Mechanical and tribological characterization of human tooth

In order to develop new dental restorative materials, it is imperative to evaluate and understand the structure–property relationships of the human tooth. Three major structural parts of human tooth i.e. enamel, dentin and dentin–enamel junction have been characterized in the present work in terms of microstructure, phase analysis and compositional gradient. It has been observed that microindentation hardness varies from enamel to dentin with the highest hardness observed for enamel at the outermost surface (around 3.5 GPa). Hardness values monotonically decrease with depth to less than 1 GPa, measured at the interior dentin. Furthermore, the measured hardness variation is found to have a noticeable correlation with the compositional variation.In order to evaluate the tribological properties of the human tooth, fretting wear tests were carried out against sintered alumina under a load of 1 N for 2000 to 10,000 cycles. A variation in coefficient of friction (ranging from 0.12 to 0.55) was measured in our experiments. The wear mechanism is dominated by fretting fatigue and adhesive wear, involving the formation of oxidized calcium phosphate based compounds and its subsequent transfer from tooth to alumina surface. The experimental results also reveal that the human tooth is more susceptible to adhesion wear than abrasion or attrition at fretting contacts.