZs, they can monitor ions effectively [ 32 ]. NZs have significantly advanced research in the fields of periodontics and implantology, specifically about the maintenance of periodontal health and the enhancement of implant success rates. We examine NZs for antimicrobial therapy, anti-inflammatory therapy, promotion of tissue regeneration, and synergistic effects in periodontal and peri-implant diseases to illustrate this development [ 39 , 40 , 41 ].

Plaque accumulation undoubtedly results in gingival inflammation; its elimination, however, induces a decrease in inflammation. Consequently, patient-assisted plaque eradication is an essential component of non-surgical treatment. This includes interdental cleansing, chemical plaque control, and teeth flossing [ 42 ]. Although ultrasonic scaling is a viable initial method for plaque removal, it is inconvenient and necessitates medical intervention. Furthermore, it is imperative to employ a laser of a suitable wavelength that can effectively eliminate calculus while preventing thermal injury to the dentin or structure of the tooth. The ablated surface must be conducive to the reattachment of the soft tissue. Because the wavelength of carbon dioxide lasers is readily absorbed by water, they are suitable for soft tissue surgery. However, because they cause severe thermal injury, they are unsuitable for calculus removal and root surface modification. Furthermore, laser debridement of the root surface is still in its nascent stages. Comparing the numerous studies regarding the protocols and types of lasers employed presents a challenge. However, specific lasers can eliminate calculus and plaque to an extent comparable to that achieved with hand or ultrasonic instrumentation. Nevertheless, they have a documented record of notable adverse effects, most prominently thermal injury to the surface of the roots. Given their relatively high cost, there appears to be a shortage of evidence supporting their use at this time [ 42 , 43 ].

Furthermore, there is no anti-biofilm effectiveness in anti-demineralization materials presently on the market, such as fluorides, resins, and ceramics. Instead of using invasive restorative treatment, dental nanomaterials, such as nanocatalysts, are being developed to address these issues and react to local environmental stimuli and physiological changes to prevent dental caries [ 44 ]. Scientists have made noteworthy advancements in creating innovative, reliable, and effective oral antibacterial medications that induce enzyme activity. In root canals, NZs aid in the prevention of biofilm infection. According to the research by Koo, biofilm plaque can be efficiently eliminated from the surface of dentinal tubules and root canals by activating H 2 O 2 [ 45 ].

Furthermore, the vast majority of microbial infectious diseases are effectively treatable with the extraordinary variety of antimicrobials that are presently accessible. Nevertheless, significant global health challenges include antimicrobial resistance (AMR), adverse effects, and the excessive expense associated with antimicrobials. There is a growing trend of antibiotic resistance among Gram-positive and Gram-negative bacteria that causes infections in hospitals and communities. For instance, nearly forty percent of hospital-acquired Staphylococcus aureus (S. aureus) strains are now vancomycin and methicillin-resistant. Moreover, AMR could affect approximately 230 million people annually by 2050 and cumulatively cost the global economy $100 trillion between 2014 and 2050. At present, an estimated 700,000 individuals succumb to fatal infections caused by AMR; this figure is projected to escalate to 10 million by 2050 [ 46 , 47 ]. The enzymatic breakdown of bacterial cell walls or biofilms, which results in bacterial death, is often described as the antibacterial mechanism of enzybiotics. However, most natural enzymes are unstable during industrial manufacture, which restricts their large-scale use and raises prices. Although further modification and immobilization may somewhat enhance the stability of natural enzymes, they also increase manufacturing costs and operational complexity. When compared to natural enzymes, NZs are a kind of nanomaterial that exhibits enzyme-like activity and are more affordable and stable. Currently, by imitating the enzyme-like properties of natural enzymes, NZ-based nanozybiotics have shown excellent antibacterial application prospects against resistant bacteria. Combining their enzyme-like characteristics with other physiochemical features of NZs, such as PTT and PDT, might enhance their antibacterial efficacy even further. There is still a long way to go until antibacterial tests are clinically transformed since most of them were validated in vitro or topically given using in vivo models. Therefore, it is crucial to investigate novel biocompatible nanozybiotics that use enzyme-like NZs with various antibacterial properties and relevant situations. Researchers think the class of antibiotic substitutes known as nanozybiotics, which are based on NZs with enzyme-like action, is novel [ 48 ].

Additionally, CAT, glutathione peroxidase-like (GPx), and superoxide dismutase (SOD) are NZs exhibiting antioxidant properties that demonstrate the potential in mitigating inflammation. As an illustration, scientists utilize mesoporous silica (MSN@Ce) laden with ceria oxide and modify it with polyethylene glycol (MSN@Ce@PEG) to enhance dispersion and biocompatibility. This enabled periodontal ligament stem cells (PDLSCs) to modulate ROS within the cells and promote osteogenic development, thereby protecting them from oxidative stress caused by periodontitis [ 49 , 50 ].

Before highlighting the significant contribution of NZs to dental health, an overview of the overall research progress of multifunctional NZs in the treatment of oral-related diseases such as periodontitis and peri-implantitis, dental caries, dental pulp diseases, oral ulcers, and periodontal and peri-implant diseases is provided. Furthermore, we discuss the outstanding obstacles that remain in the realm of NZ research and application, as well as anticipate forthcoming issues. We are confident that in the future, novel catalytic nanomaterials will have a significant impact on dentistry.

Classifications of antibacterial nanozymes

Classifications and modes of action for NZs Numerous nanomaterials that operate like enzymes have been discovered up to this point. The constituents of NZs typically consist of metal oxide NPs, noble metal nanomaterials, and other materials that primarily display four primary catalytic properties: SOD, CAT, OXD, and POD. Through various techniques, scientists have improved their catalytic qualities, allowing them to selectively and effectively react with specific target molecules [ 51 ]. To date, considerable effort has been devoted to the development of antibacterial NZs, which primarily consist of carbon-based nanomaterials, transition metal dichalcogenides/peroxides/oxides, single-atom nanozymes (SAzymes), and metal–organic frameworks (MOFs)-based compounds [ 21 , 52 , 53 ] (Fig.  1 ).

The classification and functions of nanozymes (NZs), including ( A ) metal and metal-oxide NZs ( B ) carbon-based NZs ( C ) single-atom NZs ( D ) metal organic framework-based NZs, prussian blue NZs. E To facilitate comprehension in this section, NZs are divided into two categories: (1) oxidoreductase family, which consists of enzymes such as nitrate reductase, oxidase, peroxidase, CAT, and superoxide dismutase; and (2) hydrolase family, which comprises the following enzymes: nuclease, esterase, phosphatase, protease, and silicatein [ 17 ]

Metal-based nanozymes

Several NZs composed of noble metals (e.g., platinum, Ag, and gold (Au)) exhibit significant catalytic activity. Mercaptopyrimidine-conjugated Au nanoclusters (NCs) were developed by Zheng et al. to target resistant superbugs both in vitro and in vivo. The simple adhesion of the NZs to the bacterial surface and subsequent disruption of the cell membrane were facilitated by their positive charge. The induction of intracellular ROS production in bacterial cells was primarily ascribed to intrinsic OXD-like and POD-like activity, which promoted wound healing and killed approximately 99% of bacteria [ 54 ]. In addition to its antibacterial efficacy, Zhang et al. assessed the POD-like and ferroxidase-like properties of bimetallic platinum–copper (PtCu) alloy NPs in a mildly acidic media, as well as the ability to detect Fe 2+ . Similarly, Cai et al. created morphology-dependent bactericidal activity in core–shell Pd@Ir bimetallic nanostructures by seed-mediated development. According to this research, the Pd@Ir octahedron’s increased OXD-like activity explained its superior antibacterial activity above Pd@Ir cubes. The Vmax value for the oxidation of 3,3′,5,5′-tetramethylbenzidine catalyzed by Pd@Ir nanocubes was 1.7 times greater, and for the Pd@Ir nano octahedron, it was 4.4 times greater than when catalyzed by Pd cubes alone. Furthermore, it was disclosed in the study that the OXD-like activity of Pd@Ir exhibited an increase when exposed to naturally occurring organic matter. The NZ, when in contact with humic acid (HA), induced significant levels of ROS and facilitated the internalization of the nanostructure by cells [ 55 ].

Metal oxide/sulfide-based nanozymes

A classic example of a biological catalyst, cerium oxide (CeO 2 ) NPs possess high POD-like activity due to a reversible redox transition between Ce 4  + and Ce 3  + ions. The CeO–H 2 O 2 system promotes ROS more readily due to its exceptionally high and efficient POD-like activity. Multiple enzymatic activities, including those of SOD, CAT, POD, and OXD, are induced by the surface-rich oxygen (O 2 ) vacancies, smooth O 2 diffusion, and high redox potential of nanoceria of varying sizes and morphologies. Luo et al. created an electrospun nanofibrous membrane (PIL-Ce) composed of imidazolium-type poly (ionic liquid) (PIL)/cerium (IV) ions. In an MRSA-infected mouse model, PIL-Ce demonstrated DNase mimetic catalytic activity and accelerated wound healing. To prevent the spread of drug resistance, the disintegration of resistant genes and the high antibacterial potential of PIL-Ce were both investigated [ 56 ]. Since ferromagnetic (Fe 3 O 4 ) NPs were first shown to exhibit enzyme-like activity in 2007, much research has been done on NZs, including in-depth analyses of a wide range of NZs and the rapid development of associated nanotechnologies. NZs have opened up new avenues for clinical care, food safety, environmental monitoring, and chemical synthesis as viable substitutes for natural enzymes [ 57 ].

For example, fungal infections are considered the largest threat to the global health of all microorganisms, according to the World Health Organization. Enhancing antifungal effectiveness at the infection site while avoiding medication resistance, fungal spread, and off-target effects remains a challenging challenge. In this work, Jun Oh et al. describe a microrobotic platform based on NZs that allows for targeted fungal eradication by accurately guiding localized catalysis to the infection location at the microscale. Dynamic shape transformation and precisely tunable catalytic activation may be achieved in structured iron oxide NZ assemblies via fine-scale spatiotemporal control and electromagnetic field frequency modulation. Motion, velocity, and shape all have an impact on catalytic activity, which makes it possible to control the generation of ROS. Surprisingly, fungal cell surfaces ( Candida albicans ) are addressed by NZ assemblies, which allow targeted ROS-mediated destruction in situ and concentrated accumulation. Using these tunable characteristics and selective binding to fungus, localized antifungal efficacy is achieved using in vivo-like cell spheroid and animal tissue infection models. Structured NZ assemblies are guided toward Candida albicans infection sites using programmable algorithms. This allows accurate directed spatial targeting and on-site catalysis, both of which help to eradicate the fungus quickly. Using this NZ-based microrobotics method, pathogens may be eliminated at the site of infection using a highly targeted and effective treatment strategy [ 58 ]. Robots powered by magnetism can perform intricate tasks in biological settings with little harm. However, robots designed to injure detrimental biostructures might potentially have a significant impact. In light of the approaching antibiotic age, innovative methods for eliminating bacterial biofilms are crucial. Biofilms are enduring, tightly adherent forms often connected to the emergence of illnesses resistant to drugs and the deterioration of surfaces. Reinfection results from existing therapies' insufficient ability to eradicate microorganisms. In a study, researchers created catalytic antimicrobial robots (CARs) that have remarkable effectiveness and control in the removal, degradation, and elimination of biofilms. Iron oxide NPs, which have both catalytic and magnetic capabilities, are used in CARs. These NPs: (i) generate bactericidal free radicals; (ii) break down the biofilm's exopolysaccharide (EPS) matrix; and (iii) use magnetic field-driven autonomous assemblies to remove the scattered biofilm debris. Researchers develop two distinct CAR systems. The first platform, the biohybrid CAR, is made of NPs and waste products from the breakdown of biofilms. Magnetic field gradients assemble NPs and the biodegraded products into a plow-like superstructure after EPS rupture and catalytic bacterial death. The biohybrid CAR effectively and selectively removes biomass when exposed to an external magnetic field, which prevents biofilm from regenerating. To accomplish targeted elimination with microscale precision, biohybrid CARs may rove along predefined trajectories or cover large surface regions. The second platform, the 3D molded CAR, is a flexible robotic polymer with integrated catalytic-magnetic NPs. It is created in a specially made 3D printed mold and intended to carry out certain functions inside limited areas. Vane-shaped CARs remove biofilms from the curved walls of cylindrical tubing, whereas helicoid-shaped CARs break through biofilm obstructions and kill bacteria. Moreover, researchers demonstrate how CARs may be applied to anatomical areas that are very limited within the human dentition. 'Kill-degrade-and-remove' CARs systems have the potential to significantly reduce biofouling on a variety of surfaces and medical equipment as well as tackle chronic biofilm infections [ 59 ].

Carbon-based nanozymes

The biomedical field has extensively used carbon-based nanomaterials, including CDs, CNTs, graphene and its derivatives, carbon nitride, and fullerene, due to their biocompatibility, physiochemical properties, and ability to mimic multiple enzymes. In a broad pH range, Wang et al. synthesized a series of CNTs (o-CNTs) that were abundant in oxidized groups and exhibited superior POD-like activity. The active catalytic centers on the surface of o-CNTs were the carbonyl group, while the competitive sites were the carboxyl and hydroxyl groups [ 60 ]. The carboxyl group has a stronger inhibitory tendency on the catalytic propensity than the hydroxyl group because of its intrinsic negative charge and propensity to create hydrogen bonds. Consequently, o-CNTs-BrPE, or 2-bromo-1-phenylethanone-modified o-CNTs, were made to lessen the carboxyl group in the NZ's inhibitory function. o-CNTs-BrPE demonstrated strong POD-like action as the number of competing sites dropped, allowing catalysis of H 2 O 2 to ·OH and eliminating bacteria and shielding tissues from purulent inflammation and edema brought on by bacteria [ 56 , 61 ].

Metal–organic frameworks (MOFs)

MOFs are distinct crystalline and porous nano/microstructures produced by organic linkers with two or more coordinating positions bridging metallic nodes of single metal ions or clusters of few metal ions. A novel porous coordinating polymer structure is attributed to the labile bonds between organic linkers and metal ions or clusters. MOFs exhibit remarkable mechanical and chemical properties. When juxtaposed with traditional NZs, MOFs-based NZs possess several significant benefits: (i) The wide array of active metal ions/clusters and organic linkers at one's disposal provides opportunities for the development of numerous NZs that possess inherent and modifiable enzyme-like characteristics [ 22 ]. (ii) Exposed active catalytic sites with improved enzyme-mimicking qualities are provided by the metal nodes and organic linkers systematically placed in an architectural framework. (iii) Natural enzymes for various cascade systems may be accommodated by the porous structure with nano/micropores, which can also promote high substrate channeling to the active sites. (iv) MOFs’ adaptable porosity and varied forms allow for effective size control of reacting molecules, enhancing catalytic activity with a high degree of substrate selectivity [ 62 ]. (v) MOFs with high specific surface area have a varied geometric structure that provides a tunable platform for further modification, which enhances their catalytic activity by adding new features. Because of these benefits, a lot of work has been put into creating MOFs-based NZs for biological catalysis and sensing in recent years. MOF-based NZs have shown remarkable potential in the biomedical domain owing to their adaptable architectures, high activity, and strong stability. Interestingly, the investigation of MOFs with enzyme-mimicry characteristics for bacterial theranostics applications was aided by the rapid creation of catalytic nanomedicines. For the creation of innovative NZs with hereditary catalytic activity for the treatment and diagnosis of bacterial infections, MOF is thought to be a viable platform [ 63 ].

Because H 2 O 2 is a prevalent ROS, it has been utilized extensively to combat pathogenic bacterial infections. However, excessive H 2 O 2 can cause harm to healthy tissues and impede the healing process. POD-like nanomaterials exhibit great potential as NZs in this context due to their ability to enhance the antibacterial activity of H 2 O 2 without introducing the toxicity associated with high concentrations of H 2 O 2 . Using in situ reduction, ultrasmall Au NPs (UsAuNPs) are produced on ultrathin 2D MOFs in this study. Combining the benefits of UsAuNPs and ultrathin 2D MOFs, the UsAuNPs/MOFs hybrid exhibits an exceptional POD-like activity in decomposing H 2 O 2 into toxic hydroxyl radicals (·OH). The UsAuNPs/MOFs NZ, in its as-prepared state, demonstrates remarkable antibacterial efficacy against S. aureus and Escherichia coli ( E. coli ), two Gram-negative and Gram-positive bacteria, respectively, when a minimal amount of H 2 O 2 is added. This study presents compelling evidence regarding the antibacterial potential of a hybrid NZ and underscores its significant potential for forthcoming clinical implementations [ 64 ]. Furthermore, it is noteworthy that while SAzymes containing MOF derivatives have been documented, the utilization of single-atom dopped MOF as NZs in periodontitis treatment has not been documented nor implemented to the best of our knowledge [ 65 ].

Single-atom nanozymes (SAzymes)

NZs, nanomaterials that exhibit enzymatic activity, have been the subject of extensive research. Inadequate substrate selectivity, a complex composition, and a low density of active sites have impeded the maturation and widespread adoption of NZs. A leader in the field of catalysis, enzymes with atomically dispersed active sites are distinguished by their outstanding performance. Researchers highly value the following characteristics of SAzymes: optimal atom utilization rate, economical cost, clearly defined coordination structure, and active sites [ 66 ]. SAzyme is the current focal point of NZ research. Its inherent characteristics, including high activity, stability, and affordability, make it an excellent alternative to natural enzymes. Furthermore, compared to conventional NZs, its intrinsic qualities—namely, optimized atom utilization and precisely defined geometric and electronic structures—contribute to its superior catalytic activities and specificity [ 67 ]. An instance of this can be seen in the synthesis of alternative Cu SAzymes featuring atomically dispersed Cu sites anchored on ultrathin 2D porous N-doped carbon nanosheets (CuNx-CNS) and tunable N coordination numbers in the CuN x (x = 2 or 4) sites is described by researchers utilizing a Cu and silk fibroin (Cu-SF) complex strategy. The triple POD, CAT, and OXD-like activities of the CuNx-CNS SAzymes enable the conversion of H 2 O 2 and O 2 to ROS via parallel POD and OXD-like reactions or cascaded CAT and OXD-like reactions. In contrast to CuN 2 -CNS, increasing the N coordination number from 2 to 4 confers greater multienzyme activities upon the SAzyme (CuN 4 -CNS), attributed to its enhanced electron configuration and reduced energy barrier. In contrast, CuN x -CNS exhibits robust absorption in the second near-infrared (NIR-II) biowindow, facilitating photothermal treatment in deep tissues and NIR-II-responsive enhancement of ROS production. The optimal CuN 4 -CNS inhibits multidrug-resistant bacteria and eliminates resistant biofilms, demonstrating high therapeutic efficacy against both superficial skin wounds and deep implant-related biofilm infections, as shown by in vitro and in vivo results [ 68 ].

