In this paper, the orientation dependence of the Poisson's ratio of teeth’s dentin and enamel on the basis of matrices of elastic constants and the compliance coefficients of hexagonal crystals, such as crystals of dentine hydroxyapatite, was obtained for the first time. The results of calculating the Poisson's ratios of dentin and enamel as a crystalline system with a hexagonal structure are presented in the form of tables and diagrams in the polar and Cartesian coordinate systems. It is shown that the maximum value of the Poisson's ratio of dentin (0.54) is greater than the upper limit for the Poisson's ratio of isotropic materials, including known restoration materials, which in some cases may reduce the quality of restorations. The effective elastic characteristics of dentine and enamel, including Poisson's ratio using different averaging methods, are calculated.
enamel, dentin, Poisson's ratio, crystals of hydroxyapatite
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