Evaluation of the influence of white spot lesion on the mechanical properties of human tooth enamel and dentine

In the present paper the influence of early caries (white spot lesion) on the mechanical properties of human tooth enamel and dentine was ex vivo investigated. Optical microscopy made it possible to study the shape of the enamel caries area on a prepared longitudinal section of a human molar. Evaluation of the mechanical properties of each of the areas that are important from a practical point of view for a dental clinician (pathological enamel, dentine in its vicinity, sound enamel and sound dentine in its vicinity) was carried out using nanoindentation. In addition, maps of the mechanical properties were constructed for the section of the tooth containing the area of pathological enamel, enamel in its vicinity, the adjacent dentine-enamel junction and dentine in its vicinity. In the course of the analysis of the results of indentation by the Oliver - Pharr method, a decrease in the values of the reduced Young's modulus and indentation hardness was found both for the focus of the caries of the enamel, and for the visually sound enamel adjacent to this focus, as well as for the dentine in their vicinity, for which the diagrams "indentation force - indentation depth " demonstrated a violation of the load resistance mechanism. To describe the reasons for the decrease in the mechanical properties of tissues, scanning electron microscopy of pathological areas was used.