Center for Clinical Research and Dental Materials and Biomaterials Program, Integrative Biology and Infectious Diseases Branch, DER, NIDCR
The intent of this initiative is to support research on the development of novel or enhanced Class V dental restorative materials that demonstrate superiority in clinical service life in the oral environment over the currently used restorative options. Restoration of Class V lesions (those lesions in the gingival third of the exposed tooth) are complex due to the unique material characteristics required by the oral environment and the complications hindering dental treatment in this region. For these reasons, a fundamental change in the design of a Class V restorative dental material is required to maintain overall periodontal health; that is, the restorative material needs to protect and strengthen the remaining non-carious tooth structure with a heightened focus on maintaining the integrity of the restorative margins and surrounding periodontal tissues. In addition to the above unique requirements, this material should also meet the following criteria: biocompatibility; aesthetically pleasing; low shrinkage; mechanical superiority and durability to current Class V restorative dental materials; resistance to degradation in the oral cavity; satisfactory handling properties; and limited leaching of the restorative components. Investigators involved with restorative materials development such as materials scientists, chemical engineers, bioengineers, clinicians, polymer chemists, organic chemists, microbiologists, and computational scientists with expertise in evaluation of restorative systems are encouraged to collaborate. Investigators with expertise in research areas traditionally not focused on dental restorative materials are encouraged to participate in these collaborative multidisciplinary teams. The evaluation of these restorative materials must include a physiologically relevant oral microbial and host environment. Other properties of the material such as the ability to self-heal, biomimetic potential, and direct integration with the host cementum/dentin/enamel interface without an adhesive would add significant value to the design.
People are living longer and retaining more of their natural teeth. One consequence of tooth retention in older age is an increased risk for development of root caries that has been estimated at an annual incidence of 23.7% in selected adult populations. The Northwest Practice-based Research network found 19.6% of adults aged 45 years and older had root caries. In tooth restoration classifications, root caries are treated as a Class V restoration. Individuals who are institutionalized and those with complex medical conditions have an increased prevalence of root caries, as do those individuals with severe salivary gland hypofunction. In addition, root caries is an important problem in the periodontal patient, as exposed root surfaces after therapy are at risk for new caries and complicate long term survival of affected teeth.
One longitudinal cohort study of 1,000 restorations found that Class V restorations placed solely in dentin fail more quickly than restorations placed in both dentin and enamel, and failure increases with age. Over 30% of Class V restorations failed by five years in those 50 years and older, and older age was associated with early failure (by two years). The main issue is not the failure of the restorative material, but the increased susceptibility to degradation of the surrounding tooth structure encircling the restoration and lack of integration with the surrounding periodontal ligament (i.e., increased probing depths). These restorative margins may be subgingival, hindering cleaning and providing areas for bacterial growth. Other factors promoting failure are the advancing age of the patient, altered oral bacteria, and a potential decrease in saliva. In addition, the root tooth structure is missing the protective enamel, which means the dentin/cementum composition is less mineralized and contains more water and collagen that renders the tooth more susceptible to acid etching from the normal oral bacteria. Enamel requires a pH of 5.5 to undergo acid attack, whereas dentin/cementum will begin to dissolve at a pH of 6.5. The Class V region without the enamel protection is more susceptible to the flexing forces during mastication, and the collagen is susceptible to enzyme attacks from the oral bacteria that further weaken tooth structure. Other factors complicating successful restoration of Class V lesions are the highly curved root surface, limited access to some teeth with Class V lesions, and the difficulty of placing a rubber dam to isolate the treatment area. In addition, older individuals may have increased medication use that reduces saliva flow and promotes cariogenic oral bacteria, limited ability to clean the teeth, and diets higher in acid and sugar content. Therefore, novel or enhanced Class V restorative materials will require enhanced bonding (protection) of the organic (collagen) and inorganic (hydroxyapatite) material, an ability to accommodate large changes in water content from potential dry mouth conditions, resistance to attack from a constantly changing oral bacterial biofilm, potential to integrate with surrounding soft tissue where appropriate (i.e., periodontal ligament) and the ability to provide reinforcement of the tooth structure to minimize flexing from mastication.
