Viscoelasticity of Dental Hard Tissues

The results of a study of the mechanical properties of dental hard tissues by nanoindentation are presented. With quasi-static nanoindentation, the analysis of the Berkovich indenter unloading curve allowed to determine the hardness and modulus of elasticity of dental enamel, dentin, and photopolymer composite, which is used for splinting and filling. The hardness and modulus of elasticity of dental enamel was shown to approach that of glass. The hardness and modulus of elasticity of dentin is noticeably lower than that of enamel. The tests revealed the viscoelastic mechanical behavior of enamel, dentin, and photopolymer composite fillings. To determine the viscoelastic characteristics of dental hard tissues, nanoindentation with pulsed load application to the indenter with tracking the change in the depth of impression as a result of viscoelastic deformation relaxation in the nanocontact after the rapid unloading of the indenter was used. For the first time, relaxation times for enamel and dentin have been determined. Rapid indenter unloading made it possible to separate the deformation components (elastic, viscoelastic and plastic) in the nanocontact for these materials. While the proportion of viscoelastic deformation in the total deformation for dental enamel is insignificant (about 2%), for dentin and photopolymer fillings it is significantly higher (~10%). The results indicate that increasing the content of organic components in biomaterials reduces their hardness and modulus of elasticity and increases their viscoelasticity.