Nanozymes in antibacterial applications

Living things include enzymes that can change a range of substrates into ROS, used to fight bacterial invasion. Oxidative salivary enzymes, which support the host's natural defense mechanism, prevent or limit the growth of oral pathogens; polysaccharide hydrolases, such as mutanases and dextranases, break down essential carbohydrate components of the biofilm matrix; and proteases alter cell-to-cell interactions or prevent bacteria from adhering to oral surfaces [ 69 ]. Bacteriostatic hypothiocyanite (OSCN-), a mild oxidizing agent, is generated through the enzymatic catalysis of thiocyanate ion (SCN-) oxidation by hydrogen peroxide (H 2 O 2 ) by the enzyme lactoperoxidase (LP). This process takes place within secretory fluids. However, H 2 O 2 retains its antibacterial characteristics without thiocyanate (SCN-) and LP. Consequently, LP has the potential to either protect bacteria from the harmful effects of H 2 O 2 by transforming it into a less potent oxidizing agent or it can enhance antibacterial efficacy by utilizing H 2 O 2 to produce a more potent growth and metabolism inhibitor for bacteria. An investigation was conducted to determine the function of LP by assessing the antibacterial properties of H 2 O 2 and the LP-H 2 O 2 -SCN system through the inhibition of bacterial growth and metabolism and the loss of viability. Streptococci are protected from H 2 O 2 mortality by LP and SCN, and elevated concentrations of H 2 O 2 for protracted periods result in a potent bactericidal effect, according to the findings. As an inhibitor of bacterial growth and metabolism, LP, H 2 O 2 , and SCN-combinate significantly outperform H 2 O 2 alone [ 70 ]. Streptococcus sanguinis ( S. sanguinis ) is a strain of Gram-positive bacteria that causes dental caries. Creating new antibacterial agents is crucial as many antibacterial agents are resistant to microorganisms. Among the enzymes that support the cell wall is the enzyme murA. The first stage of peptidoglycan biosynthesis, which includes the creation of the cell wall, is catalyzed by MurA. By suppressing MurA, the germs may be eliminated with effectiveness and efficiency. Medicinal plants and other natural items include bioactive chemicals and antibacterial agents. According to reports, Piper betle L. possesses potent antibacterial properties. A minimum inhibitory concentration (MIC) and maximum barrier concentration (MBC) of 39.1 and 78.1 μg/mL, respectively, were the results of the antibacterial compound allylpyrocatechol’s inhibitory activity against S. sanguinis at a concentration of 1%. An inhibition zone of 11.85 mm was also observed. Two allylpyrocatechol derivatives, which were found to be more powerful than the reference molecule fosfomycin and had binding activities of − 5.4 and − 4.6%, respectively, were used to anticipate the molecular inhibitory mechanism of allylpyrocatechols against MurA [ 71 ]. However, several inherent drawbacks, such as their high cost, low stability, and restricted capacity for production scaling, significantly impede their continued use as antibacterial agents. Therefore, it is necessary to investigate effective antibacterial drugs at clinical translations [ 72 ]. Upon interaction with a bacterium, engineered NPs have the potential to induce ROS, discharge heavy metals, impair proton efflux pumps, disrupt electron transport chains, and rupture cell membranes. One such strategy is ROS, which has demonstrated rapidity, efficacy, and broad-spectrum activity against bacteria and cancer, and notably, does not appear to promote the development of drug-resistant microorganisms. Additionally, ROS reacts with the DNA and lipids of latent bacteria, specifically “superbugs” and recalcitrant biofilms, and possesses potent antibacterial properties [ 73 ].

The advent of nanotechnology has facilitated the creation of NZs, which offer a potential therapeutic approach for bacterial infections. It is widely recognized that the antibacterial mechanism of NZs can be broadly classified into the subsequent categories: By converting the corresponding substrate H 2 O 2 or O 2 into ROS such as ·OH or singlet oxygen ( 1 O 2 ), POD or oxidase mimics are capable of producing an antibacterial effect. Furthermore, prodrugs can be converted to antibiotics in the presence of NZs via bio-orthogonal techniques, producing drugs with an antibacterial adequate impact. Moreover, the phospholipid structure of bacterial cell membranes will be decomposed due to the phosphatase-like activity of NZs, resulting in bacterial mortality. The first antibacterial pathway has received the most research to date. Although numerous researchers have investigated NZs for antibacterial purposes, most NZ-based systems lack targeting capabilities. As a result, complications regarding the adverse effects and therapeutic efficacy may arise. In light of these considerations, several research studies have modified small molecular groups on the surface of NZs to target bacteria. The NZ-based targeted antibacterial system consists primarily of aptamers and particular small molecules, including mannose, C18-PEGn-benzeneboronic acid (CPB), dextran, and others. By forming specific bonds with bacteria, these substances are capable of causing bacterial death via the catalytic activity of NZs. This section focuses primarily on the targeting effect of NZs as an antibacterial system application [ 74 ].

A prospective alternative for combating microbes, NZs have recently become a research hotspot due to their low cost, high stability, scalability, and multiple functionalities. In contrast to conventional antibiotics, NZs exhibit a reduced propensity to induce bacterial resistance by capitalizing on the advantageous properties of nanomaterials, including favorable membrane permeability and innocuous biocompatibility. In contrast, antibacterial methods based on NZs exhibit distinct advantages compared to alternative antibacterial strategies [ 75 ]. Moreover, their catalytic activities can efficiently eliminate bacterial biofilms. Beyond that, the distinctive physicochemical properties of NZs enable them to possess additional functionalities not found in natural enzymes, thereby facilitating catalytic activities modulated by composition, size, and shape. The unique physicochemical characteristics of these substances present an opportunity to create multifunctional antibacterial agents. It is essential and highly recommended to develop novel bactericides that effectively eliminate bacteria without fostering the growth of resistance or causing biosafety concerns. NZs, which are inorganic nanostructures possessing inherent enzymatic activities, have garnered increasing attention from scientists due to their remarkable properties. NZs are more effective than natural enzymes at destroying a wide variety of Gram-positive and Gram-negative bacteria, thereby bridging an essential gap between biology and nanotechnology. NZs, being highly effective nanoantibiotics, exhibit remarkable broad-spectrum antimicrobial characteristics while exhibiting minimal biotoxicity [ 22 ].

Additionally, NZs have antibacterial applications. It is essential to eliminate S. mutans and the biofilm that forms on the tooth's surface to prevent dental caries. Scholars have developed a collection of NZs capable of operating effectively in acidic pH environments [ 50 ]. The utilization of NZs possessing OXD-like and POD-like characteristics to catalyze the conversion of the corresponding substrate to ROS in a physiological setting has the potential to expand the range of applications in the antibacterial field. However, the efficacy of the generated ROS against bacteria is hindered by their short diffusion distance in the environment and their high reactivity; this compromises the biosafety and antibacterial activity of the ROS. Therefore, the secret to achieving the effective antibacterial activity of NZs is the combination of enzyme-like activity and bacterial binding ability [ 75 , 76 ].

By generating ROS through enzyme-mimetic catalytic reactions, NZs can efficiently and swiftly destroy bacteria, rendering them viable substitutes for antibiotics in antibacterial applications. Despite this, the ability of NZs to eradicate bacterial infections is severely hampered by their inadequate catalytic activity. Enzymes that possess an atomical dispersion of active metal sites have demonstrated exceptional enzyme-like activities and have made significant strides in recent years in the field of antibacterial applications by maximizing atom utilization. Stunningly superior enzyme-like activities have been exhibited by SAzymes as a result of their atomic dispersion of active metal actives and similar atomic configuration to that of natural enzymes; this enables them to generate an abundance of ROS to eliminate bacteria. SAzymes, which are advantageous because they are inexpensive, highly stable, and compatible, have generated considerable interest in antibacterial applications [ 77 ]. Dental caries is still the most common illness in humans because of oral biofilms, even with the widespread use of fluoride as the major antibiotic. It has been established that hydrogen peroxide catalytic activation of ferumoxytol (Fer), an iron oxide NP that was recently licensed by the FDA, breaks down and destroys biofilms that cause tooth caries. Conversely, fer has no impact on the demineralization of enamel acid. Researchers established that stannous fluoride (SnF 2 ) and ferric chloride exhibit a strong synergy that significantly outperforms each element alone in inhibiting biofilm growth and enamel damage. Surprisingly, adding Fer to aqueous solutions improves SnF 2 's stability while simultaneously increasing Fer’s catalytic activity naturally and without the need for additions. Notably, even at four times lower concentrations, the combination of SnF 2 and Fer shows significant effectiveness against dental caries in vivo without adversely affecting the oral microbiota or host tissues. The results of this study show that authorized medications and SnF 2 stabilization have a solid therapeutic synergy that may be used to lower fluoride exposure and prevent widespread oral illnesses [ 78 ].

Application of nanozymes in oral antibacterial treatment

Bacterial infection remains an escalating concern in global health, where antibiotics remain the most widely acknowledged treatment paradigms [ 79 ]. Nevertheless, the misuse and overuse of antibiotics have resulted in a surge in multidrug resistance, which has adversely affected therapeutic efficacy and contributed to elevated mortality rates [ 80 ]. Moreover, the propensity of bacteria to establish biofilms on both living and nonliving surfaces exacerbates the challenge of combating bacteria, as the extracellular matrix can serve as a formidable barrier to environmental stress and antibiotic penetration [ 81 ]. The failure to eradicate microbes and biofilms frequently results in the development of persistent infections, malfunctioning implants, and harm to the device. Hence, the development of alternative antimicrobial agents that prevent the emergence of bacterial resistance is critical [ 82 ]. By studying the mechanisms by which natural enzymes disrupt metabolism, such as quorum sensing, programmed death, and cellular structural integrity, artificial enzymes that imitate the functions of these enzymes will offer unparalleled prospects for the fight against bacteria [ 83 ]. Furthermore, unlike natural enzymes, synthetic enzymes exhibit significantly enhanced resistance to extreme conditions, catalytic activity that is more easily modifiable, and the capability to be produced on a large scale for practical applications [ 19 ].

A multitude of NZ-assisted approaches have been successfully developed thus far to serve as theranostics for various diseases. These approaches capitalize on the low cost, high stability, and multienzyme-like properties of NZs [ 50 ]. Oral infection, being the most prevalent oral disease, presents a worldwide threat to human health, and the available therapeutic alternatives are inadequate to address all the clinical complications. NZs, by their remarkable efficacy, can be routinely utilized in the detection and management of a multitude of oral infectious diseases [ 84 ]. Even more significantly, NZs can have their shape, size, and composition modified, which confers an extensive array of enzymatic and antibacterial properties. Metal-based compounds, carbon-derived nanomaterials, transition metal dichalcogenides, peroxides, oxides, SA enzymes, and MOFs have all been employed in antibacterial research [ 85 ]. Firmicutes, Bacteroidetes, Proteobacteria, Actinobacteria, Spirochaetes, and Fusobacteria predominated in the oral bacterial community. Among these, Streptococcus mutans ( S. mutans ) and Lactobacillus have been the subject of extensive research and are regarded as specific caries pathogens. Periodontitis has been linked to several microorganisms, including Porphyromonas gingivalis, Treponema denticola , and Tannerella forsythia [ 86 ]. Furthermore, the antibacterial activity of NZs is predominantly mediated by the catalytic processes of POD and OXD, which convert H 2 O 2 into ·OH to control ROS. ROS are a class of small molecules that the host's phagocytes can produce; examples include ·OH, superoxide radicals, and H 2 O 2 [ 87 ]. The generation of ROS by negatively charged metal NPs upon interaction with positively charged bacterial cell wall surfaces has exhibited antibiotic-like properties across a range of disorders [ 88 ]. Several NZs exhibit distinct benefits in oral antibacterial therapy, according to another study, even though their active mechanisms have not been exhaustively investigated and comprehended. A synopsis of the primary procedure follows: After brief local exposure, NZs remain within the biofilm structure of three-dimensional (3D) dental plaque, and H 2 O 2 swiftly converts to free radicals at acidic PH to degrade EPS and eliminate bacteria [ 89 , 90 , 91 ].

NZs play three preeminent functions in this procedure. (1) Adequate bioavailability requires that the substance remains in the plaque biofilm and maintains its activity; (2) Stable in physiological environments but activated in a PH-dependent manner in specific acidic pathogenic microenvironments produced by plaque biofilms. For instance, Fe 3 O 4 NPs possessing POD-like activity catalyze H 2 O 2 exclusively after penetrating the plaque biofilm. (3) Mitigate the detrimental effects on healthy tissues induced by comparatively high concentrations of H 2 O 2 (0.5–3%) commonly employed in conventional antibacterial methods. By converting H 2 O 2 to free radicals, POD-like NZs are capable of generating an exceptional antibacterial effect, reducing the concentration of H 2 O 2 used for antibacterial purposes significantly, and enhancing biological safety. Furthermore, oral antibacterial applications encompass the following: prevention of peri-implantitis, treatment of dental caries and pulp disease, and treatment of oral ulcers [ 32 ].

The U.S. Food and Drug Administration has approved Fer, an NP formulation, for systemic administration to treat iron deficiency. Furthermore, researchers demonstrated that Fer inhibits tooth decay (dental caries) and disrupts intractable oral biofilms via intrinsic POD-like activity. Fer forms a complex with the ultrastructure of biofilms and produces free radicals from H 2 O 2 , which induce in situ bacterial mortality through the disruption of cell membranes and degradation of extracellular polymeric substance matrices. When combined with modest concentrations of H 2 O 2 , Fer prevents acid injury to the mineralized tissue and inhibits biofilm accumulation on natural teeth in an ex vivo biofilm model derived from humans. In a rodent model of the disease, topical oral treatment with Fer and H 2 O 2 inhibits the development of dental caries in vivo, thereby averting the initiation of severe tooth decay (cavities). Gingival and mucosal tissues, as well as the diversity of oral microbiota, are not negatively impacted, according to histological and microbiome analyses. Investigators' findings demonstrate that Fer has a novel biomedical application as a topical treatment for a common and expensive oral disease caused by biofilm. Additionally, our group investigated topical Fer as a NZ to prevent dental caries (tooth decay) by killing bacteria and disrupting biofilm. In this experimental setup, 1% H 2 O 2 exposure was followed by topical administration of Fer at a concentration of 1 mg/ml in the oral cavity, which served as a rodent model of dental caries. In a recent study, researchers utilized an analogous topical treatment protocol to specifically target biofilms that are accountable for tooth caries in the human oral cavity [ 90 , 92 , 93 ] (Table  1 ) (Fig.  2 ).

The antibacterial processes and properties of nanozymes (NZs). A Streptococcus mutans and Lactobacillus are the two most prevalent species of bacteria that cause dental cavities. Gum disease may result from the growth of Treponema denticola and Porphyromonas gingivalis , which can make your gums swell. B As we all know, the antibacterial mechanism of NZ is mainly divided into the following categories: POD or oxidase mimics can transfer corresponding substrate H 2 O 2 or oxygen (O 2 ) into ROS such as ·OH or singlet oxygen ( 1 O 2 ), thereby achieving antibacterial effect [ 94 ]

Dental caries can be induced by acidogenic oral biofilms, which demineralize the enamel-apatite present on teeth. At present, antimicrobial agents exhibit limited effectiveness and fail to target the protective matrix or acidic pH present in biofilms. It was recently demonstrated that catalytic NPs could disrupt biofilms, but they lacked the stabilizing coating for clinical applications. In this study, researchers presented dextran-coated iron oxide nanoparticles (Dex-NZM) that exhibit potent catalytic (POD-like) activity at acidic pH levels, selectively target biofilms to prevent severe caries, and do so in vivo without affecting adjacent oral tissues. NP formulations with dextran coatings (ranging in molecular weight from 1.5 to 40 kDa) were produced and evaluated for their bioactivity and catalytic performance. The optimal dextran coating for catalytic activity, biofilm assimilation, and antibiofilm properties was determined to be 10 kDa. The catalyst activity is attributed to the presence of iron oxide centers, according to mechanistic investigations. Stability is maintained by the dextran on the NP surface, which does not impede catalysis. Coating NZM with dextran enabled its incorporation into the structure of EPS and its binding to biofilms; this interaction triggered the production of H 2 O 2 to destroy bacteria locally and degrade the EPS matrix. Unexpectedly, dextran coating prevented gingival cell binding while increasing selectivity toward biofilms. In addition, treatment with Dex-NZM/H 2 O 2 significantly decreased the initiation and severity of caries lesions (in vivo, without affecting gingival tissues or oral microbiota diversity) compared to the control group or treatment with Dex-NZM or H 2 O 2 alone. Hence, dextran-coated NZs exhibit promise as a viable alternative therapeutic approach for managing dental caries and potentially other diseases associated with biofilm [ 95 ] (Fig.  3 ).

A The microbial balance between commensals and pathogens can be disrupted by frequent sugar consumption and poor oral hygiene. B Dex-IONP was supplemented with glucose oxidase (GOx) by Koo's group to produce the Dex-IONP-GOx bifunctional nanohybrid system. GOx can convert glucose into H 2 O 2 within the plaque biofilm, thereby depriving S. mutans of its food source. Without additional H 2 O 2 , Dex-IONP can directly catalyze H 2 O 2 in an acidic microenvironment and generate ROS to destroy microorganisms. C Their findings indicate that the efficacy of this system surpasses that of Dex-IONP alone by a substantial margin. Moreover, it exhibits a more precise targeting of S. mutans (> 107 reduction) while displaying minimal impact on other symbiotic beneficial bacteria [ 96 , 97 ]

Commensal bacteria aid in regulating opportunistic pathogens by producing bioactive byproducts like H 2 O 2 . However, excessive sugar intake disrupts homeostasis and encourages the accumulation of pathogens in acidic biofilms, which are responsible for tooth caries. In this study, scientists utilize a nanohybrid system to increase intrinsic H 2 O 2 production and induce pH-dependent ROS generation to effectively target biofilm virulence under pathological (sugar-rich/acidic) conditions. The nanohybrid material comprises glucose-OXD, which facilitates the conversion of intrinsic H 2 O 2 to ROS at acidic pH by iron oxide NPs with POD-like activity. Significantly, it eliminates S. mutans (the pathogen) while leaving Streptococcus oralis (the commensal) unaffected using preferential pathogen-binding and in situ ROS production. In addition, in a rodent model, nanohybrid interventions significantly diminished dental caries. In contrast to chlorhexidine, which disrupted the diversity of oral microbiota as the positive control, the nanohybrid exhibited a considerably greater efficacy while modulating microbial activity associated with dental health in vivo, without affecting soft-tissues or the oral-gastrointestinal microbiomes. The therapeutic specificity of a bifunctional hybrid NZ against a biofilm-associated disease was demonstrated by the data in a controlled fashion when activated under pathological conditions [ 96 ].

