Design of functionally graded dental materials by additive manufacturing – CMADENT

Tooth shows a natural gradient of elastic modulus due to the presence of dentin (porous mineral tissue) and enamel (highly mineralized, 2 to 4 times stiffer), connected by a transition zone of a few microns. Restoration of voluminous tooth substance loss by Computer Aided Design and Manufacture (CAD/CAM) does not reproduce this gradient of elastic modulus and limits the restauration's durability. The objective of the CMADENT project is to propose an alternative to CAD/CAM dentistry by (i) replacing conventional machining with an additive manufacturing technique that limits the loss of material while guaranteeing properties superior to those of direct restorations, (ii) mimicking the natural property gradients of the tooth, and (iii) developing new materials that are less toxic and bioactive in order to prevent the appearance of secondary caries. The chosen DLP (Digital Light Processing) process is relatively fast (a dozen printed parts vs. 3 in conventional CAD/CAM) and inexpensive (15 k€ vs. 100 k€ for a CAD/CAM production machine), two important advantages to allow a quick adoption by practitioners. Several scientific and technological challenges must be overcome. DLP machines currently work with unfilled resins. Their mechanical properties are insufficient for the intended application. It will therefore be necessary to develop a composite matrix, if possible from sustainable chemistry, adapted to the DLP technology and presenting optimal mechanical properties. Different types of fillers will be studied. Several strategies will be implemented to obtain gradients of properties, for example by playing on the printing pattern or, after modification of a DLP machine by reverse engineering, by alternate "dipping" of the printer plate in resin tanks with different filler ratios. The consortium will be able to rely on experimental, analytical and numerical tools developed and validated in a previous ANR project (TOOTHBOX). They will be further improved to predict and thus optimize the mechanical properties of composites, knowing the properties of their constituents. They will also be used to perform a topological optimization to generate optimal printing patterns and propose an optimal distribution of fillers to achieve the targeted property gradients and thus approach the mechanical properties of enamel and dentin. The consortium is composed of experts from complementary disciplines (chemists, physical-chemists, process engineers, and mechanics) as well as hospital practitioners and the only industrialist in the field to produce dental biomaterials in France. Their presence guarantees that the developments will always be carried out with the aim of being usable in fine by dentists for the benefit of patients.