Marshall G W, Balooch M, Gallagher R R, Gansky S A, Marshall S J
Division of Biomaterials and Bioengineering, Department of Preventive and Restorative Dental Sciences, University of California, San Francisco, CA 94143-0758, USA.
J Biomed Mater Res. 2001 Jan;54(1):87-95. doi: 10.1002/1097-4636(200101)54:1<87::aid-jbm10>3.0.co;2-z.
The dentinoenamel junction (DEJ) is a complex and poorly defined structure that unites the brittle overlying enamel with the dentin that forms the bulk of the tooth. In addition, this structure appears to confer excellent toughness and crack deflecting properties to the tooth, and has drawn considerable interest as a biomimetic model of a structure uniting dissimilar materials. This work sought to characterize the nanomechanical properties in the region of the DEJ using modified AFM based nanoindentation to determine nanohardness and elastic modulus. Lines of indentations traversing the DEJ were made at 1-2 microm intervals from the dentin to enamel along three directions on polished sagittal sections from three third molars. Nanohardness and elastic modulus rose steadily across the DEJ from bulk dentin to enamel. DEJ width was estimated by local polynomial regression fits for each sample and location of the mechanical property curves for the data gradient from enamel to dentin, and gave a mean value of 11.8 microm, which did not vary significantly with intratooth location or among teeth. Nanoindentation was also used to initiate cracks in the DEJ region. In agreement with prior work, it was difficult to initiate cracks that traversed the DEJ, or to produce cracks in the dentin. The fracture toughness values for enamel of 0.6-0.9 MPa . m(1/2) were in good agreement with recent microindentation fracture results. Our results suggest that the DEJ displays a gradient in structure and that nanoindenation methods show promise for further understanding its structure and function.
牙釉质牙本质界（DEJ）是一种复杂且定义不明确的结构，它将脆弱的表层牙釉质与构成牙齿主体的牙本质结合在一起。此外，这种结构似乎赋予牙齿出色的韧性和裂纹偏转特性，作为一种结合不同材料的结构的仿生模型，它引起了相当大的关注。这项工作旨在使用基于改进原子力显微镜的纳米压痕来表征DEJ区域的纳米力学性能，以确定纳米硬度和弹性模量。在来自三颗第三磨牙的抛光矢状切片上，沿着三个方向从牙本质到牙釉质以1-2微米的间隔制作横穿DEJ的压痕线。纳米硬度和弹性模量从牙本质主体到牙釉质在整个DEJ区域稳步上升。通过对每个样本以及从牙釉质到牙本质的数据梯度的力学性能曲线位置进行局部多项式回归拟合来估计DEJ宽度，其平均值为11.8微米，在牙内位置或不同牙齿之间没有显著差异。纳米压痕还用于在DEJ区域引发裂纹。与先前的工作一致，很难引发横穿DEJ的裂纹，也很难在牙本质中产生裂纹。牙釉质的断裂韧性值为0.6-0.9MPa·m(1/2)，与最近的微压痕断裂结果高度一致。我们的结果表明，DEJ在结构上呈现出梯度变化，并且纳米压痕方法有望进一步理解其结构和功能。