A methodology is presented by researchers wherein NZs possessing POD-like activity are integrated with bacteria producing biogenic H 2 O 2 to eradicate oral biofilms in the context of caries treatment. To replicate the oral environment, we examine the impact of iron oxide NZs or iron sulfide NZs on an S. mutans biofilm in the presence of H 2 O 2 -producing S. gordonii using a saliva-coated hydroxyapatite disc and a sectioned human tooth. The results of bacterial viability assays and biofilm morphology characterization indicate that the co-administration of NZs and bacteria results in a significant reduction of both the bacterial population (5 lg) and the biofilm matrix (85%). Hence, integrating H 2 O 2 -producing bacteria and iron-based nanozymes (FeSN) could potentially offer a novel approach to eradicating oral biofilms during dental caries therapy [ 98 ].

Nanozyme in the treatment of dental diseases

The escalating global incidence of periodontal and peri-implant diseases has garnered considerable interest. NZs, which possess enzyme-like activity and are multifunctional nanomaterials, have established a presence within the biomedical domain. NZs have made significant contributions to plasmonics and implantology research concerning the maintenance of periodontal health and the enhancement of implant success rates [ 41 ]. In most cases, oral diseases result from bacterial infection and inflammation. ROS, produced by bacterial infection and autologous inflammation tissue, are crucial to this process. Consequently, eliminating an excess of intracellular ROS may represent a viable anti-inflammatory treatment strategy. In treating inflammation-related diseases, NZs, which can maintain intracellular redox balance and safeguard cells from oxidative damage, have demonstrated promising application prospects due to the accelerated development of nanomedicines [ 99 ]. Conventional dental materials exhibit a limited number of inevitable drawbacks that detrimentally impact the efficacy of dental procedures and ultimately result in treatment failure. Dental research investigates the potential of various nanoenzymes to treat periodontitis, caries, and oral ulcers. Based on their anti-inflammatory, antibacterial, and immunomodulatory properties, the enzymes find use. The preponderance of research published within the last two to thirty years has focused on NPs, suggesting that nanotechnology and the characteristics of resources at these dimensions are of immense interest [ 100 ]. Plaque dental caries is a prevalent infectious oral disease affecting one billion people globally. Oral biofilm is the source of numerous diseases that pose a threat to oral health and have the potential to progress to systemic conditions, including Alzheimer's disease, diabetes, and atherosclerosis. These conditions entail substantial financial burdens and catastrophic complications. Prominent progress has been achieved by scientists in the development of novel, consistent, and productive oral antibacterial drugs that stimulate enzyme activity. NZs contribute to the prevention of biofilm infection in root canals. Activating H 2 O 2 can effectively eradicate biofilm plaque from the surface of a root canal and dentinal tubules, according to Koo's research [ 101 , 102 , 103 ]. Oral ulcers have been linked in numerous studies to bacterial and viral infections, allergies, deficiencies in vitamins and trace elements, systemic diseases, and genetic susceptibility. Present treatment methods lack unique pharmaceutical agents; therefore, it is necessary to develop therapeutic approaches that boost the immune system and promote ulcer healing. Naha et al. report that the healing of oral ulcers is accelerated by vitamin B 2 -modified Fe 3 O 4 NZs exhibiting anti-inflammatory and antibacterial properties [ 104 , 105 ]. As stated by the researchers, this alteration substantially enhanced its SOD-like activity and propensity to scavenge ROS. Research on cellular antioxidation demonstrated that these enzymes exhibited biocompatibility and cellular protection against H 2 O 2 . Killing S. mutants , reducing local inflammatory factors, and removing ROS, these NZs accelerate the healing of rodent oral ulcers. This antibacterial mediator resembling an enzyme may represent a viable treatment for oral ulceration [ 95 ]. POD, SOD, OXD, and CAT-like activities comprise the majority of the NZs' catalytic activity in dental applications and research. These activities have the potential to induce irreversible bacterial and biofilm annihilation. Given that NZs may exhibit a substantial increase in enzymatic activity upon exposure to DNA or ions, they possess the potential to function as colorimetric biosensors for the detection of oral cancer-associated bacteria, ions, or DNA. NZs can foster the regeneration of both soft and hard tissues by facilitating cell adhesion, proliferation, and differentiation within a sterile milieu. The utilization of NZs in dentistry has demonstrated encouraging outcomes by addressing the limitations of traditional H 2 O 2 concentrations, mitigating oxidative stress induced by the environment during cellular proliferation and differentiation, eradicating oral flora through biofilm degradation, and rapidly and easily monitoring oral flora and S. mutants [ 100 ].

Despite the increased use of fluoride, the mainstay anticaries (protectants for tooth enamel), dental caries (tooth decay) remains the most prevalent human disease caused by oral biofilms, afflicting nearly half of the world's population, according to another study. In recent studies, it has been demonstrated that an iron oxide NZ formulation (Fer) that has been approved by the FDA can specifically and catalytically activate H 2 O 2 to disrupt caries-causing biofilms; however, it does not exhibit the ability to interfere with enamel acid demineralization. The results of this investigation demonstrated that the combination of ferrous fluoride (Fe) and SnF 2 inhibits biofilm accumulation and enamel degradation significantly more effectively than either element used alone. Unexpectedly, the data indicate that SnF 2 substantially increases ROS production and antibiofilm activity while enhancing the catalytic activity of Fer. Fer, when combined with SnF 2 , demonstrates remarkable efficacy in the in vivo management of dental caries. It completely inhibits enamel demineralization and cavitation without inducing detrimental effects on host tissues or altering the diversity of the oral microbiota. Additionally, the combination of SnF 2 and Fer increases its efficacy, resulting in comparable therapeutic effects at a fluoride concentration four times lower [ 106 ] (Fig.  4 ).

Effective applications in periodontology and implantology result from the A synergistic effects, B antibacterial, C regeneration-promoting, and D anti-inflammatory of nanozymes (NZs) that mimic enzyme functions. Several significant developments in the discipline are highlighted, in addition to forthcoming obstacles [ 41 ]

Nanozyme in treatment of implant infections

Dental implants are the prevailing therapeutic modality utilized to address tooth loss and injury. Implant failure rates can reach 23% despite technological advances in treatment when peri-implantitis, a multispecies bacterial infection, is the underlying cause. As the number of implant placements increases by 8.78% annually, bacterial infection-related implant failure is a significant oral and general health concern. Implant failure is exacerbated by the increase in antibiotic resistance among oral microorganisms; therefore, adjunctive therapy is required to enhance implant outcomes [ 107 ]. Deep soft tissue infections associated with implants are notoriously challenging to treat with antibiotics due to their profound nature and frequent association with methicillin-resistant S.aureus (MRSA). Incision, drainage, and long-term administration of high-dose antibiotics are typically required to achieve this objective. However, it is more probable that these courses of action will facilitate the evolution of bacteria into superstrains [ 108 , 109 ]. Biofilms, also referred to as bacterial communities, are considerably more difficult to eradicate from the surfaces of subsurface sites, including implants, due to their intrinsically high reproduction and strong adhesion [ 110 , 111 ]. Antibiotic treatment failure is on the rise, and persistent systemic infections in human hosts are an unavoidable consequence. Thus, it is critical to devise in situ, antibiotic-free approaches that are efficacious in combating infections affecting deep tissues [ 112 ].

On the contrary, a novel era of potent tools to combat bacterial infections without inducing AMR has arrived with NZ-based antibacterial therapy. The antibacterial mechanism relies on enzyme-mimetic catalysis to produce exceedingly toxic agents, including ROS. The agents mentioned above can inflict rapid and irreversible harm upon the cell wall, membrane, DNA, and proteins of bacteria, in addition to extracellular DNA and biofilm polysaccharides [ 85 , 113 ]. However, due to restricted substrate diffusion, the catalytic ROS production of NZs undoubtedly decreases in deep tissues. Deep infections necessitate NZs with increased activity to generate inhibitory levels of ROS at lower concentrations of substrate [ 68 ]. Following the efficacy of NZ treatment for periodontitis, there is considerable potential for the application of NZs in treating peri-implant diseases via modulation of the implant surface to enhance its antibacterial, anti-inflammatory, mechanical, and osteogenesis characteristics [ 41 ].

According to different research, the exceptional mechanical qualities and biocompatibility of Titanium (Ti) and its alloys have made them popular for usage as subcutaneous and percutaneous implants. Nevertheless, the accumulation of ROS and enduring inflammatory reactions at the implant location negatively impact the soft tissue integration of titanium implants, leading to several biological issues. This work used solvothermal and anodic oxidation to create Fe-nitrogen-doped carbon SAzymes (Fe-NC NZs) loaded Ti oxide nanotube arrays (Fe-NC@TNT) on medicinal Ti surfaces to solve this problem. Fe-NC@TNT was examined for its physical composition, surface morphology, enzyme-like catalytic activity, inflammatory response, and compatibility with soft tissues. By utilizing a distinctive nanotube array, the active sites of Fe-NC NZs are entirely exposed, leading to a substantial improvement in their enzyme-like catalytic capabilities. This enhancement eliminates superoxide anion, H 2 O 2 , and more hazardous ·OH. Consequently, this reduction in intracellular ROS levels in macrophages and fibroblasts effectively hinders inflammatory responses of macrophages and stimulates the functional expression of fibroblasts. Fe-NC@TNT has also been shown in vivo animal trials to successfully control the immune response and facilitate the integration of the implant with the surrounding soft tissues. The present study included the preparation of Ti oxide nanotube arrays (TNT) by anodic oxidation, which were then loaded with Fe-NC NZs on their surface via the polymerization reaction between formamide and Fe 3+ . Fe-NC NZs provided the samples with a significant antioxidant capacity and may further increase the hydrophilicity and corrosion resistance of TNT. They also efficiently scavenged superoxide anions, H 2 O 2 , and ·OH in the surrounding environment [ 114 ].

In addition to impairing the functions of osteogenic-relative cells, bacterial infection and the subsequent inflammatory response result in the ineffectiveness of Ti-based implantation. To treat this tissue, it is critical to develop multifunctional Ti implants (antimicrobial, anti-inflammatory, and pre-osteogenesis). In this study, TNTs were coated with zeolitic imidazolate frameworks-67 (ZIF-67) laden with osteogenic growth peptide (OGP) to produce a TNT-ZIF-67@OGP surface. The pH-sensitive ZIF-67@OGP coating underwent rapid dissolution in an acidic environment. Furthermore, the TNT-ZIF-67@OGP demonstrated potent antibacterial efficacy against S. aureus , MRSA, E. coli , and S. mutans due to ZIF-67 NP hydrolysis and the creation of an alkaline microenvironment. The implants exhibited excellent biocompatibility with macrophages and mesenchymal stromal cells (MSCs). Notably, in an inflammatory setting, TNT-ZIF-67@OGP may promote MSC cellular differentiation and reduce the inflammatory response. The in vivo research also showed that TNT-ZIF-67@OGP implants had potent antibacterial and anti-inflammatory characteristics early in the implantation process, which improved the late-stage osteointegration of the implant. Therefore, this multifunctional titanium implant that combines antibacterial and osteoimmunomodulatory properties is a good option for implant-associated infection bone regeneration [ 115 ].

According to different research, after implant-related surgery, the risk of biofilm-associated infections (BAIs) recurring is still high. It has been shown that biofilms on the surface of implants shield bacteria from antibiotics and thwart innate immune responses. Furthermore, there is still a lack of knowledge on removing lingering bacteria that might cause biofilm reinfection. This work reports a new "interference-regulation strategy" for fighting BAIs that uses bovine serum albumin-iridium oxide NPs (BIONPs) as an immunomodulator and biofilm homeostasis interrupter via 1 O 2 -sensitized mild hyperthermia. By efficiently converting the abundant H 2 O 2 in the biofilm microenvironment (BME) to sufficient O 2 , the CAT-like BIONPs can increase the production 1 O 2 when exposed to near-infrared irradiation. The perturbation of biofilm homeostasis induced by 1 O 2 (e.g., sigB, groEL, agr-A, icaD, eDNA) has the potential to disrupt the intricate defense mechanisms of biofilms, thereby increasing their susceptibility to mild hyperthermia. Furthermore, the bacterial membrane disintegration induced by moderate hyperthermia leads to protein leakage and 1 O 2 penetration, effectively eliminating bacteria within the biofilm. Following this, the immunosuppressive microenvironment re-rousing induced by BIONPs effectively re-orients macrophages to adopt a pro-inflammatory M1 phenotype in vivo, to consume any remaining biofilm, and to impede biofilm reconstruction. By combining 1 O 2 -sensitized mild hyperthermia, immunotherapy, biofilm homeostasis interference, and mild hyperthermia, this approach offers a novel and efficacious method for treating refractory BAIs [ 116 ].

Because of compromised immune responses and antibiotic tolerance from bacterial biofilms, implant infections are challenging to treat with conventional antibiotic treatment. Therapeutic medicines must eradicate bacteria and control immune cell inflammation throughout the biofilm removal phase to effectively treat implant infections. Here, pH-responsive enzyme-like activities were used to construct multifunctional smart hollow Cu 2 MoS 4 nanospheres (H-CMS NSs) that can self-adapt to eliminate biofilms and control macrophage inflammation in implant infections. The tissue milieu around implants becomes acidic during biofilm infection. Catalyzing the production of ROS that destroy bacteria directly and polarize macrophages toward a proinflammatory phenotype are H-CMS NSs with OXD/POD-like activities. Subsequently, ultrasound (US) irradiation can augment the POD-like activity and antibacterial characteristics of H-CMS NSs. Once biofilms have been eliminated, the tissue microenvironment surrounding implants becomes neutral rather than acidic. H-CMS NSs eradicate excessive ROS and exhibit CAT-like activity, thereby polarizing macrophages toward an anti-inflammatory phenotype and promoting infected tissue healing. This study presents a self-adaptive NZ that controls the immune response and antibiofilm activity by modulating the generation and elimination of ROS in response to the various pathological microenvironments encountered in implant infections throughout the therapeutic process [ 117 ].

In this study, researchers described Cu-doped CDs that exhibit increased catalytic (CAT-like, POD-like) activity in the oral environment. These CDs inhibit the initial bacterial adhesion of S. mutans and subsequently eradicate biofilms without causing harm to the surrounding oral tissues through the generation of ROS or O 2 . In particular, Cu-CDs have a strong affinity for peptidoglycans (PGN) and lipopolysaccharides (LPS). This gives them excellent antibacterial properties against Gram-positive ( S. aureus ) and Gram-negative ( E. coli ) bacteria, preventing wound purulent infection and accelerating wound healing. In addition, the Cu-CDs/H 2 O 2 system exhibits superior tooth whitening performance compared to other alternatives, such as clinically utilized H 2 O 2 and CDs, due to its negligible enamel and dentin degradation. The biocompatible Cu-CDs described in this study are expected to function as a potentially effective nano-mouthwash to remove oral pathogenic biofilms, promote wound healing, and whiten teeth. These results underscore the importance of Cu-CDs in the management of oral health [ 118 ] (Table  2 ).

Nanozyme in treatment of peri-implantitis

A site-specific infectious condition called peri-implantitis results in soft tissue inflammation and bone loss surrounding an osseointegrated implant when it is not functioning correctly. The state of the surrounding tissue, the implant's design, its degree of roughness, its external morphology, and an excessive mechanical strain all influence the etiology of implant infections. Spirochetes and mobile Gram-negative anaerobes are the bacteria most often linked to implant failure unless the cause is a straightforward mechanical overload [ 119 ]. When an osseointegrated implant is not operating as intended, the surrounding soft tissue becomes inflamed, and bone is lost, a condition known as peri-implantitis. The two categories of current techniques should be surface NZ modification of implants or local NZ therapy. Numerous researchers have focused on altering the surface of implants to enhance clinical results. In particular, they have prepared various physical and chemical alterations to enhance the osseointegration between the implant surface and alveolar bone. Additionally, improving osseointegration is a goal of the bioactive coatings that encourage the adhesion and colonization of cells and proteins relevant to osseointegration. Meanwhile, enhancing the implant surface's antibacterial capabilities may prevent bacterial adherence and activity, preventing implant-related inflammation [ 120 ]. To combat the bacterial pathogen epidemic, alternative antibacterial medicines based on ultrasound (US) have recently been investigated. A great alternative is antimicrobial sonodynamic treatment (aSDT), which uses US irradiation to create ROS and accomplish antibiotic-free mediated antimicrobial actions. Furthermore, aSDT has tremendous promise in treating deep infections because of its greater tissue penetrability of US compared to light irradiation. While ROS generation for antimicrobial activity is achievable with conventional sonosensitizers, unsatisfactory sterilization in aSDT is caused by several constraints, including limited penetration rate, nonspecific dispersion, and poor ROS production under hypoxic settings. As high-performance agents in aSDT, newly developed nanosonosensitizers provide significant benefits over traditional sonosensitizers, as previously mentioned. Thus, controlling bacterial infections by nanosonosensitizer-mediated aSDT has a promising future [ 121 ]. Host immune systems, which function as critical barriers against biofilm-associated implant infections, are vital resistance mechanisms. However, biofilms impede the entry of antibacterial species, obstruct the phagocytosis of immune cells, and thwart inflammatory responses of the host, ultimately undermining the ability of the host immune system to eliminate biofilms. Through the encapsulation of erythrocyte membrane fragments on the surface of microbubbles fabricated from Fe 3 O 4 NPs and subsequent loading with hydroxyurea (EMB-Hu), a cell-like construct is created. When stimulated with the US, EMB-Hu endures a stable oscillation process that functions as an “exocytosis” mechanism. This mechanism facilitates the disruption of biofilm, the release of agents, and the enhancement of the penetration of catalytically generated anti-bacterial species within biofilms. Furthermore, EMB-Hu-stimulated “exocytosis” induced by the US can enhance macrophage phagocytosis and pro-inflammatory macrophage polarization, both of which are essential for the removal of disrupted biofilms. In summary, this research has demonstrated the utilization of cell-like microbubbles containing “exocytosis” mechanisms stimulated by the US to traverse the biofilm barrier and activate macrophages in an inflammatory response to methicillin-resistant Staphylococcus aureus (MRSA) biofilms-induced implant infections. As a result, beneficial therapeutic outcomes have been achieved [ 122 ]. Environmentally sensitive therapeutic platforms with low dose-limiting toxicity, good selectivity, and low drug resistance have attracted much attention. When antibacterial activity in therapeutics is activated on demand by exogenous or endogenous triggers, they may demonstrate remarkable therapeutic results. Ultrasound, microwaves, light, and magnetism are examples of external stimuli. Most endogenous stimuli are pathological characteristics of bacterial infections, such as acidic pH, altered enzymatic activity, and aberrant temperature [ 123 ].

