Anisotropy of the mechanical properties of human dental enamel

Abstract

Human dental enamel is oriented hierarchical biological structure, which covered the upper part of a tooth. Its high biomechanical properties provide protection of a tooth from influence of such external factors as imposed loads and oral environment. In this work, we examine how orientation of enamel rods rules by the mechanical properties of human enamel, using experimental mechanics. Shear testing of the enamel samples in the three planes relatively to the direction of enamel rods shed new light on the mechanism of stress accommodation in human dental enamel. It was revealed that enamel is macroscopically anisotropic hard tissue insomuch as its strength and the deformation in direction, which is normal to the enamel rods, is in ~3 to 7 times higher than in directions parallel to the enamel rods. Despite it can be considered as isotropic solid up to ~5% of shear deformation. Irreversible deformation of enamel occurs when loading is applied normally to the enamel rods.