Shen Lu, Barbosa de Sousa Frederico, Tay NamBeng, Lang Teo Siew, Kaixin Vivian Lin, Han Jongyoon, Kilpatrick-Liverman LaTonya, Wang Wei, Lavender Stacey, Pilch Shira, Gan Hiong Yap
Engineering Cluster, Singapore Institute of Technology, Singapore.
Department of Morphology, Health Sciences Center, Federal University of Paraiba, Joao Pessoa, Cidade Universitaria, Paraiba, Brazil.
J Mech Behav Biomed Mater. 2020 Aug;108:103799. doi: 10.1016/j.jmbbm.2020.103799. Epub 2020 Apr 19.
Tooth enamel has an important mechanical function for human dental health, yet characterizing its mechanical properties is not trivial due to its complex nanoporous structures. We examined the distribution of hardness and modulus across the lingual-buccal enamel cross-section by nanoindentation. At the occlusal surface, the hardness and modulus of enamel were found to be 5.00 ± 0.22 GPa and 97.12 ± 2.95 GPa, respectively. At the area close to the enamel-dentine-junction (EDJ), the hardness and modulus were 3.72 ± 0.35 GPa and 76.83 ± 5.71 GPa, respectively. At the middle region in between the EDJ and the outer enamel layer, the hardness and modulus were found to be 4.23 ± 0.18 GPa and 87.62 ± 2.50 GPa, respectively. The surface and area underneath the nanoindent were analyzed using the following microscopy tools: Scanning Electron Microscopy, Focused Ion Beam imaging, and Transmission Electron Microscopy. The deformation mechanisms of enamel were found to be location dependent and influenced by changes in the chemical composition within enamel. The EDJ forms the interface between enamel and dentin. The deformation behavior differed at the EDJ, due to the increased organic phase at the interface. Within the intermediate enamel region, intra-rod cracks were formed at the center of enamel rods and propagated into the neighboring inter-rod region at deviated directions along the orientation of the local crystallites. At the outer enamel layer, crack propagation was constrained by the rigid structure surrounding the indented site. Most of the cracks were formed close to the surface. A significant amount of material was also pushed upwards and delaminated from the enamel surface of the indentation area.
牙釉质对人类牙齿健康具有重要的机械功能，然而，由于其复杂的纳米多孔结构，表征其机械性能并非易事。我们通过纳米压痕法研究了舌侧 - 颊侧牙釉质横截面的硬度和模量分布。在咬合面，牙釉质的硬度和模量分别为5.00±0.22 GPa和97.12±2.95 GPa。在靠近牙釉质 - 牙本质交界处（EDJ）的区域，硬度和模量分别为3.72±0.35 GPa和76.83±5.71 GPa。在EDJ和牙釉质外层之间的中间区域，硬度和模量分别为4.23±0.18 GPa和87.62±2.50 GPa。使用以下显微镜工具分析纳米压痕下方的表面和区域：扫描电子显微镜、聚焦离子束成像和透射电子显微镜。发现牙釉质的变形机制与位置有关，并受牙釉质内化学成分变化的影响。EDJ形成牙釉质和牙本质之间的界面。由于界面处有机相增加，EDJ处的变形行为有所不同。在中间牙釉质区域，釉柱中心形成了柱内裂纹，并沿局部微晶的方向以偏离的方向扩展到相邻的柱间质区域。在牙釉质外层，裂纹扩展受到压痕部位周围刚性结构的限制。大多数裂纹在靠近表面处形成。大量材料也被向上推并从压痕区域的牙釉质表面分层。