Despite the exponential annual growth in dental implant procedures, peri-implantitis continues to be a significant concern for numerous physicians. Under the influence of bacteria, peri-implantitis is an inflammatory reaction of the tissue surrounding the implant; it is the leading cause of dental implant failure. To mitigate the risk of peri-implantitis, it is crucial that patients practice appropriate oral hygiene and that their dentists select suitable implant materials and designs (e.g., only implant when the patient's periodontal health is stable). NZs, on the other hand, are can rapidly protect the tissue surrounding the implant from peri-implantitis by their antibacterial properties. Moreover, numerous light-responsive NZs can treat peri-implantitis when exposed to light. Thukkaram et al. discovered that Fer coating inhibits bacterial vitality and prevents bacterial adhesion to the surface of biological materials [ 124 , 125 ]. Produced using chemical microwave technology, the controllable ultrafine CeO 2 NPs are capable of penetrating cells and producing O 2 free radicals, which inhibit the development of microorganisms. Interleukins and inflammatory factors contribute to peri-implantitis. In contrast to Ce 4+ , Ce 3+ exhibits enhanced SOD activity and a more robust capacity for ROS removal. Li et al. synthesized an unprecedented octahedral CeO 2 with an elevated Ce 3+ value. The application of octahedral CeO 2 coating onto the implant's surface effectively impedes the initial colonization of S. sanguis , thereby suppressing the development of plaque biofilm. Applying NZs onto implants has demonstrated remarkable antibacterial and anti-inflammatory properties, suggesting that they could be utilized to eradicate peri-implantitis [ 32 ]. Another research revealed that one of the main reasons dental implants fail is peri-implantitis. An extensive decline in oral health results from bacterial biofilm contamination on the implant, which causes soft tissue irritation and adjacent bone resorption. On decontaminated implant surfaces, however, re-osseointegration cannot be induced by standard biofilm removal techniques such as mechanical cleaning and antiseptic treatment. This results from two factors: (1) decontamination procedures that fail to altogether remove biofilm from inaccessible areas and (2) modifications to the physicochemical properties of implant surfaces. Researchers presented a novel therapeutic strategy for peri-implantitis that is both safe and efficacious. The method entails decontaminating biofilms adhered to implants by utilizing the kinetic energy of microsized O 2 bubbles produced by a catalytic reaction involving manganese oxide (MnO 2 ) NZ sheet-doped silica diatom microparticles (Diatom Microbubbler, DM). Compared to conventional antiseptics like chlorhexidine or 3% H 2 O 2 when used alone, rapidly moving microsized DM particles can penetrate narrow spaces between implant screws, exerting just the right amount of force to destroy biofilms without harming the surrounding mucosa or implant surfaces. As a result, DM cleaning on the implant surface impacted by peri-implantitis promotes effective re-osseointegration. In conclusion, our novel DM-based treatment strategy will emerge as a viable substitute to address clinically complex peri-implantitis issues [ 126 ].

The investigators of this study present a new approach to biofilm removal that does not involve antibiotics. They suggest a BME-responsive double-layered MOF bionanocatalysts (MACG) made of MIL-100 and CuBTC as a synergistic bionanocatalysts-driven heat-amplified chemodynamic therapy (CDT) and innate immunomodulation. It is possible to release GOx and an activable photothermal agent, 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), sequentially once CuBTC has degraded due to acidity at the acidic BME. GOx breaks down glucose into gluconic acid and H 2 O 2 , which might further acidify the BME and hasten the release of GOx and ABTS, as well as the breakdown of CuBTC. The findings, both in vitro and in vivo, demonstrate that MIL-100, which mimics horseradish POD (HRP), may catalyze the oxidation of ABTS into oxABTS when self-supplied H 2 O 2 is present. This produces a photothermal impact that damages eDNA and disrupts the biofilm structure. In addition to depleting glutathione, the Cu ion released from the broken down CuBTC may also split H 2 O 2 into OH, which can efficiently penetrate heat-induced loose biofilms and kill sessile bacteria (up to 98.64%), including MRSA and E. coli . Specifically, by secreting pro-inflammatory cytokines (e.g., IL-6, TNF-α, etc.) and creating a persistently pro-inflammatory milieu in peri-implant biofilm-infected rats for at least 14 days, MACG-stimulated M1-macrophage polarization reduces the biofilm regeneration. With minimal side effects, this BME-responsive approach has the potential to eradicate resistant peri-implant biofilm infections accurately [ 127 ].

According to another study, peri-implant infection induced by bacterial biofilm constitutes the primary cause of failed dental implant repairs. The efficacy of infection control primarily hinges on the eradication of bacterial biofilm. However, as bacterial resistance increases, traditional medicine treatments become impractical. Ultrasound-activated antibacterial sonodynamic therapy (aSDT) has gained recognition in recent times as a promising approach to the treatment of biofilm infections. For aSDT, an activatable nanoplatform (Au-TNT) fabricated on the implant’s surface is proposed in this investigation. Under ultrasonic irradiation, Au-TNT could swiftly generate O 2 , thereby alleviating the hypoxic microenvironment of biofilm and enhancing the anti-biofilm efficacy of aSDT. In addition, it can produce ·OH and 1 O 2 , which confer an exceptionally potent antibacterial effect against pathogenic biofilms of various species, as determined by bacterial survival rate, cell membrane rupture, biofilm metabolism, and thickness. In contrast, Au-TNT demonstrated remarkable antibacterial efficacy in vivo, as evidenced by a three-log reduction in colony-forming units (CFU) compared to the control group. Notably, the results also demonstrated that Au-TNT inhibited the expression of inflammatory factors and stimulated bone repair. Therefore, this research presents a nanoplatform catalyzed by sonodynamics that effectively eliminates biofilm and treats peri-implant infections. By loading Au NPs onto TNT, researchers have proposed a simple and long-lasting antibacterial system for dental implant surfaces. As a sonosensitizer, TNT produced by anodization on Ti implants was utilized; introducing Au NPs improved their catalytic performance. Electrons migrate from the TNT to the Au NPs in response to US irradiation, thereby preventing the recombination of electron–hole pairs and increasing the yields of O 2 and ROS [ 128 ].

An alternative study proposes a safe and efficacious therapeutic strategy for peri-implantitis that utilizes the kinetic energy of microsized O 2 bubbles produced by the catalytic reaction of manganese oxide (MnO 2 ) NZ sheet-doped silica DM to decontaminate implant-bound biofilms. As opposed to conventional antiseptics like chlorhexidine or 3% H 2 O 2 when used alone, rapidly moving microsized DM particles are capable of penetrating the narrow spaces between implant screws and exerting precisely the right amount of force to destroy biofilms without harming the surrounding mucosa or implant surfaces. Decontamination with DM promotes re-osseointegration on the surface of the implant afflicted by peri-implantitis [ 126 ].

Peri-implantitis can be exacerbated and peri-implant tissue regeneration can be hindered, because sustained pathological stimuli can accelerate macrophage-mediated inflammation, facilitated by the microgap between the implant and surrounding connective tissue. The abutment, being the transmucosal component of the implant, must be biofunctionalized to facilitate the restoration of the gingival barrier. An implant abutment coating inspired by mussel biology, which comprises tannic acid (TA), cerium, and minocycline (TA-Ce-Mino), is described in this article. To facilitate cell adherence, pyrogallol, and catechol groups are introduced by TA. In addition, the enzyme-mimetic activity of the Ce 3+ /Ce 4+ conversion to remove ROS while producing O 2 promotes the polarization of anti-inflammatory M2 macrophages, which aids in forming a regenerative environment. On the TA surface, minocycline is utilized to generates local drug storage for responsive antibiosis. Furthermore, the therapeutic mechanism underpinning the coating's exogenous and endogenous antioxidative effects is elucidated: exogenous antioxidation is facilitated by the inherent properties of Ce and TA; endogenous antioxidation is achieved by promoting antioxidants and maintaining mitochondrial homeostasis. Furthermore, it incites integrin activation, which enhances VEGF-mediated angiogenesis and tissue regeneration via the PI3K/Akt and RhoA/ROCK pathways. By integrating multidimensional orchestration and antibiosis, TA-Ce-Mino effectively restores function to effector cell differentiation and soft tissue barriers, thus creating an immune microenvironment impervious to pathogen invasion. This study therefore offers crucial insight into the biological mechanism and design of abutment surface modification for peri-implantitis prevention [ 129 ].

Using orthodontic brackets fosters the development of S. mutans biofilm, thereby augmenting the likelihood of developing dental caries and white spots. For the eradication of biofilm, a MnO 2 NZ-doped DM was recently developed. By simulating the activity of CAT in an H 2 O 2 solution, DM is capable of producing O 2 and moving with the ejection of O 2 microbubbles, thereby creating a mechanical self-cleaning effect. Following the protocol, DM was prepared and examined with a scanning electron microscope (SEM). S. mutans biofilms were subjected to various treatments, including phosphate-buffered saline (PBS) for the PBS group, 0.12% chlorhexidine for the CHX group, 3% H 2 O 2 for the H 2 O 2 group, and co-treatment with 3% H 2 O 2 and 3 mg/mL of DM for the DM group. The results of the crystal violet assay indicated that the DM group eliminated biofilms more efficiently than the CHX group and that the CHX group eliminated a greater quantity of biofilms than the control group. According to SEM and CLSM images, CHX eradicated S. mutans but was incapable of eliminating the majority of biofilms on brackets. On debonded brackets, DM successfully eliminated biofilms and mature multispecies biofilms [ 130 ] (Fig.  5 ) (Table  3 ).

MnO 2 nanozyme-doped diatom microbubbler (DM) antibacterial effects in peri-implantitis. A MnO 2 NZ-doped DM was recently developed. B and C By simulating the activity of CAT in H 2 O 2 solution, DM is capable of producing oxygen and moving with the ejection of oxygen microbubbles, thereby creating a mechanical self-cleaning effect. CHX eradicated S. mutans but was incapable of eliminating the majority of biofilms on brackets [ 130 ]

Nanozyme in treatment of periodontitis

Periodontitis is a chronic inflammatory disease induced by the invasion of periodontal tissues by bacteria in dental detritus. As the condition advances, it frequently induces periodontal pocket formation, loosening of teeth, and receding gums, all contributing to the eventual demise of the affected teeth. More than ten percent of the world's population suffers from severe periodontitis [ 131 ]. As antibiotics are generally ineffective against biofilms, the prevailing clinical approach to managing periodontitis involves a dual-pronged approach involving antibiotic therapy and mechanical debridement. This strategy aims to eliminate the bacteria in the periodontal pocket before eliminating the biofilm. In contrast, mechanical debridement frequently results in patient discomfort, hemorrhage, and gingival damage. In contrast, the antimicrobial effect of antibiotics is gradual and susceptible to loss in the oral environment, necessitating frequent administration. Furthermore, the proliferation of antibiotic usage may give rise to bacterial resistance, an even more severe dilemma. Therefore, it is necessary to develop an antibiotic-free, non-invasive, rapid, and effective anti-biofilm treatment [ 132 ]. Periodontitis is an inflammatory condition distinguished by the resorption of alveolar bone and tooth loss. Periodontitis is initially caused by bacteria, and an excess of ROS promotes and exacerbates inflammation [ 133 ]. The escalating global incidence of periodontal and peri-implant diseases has garnered considerable interest. NZs, which possess enzyme-like activity and are multifunctional nanomaterials, have established a presence within the biomedical domain. NZs have significantly advanced research in the fields of periodontics and implantology, specifically about the maintenance of periodontal health and the enhancement of implant success rates. Review NZs for antimicrobial therapy, anti-inflammatory therapy, promotion of tissue regeneration, and synergistic effects in periodontal and peri-implant diseases to underscore this development [ 41 ].

Researchers presented an in-situ injection of CeO 2 NPs as a therapeutic approach for managing periodontitis in this study. Furthermore, ideal results could be achieved by synthesized CeO 2 NPs functioning as ROS scavengers in the inflammatory microenvironment. Experiments in vivo and in vitro provide substantial evidence that CeO 2 NPs scavenge multiple ROS and inhibit lipopolysaccharide-stimulated ROS-induced inflammatory responses. Additionally, CeO 2 NPs can impede the MAPK–NFκB signaling pathway, thereby inhibiting inflammatory factors. Furthermore, the findings obtained from a rodent model of periodontitis indicate that CeO 2 NPs can significantly inhibit alveolar bone resorption, reduce osteoclast activity and inflammation, and thus enhance the regeneration of damaged tissues. In its entirety, the current investigation highlights the promising prospects of CeO 2 NPs as a therapeutic agent for periodontitis and offers significant knowledge regarding the utilization of NZs in inflammatory disorders. As a result, CeO 2 NPs with high CAT-like and SOD-like activity, in addition to ˙OH scavenging capability, were synthesized. ROS scavenging activity was demonstrated by these NPs in vitro and in vivo. Furthermore, their anti-inflammatory and antioxidant properties were shown by their ability to inhibit the MAPK–NFκB signaling pathway and activate the Nrf2–HO-1 pathway, respectively. In a rat periodontitis model, CeO 2 NPs were found to inhibit inflammation and bone loss. Consequently, CeO 2 NPs exhibit considerable potential in clinically treating periodontitis [ 65 ] (Fig.  6 ).

A schematic representation of the therapeutic impact of CeO 2 nanoenzymes on periodontitis [ 65 ]

An additional study demonstrated that through ongoing investigation, catalysis systems based on MOFs and single-atom catalysis have emerged, offering more extensive potential for implementation in biological contexts. MOF-based catalysis systems have more catalytic sites than conventional catalysis systems due to their 3D and highly porous structure. By employing metal atom dispersion, single-atom catalysis systems achieve significantly greater catalytic activity while consuming significantly less metal. Given this consideration, researchers postulated that introducing single atoms possessing enzyme-like activity into MOF could substantially enhance its catalytic activity. Single-atom dopped MOF-based catalysis systems for the treatment of biofilm-induced periodontitis are described in this article. In this study, the researchers aim to develop an injectable ointment that exhibits potent anti-biofilm activity and favorable biocompatibility. To achieve this, they will utilize MOF-based single-atom catalysis systems and a porphyrin metal–organic framework (PCN-222-Pt) infused with Pt single atoms. Using theoretical screening, it has been determined that incorporating single metal atoms (Pt, Au, Cu, Ru) into PCN-222 can enhance its OXD-like activity, thereby diminishing the adsorption and activation energies of O 2 . PCN-222-Pt, which generates ROS spontaneously and exhibits potent OXD-like and POD-like activities, demonstrates exceptional anti-biofilm efficacy (98.69% against S. aureus biofilm, 99.91% against E. coli biofilm) in vitro within one hour. In contrast to the clinically prescribed periocline, the injectable PCN-222-Pt ointment demonstrated a reduced bone degradation rate, healthier periodontal tissue, and an alleviation of inflammation response in treating biofilm-induced periodontitis. Without antibiotics, this work presents a rapid, effective, non-invasive, and practical method for treating periodontitis [ 134 ] (Fig.  7 ).

Theoretical evaluation of MOF-based single-atom catalysts for periodontitis treatment. A Schematic of MOF-based single-atom catalysis systems and a porphyrin metal–organic framework (PCN-222-Pt). B PCN-222-Pt, which generates ROS spontaneously and exhibits potent OXD-like and POD-like activities, demonstrates exceptional anti-biofilm efficacy (98.69% against S. aureus biofilm, 99.91% against E. coli biofilm) in vitro within one hour [ 134 ]

An additional investigation demonstrated that oral diseases induced by pathogenic biofilms, including F. nucleatum -induced periodontitis, have a substantial effect on human health. Despite the implementation of scaling and antibiotics, clinical treatment for diseases caused by oral biofilm continues to face obstacles such as unavoidable hemorrhage, drug resistance, and inadequate therapeutic efficacy. In recent times, the emergence of NZ has presented a novel approach to the inhibition and elimination of oral biofilms, and by replacing Pt atoms in the structure of Au/Pt NCs researchers created a bimetallic clusterzyme with enhanced POD-like activity. The enzyme exhibited a high catalytic activity towards H 2 O 2 due to the synergistic effect between Au and Pt atoms. With the coupling of GOX to Au/Pt NCs (Au/Pt NCs@GOX), a clusterzyme was developed that exhibited excellent biocompatibility and self-promoting antibacterial properties. This clusterzyme took advantage of the nutrient-rich oral environment to catalytically convert nontoxic glucose into highly toxic ·OH via a cascade reaction. Consequently, it effectively inhibited and eliminated biofilm induced by F. nucleatum in vivo. Additional evidence was obtained from in vivo animal experiments demonstrating that the Au/Pt NCs@GOX clusterzyme effectively and safely treated periodontitis in rats, inhibited inflammation, and stimulated periodontal tissue regeneration. Overall, this study's cascade clusterzyme offers a promising avenue for the future clinical application of a safe and effective method to treat oral biofilm-induced periodontitis. In addition, this cascade catalytic system was developed to eliminate biofilm induced by F. nucleatu m and eliminate planktonic F. nucleatum . In conclusion, the therapeutic efficacy of the Au/Pt NCs@GOX catalytic system against F. nucleatum -induced periodontitis was assessed using a periodontitis model. Biocompatibility and exceptional antibacterial and antibiofilm activity confer a promising application outlook for the ultra-small clusterzyme in treating oral diseases [ 38 ].

Periodontitis, according to another study, is a chronic inflammatory disease caused by dental plaque that destroys periodontal tissues due to the excessive accumulation of ROS, matrix metalloproteinase (MMP), and other substances. Currently, the primary therapeutic approaches—including local mechanical debridement and antibiotic delivery—face challenges in effectively addressing the persistent bacterial biofilm, mitigating the excessive inflammatory response, and regenerating the damaged periodontal tissues. The TM/BHT/CuTA hydrogel system, which is composed of Cu-based NZs (Cu tannic acid coordination nanosheets, CuTA NSs) and triglycerol monostearate/2,6-di-tert-butyl-4-methylphenol (TM/BHT) hydrogel, has been proposed by researchers. By retaining the inflammatory sites with a positive charge via electrostatic adsorption, the negatively charged TM/BHT/CuTA can hydrolyze in response to the increasing MMP of periodontitis, thereby enabling the on-demand release of the CuTA NZ. CuTA NZ, which was liberated, possesses antibacterial and antiplaque properties. In contrast, it can scavenge numerous ROS by simulating the cascade process of SOD and CAT as a metal-phenolic NZ. Moreover, by modulating macrophage polarization from M1 to M2 via the Nrf2/NF-κB pathway, the CuTA NZ alleviates inflammation and expedites tissue regeneration in the context of periodontitis by decreasing pro-inflammatory cytokines, increasing anti-inflammatory cytokines and promoting the expression of osteogenetic genes in that order. In its entirety, the TM/BHT/CuTA multifunctional NZ on-demand release platform presents an advantageous approach to managing periodontitis [ 135 ].

