Xie Zonghan, Swain Michael, Munroe Paul, Hoffman Mark
Center for Integrated Nanotechnologies, MPA-CINT, MS K771, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
Biomaterials. 2008 Jun;29(17):2697-703. doi: 10.1016/j.biomaterials.2008.02.022. Epub 2008 Mar 21.
Tooth enamel is the hardest tissue in the human body with a complex hierarchical structure. Enamel hypomineralisation--a developmental defect--has been reported to cause a marked reduction in the mechanical properties of enamel and loss of dental function. We discover a distinctive difference in the inelastic deformation mechanism between sound and hypomineralised enamels that is apparently controlled by microstructural variation. For sound enamel, when subjected to mechanical forces the controlling deformation mechanism was distributed shearing within nanometre thick protein layer between its constituent mineral crystals; whereas for hypomineralised enamel microcracking and subsequent crack growth were more evident in its less densely packed microstructure. We develop a mechanical model that not only identifies the critical parameters, i.e., the thickness and shear properties of enamels, that regulate the mechanical behaviour of enamel, but also explains the degradation of hypomineralised enamel as manifested by its lower resistance to deformation and propensity for catastrophic failure. With support of experimental data, we conclude that for sound enamel an optimal microstructure has been developed that endows enamel with remarkable structural integrity for durable mechanical function.
牙釉质是人体中最坚硬的组织，具有复杂的层级结构。据报道，釉质矿化不足——一种发育缺陷——会导致釉质机械性能显著降低并丧失牙齿功能。我们发现，健康釉质和矿化不足釉质的非弹性变形机制存在显著差异，这显然受微观结构变化的控制。对于健康釉质，在受到机械力作用时，控制变形机制是在其组成矿物晶体之间的纳米厚蛋白质层内进行分布式剪切；而对于矿化不足的釉质，在其结构较疏松的微观结构中，微裂纹及随后的裂纹扩展更为明显。我们建立了一个力学模型，该模型不仅确定了调节釉质力学行为的关键参数，即釉质的厚度和剪切性能，还解释了矿化不足釉质的退化现象，表现为其较低的抗变形能力和发生灾难性破坏的倾向。在实验数据的支持下，我们得出结论，对于健康釉质，已形成了一种最佳微观结构，赋予釉质卓越的结构完整性以实现持久的机械功能。
