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

牙齿在自然界中很少断裂，当它们发生断裂时，是由于突然的冲击和撞击造成的极端过载，事故或牙齿材料严重破坏和龋齿损坏造成的失效。然而，牙科陶瓷假体确实经常灾难性地失败。口腔内性能的显著差异在于微观结构的主要差异：牙齿是由几种低矿化和高矿化的复合材料组成的分层结构物体，这直接影响了它们的强度和韧性。因此，牙齿是发展改良陶瓷结构的绝佳模型。我们将机械测试与先进的材料表征方法相结合，研究牙齿的分层设计原则及其在合成陶瓷中的适用性。分层工程的重要关键要素包括性质梯度、界面和孔隙度变化带。电泳沉积（EPD）是最具前景的主要加工方法，而由于不同长度尺度的机制，所建立的陶瓷的主要目标性能是优越的抗裂性和高韧性。通过结合非接触光学变形映射（ESPI/剪切成像）、原子力显微镜、拉曼光谱等常规和x射线显微镜方法的力学测试，研究了不同增韧机制对抗断裂性能的贡献。利用计算机模型模拟，越来越复杂的结构正在被制造出来。在下一个项目阶段，我们还将研究天然牙齿和合成陶瓷模型系统的热响应性。

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.