Institute of Advanced Ceramics, Hamburg University of Technology, Hamburg, Germany.
Biomaterials. 2010 May;31(14):4238-47. doi: 10.1016/j.biomaterials.2010.01.127. Epub 2010 Feb 18.
Enamel and dentin compose the crowns of human teeth. They are joined at the dentinoenamel junction (DEJ) which is a very strong and well-bonded interface unlikely to fail within healthy teeth despite the formation of multiple cracks within enamel during a lifetime of exposure to masticatory forces. These cracks commonly are arrested when reaching the DEJ. The phenomenon of crack arrest at the DEJ is described in many publications but there is little consensus on the underlying cause and mechanism. Explanations range from the DEJ having a larger toughness than both enamel and dentin up to the assumption that not the DEJ itself causes crack arrest but the so-called mantle dentin, a thin material layer close to the DEJ that is somewhat softer than the bulk dentin. In this study we conducted 3-point bending experiments with bending bars consisting of the DEJ and surrounding enamel and dentin to investigate crack propagation and arrest within the DEJ region. Calculated stress intensities around crack tips were found to be highly influenced by the elastic modulus mismatch between enamel and dentin and hence, the phenomenon of crack arrest at the DEJ could be explained accordingly via this elastic modulus mismatch.
牙釉质和牙本质构成了人类牙齿的牙冠。它们在牙本质-釉质交界处（DEJ）结合，尽管在一生中咀嚼力的作用下牙釉质内会形成多个裂纹，但这个交界处是一个非常坚固且结合良好的界面，不太可能在健康的牙齿中失效。这些裂纹通常在到达 DEJ 时被阻止。在许多出版物中都描述了 DEJ 处裂纹停止的现象，但对于其潜在的原因和机制尚未达成共识。解释范围从 DEJ 的韧性大于牙釉质和牙本质到假设不是 DEJ 本身导致裂纹停止，而是所谓的 mantle dentin（靠近 DEJ 的一种比牙本质略软的薄物质层）导致裂纹停止。在这项研究中，我们进行了三点弯曲实验，使用包含 DEJ 以及周围牙釉质和牙本质的弯曲棒，以研究 DEJ 区域内的裂纹扩展和停止。发现裂纹尖端周围的计算应力强度受牙釉质和牙本质之间的弹性模量不匹配的强烈影响，因此，通过这种弹性模量不匹配，可以相应地解释 DEJ 处的裂纹停止现象。