Alignment with Institute Goals, Strategies and Implementation Plan
Recurrent caries and root caries are prevalent among adults and the elderly, and caries is more prevalent among disadvantaged groups of the U.S. population. These carious lesions require the placement of dental restorations. The objective of this initiative is consistent with the NIDCR Strategic Plan 2014-2019: Goal I, Objective 1-1: Enable basic research to advance knowledge of dental, oral, and craniofacial health; Goal I, Objective 1-3: Conduct translational and clinical investigations to improve dental, oral, and craniofacial health; and Goal 2, Objective 2-1: Support research toward precise classification, prevention, and treatment of dental, oral, and craniofacial health and disease. Interdisciplinary research among chemists, chemical engineers, bioengineers, materials scientists, microbiologists, cariologists, and clinicians together with investigators from new disciplines such as computational chemists and interface scientists will be necessary to design and develop an enhanced dental restorative material.
Recent consultations with industry researchers and product development experts, dentists, polymer scientists, bioengineers, and dental insurance representatives suggest pragmatic acceptance of the status quo. There is no apparent financial incentive or consumer demand to drive change in material composition and/or performance, but the clinical need is apparent. Therefore, external research investment is essential to initiate and advance improvements in restorative materials. The different expertise needed for this project is available, but may be present outside the traditional dental research community. The approach is to encourage multidisciplinary studies to design and develop Class V restorative materials that will be evaluated in simulated oral environments and include microbiological, physical, and chemical components for in vitro testing of leaching and degradation properties.
Current Portfolio Overview
There is currently a cluster of projects focusing on the Design and Development of Novel Dental Composite Restorative Systems, in the Dental Materials/Biomaterials Program that consists of six cooperative agreements awarded to develop novel dental restorative resin systems for any tooth surface. These projects require data and methods sharing among research laboratories to accelerate progress. At present, no grantee in this program is focused on development of materials primarily for root surfaces. The NIDCR participates in an interagency agreement with the National Institute of Standards and Technology on Standard Test Methods and Reference Materials for Dental Restorative Materials with an emphasis on developing clinically relevant standards. The focus is to identify, develop, and implement standard methods related to polymeric dental materials, measurement platforms for assessing material properties at the tooth/composite interface, and measurement techniques for evaluating interface durability under bacterial challenge in an oral-like environment.
Bignozzi I, Crea A, Capri D, Littarru C, Lajolo C, Tatakis DN. Root caries: a periodontal perspective. J Periodontal Res. 2014; 49:143-163.
Chi DL, Berg JH, Kim AS, Scott J; Northwest Practice-based REsearch Collaborative in Evidence-based DENTistry. Correlates of root caries experience in middle-aged and older adults in the Northwest Practice-based REsearch Collaborative in Evidence-based DENTistry research network. J Am Dent Assoc. 2013 May;144(5):507-16.
Gluzman R, Meeker H, Agarwal P, Patel S, Gluck G, Espinoza L, Ornstein K, Soriano T, Katz RV. Oral health status and needs of homebound elderly in an urban home-based primary care service. Spec Care Dentist. 2013; 33(5):218-26.
Oginni AO, Adeleke AA. Comparison of pattern of failure of resin composite restorations in non-carious cervical lesions with and without occlusal wear facets. J Dent. Jul;42(7):824-30.
Stewardson DA, Thornley P, Bigg T, Bromage C, Browne A, Cottam D, Dalby D, Gilmour J, Horton J, Roberts E, Westoby L, Creanor S, Burke T. The survival of Class V restorations in general dental practice. Part 2, early failure. Br Dent J. 2011 Jun 10;210(11):E19.
Stewardson D, Creanor S, Thornley P, Bigg T, Bromage C, Browne A, Cottam D, Dalby D, Gilmour J, Horton J, Roberts E, Westoby L, Burke T. The survival of Class V restorations in general dental practice: part 3, five-year survival. Br Dent J. 2012 May 11;212(9):E14.