Investigation of the deformation and fracture behavior of hierarchical dental enamel

在此DFG项目的前一个资助期内，我们通过实验研究了不同层次对牙釉质机械性能的影响，特别是通过拉伸和压缩下的微机械实验。我们可以第一次发现，存在着明显的机械拉伸压缩不对称性，特别是在等级制度的影响方面。这种不对称性尚未被包括在现有的理论微观力学模型。值得注意的是，我们的研究表明，它是不清楚的，无论是分层结构或硬和软的羟基磷灰石与其软蛋白质片的组合是占主导地位的特殊的机械性能的釉质。这种理解上的差距的主要原因是，不存在羟基磷灰石纳米纤维和釉质棱柱之间的界面的结构的三维结构成像。因此，该更新提案的目的是了解软蛋白的存在是否是牙釉质损伤耐受行为所必需的，或者其复杂的等级结构是否更重要。为了揭示我们想要比较有蛋白质和没有蛋白质的牙釉质样品的机械实验。同时，我们希望使用TEM断层扫描来成像羟基磷灰石纳米纤维的3D结构，它们的界面和FIB断层扫描来成像釉质棱镜的界面。我们期望，在不同层次上的微观和宏观力学实验与高分辨率成像的结合将允许回答该项目的核心科学问题。该更新建议的第二个目的是了解牙釉质作为非活体组织是否具有裂缝愈合的能力，如一篇出版物所示。它与本提案的第一个目标有关，并将阐明蛋白质在釉质中的作用。最后，我们认为本课题的研究结果将有助于开发更好的新型牙科材料和非金属工程材料。

In the previous funding period of this DFG project we experimentally investigated the influence of the different hierarchical levels on the mechanical properties of dental enamel, in particular by using micromechanical experiments under tension and compression. We could reveal for the first time, that there exists a pronounced mechanical tension compression asymmetry especially in regard to the influence of hierarchy. This asymmetry has not been included in the existing theoretical micromechanical models yet. Notably our investigations showed that it is not clear, whether the hierarchical structure or the hard and soft combination of hydroxyapatite with its soft protein sheets is dominant for the exceptional mechanical properties of enamel. A major reason for this gap in understanding is, that there does not exist a 3 dimensional structural imaging of the structure of the hydroxyapatite nanofibers and the interfaces between the enamel prisms. The objective of this renewal proposal is therefore to understand, whether the presence of soft proteins is necessary for the damage tolerant behavior of dental enamel, or whether its complex hierarchical structure is more essential. In order to reveal that we want to compare mechanical experiments with enamel samples with and without proteins. In parallel we want to use TEM tomography to image the 3D structure of the hydroxyapatite nanofibers, their interfaces and FIB-tomography to image the interfaces of the enamel prisms. We expect, that the combination of the micro- and macromechanical experiments on different hierarchical levels together with high resolution imaging will allow answering the central scientific question of this project. A secondary objective of this renewal proposal is to understand, whether dental enamel as a non living tissue has the ability of crack healing, as indicated in one publication. It is related to the first objective of this proposal and will elucidate the role of proteins in enamel. Finally we think that the findings of this project will contribute in developing better and novel dental materials and non-metallic engineering materials.