Tribological behaviour of human enamel in red wine and apple juice environments

The aim of this study was to investigate wear and friction behaviour of enamel in red wine and apple juice environments at different concentrations and pH in distilled water. Enamel specimens were prepared from freshly extracted human teeth. Dispersalloy amalgam was used to prepare a counterface. A modified pin-on-disc wear machine was employed, and wear tests were carried out under cyclic loading with a mean of 35 N and amplitude of 25 N. The machine simulated tooth wear for 3 h. Two groups of 19 samples were subjected to wear in red wine and apple juice solutions in distilled water, at volumetric concentration ranging from 5 to 95%. The worn enamel surfaces were examined by SEM. Comparative studies of Ca/P ratio before and after testing were performed by means of EDS. The wear rates of enamel varied significantly with pH ( p < 0.05) and some pH thresholds have been found. For pH values beyond 3.25 for red wine and 3.52 for apple juice solutions the wear rates were mild and relatively stable. With decreasing pH below the threshold mean wear rates significantly increased and a large extent of measurements could be observed. The results also showed that the wear rate corresponded with surface topography, i.e. different wear rates were accompanied by different wear mechanisms. Simultaneous mechanical and chemical actions occurring during sliding enamel against an amalgam counterface in a drink environment caused different wear behaviour of enamel, which substantially depended on environmental pH.