Cuy J L, Mann A B, Livi K J, Teaford M F, Weihs T P
Department of Materials Science and Engineering, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218, USA.
Arch Oral Biol. 2002 Apr;47(4):281-91. doi: 10.1016/s0003-9969(02)00006-7.
The mechanical behavior of dental enamel has been the subject of many investigations. Initial studies assumed that it was a more or less homogeneous material with uniform mechanical properties. Now it is generally recognized that the mechanical response of enamel depends upon location, chemical composition, and prism orientation. This study used nanoindentation to map out the properties of dental enamel over the axial cross-section of a maxillary second molar (M(2)). Local variations in mechanical characteristics were correlated with changes in chemical content and microstructure across the entire depth and span of a sample. Microprobe techniques were used to examine changes in chemical composition and scanning electron microscopy was used to examine the microstructure. The range of hardness (H) and Young's modulus (E) observed over an individual tooth was found to be far greater than previously reported. At the enamel surface H>6GPa and E>115GPa, while at the enamel-dentine junction H<3GPa and E<70GPa. These variations corresponded to the changes in chemistry, microstructure, and prism alignment but showed the strongest correlations with changes in the average chemistry of enamel. For example, the concentrations of the constituents of hydroxyapatite (P(2)O(5) and CaO) were highest at the hard occlusal surface and decreased on moving toward the softer enamel-dentine junction. Na(2)O and MgO showed the opposite trend. The mechanical properties of the enamel were also found to differ from the lingual to the buccal side of the molar. At the occlusal surface the enamel was harder and stiffer on the lingual side than on the buccal side. The interior enamel, however, was softer and more compliant on the lingual than on the buccal side, a variation that also correlated with differences in average chemistry and might be related to differences in function.
牙釉质的力学行为一直是众多研究的主题。最初的研究认为它或多或少是一种具有均匀力学性能的均质材料。现在人们普遍认识到，牙釉质的力学响应取决于位置、化学成分和棱柱方向。本研究使用纳米压痕技术描绘上颌第二磨牙（M(2)）轴向横截面的牙釉质特性。力学特性的局部变化与样品整个深度和跨度上的化学成分和微观结构变化相关。使用微探针技术检查化学成分的变化，并使用扫描电子显微镜检查微观结构。发现在单个牙齿上观察到的硬度（H）和杨氏模量（E）范围远大于先前报道的范围。在牙釉质表面，H>6GPa且E>115GPa，而在牙釉质-牙本质交界处，H<3GPa且E<70GPa。这些变化与化学、微观结构和棱柱排列的变化相对应，但与牙釉质平均化学成分的变化显示出最强的相关性。例如，羟基磷灰石成分（P(2)O(5)和CaO）的浓度在坚硬的咬合面最高，并向较软的牙釉质-牙本质交界处移动时降低。Na(2)O和MgO呈现相反的趋势。还发现磨牙从舌侧到颊侧牙釉质的力学性能存在差异。在咬合面，舌侧的牙釉质比颊侧更硬更具刚性。然而，内部牙釉质在舌侧比颊侧更软更具柔韧性，这种变化也与平均化学成分的差异相关，可能与功能差异有关。
