Hierarchy of microstructural features as the origin of fracture resistance in dentine and ceramic composites

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Teeth rarely fracture in nature, and when they do, it is because of sudden impact and extreme overload from blows, accidents or failure if tooth material is severely undermined and damaged by caries. Dental ceramic prostheses however, do fail catastrophically quite frequently. The marked difference in intra-oral performance lies in a major difference in microstructure: Teeth are hierarchically structured objects consisting of several low and highly mineralized composites, that directly contribute to their strength and toughness. Teeth are, therefore, excellent models for the development of improved ceramic constructs. We have combined mechanical testing with advanced materials characterisation methods to investigate the hierarchical design principles in teeth and their applicability to synthetic ceramics. Important key elements of hierarchical engineering include property gradients, interfaces and zones of varying porosity. The principal processing method showing most promising results is electrophoretic deposition (EPD), while the main target property of the established ceramics is superior crack resistance and high toughness due to mechanisms that operate at different length-scales. By mechanical tests combined with non-contact optical deformation mapping (ESPI/shearography), atomic force microscopy, Raman spectroscopy and other conventional and X-ray microscopy methods, we study the contributions of different toughening mechanisms to fracture resistance. Using simulations of computer-models, increasingly elaborate structures are being produced. In the next project phase, we will also investigate the thermal responsiveness of both the natural tooth and the synthetic ceramic model systems.