Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ, United Kingdom.
School of Dentistry, College of Medical and Dental Sciences, University of Birmingham, St Chad's Queensway, Birmingham B4 6NN, United Kingdom.
J Mech Behav Biomed Mater. 2014 Apr;32:113-124. doi: 10.1016/j.jmbbm.2013.12.014. Epub 2013 Dec 20.
The knowledge of the mechanical properties of dental materials related to their hierarchical structure is essential for understanding and predicting the effect of microstructural alterations on the performance of dental tissues in the context of forensic and archaeological investigation as well as laser irradiation treatment of caries. So far, few studies have focused on the nano-scale structure-mechanical function relations of human teeth altered by chemical or thermal treatment. The response of dental tissues to thermal treatment is thought to be strongly affected by the mineral crystallite size, their spatial arrangement and preferred orientation. In this study, synchrotron-based small and wide angle X-ray scattering (SAXS/WAXS) techniques were used to investigate the micro-structural alterations (mean crystalline thickness, crystal perfection and degree of alignment) of heat-affected dentine and enamel in human dental teeth. Additionally, nanoindentation mapping was applied to detect the spatial and temperature-dependent nano-mechanical properties variation. The SAXS/WAXS results revealed that the mean crystalline thickness distribution in dentine was more uniform compared with that in enamel. Although in general the mean crystalline thickness increased both in dentine and enamel as the temperature increased, the local structural variations gradually reduced. Meanwhile, the hardness and reduced modulus in enamel decreased as the temperature increased, while for dentine, the tendency reversed at high temperature. The analysis of the correlation between the ultrastructure and mechanical properties coupled with the effect of temperature demonstrates the effect of mean thickness and orientation on the local variation of mechanical property. This structural-mechanical property alteration is likely to be due to changes of HAp crystallites, thus dentine and enamel exhibit different responses at different temperatures. Our results enable an improved understanding of the mechanical properties correlation in hierarchical biological materials, and human dental tissue in particular.
有关牙齿材料力学性能的知识与其层次结构有关，对于理解和预测微观结构改变对法医和考古调查以及龋齿激光治疗中牙齿组织性能的影响至关重要。到目前为止，很少有研究关注化学或热处理改变的人牙齿的纳米级结构-力学功能关系。人们认为，牙齿组织对热处理的反应强烈受矿物质微晶尺寸、其空间排列和择优取向的影响。在这项研究中，使用基于同步加速器的小角和广角 X 射线散射（SAXS/WAXS）技术研究了热影响牙本质和牙釉质的微结构改变（平均结晶厚度、晶体完整性和取向度）。此外，还应用纳米压痕映射来检测空间和温度相关的纳米力学性能变化。SAXS/WAXS 结果表明，与牙釉质相比，牙本质中的平均结晶厚度分布更均匀。尽管总的来说，随着温度的升高，牙本质和牙釉质中的平均结晶厚度都增加，但局部结构变化逐渐减少。同时，牙釉质的硬度和弹性模量随着温度的升高而降低，而对于牙本质，在高温下则相反。结合温度影响对超微结构和力学性能之间的相关性分析表明，平均厚度和取向对力学性能局部变化的影响。这种结构-力学性能的改变可能是由于 HAp 晶体的变化，因此牙本质和牙釉质在不同温度下表现出不同的反应。我们的结果使人们对分层生物材料特别是人牙组织的力学性能相关性有了更好的理解。