The gradual integration of oxidoreductase NZs for ROS regulation into periodontology treatments has been documented in another study. Existing NZs for the treatment of periodontitis, on the other hand, eliminate ROS in a broad and non-specific manner, disregarding their physiological functions as they occur naturally. This may lead to uncontrolled adverse effects. By employing the MIL-47(V)-F (MVF) NZs, which emulates the activity of glutathione POD (GPx), this research suggests that ROS can be effectively regulated through the targeted elimination of H 2 O 2 , the most abundant ROS. MVF promotes periodontal regeneration, controls inflammation, and regulates the immune microenvironment using H 2 O 2 elimination. Additionally, MVF directly promotes the osteogenic differentiation of periodontal stem cells, which is facilitated by the vanadium content of MVF. By activating the Nrf2/HO-1 pathway, MVF regulates ROS. Additionally, it directly stimulates osteogenic differentiation via the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) pathway. GPx-mimicking NZs are utilized to establish a prospective periodontitis therapy strategy by their threefold effects—antioxidation, immunomodulation, and regulation of bone remodeling—which make NZs an ideal instrument for advancing precision medicine [ 136 ].

A separate investigation devised a novel FeSN, which was produced by doping histidine-doped FeS 2 and exhibited significant POD-like activity to eliminate oral biofilm and manage periodontitis. FeSN demonstrated a remarkably high level of POD-like activity, with theoretical calculations and enzymatic reaction kinetics indicating that its catalytic efficiency was around thirty times greater than that of FeS 2 . In the presence of H 2 O 2 , the antibacterial experiments demonstrated that FeSN exhibited potent antibacterial activity against F. nucleatum . This was evidenced by increased OXD coenzyme levels and a decrease in glutathione reductase and ATP levels in bacterial cells. FeSN's exceptionally high POD-like activity facilitated the identification of pathogenic biofilms and stimulated the degradation of biofilm structure. In addition, FeSN exhibited remarkably low cytotoxicity and remarkable biocompatibility with human fibroblast cells. FeSN exhibited substantial therapeutic effects in a rodent periodontitis model through the reduction of biofilm formation, inflammation, and alveolar bone loss. Collectively, researchers’ findings indicated that FeSN, which was produced via the self-assembly of two amino acids, offered considerable potential as a strategy for the elimination of biofilm and the treatment of periodontitis. This approach can surmount the constraints of existing therapeutic modalities and furnish a viable substitute for the management of periodontitis [ 30 ].

To improve the activity resembling POD, researchers created a bimetallic clusterzyme in this study by substituting Pt atoms in the structure of Au/Pt NCs. As a result of the synergistic effect between Au and Pt atoms, this enzyme exhibited a high catalytic activity towards H 2 O 2 . By coupling Au/Pt NCs@GOX, a clusterzyme with excellent biocompatibility and self-promoting antibacterial effect was developed in response to the lack of catalytic activity in near-neutral conditions and the need for a high H 2 O 2 concentration. This clusterzyme could fully exploit the nutrient-rich oral environment to convert nontoxic glucose into highly toxic ·OH via a cascade catalytic reaction, thus impeding and eliminating biofilm induced by F. nucleatum in viability. In addition, animal experiments in vivo demonstrated that the Au/Pt NCs@GOX clusterzyme could effectively treat periodontitis in rodents, reduce inflammation, and stimulate the regeneration of periodontal tissue while remaining safe to use. In conclusion, the cascade clusterzyme described in this study offers a method for future clinical implementation that is both safe and effective in treating oral biofilm-induced periodontitis [ 38 ] (Table  4 ).

Future and landscape of antibacterial nanozymes in dental diseases

Implant restoration is one of the most widely used techniques for replacing missing teeth. The primary benefits are robust retention and the absence of necessity for frequent removals. Peri-implantitis prevention and achieving adequate initial stability are two critical factors that determine the success of implant restorations. This objective can only be attained by commencing with the subsequent two factors. The first step is selecting an appropriate implant. Distinct implant designs exhibit substantial variations in osteogenesis and mechanical strength. For instance, one may opt for implants that possess antibacterial properties or promote osteogenesis [ 137 , 138 ]. Although the evidence is limited, using locally administered antibiotics alone or in conjunction with nonsurgical or surgical interventions for peri-implantitis demonstrated positive results. Combining systemically administered antibiotics with nonsurgical or surgical interventions remained controversial [ 139 ].

In many cases, peri-implantitis is the primary cause of implant failure. Implants may also benefit from the antibacterial properties of nanomaterials. An approach that could be considered is the application of antimicrobial medicines or materials to create a coating that can be modified to impart a significant antibacterial effect onto the implant's surface. An illustration of this can be seen in an in vitro test where ZnNPs modified on the implant surface and prepared as a coating demonstrated a substantial decrease in the quantity of parthenogenic anaerobic bacteria and streptococci in the medium within 96 h, as compared to implants lacking the modified coating. Furthermore, ZnO nanorods and ZnO nanorods were synthesized via the hydrothermal method by Wang et al. After Ti surface modification was applied to ZnO nanorods, ZnNPs and ZnO nanorods were subsequently modified as the outermost layer. The coating can discharge ZnO nanorods expeditiously, and this sustained discharge can impart a dual antibacterial impact. Furthermore, it was demonstrated that the application of CeO NP coating decreased the mean gene expression levels of IL-6, TNF-α, and IL-1b in per Ti tissues, thereby producing a potent anti-inflammatory impact [ 140 , 141 , 142 , 143 ].

Natural enzymes continue to be superior to NZs, even though the former has been utilized medicinally and as a toothpaste additive for centuries. They are physiologically safe and possess an effective catalytic mechanism, exhibiting high catalytic activity while demineralizing teeth and diminishing dental plaque and calculus [ 45 ]. Natural enzymes continue to be superior to NZs, even though the former has been utilized medicinally and as a toothpaste additive for centuries. These substances possess a highly effective catalytic mechanism, exhibit significant catalytic activity, and do not cause any harm to the body while whitening teeth and removing dental plaque and calculus. In contrast, the catalytic mechanism of NZs remains a subject of debate. It defies us how NZs can catalyze enzymes without catalytic activity centers. Consistently, recent research has demonstrated that the fundamental properties of nanomaterials—including size, composition, and shape—and the reaction environment—including temperature, pH, and reactants—are correlated with the catalytic activity of NZs. Changing these characteristics may only provide a partial solution to the issue of insufficient catalytic activity. For instance, metal sulfides are employed as proton-trapping agents to generate H 2 S and expose Fe 3+ , thereby enhancing the efficiency of catalysis [ 45 , 144 ]. NZs, which possess enzyme-like activity and are multifunctional nanomaterials, have established a presence within the biomedical domain. NZs have made significant contributions to phaseontics and implantology research concerning the maintenance of periodontal health and the enhancement of implant success rates [ 145 ].

Since the antimicrobial activity of NZs mainly reliant on their catalytic efficiencies, strategies such as enzyme active center mimicking, downsizing, defect engineering, catalytic processes boosted by external stimulations, and bacterial capture improvement may effectively improve the antimicrobial activity of NZs. In addition to making use of the properties of nanomaterials, NZs may serve as a special foundation for the construction of multifunctional nanoplatforms that combine several antibacterial effects, therefore addressing the limitations of NZ-based CDT on its own in real-world antibacterial treatments. New avenues for creating effective NZs with improved antibacterial activity have been opened up by sophisticated chemical design techniques. Due to the relatively small number of studies conducted so far, these well-chemically engineered NZs still have a long way to go before they are clinically translated. However, they have shown tremendous efficacy in treating bacteria-related illnesses in several in vitro or in vivo models. First off, additional enzymes that may collaborate and take part in the life cycle of microbial diseases are not as well explored as POD, OXD, or hydrolase mimics, which make up the majority of the antibacterial NZs that are now on the market. Investigating novel antibacterial NZs and deciphering their antibacterial processes is crucial. Second, although there have been many efforts to modulate substrate and product selectivity, there have been few attempts to control the catalytic activity of NZs to produce highly effective antibacterial NZs, such as single-atom NZs. Natural enzymes have a large density of active centers, but their distinct three-dimensional spatial architectures are even more crucial in explaining their exceptional specificity and activity. To get highly active and specialized NZs, the purposeful design of enzyme-comparable NZs still needs the cooperative interaction of imitating enzymatic active centers and their spatial microenvironment building. Furthermore, using theoretical stimulations and cutting-edge SAC technologies, primary enzyme-like active sites may be made more distinct and controlled, and the associated catalytic processes can be thoroughly understood in vitro. However, because of the complexity of biological microenvironments, it is difficult to investigate and comprehend the in vivo antibacterial mechanism of NZs. Lastly, even if NZs have shown a promising future in antibacterial therapy, there are still obstacles to overcome before effective disease treatment can be achieved due to their biological safety, possible toxicity, in vivo translocation, biodistribution, degradation, and metabolic pathways, among other issues [ 146 ].

Numerous research conducted recently has shown that external stimuli, such as light and ultrasonic waves, may function as a trigger to regulate the activation of NZs. These modes might provide workable solutions to get the intended noticeable site-specificity. One should take biodegradability and biocompatibility into account. Reaching a clinical use beyond the in vivo toxicity of NZs during treatments remains an obstacle. Currently, injecting NZs systemically will unavoidably harm healthy tissues. When it comes to metal-based NZs, the metallic species used to manufacture the NZs is primarily responsible for their toxicity. Although a large body of research has shown the cytoprotective function and biocompatibility of NZs, metal overload-induced metal ion release is still thought to be a potential source of adverse effects on normal tissues. For instance, an excess of copper or iron in healthy tissue or cells may cause a Fenton-like reaction, which might seriously harm nucleic acids and biomacromolecules. As a result, while evaluating the NZs for biocompatibility and biosafety, their pharmacokinetics are crucial. The ability to modify the surface of NZs offers a chance to create biosafety agents. Considering this, surface modification is one of the several approaches to get over the restriction of NZs. Furthermore, considering the ligands of NZs may affect systemic toxicity, clearance kinetics, bioavailability, and therapeutic results. According to this viewpoint, it's crucial to choose a suitable ligand and provide NZs with more biosafety [ 9 , 147 ].

Although the preponderance of NZ-based therapy systems has broad potential, they lack targeting capabilities [ 148 ]. Absorption by healthy cells may result in the induction of toxic side effects in adjacent healthy tissues to different extents. To improve the efficacy of therapy, it may be necessary to administer nanoagents in high doses, which may result in increased tissue toxicity. Due to the factors mentioned above, the development of an innovative NZ system for precise and effective disease treatment is an imperative matter [ 9 , 149 ]. The interaction between ligands and receptors in living systems can be utilized to develop targeted reagents. After that, pertinent research has progressively surfaced [ 94 ]. NZs, which catalyze the conversion of enzyme substrates and exhibit enzymatic kinetics under physiological conditions, are nanomaterials endowed with enzyme-like properties [ 150 ].

NZs, being a novel class of synthetic enzymes, offer substitute methodologies for those who rely on enzymatic catalysis. NZs are advantageous over natural enzymes because they are inexpensive, simple to prepare, and stable. These characteristics make NZs prospective for use in various disciplines, including the treatment of antimicrobial infections. Numerous studies have documented the efficacy of NZs in eradicating various resistant pathogenic bacteria, fungi, and viruses and have demonstrated remarkable curative properties against diseases induced by such pathogens [ 151 ]. The use of NZs in nanocatalytic medicine is on the rise; these enzymes interact with multifunctional nanomaterials. NZs are considered to be highly effective antibacterial agents due to their extended spectrum of activity and exceptional biocompatibility [ 152 ]. The evident potential of NZs to address the drawbacks associated with natural enzymes, including challenges in preparation, denaturation, recycling, and high cost, has been demonstrated. Through biocatalytic processes, NZs have been converted into antibacterial materials of utility. There is a shortage of a comprehensive literature review concerning the use of NZs in the treatment of oral diseases, including but not limited to dental caries, dental pulp diseases, oral ulcers, peri-implantitis, oral cancer monitoring, oral bacteria and ions, soft and hard tissue regeneration [ 153 ].

One of the obstacles encountered in the clinical application of nanocatalysis technology for topical oral use has been the requirement to administer two components simultaneously, either through containers with distinct compartments containing each component individually or in two stages (catalytic NP followed by H 2 O 2 administration). Based on researchers' preliminary testing (unpublished), the latter option, which would permit the mixing of the two constituents before the treatment, is feasible but necessitates custom packaging. Therefore, a one-step nanocatalytic formulation activated under pathological conditions via intrinsic H 2 O 2 generation could potentially serve as a more viable and precise approach to preventing oral diseases. Additional in vivo investigations into the mechanisms of action and potential toxicity of the bi-functional hybrid NZ would establish the groundwork for clinical implementations aimed at preventing dental caries in humans once its therapeutic precision and efficacy have been established. In the post-microbiome era, when treating polymicrobial diseases necessitates the precise targeting of opportunistic pathogens in mixed communities while preserving the commensals and ecological diversity of the host microbiota, this strategy may be applicable [ 90 , 95 ].

Natural enzyme mimetics may soon be capable of independently regulating their activities via conformational changes [ 154 ]. Diverse methods for modifying the activities of NZs in vitro or in vivo will emerge, thereby broadening their range of applications. NZs present a potentially advantageous resolution to enzyme-related ailments due to their activities approaching those of natural enzymes. Moreover, they may offer distinctive benefits not inherent in natural enzymes [ 155 ].

NZs are extensively utilized in clinical disease detection and therapy due to their inherent superiority over natural enzymes. Fer destroys bacteria in situ by binding to the ultrastructure of biofilms, degrading the extracellular polymeric material matrix, and generating free radicals from H 2 O 2 . When combined with modest concentrations of H 2 O 2 , Fer prevents acid injury to mineralized tissue and impedes biofilm formation on authentic teeth in an ex vivo model of biofilm derived from human tissue. The application of Fer and H 2 O 2 via topical oral therapy in a mouse model of the disease effectively suppresses the progression of dental caries in vivo, thereby mitigating the occurrence of severe tooth decay (cavities). Histological and microbiome analyses indicate no adverse effects observed on the diversity of oral microbiota or gingival and mucosal tissues. The results suggest that Fer could have a novel biomedical application as a topical treatment for prevalent and costly oral diseases caused by biofilms [ 90 ]. Researchers used a wearable intraoral device containing FerIONP to treat human participants with implanted natural tooth enamel in a randomized crossover trial. The investigation was carried out under unfavorable circumstances that encourage dental cavities. FerIONP was shown to have a solid antibacterial selectivity against biofilms, including the cariogenic pathogen S. mutans , but not against other oral bacteria. Enamel demineralization was significantly reduced as a result. Further studies revealed that FerIONP preferentially eliminated S. mutans by producing localized ROS in situ and showed a preferential affinity for the pathogen via a glucan-binding mechanism. Additionally, we proved that FerIONP might be used as a catalyst to identify cariogenic biofilms. Together, Liu et al. provide the first human investigation demonstrating the therapeutic potential of catalytic iron oxide NPs, or NZs, as a targeted nanomedicine for managing an oral infectious illness. To find out whether topical FerIONP with iron or fluoride supplements might boost protective benefits in sensitive people in a synergistic way, further study is needed. Given the established oral-systemic relationship, clinical trials could explore the potential benefits of combining repeated topical oral applications of FerIONP with its systemic use to prevent severe childhood caries and mitigate iron deficiency, which are major unresolved global health issues [ 156 ].

Fer, an iron oxide nanoparticle recently approved by the FDA, has been demonstrated to degrade and destroy biofilms that cause dental caries via hydrogen peroxide catalytic activation. Fer, on the other hand, does not affect enamel acid demineralization. The combination of Fe and SnF 2 inhibits biofilm accumulation and enamel degradation significantly more effectively than either element used alone, according to research. Unexpectedly, the stability of SnF 2 is improved when it is combined with Fer in aqueous solutions, while the catalytic activity of Fer increases unassisted without the use of any additives. It is worth mentioning that the combination of SnF 2 and Fer exhibits remarkable efficacy in vivo against dental caries, even at concentrations four times lower, while causing no detrimental effects on the oral microbiome or host tissues. Additionally, comprehensive toxicity investigations are necessary to ascertain the potential long-term consequences of daily application of Fer and SnF 2 . In the context of clinical translation and product development, it may be necessary to optimize the concentrations of Fer, SnF 2 , and H 2 O 2 . However, our findings indicate that Fer and SnF 2 enhance the therapeutic activity via unforeseen synergistic mechanisms that concurrently target the physicochemical (enamel demineralization) and biological (biofilm) characteristics of dental caries. Moreover, given the frequent association between severe childhood tooth caries and iron deficiency anemia, administering Fer may offer a twofold advantage for these individuals. The potential for utilizing SnF 2 and Fer to treat anemia and tooth decay, two of the most significant global health issues, presents a viable opportunity to incorporate combination therapy into clinical trials to prevent dental caries in high-risk patients with iron-deficiency anemia. The findings of the researchers demonstrate a powerful therapeutic synergy between approved agents and SnF 2 stabilization, which can be used to reduce fluoride exposure and prevent a common oral disease [ 78 ].Low catalytic activity and an unknown catalytic mechanism Although natural enzymes have been incorporated into toothpaste for therapeutic purposes, they remain more effective than NZs. They can whiten teeth as well as reduce dental calculus and plaque due to their potent catalytic activity, transparent catalytic mechanism, and superior biological safety [ 157 ]. However, the catalytic mechanism of NZs remains a subject of debate. Scientists are baffled as to how NZs devoid of catalytic activity centers can imitate the catalytic activity of enzymes. Current research has progressively established a correlation between the catalytic activity of NZs and the fundamental properties of nanomaterials (size, composition, and shape) as well as the reaction environment (pH, temperature, and reactants). Nevertheless, modifying these parameters can only partially mitigate the problem of diminished catalytic activity [ 158 ]. Researchers have been working to find effective catalysts and inhibitors for NZs, and they have made some headway in this area. The oxidase, peroxidase, catalase, and superoxide dismutase enzymes that were first used in dental research to demonstrate the enzyme-like properties of NZs were restricted in diversity and lacked substrate specificity. During the alteration process, the researchers added DNase activity. Conversely, NZs are unable to bind to the substrate selectively because they do not have the complex structure of a genuine enzyme–substrate binding bag. They are similar to traditional catalysts in this way [ 159 ].

