Development of bio-inspired gradient microstructure of lithium silicate glass-ceramics tailored for dental applications

• Applicants: Professor Dr. Dominique de Ligny; Professor Dr.-Ing. Ulrich Lohbauer
• Subject Area: Glass, Ceramics and Derived Composites ; Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 459555007

The sophisticated hierarchical structures present in nature demonstrate outstanding mechanical properties. Functionally graded materials are examples where the tailored microstructure inhibits crack propagation. These arrangements can be found in dental materials. The detailed knowledge acquired from the initial project allows us now to develop innovative new glass ceramics for dental restorations by tailoring the crystal fraction, their shape, and, in particular, their spatial distribution. Dental-graded glass ceramics will be produced using two different methods. The first method will involve subjecting the glass to a thermal gradient affecting spatially the nucleation process or the crystal growth. Initial finite element simulations of the thermal history and monitoring the temperature in each part of the glass during the thermal treatment will help to design the experiment and achieve good conditions more quickly. The glass compositions used for the thermal gradient method will be selected based on our recent knowledge of the effect of nucleation temperature and time on lithium silicate glasses. In the second method, functionally graded microstructures will be tailored by combining different glass compositions or using different particle sizes. This is possible due to our new understanding on the dependence of the crystallization mechanism and kinetic parameters with lithium content. The chemical dependance will be implemented in the finite element simulations to predict the final glass ceramics design and foreseen residual stresses induced by thermal history, partial crystallization and thermal expansion coefficients mismatch. The graded microstructure of this new class of dental glass-ceramics will be observed by SEM. The crystal morphology and spatial stress distribution will be monitored by Raman and luminescence spectroscopy with the aid of XRD. For the optimized tailored microstructures, spatially resolved X-ray diffraction using synchrotron tomography will be applied to obtain high-resolution 3D imaging of phase distribution. The graded microstructures will be directly related to hardness mapping. Further crack propagation observations and an indirect flexural strength approach will be used to determine how the gradient effectively inhibits crack propagation.

• DFG Programme: Research Grants