Quantitatively Studying Nano-mechanical Properties within the Prism and Organic Sheath of Enamel

摘要

Enamel is made up of enamel prisms separated by thin layer of organic sheaths. The mechanical properties of the prisms and the organic sheaths are obviously different from each other due to different compositions and microstructures. However, quantitative measurements of such differences have been a challenge in the past. The objective of this study is to accurately study the mechanical properties in the isolated domains within single enamel prism. The technique of nanoindentation combined with Atomic Force Microscopy (AFM) was employed to test the enamel specimens from mature human maxillary third molar. It was revealed that the nanohardness and elastic modulus of the sheaths were about 73.6% and 52.7% lower than those of the prisms. AFM topographies of the residual indent impressions also visually confirmed the differences. In addition to nanoindentation tests, the microstructures of enamel were carefully investigated in terms of hierarchical levels of organization to understand the structural reasons of the mechanical differences. We found a close relation between the variations of mechanical properties of enamel and its hierarchical structure. The analysis of the mechanical properties within enamel upon hierarchy is not only helpful to understand its unique property, but may also inspire ideas for the design of novel synthetic materials.