NZs that have been engineered to bind to specific substrates via DNA engineering have demonstrated remarkable efficacy in oral monitoring; however, this does not suffice. Opportunities and obstacles abound in the investigation and implementation of NZs within the field of dentistry. In pursuit of clinical application, scientists must diligently investigate the precise active mechanism of NZs and cultivate additional varieties of NZs to address treatment requirements. Dentists are obligated to propose critically resolvable clinical issues, investigate the molecular biology of the NZ mechanism collectively, and assess potential challenges in the practical implementation of NZs [ 32 ].

Although conventional dentistry has been significantly enhanced by revolutionary nanotechnology, there are still several inevitable voids that hinder its complete clinical exploration. In comparison to other areas of biological research, the current state of nanodentistry research is belated. The advancement of cost-effective and efficient nanotheranostics will be facilitated by the increased focus on patient needs in research [ 160 ]. The pharmacokinetics, absorption, metabolism, biodistribution, therapeutic duration, excretion, and toxicity of NZs need to be explored and understood at different phases of administration and therapy. According to several data on biodistribution, non-targeting NZs tend to accumulate in the lung, liver, and spleen. The primary factors influencing the progress of NZ clinical use will be their therapeutic safety and biocompatibility [ 56 ].

Although scientists have created a variety of surface-modified NZs using polymers, nucleic acids, and antibodies to imitate natural enzyme selectivity, the resulting selectivity is still inadequate for usage in real-world applications. Regarding environmental and medicinal uses, the toxicity of NZs to people and the environment is another crucial problem that has to be resolved. Future research will employ a strategy of rational screening of enzyme-like activity based on those atomic compositions which are envisaged to catalyze enzymatic reactions, in contrast to traditional research on developing NZs, which has been carried out by random screening of the enzyme-like activities of existing unspecified nanomaterials. Furthermore, by using their synergistic impact to promote electron transport across composite materials during redox reactions, a technique to produce composites should be able to overcome the primary limits that now exist with NZs of poor catalytic activity. By successfully avoiding the use of hazardous chemicals in traditional chemical synthesis, bioinspired synthesis of NZs also offers a way to manufacture benign NZs, speeding up their usage in therapeutic applications. Lastly, the sector will benefit from the development of innovative surface engineering techniques that can make NZs specific to target substrates [ 161 ]. Given the aforementioned research initiatives, we anticipate that nanoenzymes will soon be extensively used in a variety of dental infection treatments.

Conclusions

The escalating global incidence of periodontal and peri-implant diseases has garnered considerable interest. NZs, which possess enzyme-like activity and are multifunctional nanomaterials, have established a presence within the biomedical domain. NZs have significantly advanced research in the fields of periodontics and implantology, specifically about the maintenance of periodontal health and the enhancement of implant success rates. Natural enzymes have inherent drawbacks that are circumvented by NZs, including but not limited to poor environmental stability, high production costs, and storage difficulties. The development of dentistry is parallel to that of material science. Oral NZ research and utilization is emerging as a distinct subfield within nanocatalytic medicine. To underscore the significant impact that NZs have on dental health, we began by conducting a comprehensive review of the overall research advancements concerning multifunctional NZs about oral diseases. This included the treatment of dental caries, pulp diseases, oral ulcers, and peri-implantitis; the monitoring of oral cancer, oral bacteria, and ions; and the regeneration of both soft and hard tissue. In addition, the investigation and application of NZs in dentistry face a multitude of potential obstacles. Scientists must make a concerted effort to fully comprehend the precise energetic mechanism of NZs and develop novel varieties of NZs to satisfy the therapeutic demand for experimental clinical application. Urgent clinical concerns must be attended to, dental researchers must collaborate to comprehend NZ mechanisms at the molecular biology level, and they must assess potential complications in NZ application. As in vitro and in vivo research increased, we encountered a dearth of data-driven significance in the extraction data. It is highly recommended that future experimental investigations utilize a more substantial sample size, and that additional systematic assessments be undertaken to evaluate the effectiveness of these scientific experiments. Consequently, it is crucial to address the unresolved challenges through concerted efforts; doing so will significantly advance future research endeavors. It is expected that this extensive examination will not only increase the interest and enthusiasm of researchers in the domain of NZs but also furnish them with invaluable knowledge and perspectives that aid in the investigation of catalytic mechanisms intrinsic to NZs that have yet to be explored. Hence, the aforementioned obstacles symbolize the vanguard of forthcoming NZ research, compelling additional inquiry and scrutiny.

Availability of data and material

Not applicable.

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Acknowledgements

Special thanks to all the scientists and researchers who are concerned about relieving the pain of patients.

Author information

Authors and affiliations.

Department of Periodontology, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran

Mohammad Hosseini Hooshiar

Department of Oral and Maxillofacial Surgery, School of Dentistry, Qom University of Medical Sciences, Qom, Iran

Ashkan Badkoobeh

School of Dentistry, Shahid Sadoughi University of Medical Sciences, Yazd, Iran

Shirin Kolahdouz

Postgraduate Department of Prosthodontics, Dental Faculty, Tehran University of Medical Sciences, Tehran, Iran

Azadeh Tadayonfard

Department of Periodontics, Faculty of Dentistry, Qazvin University of Medical Sciences, Qazvin, Iran

Asieh Mozaffari

Department of Dentistry, Islamic Azad University of Medical Sciences, Tehran, Iran

Kamyar Nasiri

Islamic Azad University of Medical Sciences, Esfahan, Iran

Sara Salari

Restarative Dentistry, Department of Dental, Faculty Tabriz Medical University, Tabriz, Iran

Reza Safaralizadeh

Young Researchers and Elite Club, Tabriz Branch, Islamic Azad University, Tabriz, Iran

Saman Yasamineh

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S.Y., A.T., K.N., writing—original draft, M.H.H., A.B., S.K., A.M., S.S., R.S., conceptualization, supervision, writing—review & editing. All authors read and approved the final manuscript.

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• Published: 31 August 2021

How to undertake research as a dental undergraduate

• Alya Omar 1 ,
• Emma Elliott 1 &
• Sathyam Sharma 1  

BDJ Student volume  28 ,  pages 17–18 ( 2021 ) Cite this article

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By Alya Omar , Emma Elliott and Sathyam Sharma

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How do dentistry and mental health link together? What role do dentists have in addressing patient mental health? How confident do you feel about taking on that role? When you find a research question that interests you and grabs your attention, you shouldn't be afraid to approach a project alongside your studies. For a small group of us at Barts and the London Dental School, this question was related to confidence and education around patient mental health. What started as a small idea ultimately snowballed into a multi-centre research project called 'Open Up', spanning five dental schools across the UK and Ireland. Whether you have high ambitions in research, want to contribute to the field or simply want to explore an area of interest, we hope this serves as a guide to get you started.

When you first consider a research question, you should begin by looking at the literature that already exists in the field - formally known as a 'literature review'. Our research question was 'How confident are UK dental students at addressing patient mental health?'. So we took a step back and looked at the UK clinical picture and the current best available research. You should initially outline the picture within the population you are interested in and follow by evidencing the need for your research question. For example, our literature review covered the following points:

Psychiatric disorders are on the rise within the UK population with 20% of men and 30% of women professionally diagnosed with a psychiatric condition 1

Several studies had already investigated practitioner confidence when addressing patient mental health and reported low confidence 2

We found no studies that assessed UK dental undergraduate education or student confidence around patient mental health.

According to the GDC dental practitioners are in a position where we need to be able to 'identify, explain and manage the impact of medical and psychological conditions'. 3

Once you have a good grasp of the existing literature around your research question you should consider the benefit your work could bring to the dental research community. This will help you plan the project and figure out the best way to answer your research question. We wanted to see if modern dental undergraduate education was creating confident dental students who could comfortably address patient mental health. To be of benefit, we needed to survey the existing clinical year groups in the BDS curriculum and run focus groups to gather dental students' opinions on how their confidence could be enhanced. A literature review and a basic outline of the study puts you in good stead to then approach a potential supervisor.

A supervising tutor will guide your research project with their experience and will ensure you get the most out of it, advising you on how to proceed and helping you collaborate with others. This chosen person can be any tutor who is willing, but someone is much more likely to supervise you if you come to them with at least a partially-formed idea. A supervising tutor is key to helping you secure approval to run your project, assisting you in analysing your findings and guiding your project write-up if you wish to submit it to a journal.

After securing our supervising tutor and successfully pitching the project, we ran our initial study. We found that students believed an interactive workshop with case-based discussion was the best way to improve their confidence when addressing patient mental health. Dr Catherine Marshall, a clinical lecturer in psychiatry, helped us develop such an educational intervention; she also helped us develop pre- and post-workshop surveys that allowed us to see how participant confidence changed as a result of the workshop. She was instrumental in the project, giving expert input on her field. If your topic of interest requires specialist advice, do not be afraid to reach out and collaborate for the best results.

Once you have your research question, methodology and a supervising tutor, you should feel more comfortable with conducting a project alongside your degree. This is a strong starting point, but projects will inevitably change and mould around your circumstances. We initially published work based on research in a single institute, only later realising that we could think bigger and conduct the study across multiple dental schools. Don't restrict yourself, but don't bite off more than you can chew either!

When you first consider a research question, you should begin by looking at the literature that already exists in the field

You need to think ' will my project benefit from participation from a wider group of people ?' Larger groups of study participants can lead to more generalisable data, which is of greater use to researchers. Therefore, we decided to survey the confidence of dental students across multiple dental schools and then deliver our workshop intervention at each school. Student representatives were appointed at each school and were responsible for the research there. This is also a key point - when undertaking research, you should appropriately credit those involved, will they be authors or acknowledgements? It is important to consider this early on and be clear to the people you ask to help with the study.

Our representatives became authors of the study, alongside Dr Marshall and our supervisor, Dr Hurst. Expanding a project can be difficult, but if you want to work on a larger study then you can consider collaborating with students via DentSoc, (or DentSoc presidents), BDSA, conferences or even via shout-outs in the Student BDJ. Using these methods, we were able to collaborate with students at Trinity College Dublin, Newcastle, Kings College London and Dundee.

When conducting research, your circumstances will change and you will have to adapt. For us, we had to work around the COVID-19 pandemic; we had a large multi-centre project that relied on the delivery of an in-person workshop during a massive public health crisis! Admittedly, this isn't something we could have prepared for, but it highlights that research isn't always smooth sailing. We initially planned to collaborate with nine dental schools, but the pandemic meant we had to reconsider, shrink and shorten the project.

Putting your research on hold isn't ever ideal, but sometimes it is best to take a step back and reconsider how the project may need adapting to a change. The change might be something small or large - perhaps you had a personal change in circumstances and what you had planned is no longer feasible. This is fine! Just adapt the work so that what you have done doesn't go to waste.

In our case we had to adapt the research for online delivery of the workshop and restrict the study to the schools that had already made progress with surveying the student body. This change took a long time to consider, leaving the project on a long hiatus. However, once we had taken time to consider these decisions, the changes were easier to implement. Adapting to COVID-19 for us meant brainstorming with our representatives to ensure everyone knew how we were re-designing our methodology.

Sometimes, these changes can be ultimately beneficial! Despite our initial difficulties in organising online virtual webinars in place of our in-person workshops, we found that the format made things easier. It allowed the representatives to be better supported as we could drop in on the virtual sessions if they needed it. With the online format we also had the option to have the workshop delivered by the same people, thereby increasing uniformity amongst workshops.

After all these difficulties, we managed to evidence that whilst national student confidence was low when addressing patient mental health, the workshop was an effective beneficial intervention! This knowledge is of benefit to dental research as it evidences how, if we are appropriately educated, we can improve patient outcomes, better supporting and understanding those with poor mental health. You too can make such an input in the field of dental research; if you have an inkling of an idea or a more fleshed out question you want to explore, why not consider research alongside your degree? It can be as much of a benefit to yourself (via conferences, collaboration and project management) as it can be to others and our patients.

Top tips for research around studies

Perform a literature review around your concept to identify gaps in research and to ensure thorough understanding of the field

Choose who to work with - as an undergraduate you will always need a supervisor, but do you want to work with others? This can split the workload but you must ensure everyone is appropriately credited

Consider what impact your research could have and design your methodology appropriately to ensure your data answers your research question

If you want to collaborate with other schools and do a larger study, you can reach out via DentSoc, BDSA or BDJ Student

Be prepared to adapt and make changes as you go, things will not always go to plan!

Mental Health Foundation. Fundamental Facts About Mental Health. [ebook] London: Mental Health Foundation. 2016. Available at: https://www.mentalhealth.org.uk/publications/fundamental-facts-about-mental-health-2016 (Accessed July 2021).

Freeman R. Have dentists a role in identifying mentally ill patients? Br Dent J 2001; 191: 621.

Preparing for Practice: Dental Team Learning Outcomes for Registration (2015 Revised Edition). General Dental Council.

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Dental caries prevalence in relation to the cardiovascular diseases: cross-sectional findings from the Iranian kurdish population

• Zahra Ghanbari 1 ,
• Yousef Moradi 2 ,
• Negin samiee 1 &
• Farhad Moradpour 3  

BMC Oral Health volume  24 , Article number:  509 ( 2024 ) Cite this article

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Oral and dental health (ODH) is a significant public health concern globally, affecting billions of people. This cross-sectional study aimed to examine the prevalence of dental caries using the DMFT index and investigate its relationship with cardiovascular diseases in the Iranian Kurdish population.

A total of 3,996 individuals aged 35–70 years were included from the Dehgolan prospective cohort study (DehPCS). Clinical examinations were performed to assess decayed (DT), missing (MT) and filled (FT) teeth (DMFT index). Data on demographics, socioeconomic status, medical history, oral hygiene practices were also collected. Cardiovascular disease (CVD) history was self-reported via questionnaires assessing heart disease, heart attack and stroke. Logistic regression was used to assess associations between oral health indicators and self-reported CVD, adjusting for potential confounders.

The mean DMFT score was 18.18 ± 19, indicating a high oral disease burden. Specifically, 60.04% had DT, 37.82% had more than 16 MT, and 38.83% had FT. Only 13.21% reported flossing regularly and 43.17% brushed less than daily, showing suboptimal oral hygiene. The overall CVD prevalence was 9.21%. Individuals with high DMFT (≥ 14) scores had approximately two times higher CVD prevalence than those with low DMFT. DMFT decreased by 10.23% with increase in education level, and by 5.87% as economic status increased In adjusted analyses, high DMFT scores (OR = 1.5, 95%CI: 1.2–1.9) and MT (OR = 1.5, 95%CI: 1.1–2.1) were associated with 50–150% increased odds of CVD, though associations weakened after adjusting for age. Among men, DMFT remained a significant predictor for CVD after age adjustment, with an odds ratio of 2.37 (95% CI: 1.22–4.60).

This population had substantial oral disease and poor oral hygiene. Higher DMFT scores and MT positively correlated with increased CVD prevalence. Promoting preventive oral care and health education could help reduce dental issues and potentially lower CVD risk. Further research is needed to clarify biological mechanisms linking oral and systemic health.

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Introduction

Oral and dental health (ODH) is widely recognized as a crucial public health concern in numerous countries across the globe. Although the World Health Organization(WHO) has highlighted the importance of ODH and its significant influence on individuals’ daily lives, the lack of focus on ODH and related diseases has had a detrimental effect on over 5.3 billion people globally [ 1 , 2 ]. Among these, gum inflammation and dental decay are considered the most prevalent diseases related to ODH [ 3 , 4 ].

Dental decay affects 60 to 90% of students and 100% of adults worldwide, and furthermore, approximately 30% of individuals aged 65 to 74 globally have no natural teeth [ 5 ]. Decayed, missing, filled teeth (DMFT index) is the most commonly used scoring system for assessing ODH on a global scale. This index reflects an individual’s oral health status throughout their lifetime, based on their experience of decay [ 6 , 7 ]. The interplay between ODH and the overall health of other organs, including the cardiovascular system, has been a subject of attention for many years. Dental issues such as dental caries follow a chronic process and, without proper hygiene and a healthy diet, can negatively impact an individual’s health, including their cardiovascular well-being [ 8 ]. Advanced/severe stage dental caries was significantly associated with an increase in coronary heart disease (CHD) risk among middle-aged individuals [ 9 ].

Moreover, oral and dental diseases share common risk factors with cardiovascular diseases, which are multifactorial in nature, influenced by lifestyle choices, diet, physical activity, tobacco use, and more [ 10 ]. Studies have shown that oral microbiota, in addition to these risk factors, can contribute to the incidence of cardiovascular diseases [ 11 ].

Despite the overall decline in global mortality rates, cardiovascular diseases stemming from oral and dental diseases continue to be recognized as the leading cause of death and morbidity worldwide. These diseases are responsible for approximately 70 to 80% of deaths and chronic illnesses in both developing and developed countries, accounting for 4 million deaths annually in Europe [ 12 ].

While previous studies have primarily focused on clarifying the association between cardiovascular diseases and periodontitis among oral diseases [ 13 ], less attention has been given to investigating the relationship between cardiovascular diseases and other dental problems, such as dental caries, filled teeth, and missing teeth [ 7 ]. Therefore, considering the paramount importance of ODH and its significant impact on maintaining cardiovascular health, conducting research in this area is imperative. The objective of this study is to assess the prevalence of the DMFT index and explore its association with cardiovascular diseases using data from the Dehgolan prospective cohort study (DehPCS).

Materials and methods

Study design and population.

The present study is based on data collected during the initial phase of the DehPCS, which is a part of the Prospective Epidemiological Research Study in Iran (PERSIAN). DehPCS aims to investigate the incidence, prevalence, mortality, and risk factors of non-communicable diseases among 3,996 study participants aged 35–70 who are permanent residents of Dehgolan, Iran [ 14 ]. The study gathered information on demographic characteristics, socio-economic status, and medical history. Excluded from the study were individuals who encountered communication challenges due to conditions like blindness, deafness, and severe mental and psychological illnesses. Additionally, individuals who were excluded included those with tooth loss resulting from factors other than decay, such as trauma and periodontal diseases. The study received approval from the Ethics Committee of Kurdistan University of Medical Sciences under the code of IR.MUK.REC.1402.044.

Data collection and measurement

Data collection involved face-to-face interviews with individuals. Systematic clinical examinations were performed by tow well-trained nurses according to the WHO criteria to determine the DMFT index scores of participants, providing an objective assessment of caries experience for analysis in relation to cardiovascular health history.

