Tooth wear is the loss of dental hard tissue caused by the friction between tooth surfaces as well as that between the tooth surface and food when the teeth are in chewing and non-chewing motions. From the perspective of tribology, four types of natural tooth wear exist: two-body, three-body, fatigue, and chemical etching wear. Research methods for the analysis of friction and wear property of natural teeth are primarily clinical studies in vivo, experimental studies in vitro, and experimental studies in vitro and in vivo. In these methods, the test parameters can be adequately controlled by experimental studies in vitro. Research on natural tooth friction and wear is divided into two categories, namely, evaluation of tribological properties and research on wear properties and mechanisms. Several scholars simulated mastication and bruxism through wear in vitro and evaluated the wear amount by the loss of weight. A few focused on the study of the wear resistance of enamel at different ages. Other researchers evaluated the wear resistance of natural enamel at different cross sections with a TA2 titanium ball. Several measured the anisotropy wear resistance of natural teeth by nanoscratch technique, and others studied wear mechanisms by wear scar morphology. The results of these previous studies on the friction and wear of the natural tooth and its mechanisms are inconsistent. Thus, verifying the wear failure mechanisms of the natural tooth is difficult. The incomplete understanding of the failure mechanisms of the natural tooth has become the key factor that limits the development of dental materials.
