Objectives

The local structures and mechanical properties within tooth dentin-enamel-junction (DEJ) regions have been focused for numerous studies. The reported results, however, remain inconsistent particularly on the functional width and gradient architecture of the DEJ. The current study aims at systematically determining the mechanical gradient of the DEJ at different intratooth locations such that a clearer understanding on the tooth properties and the potential correlations with the tooth function could be obtained.

Methods

We re-examined how mechanical properties such as elastic modulus and hardness transitioned from those of dentin to those of enamel using combined static and dynamic nanoindentation mapping techniques. A new mapping method and associated image processing procedures were developed to improve the measurement accuracy and resolution.

Results

A thin, sigmoidally-transitioned interphase layer of the DEJ was identified with an accurate functional width of 2–3 μm. The DEJ width and gradient architecture were found intratooth location-dependent, with the DEJ at the occlusal sites being wider and transitioning smoother than that at the cervical sites. Such different widths and architectures of the interphase layer at sites subjected to different types and magnitudes of loadings during mastication could promote more efficient stress transferring between enamel and dentin without compromising the overall stiffness of the tooth.

Significance

The presented study not only adds our understanding in the local mechanical properties within tooth DEJ regions, it could also further advance the development of DEJ-mimetic, functional gradient interphase for strong and ultra-durable jointing between dissimilar materials.

中文翻译：

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绘制人牙本质-牙釉质交界处不同牙内位置的机械梯度

目标

牙本质-牙本质-牙釉质结（DEJ）区域内的局部结构和力学性能已成为众多研究的重点。但是，报告的结果尤其在DEJ的功能宽度和梯度结构上仍然不一致。当前的研究旨在系统地确定不同牙齿内位置的DEJ的机械梯度，从而可以更清晰地了解牙齿的性质以及与牙齿功能的潜在相关性。

方法

我们使用静态和动态纳米压痕映射技术重新检查了机械性能（如弹性模量和硬度）如何从牙本质转变为牙釉质。开发了一种新的映射方法和相关的图像处理程序，以提高测量精度和分辨率。

结果

确定了DEJ的一个薄的，S型过渡相间层，其精确功能宽度为2-3μm。发现DEJ的宽度和梯度结构取决于牙齿内的位置，在咬合部位的DEJ比宫颈部位的DEJ宽且过渡平滑。在咀嚼期间经受不同类型和大小的载荷的位置处的相间层的这种不同宽度和构造可以促进牙釉质和牙本质之间更有效的应力传递，而不会损害牙齿的整体刚度。

意义

提出的研究不仅增加了我们对牙齿DEJ区域内局部力学性能的了解，而且还可以进一步推进模拟DEJ，功能梯度相间的发展，以实现异种材料之间牢固而超耐用的接合。