The questionnaire collected information on demographic characteristics, wealth index, body mass index (BMI), personal habits such as smoking and alcohol consumption frequency, dental hygiene practices including dental floss and toothbrush usage, as well as medical history and medication use. The wealth index, which is a composite measure of a household’s living standard, was assessed through a survey conducted at both the household and individual levels. BMI was calculated using a weight (kg)/ height 2 formula, categorizing individuals into three groups: normal weight (≤ 24.9), overweight (25-29.9), and obese (≥ 30). Smoking status was classified into three groups: non-smoker (an individual who has smoked less than 100 cigarettes in their lifetime), smoker (an individual who has smoked more than 100 cigarettes in their lifetime, ex-smoker (smokers who have not smoke during past 30 days). Alcohol consumption was categorized as individuals consuming 200 milliliters of beer or 45 milliliters of alcohol at least once a week for a minimum of 6 months. Use of Morphine, Heroin, Methamphetamine, Crack, and Cocaine once a week for at least 6 months was considered as illicit/ illegal drug use. Participants were also questioned about their history of ischemic heart disease (including heart failure, angina, and heart attack).

Oral and dental health assessment

The clinical examination process involved assessing the 32 permanent teeth using the decayed, missing, and filled teeth (DMFT) index [ 15 ]. According to standardized guidelines, teeth such as impacted teeth, congenitally missing teeth, supernumerary teeth, deciduous teeth present in adulthood, and teeth lost due to reasons other than decay (such as trauma and periodontal disease) were excluded from the study. Teeth with decay on one surface and restoration on another surface were classified as decayed teeth. The overall score for an individual’s teeth was determined based on the following criteria: 0 (no decayed, missing, or filled teeth) and ≥ 1 (one or more decayed, missing, or filled teeth). Subsequently, individuals were categorized into two groups: high DMFT (DMFT score ≥ 14) and low DMFT (DMFT score < 14) [ 16 ]. Missing teeth were classified into three categories of ≤ 5, 6–15, and ≥ 16 missed teeth [ 17 ]. In addition to the clinical examination, a questionnaire regarding brushing and flossing frequency was administered and completed by the participants. Calibration exercises involving blinded re-examination of a subsample of participants preformed to check for consistency in DMFT scoring between interviewers.

Cardiovascular diseases Assessment

Participants were asked questions regarding the presence or absence of common cardiovascular diseases including heart attack, stroke, congestive heart failure or history of any ischemic heart diseases [ 18 ]. If they responded positively, additional information was collected, including age at diagnosis, current treatment under a physician’s care, and details about medication type, dosage, and duration.

Statistical analysis

Descriptive statistics including mean numbers of decayed, missing, filled teeth and DMFT index were reported along with their standard deviations. Prevalence of CVD and dental caries were calculated across different variables based on the standard approach as number of individual with positive criteria in numerator divided by all eligible participants in denominator. T-test and one-way ANOVA were used to compare the mean scores across categories. Chi square test also was used to compare outcome of interest between groups. Inter-rater agreement were investigated by calculating kappa statistics. Both unadjusted and adjusted logistic regression models were fitted to examine the associations between DMFT index/components and CVD, presenting odds ratios and 95% confidence intervals. Model 1 adjusted for gender, education, socioeconomic status, BMI, smoking, alcohol, drug use, sugar intake and oral hygiene behaviors. Model 2 further adjusted for age in addition to the covariates in Model 1. All tests were two-tailed with statistical significance set at p- value < 0.05. Statistical analysis were performed using STATA version 17.

Prevalence of DMFT, DT, MT, FT

Table  1 presents the DMFT score over different characteristics of study participants. The mean number of DMF among those with at least one decayed and/or missing and/or filling tooth was about 18 ± 19. Prevalence of DT, MT (> 16), and FT were 60.04% (CI: 58.50-61.55), 37.82% (36.32–39.34), and 38.83% (CI: 37.32–40.36) respectively. Approximately all participants suffered from at least one DMFT including DT (female: 57.14% and Male: 63.78%), MT (female: 96.91% and Male: 95.84%), and FT (female: 40.54% and Male: 36.63%). DMFT decreased by 10.23% with increase in education level, and by 5.87% as economic status increased. Only 13.21% of participants used flossing, 43.17% did not brush their teeth daily, 35.35% brushed 1–2 times and 21.58% brushed 3–4 times a day.

CVD history

Cardiovascular disease history affected 366 (9.21%) of all participants. The mean age for those with CVD and Not reported CVD history were 54.56 ± 8.8 and 47.71 ± 8.68 respectively. As shown in Table  2 CVD history was not different among males and females, but increased incrementally with a 19.3 prevalence difference between low and high age groups. Taking oral health behavior such as brushing and flossing are accompanied by a lower proportion of CVD history of 6.11 and 5.55% respectively. CVD proportion in people with high DMFT scores was about 2 times more than low DMFT category. As the number of missing teeth increased, there was a corresponding increase in the prevalence of CVD, with a mean of 4.5 (Cochrane-Armitage p-value for trend < 0.001). Additionally, decayed and filled teeth were found to be associated with a lower proportion of reported CVD, approximately 5%.

Chi square test.

Correlates of CVD

The associations of various correlates and confounding variables with CVD were presented in Table  3 . Alongside traditional risk factors like age, BMI, smoking, illicit drug use, and education, the practice of teeth brushing and flossing showed a significant association with lower odds of CVD in the population. The practice of teeth brushing (OR = 0.48, 95% CI: 0.39–0.60) and flossing (OR = 0.42, 95% CI: 0.27–0.64) showed a significant association with lower odds of CVD in the population. Notably, the specific ORs were not reported in Table  3 .

Additionally, in the unadjusted analysis, both the DMFT index and missing teeth were positively associated with CVD, while decayed and filled teeth were negatively associated with CVD. However, in the multivariable analysis, after adjusting for several confounders including gender, education, socioeconomic status, BMI, smoking, alcohol use, illicit drug use, and sugar consumption and ODH behaviors (model 1), the DMFT index and high missing teeth were shown to increase the odds of CVD by approximately 50%, with an OR of 1.54 (CI: 1.13–2.09) and 1.58.

(1.03–2.43) respectively. On the other hand, decayed teeth were found to decrease the odds of CVD by 31% with an OR of 0.69 (CI: 0.53–0.90).

Further adjustments for age (model 2) weakened the associations between DMFT index and missing teeth with CVD, although the association remained statistically significant for dental caries OR = 0.75 (CI: 0.57–0.99). Because of significant interaction between gender and DMFT (p-value < 0.05) results were also reported based on gender strata. In the gender-stratified analysis, after performing additional adjustments for age (model 2), most of the associations diminished among women. However, among men, DMFT remained a strong positive predictor 2.37 (CI: 1.22–4.60) for CVD.

The results of this study provide important insights into the oral health of the population and its relationship with CVD. Results provide a mean DMFT score of 18.18 including 60.04% DT, 37.82% of high MT, and 38.83% FT. DMFT with an OR of 2.37 presents a moderate effect size on CVD in men. Compared to global data, our DMFT is lower than the global median of 21.9 reported for ages over 60 years in a 2021 systematic review [ 19 ]. Studies across Asia have found various DMFT of 21.9 in Turkey [ 20 ], 22.5 in China [ 21 ], and 14.3 in Vietnam [ 22 ]in comparable age groups. Previous studies have reported lower mean DMFT score of 7.8 [ 23 ], and 14.8 in the regional and national level respectively [ 24 ].The divergent DMF index reported may reflect context-specific population differences. Notably, a recent comparable study in culturally similar Kermanshah, Iran found a near-identical 18.08 DMFT, corroborating socio-cultural impacts on oral health [ 25 ].

The high prevalence of untreated caries in our study can be concerning for functional impairment and quality of life. Studies from United States, Malawi [ 26 ], Egypt [ 27 ] and Pakistan in similar age groups found decay teeth prevalence of 21.5, 49 and 56.6% respectively, lower than our prevalence. High prevalence of missing teeth about 96% in our study is much more the other studies in Malawi 63%, Egypt 76%, likely indicates inadequate preventive dental care and unmet treatment needs in population. This study indicate high level of caries experience according to the WHO [ 15 ]. The combination of obstacles relating to diet, oral hygiene, socioeconomics, geography and health literacy have created an environment conducive for extensive dental caries to take hold in this population [ 28 ].To our knowledge, only 13% of our participants used dental floss and 43% did not brush daily, indicating suboptimal oral hygiene practices significantly less than other international and national studies in the Malawi, Egypt [ 27 ] and Tehran [ 29 ] which reported 2.9 and 23 and 19% did not daily brushing their teeth.

The study found that individuals with poor oral health, as indicated by high DMFT scores and missing teeth, had a higher prevalence of CVD. In contrast, decayed and filled teeth were associated with a lower proportion of reported CVD. MT could reflect worse long-term oral health status and cumulative caries burden over many years, capturing the influence of chronic inflammation on systemic health. On the other hand, DT represents more active but potentially treatable disease states. Those with high DT may practice better oral hygiene or have better access to care, reducing inflammatory impacts [ 30 ]. We also found that oral health behaviors such as brushing and flossing were associated with a lower proportion of CVD history. This is consistent with previous studies conducted in German [ 31 ] and Finnish [ 32 ] population. People who regularly use dental floss and toothbrush have lower levels of C-reactive protein (CRP) in their bloodstream. This protein is an indicator of inflammation in the body, and an Increase in Its amount in the body is associated with an increased risk of cardiovascular diseases [ 33 ].

The prevalence of CVD in individuals with high DMFT was more than twice as high as those with low DMFT and is consistent with the results of a study conducted in Japan [ 34 ]. While the current study did not investigate potential biological mechanisms, prior research has implicated the oral bacterium Streptococcus mutans, commonly associated with dental caries development, as one possibility warranting further study in relation to cardiovascular disease risk [ 35 ].

The findings of the present study indicate a positive correlation between the prevalence of heart diseases and the number of missing teeth. This observation aligns with a recently published systematic review that has established a connection between tooth loss and the occurrence of cardiovascular events, including coronary artery disease (CAD), peripheral arterial disease, and an elevated risk of stroke-related mortality [ 36 ]. The possible pathways In this mechanism may include a link between chronic systemic inflammation associated with periodontal disease, an Indirect effect on the cardiovascular system through dietary changes resulting from tooth loss, and the loss of normal gum tissue following progressive dental injury, which leads to the accumulation of oral microbes in the depths of the oral tissue. As these microbial accumulations grow and progress, they put the individual at risk for cardiovascular disease [ 37 , 38 ].

After adjustment for several confounding variables, including gender, education, socioeconomic status, BMI, smoking, alcohol use, illicit drug use, sugar consumption, brushing, flossing (model1) high DMFT index and high MT were associated with a 1.5-fold increase in the chance of CVD. Further adjustment for age (model 2) revealed that age play a major confounding role in the association between oral health and CVD. An interesting finding of our study is interaction between DMFT and gender. So, gender-stratified analysis showed that after adjusting for covariates, there was a significant association between a high DMFT index and self-reported history of CVD among males, but not females [ 39 ]. Age plays a significant role in confounding factors for females, primarily due to variations in the timing of reproductive and hormonal changes throughout their lifespan, which in turn influence disease risk. When adjusting for age, a greater portion of the association is accounted for in females [ 40 ]. DMFT scoring system as a surrogate for ODH represents past and present dental caries [ 7 ]. Studies show that dental caries is the primary driver for tooth extractions and the main factor causing tooth loss when looking at causes in individuals [ 41 ]. Given that our study was cross-sectional the high prevalence of missing teeth, even with prevalence of decayed/filled teeth, suggests that extraction may have been prioritized over restoration in the treatment of dental caries. Tooth loss (≥ 8) following decay can lead to changes in dietary patterns, resulting in elevated levels of total cholesterol and triglycerides, as well as the potential for obesity, high blood pressure, and ultimately cardiovascular diseases [ 11 ]. On the other hand, inflammation in periodontal pockets following tooth loss can trigger chronic systemic inflammation, thereby increasing blood pressure and the risk of cardiovascular diseases [ 17 , 42 ]. Although other studies have concluded there is an independent relationship between missing teeth and CVD, there has been no study investigating the DMFT index as a surrogate for lifetime dental caries experience [ 43 , 44 , 45 ]. However, our study findings highlight a high DMFT index as a significant factor in the cardiovascular health of older adults.

This study has several strengths. It makes use of recent and representative data from a large sample of the Kurdish population, which has not been done before. Comprehensive list of risk factors was included in the logistic regression model to address residual confounding. However, the limitations inherent in the study design should be considered when interpreting the results. As is typical with cross-sectional designs, while connections can be identified, the timeline of relationships and underlying causation cannot be validated. This work also relied on self-reported information, allowing for possible recall/reporting bias.

This study found a high burden of oral diseases among Kurds based on a high mean DMFT score, substantial untreated dental caries and missing teeth. Poor oral hygiene practices were observed versus other studies. Poor oral health as indicated by a higher DMFT score would be positively associated with cardiovascular disease. Promoting preventive oral care and oral health education could help reduce preventable dental issues and potentially lower long-term cardiovascular morbidity and mortality. The study emphasizes the importance of integrated oral-overall health approaches and highlights unmet oral health needs, underscoring the need for dental-medical collaborations to advance oral health and cardiovascular well-being through addressing modifiable risk factors.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

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The Iranian Ministry of Health and Medical Education has contributed to the funding used in the PERSIAN Cohort through Grant no 700/534.

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Ghanbari, Z., Moradi, Y., samiee, N. et al. Dental caries prevalence in relation to the cardiovascular diseases: cross-sectional findings from the Iranian kurdish population. BMC Oral Health 24 , 509 (2024). https://doi.org/10.1186/s12903-024-04280-z

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Dr. George Kotsakis is a Diplomate of the American Board of Periodontology and he currently serves as Professor & Assistant Dean of Clinical Research at Rutgers SDM. He received his DDS from the University of Athens and after graduation he practiced in Athens, Greece for several years prior to coming to the US. He then completed his residency in Periodontics and MS in Science at the University of Minnesota when he first got involved in Peri-implantitis research. Following his training, he became an Assistant Professor in the Department of Periodontics at the University of Washington, Seattle, WA. In 2018, he moved to UT Health at San Antonio where he was Associate Professor of Periodontics, UTHSCA, San Antonio, TX and Director of the ITI Scholarship Center. He also held the Roland Meffert Endowed Chair in Implant Dentistry.

He is a clinical & translational researcher focusing on bone regeneration procedures in Implant surgery and Peri-implantitis Therapy. At Rutgers, he is the Director of research and directs the NIH-funded Clinical Research Center conducting research on the biological mechanisms underlying peri-implant bone loss and developing novel treatments for dental and biomedical implants. Dr. Kotsakis has published over 100 peer-reviewed scientific articles and textbook chapters with more than 23,000 citations of his work. He is one of the few Dental researchers to have been published in prestigious medical publications, such as the Lancet and PNAS.

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Dr Chambrone currently serves as Section Editor of Clinical Research for The International Journal of Oral Implantology and Section Editor of Periodontics for the Journal of Esthetic and Restorative Dentistry.

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Titanium particle-mediated Peri-implantitis: Evidence-Driven Treatment Recommendations (AM Session) During this lecture, participants will:

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The motivation and confidence in choosing dentistry as a career amongst dental students: A mixed‐methods study

Mai e. khalaf.

1 Department of General Dental Practice, Faculty of Dentistry, Kuwait University, Jabriya Kuwait

Neamat H. Abubakr

2 Department of Biomedical Sciences, School of Dental Medicine, University of Nevada, Las Vegas Nevada, USA

Hanadi Alenezi

Hassan ziada.

3 Department of Clinical Dental Sciences, School of Dental Medicine, University of Nevada, Las Vegas Nevada, USA

Associated Data

The data that support the findings of this study are openly available in preprint server Research Square Pre‐print Platform. The link to it is as follows https://www.researchsquare.com/article/rs‐22532/v1

An insight into students’ motivation and confidence in the choice of entering and remaining in dental education is essential. The understanding of how choices are made can help universities in the planning of admission policies. This study aimed to evaluate the career choice influences, motivation and confidence in the choices made into dental education.

A mixed‐method design was employed, using both quantitative and qualitative data. One hundred seventy‐three questionnaires were distributed to all registered dental students, with a response rate of 85%. The questionnaire explored students’ demographics and factors that influenced their career choice. Seven focus groups were facilitated with related data recorded and transcribed verbatim.

The quantitative data revealed the desire to help others, and socioeconomic factors were influential, whilst for parents’ influence, the mother's influence was statistically significant. Qualitatively, results converged and complemented quantitative data; there was a balance between helping others and socioeconomic and familial influences. There was an increase in confidence in the choice made as students advanced in their dental education. The results indicate that informed awareness of the dental programme structure is essential before embarking on a dental career.

Conclusions

The factors that impacted on choice were helping others, socioeconomic factors and the influence on choice from family. They were generally satisfied with their choice and were confident in the choice they made. This confidence, however, was not reflected until the more advanced clinical stages of their dental education.

1. INTRODUCTION

Diverse factors motivate dental students into a career in dentistry. These may be driven by socioeconomic backgrounds, gender, professional prestige and the desire to help others. 1 , 2 Previous studies found students attend dental schools because of the desire for independence (with a higher possibility of self‐employment), serve others, as well as the attraction of the psychomotor skill of the profession, the acquired social status and/or financial security; being upwardly socially mobile and having a flexible work schedule. 3 , 4 Dental students reported monetary incentives, such as income and financial security as the main factors in students’ decisions to study dentistry. 4

In the last two decades, data from various countries show an unprecedented change in gender ratios in the workforce, with the rise in the number of female workers in several fields of the labour market; this is particularly evident in the field of dentistry. 5 Females were found to choose dentistry because they believe they will balance their personal and professional lives effectively as dentists. 5 They were also less concerned with the business component of a career and more concerned with the caring and people factors. 6 , 7 , 8

In the Middle East, females in a Yemeni study indicated that they would choose dentistry because, in this sector, jobs were readily available, and the desire to improve the health of individuals and the community were also factors. 9 Jordanian female students had similar desires namely, “helping people,” placing as the highest rated reason. 10 A study conducted in Iran revealed that “matrimonial considerations” amongst females had an influence on study motivation in addition to “social status,” “income” and “work independence.” 11

The evaluation and understanding of the influences on students’ choices and factors that affect these choices can be beneficial, since it may help in planning health care policies and design appropriate and effective recruitment, as well as setting entrance structures and requirements for dental schools. 12 Moreover, an insight into students’ motivation could assist in designing and evaluating dental curricula, as well as enabling productive communication between students and educators. 1

Dental education in Kuwait spans seven years, where four years are in predental years in conjuncture with medicine, enrolled in a BSC in Biomedical Sciences. The choice to do dentistry is made at the beginning of this BSc. After completing the BSc, students start their preclinical and clinical dental years. This education is provided free of charge by the government of the country. Insight into the motivators for this choice and confidence in the choice made as students’ progress in their dental education can help in evaluating methods to ensure the productivity and satisfaction of the national dental work force as graduates of the programme are recruited to work there.

This study aimed to evaluate the influences and motivators of career choice into dental education by dental students and to explore and analyse factors involved in choice and motivation. It also aimed to evaluate students’ confidence in the choices made to allow for insight, which could help in planning university admission policies, as well as providing an understanding into what students need to know about the career choice in dentistry before embarking on it.

