Experimental and numerical toolbox for the development of longer-lasting dental composites – TOOTHBOX

Who is likely to benefit from the results of this project and why? According to the support letters received by the project coordinator (from composite manufacturers, normative institutions, dental education groups …): Everybody! Tooth decay is indeed the most widely spread pathology in the world. Dental restorations have limited longevity, with mean annual failure rates of approximately 2 %. A dentist spends actually as much time fixing defective restorations as dealing with initial tooth decay lesions. The biological and economical consequences are dramatic. When a patient gets involved in a repairing care cycle, he gets into a spiral that can lead to a weakening of the tooth and to heavier therapeutics. Replacing defective dental fillings has been evaluated to cost about five billion dollars per year in the US.
What are the reasons of this dramatic situation? The design procedures for creating new materials are nowadays largely based on the know-how of the manufacturing companies. There are currently two opposite strategies in the field: on the one hand, large groups tend to commercialize many new products, using patients for testing, and withdrawing quickly these products in case of emerging problems. On the other hand, SMEs tend to come out with less new products but pay more attention to quality since this is their only way to increase their market share. This second strategy requires R&D facilities that can be an issue for SMEs; most of them do not have access to a global competence network. This is what this project offers. Tooth-colored polymer-ceramic composites are often preferred to silver amalgam fillings. But these bulk materials also exhibit a 3% setting shrinkage that exacerbates the interfacial stresses on the adhesive joints. Despite numerous attractive properties of these biomaterials, many adverse clinical problems can arise. This is a major potential cause of adhesive failure.
What are the objectives and outputs of the project? The dental and composite material thermal, mechanical and physico-chemical properties will be investigated. In situ measurements during polymerization will allow to identify how composites behave, especially in terms of shrinkage. In order to study the debonding phenomenon, the design and manufacture of an artificial x-ray transparent tooth is planned. Different materials will be tested. Additive manufacturing techniques will be evaluated to check whether it is a convenient and efficient way of getting different cavity geometries. A finite element model will be developed, at both microscale and macroscale levels, in order to predict the polymerization shrinkage and the mechanical properties of the modelled composites, depending on filler fraction and material properties of the resin matrix. It will also predict critical areas, where cracks may initiate. Sensitivity analyses to various input data will be performed using the numerical model, in order to determine for instance the best filler fraction required to provide the desired material properties. Project results will be disseminated among companies and dental practitioners thanks to a close cooperation with normative institutes that already expressed their interest for our work, as mentioned in their supporting letters.
How the consortium has been set up? Dentistry and mechanics being two different fields, we have built a consortium gathering experts from both sides. Researchers from LMI come from the dental field. They will work on the characterization of dental composite materials. ARMINES-CEMEF will bring its expertise in numerical modelling of biological and biocompatible materials and in fracture modelling. 3D complex microstructures require high resolution X-Ray tomography to be deeply studied. MATEIS provides the consortium with tomography and an internationally recognized expertise in this field.