2.1. Study setting

The present study was conducted at the Faculty of Dentistry (FOD), Health Science Center, XXX University. The Faculty of Dentistry was established in 1996 and follows a seven‐year programme. The programme of study is publically funded and is the only dental programme in the country. The programme has students integrated with the medical students in the first four years of study. The total number of dental students registered from years 1–7 at the Faculty of Dentistry, Kuwait University at the time the study was 173.

2.2. Participant recruitment

Participants were invited by email to participate in the study. They were recruited from all the dental education stages, which included all students enrolled in the dental programme from years 1–7 (n = 173). Participation was voluntary and anonymous. The purpose of the study was elucidated to all participants, who signed consent forms before participation.

2.3. Data collection

A mixed‐method design was employed in this study (method triangulation) to increase confidence in the findings and avoid potential bias arising from using a single methodology. Creswell (1999) describes mixed‐method research as “research that incorporates both quantitative and qualitative methods of data collection and analysis. This type of research assists investigators to comprehend complex phenomena qualitatively as well as to explain the phenomena through numbers and basic statistical analyses.” 13

2.4. Quantitative data

A 23‐item questionnaire was developed to explore gender, demographics and the factors and influences on students’ career choices. The questions were measured on a 4‐point Likert scale (strongly agree, agree, disagree and strongly disagree). A pretest of ten questionnaires was conducted to identify any necessary modifications and eliminate unclear points for validity. These were used to conduct face validity by the researchers through a subjective judgement of experts to ensure correct and clear writing and transparency. 14 Furthermore, 15% of the sample, which represents 27 respondents were used to calculate the validity and reliability of the questionnaire. In this regard, the acceptable value of alpha is >0.6 and once the value of alpha Cronbach increases the reliability of the measure increases. In this study, the alpha Cronbach value was 0.696 and the validity was 0.834.

2.4.1. Quantitative data analysis

The dependent variables were factors relating to decision to select dentistry (personal choice, influence of mother, father, dentist, teacher or friend), factors motivating a choice of dentistry (desire to help, reputation of the profession, independence, financial aspects, academic interests, job prestige, working hours and job security). The independent variables were the students’ demographic data including age, gender, marital status and mothers and fathers’ academic qualifications.

The analysis was conducted using SPSS software (SPSS version 20.0; SPSS Inc., Chicago, Il, USA). Descriptive statistical analysis was made, and Pearson chi‐square tests were conducted to evaluate significant factors influencing the decision to study dentistry.

2.4.2. Qualitative data

The students from each year level were invited by email to volunteer into the focus groups. The plan was to have at least seven students to form seven focus groups, each representing a year of study level. These facilitated focus groups were conducted in a room in the Faculty of Dentistry; facilitated by a member of the research team, asking a series of open‐ended questions. These were questions developed by the research team with all groups asked the same open‐ended questions (Table  1 ). The focus groups were conducted in an open conversational style, and the conversations were digitally and professionally transcribed verbatim and notes were made after each focus group session.

Focus groups questions

Each participant in the focus group was assigned a number to protect their anonymity. The facilitator (HZ) was not involved in any activities relating to the participants’ teaching and assessment.

2.4.3. Qualitative data analysis

The qualitative data analysis used the principles of the constant comparative method of grounded theory (GT). 15 , 16 The transcripts were checked by the research team to approve the accuracy of transcriptions and that adequate participant involvement had taken place. This was also to ensure limited input from the facilitator, allowing the capture of rich, authentic data.

The transcripts were entered into a qualitative software package (NVivo 12 plus; QSR International, Melbourne, Australia) and coded continuously whilst reading through the transcripts. The NVivo software permits qualitative data to be managed and organised into various categories and themes. A coding framework was then made around the topic, and key themes were identified as the data were analysed.

The analysis was conducted by authors independently reading through the transcripts several times, to familiarise themselves with the data/transcripts, without coding at this stage. Following that, independent coding (investigator triangulation) was made by two authors, trained in qualitative methodology (HZ and NH). For validation, codes were compared for commonalities and parallels, with revisions made during the process. Further refinements were made to codes and categories of the transcripts during grouping. 16 This was followed by evaluating the text under each code to check whether the codes were acceptable and justifiable. More understanding of the data and its credibility was assured at frequent meetings between the two coders and that the interpretations were acceptable and coherent with adequate connections and commonalities.

Thematic analysis was then completed iteratively and inductively, to identify, analyse and report patterns within the data, again independently by two researchers trained in qualitative methodology. Thematic analysis is a descriptive and interpretive process of selecting codes and constructing themes. 16 Braun and Clark (2006) described this as an independent six‐stage qualitative descriptive approach to thematic analysis, which was used in this study. The Thematic Analysis, described by Braun and Clark 2006, has been used widely and has demonstrated effectiveness and rigour in healthcare education investigations. 17 The software of the NVivo version 12 plus (NVivo 12 plus; QSR International, Melbourne, Australia) facilitated coding of the data into meaningful units and grouped units into patterns and themes. This allowed the revisions, interpretation and addition of new codes when required.

Reliability was assured by triangulation, which is one of the strategies used to enhance the trustworthiness in qualitative research. Through inductive and deductive processes, involving several repeats and refinements a code book was developed. The final version that was believed to be efficient for the analysis was agreed upon by the researchers. 18 , 19 To demonstrated rigour, validity and inter‐rater/coder reliability, we used the formula suggested by Miles and Huberman 1994, 18 , 19 , 20 and for the present study, the inter‐rater/coder reliability was 80%.

2.5. Ethics

A study protocol was submitted for ethical approval to the Joint Committee for the Protection of Human Subjects in Research of the Health Science Center, Kuwait University, and approval granted (VDR/EC/33). Information sheets about the study objectives were distributed to the participants; to ensure that they were well informed and that their participation was voluntary in nature.

The total number of dental students registered from years 1–7 at the Faculty of Dentistry, XXXX University, at the time of the study was 173. A total of 147 completed the questionnaire, a response rate of 85%. The age range was 18–24 years old, with an average age of 21 years. Ninety‐three per cent of respondents were females (Table  2 ).

Students socioeconomic characteristics

We used the contingency coefficient analysis for the association between gender and the decision to choose dentistry, and no statistical significance was observed. The option "do not know" was excluded from the calculation and treated as missing, since it does not show any agreement and may inflate the average.

When asked about their perception of what influenced their decision to select dentistry as a career, personal decision predominated (96.5%). We dichotomised the response to agree and disagree and used the Fisher exact test. There were no statically significant differences (p‐value 0.461) (Table  3 ). The contingency coefficient analysis for the association between personal decision and motivation also showed no statistical significance ( p ‐value <0.001) (Table  4 ).

Fisher exact test of the association between gender and personal decision‐making

The association between personal decision and motivation

Parents’ influence was split between mothers and fathers, and the contingency coefficient on the fathers and mothers’ influences and gender effects; the mothers’ influences were found to be statistically significant (p‐value 0.02) in decision‐making (Table  5 ).

The association between parent's influence and choice

The factors that impacted on the choice to pursue a career in dentistry where dichotomised into agree and disagree. The desire to help was the main factor, whilst job security was the least factor (Figure  1 ). When asked why medicine was not chosen as a career path, only 37% agreed that medicine would have been a longer, more challenging career path. Seventy‐four per cent felt that a career in medicine would involve long working hours, and 71% felt that medicine would be stressful. Seven per cent of respondents felt that they wanted medicine but did not enrol in medicine because they did not have the grades for it, and 2% regretted their choice of dentistry.

The factors impacting on career choice in dentistry

3.1. Qualitative analysis

Three main themes emerged from the qualitative data, which seemed to interrelate (Table ​ (Table6). 6 ). The customary practice in qualitative research is to present direct quotations from the participants to illustrate themes. Given the extensive number quotations, we include a summarised version of the thematic analysis. More details of the thematic analysis are available in Appendix  1 .

The frequency distribution of codes deduced from the text within each theme

3.2. Theme 1: Factors and influences on choice

The combination of helping others and financial factors were voiced in this investigation.

“I always knew I wanted to help people, so that was a big aspect and you know also if I get to help people and make money at the same time that’s awesome”.

Whilst there were students who made their own personal choice however, the immediate family expectations influence on career choice were prominent. There was also the perception that some students were keeping their parents happy by making the choice of dentistry. Parents’ personal experiences through the generations also had some influence on choice.

“My parents wanted me to be a dentist, so I went for it.” “My dad was very supportive of the choice because he always wanted to be a dentist”.

Influences from siblings, cousins or distant family were also voiced. Given the close culturally netted extended family ties in this region, distant family involvement was expected, particularly amongst those who had a parent or relatives within the profession.

“I think they were many factors from parents, from a family that worked as dentists.”

Family expectations can be formed by cultural and acceptable norms, particularly for females, who formed the overwhelming number of students. Marriage and starting a family at a certain age are also very important culturally, particularly for females.

“I want to start a family; the work hours are a lot easier than being a physician, so that made up my mind.”

Choices were also dominated by logically thought processes. The potential of flexible, shorter working hours and guaranteed employment also made dentistry an attractive choice.

“I think 90% of my decision‐making process is the logical aspect, merely for guaranteed employment and good financial status especially”

The students’ experience with a dentist and how that influenced shaping the choice was also voiced by several participants.

“I would go to my orthodontist every two months so I told them I was considering dentistry and he was very enthusiastic about it, and he just kept telling me.” And every time I would go to the clinic after that he was like, “Hey my future colleague.” So, yeah, that was really nice.”

A mixture of influences and factors was also visible in some of the comments’ students made.

“So, definitely family, economic aspect of course, is important and can’t be denied for sure and I guess personally as well because I also wanted to help people somehow”.

3.3. Theme 2: Confidence in the choice made

There was some doubt in confidence in the choice made, particularly, those still at the basic sciences and preclinical years.

“I still don’t know, I’m still in the academic year, so I don’t know if I made a good choice.”

Conceivably not starting the dental curriculum earlier may have increased the lack of confidence in dentistry as a choice. After studying medicine for four years, some felt maybe they should have continued with medicine and completed medicine instead.

“Even now after four years I think it will be hard for us to let go of all this information, all this knowledge that we have acquired, it will all be somewhat useless.”

The confidence in choice made increased as students moved past the preclinical years.

“Yeah I love it. I like drilling apparently, and even more today because we’re also shadowing 7 th year.”

This might be a testament for support of early dental related patient contact, even if it is at the level of shadowing more senior students. Nevertheless, there were students who were happy with having to learn their preclinical years similar to medicine and felt that this strengthened their learning.

Several students experienced some difficulty in negotiating the thought process, regarding their confidence in the choice they made.

“I think dental students have biased judgments because you know that you’re already accepted into dentistry.”

The sixth year, in particular, had a significant number amongst them who were not confident about their choice. For this particular cohort, at entry, the regulations changed; as a result, many students who wanted to do medicine ended up in dentistry. The dental school entry traditionally required the highest GPA, particularly compared to medicine; this was reversed for this cohort. Whilst they enjoyed the preclinical years, they felt resentful being in this position. The expression of resentment and regret was to the extent that they will not choose dentistry if given the choice again and would shift to medicine if permitted.

“No, I don’t think that it’s the correct decision; I feel if I were in medicine, I would have been doing better than now.” “I would go to medicine if I was allowed to shift after the 4th year.”

When weighing potential career options considering culture, family circumstances and career aspiration, an interesting picture emerged. Students feel that compared to career choices globally, the choices for them were limited.

“I don’t think we have that many options to begin with of what we are going to do”

3.4. Theme 3: Awareness of the program of study and choice

The students reflected on two issues; the dental curriculum and duration of study; not starting till the end of the 4th year, after completing the Bachelor in Medical Science with medical students, and having the same curriculum in Anatomy, Physiology, Biochemistry, etc.” Some felt that they should have been allowed to choose at the stage when they completed the fourth years with medicine rather than earlier or at entry to the school.

“I think that it would be better if students were able to choose dentistry or medicine after year four.”

There were also some expressions of unfairness that they have to study seven years to become dentists, whilst their counterparts who study abroad would complete it in less time with the potential of having more time and hands‐on preclinical and clinical dental training.

“I think seven years are too long for dentistry. Like we see our colleagues graduate from other universities before us, and they get more experience in dentistry because we have four years of medicine. So, we only get three years of dentistry while other students get approximately five years. So, they gain more experience than us, and this upsets me.”

The role of precollege orientation or career advice seems to be lacking in the students’ experiences, and they did not feel that they were given enough career advice. Many students relied on social media for their search to help choose their career choice.

“I just searched on the internet and asked a few of my friends, and so they helped me choose this faculty.”

Some of the schools’ career advice approach seems to orient their students with a view of specifically going abroad to study and in particular medicine rather than studying locally and with an opening for several choices.

“Yeah, they were like, Study abroad, and if you are going to be a doctor even if you are going into a medical field, be a doctor and not a dentist.”

The length of curriculum was a deciding factor in choice; if they were aware of what was involved in studying dentistry in comparison with other universities; their choice might have been different.

“If I knew that I was going to study in such great detail in medicine, such as renal or reproduction, I maybe wouldn’t have entered dentistry.”

4. DISCUSSION

The study aimed to explore the factors and influences that affect a career in dentistry, and the confidence in choice, to provide insight and a deeper understanding. This may ensure that students who enrol in dental programmes will eventually be content with their choice and play a significant role in a satisfied, productive workforce. This information may also help in the strategic planning of educational programmes, which would ultimately impact the national workforce.

Dental education is a costly burden on the individuals and their communities, particularly in countries where the educational expenses are government‐supported or subsidised, as in this cohort. The loss of any dental student after a long and expensive training is a considerable loss of resources and also a potentially lost opportunity for another candidate who may become a more productive member of the dental workforce.

In the present study, the majority of students enrolled in the dental programme were females. This may be attributed to local, cultural influences that place preference for females to study in their home countries instead of choosing to study dentistry abroad since this option is available. However, this may not be regarded as the only reason for the gender distribution reported since research and official government data show a rise in the number of female workers in several fields of the labour market in the last two decades. This seems to be related to the expansion of schooling and female access to universities. 21 The trend is also visibly reflected in dentistry. 22

A commonly reported factor from the questionnaires and the focus groups is the financial and prestigious expectations associated with dentistry career choice. This element is not a contemporary one. Since the early 1960 s, More and Kohn found that the prestige of the profession and financial earnings were commonly reported occupational motivations for studying dentistry. 23

Continued research on the topic of motivations behind a career in dentistry found that factors such as financial stability remained dominant themes amongst both males and females. 24 In Malaysia, the emerging dental workforce also seem to indicate the desire for financial stability. 24 An Australia study also reported on students’ motivation to study dentistry, where males were found to indicate that income and status of the profession as motivators. 25 It seems that, similar to medical students, career choice intentions are complex with multiple modifiable and non‐modifiable factors, where financial reward and prestige rank high. 26 Finances and prestige seem to resonate worldwide in association with the dental profession. This information is important as it highlights the fact that younger candidates, as in this cohort, should be given insight into average incomes associated with various disciplines of related choices.

The reasons for choosing dentistry as an occupation differ from one country to another. In 2009, it was reported that the most frequent reason amongst Swedish dental students was “helping other people,” 27 which comes into agreement with the present findings; whilst the most frequent one for the Japanese dental students was “family expectations,” 27 which also seem to be evident influence in the qualitative data.

There was a convergence between the questionnaire and qualitative data in that factors and influences on career choice are helping others, family expectations and the socioeconomic aspects of a career in dentistry. The interaction between socioeconomic aspects, cultural and lifestyle issues, studies conducted worldwide have reported that lifestyle issues have also been highlighted as prominent in medical students’ choice of a career. 25 , 26 , 28 Of course, cultural issues vary and exert their influences in different ways, perhaps a subject of future research, to investigate the cultural influences on career choice in different parts of the world. Dental school admissions within this region should perhaps consider and provide such related information to applicants and their parents that could help make a more informed decision.

Emerging from the focus groups’ narrative, one crucial issue that needs to be addressed relates to the structure of the programme of study. Dental programmes worldwide vary in length from five to eight years. Within this cohort, the programme's content and integration with the medical curricula were associated with some degree of frustration. Many students reported not to have realised the breakdown of the didactic programme, along with the timeline of the introduction to dental subjects, may have influenced how they feel about the choice they made; in fact, it made some of them unhappy with their choice.

The element of confidence in the choice made is essential, acting as a motivator, which sees students through difficult times during their study years and enables them to accept their chosen career with greater satisfaction. The implication is reduced number of losses of dental graduates who may not join the workforce after graduation due to uninformed choices. The financial impact of this loss in addition to the lost opportunities to others who did not get the opportunity is significant. The focus groups revealed that students in the preclinical years had more doubt in their choice. This doubt reduced once students entered their clinical years. This highlights the impact of early patient contact, which first can help ensure students’ choices are met and second identify those who are unhappy, and if realistically, they will be able to continue in this field. This is quite relevant as our study reports that some females – who are increasing in percentage, felt as though their overall choices of study are limited compared to their counterparts globally. Within these limited options, they need to be given a chance to understand the nature of the career that they have accepted and make an informed decision early on whether they choose to continue with it.

This study has limitations; it is cross‐sectional, evaluating the opinions of students locally. Generalisability cannot be claimed, since it does not consider the students who study dentistry abroad, and who make a large part of the local workforce. However, it would apply to a similar setting or cohort.

Furthermore, reproducibility in qualitative and mixed‐method analysis is through the concept of triangulation, in combining different data sources, methods (quantitative and qualitative), researchers or perspectives (students’) in the study of the same complex phenomenon (career choice), that then ensures validity, which was the case in this study. Therefore, analysis of such qualitative transcripts would not be compatible with statistical probabilities. Additionally, the results of the qualitative part should not be valid for population groups in general, but should be descriptions or theories relevant to a specified setting. 29

We combined quantitative and qualitative methods to evaluate Kuwait University dental students’ choice in the dentistry and the factors and influences on their choices. There was convergence in the data between the qualitative and quantitative, and both data were also complementary to each other. This we believe have increased validity since it promoted a more comprehensive understanding of the factors and the influences on choice. 30

5. CONCLUSIONS

The study found that the factors and influences on career choices amongst dental students are broad and included the desire to help, socioeconomic factors, as well as job prestige and security. Parent's influences have an effect with mothers’ being more significant. Overall, students were confident in their career choice; however, this confidence was not clear until the more advanced clinical stages of their dental education.

CONFLICT OF INTEREST

The authors declare no interest that may pose conflict with any party.

Supporting information

Supplementary Material

This study was supported by Grant DG01/19 by the Office of Vice President of Research, Kuwait University.

DATA AVAILABILITY STATEMENT