Effect of saliva viscosity on tribological behaviour of tooth enamel

Employing a special device simulating conditions of the masticatory process, two series tests were conducted involving studies of the tribological behaviour of enamel subjected to two- and three-body tests at different saliva viscosities. The studies showed no significant influences of saliva viscosity on the mean of the friction coefficient. However, below 2.08 mPa s the coefficient was unstable, i.e. scatter was observed. Both higher wear rate and higher scatter were observed for viscosities below of 1.68 mPa s. Comparing the wear results of the three- and two-body tests, no significant differences were obtained for viscosities above 1.68 mPa s, although for lower viscosities the wear rate in the presence of abrasive particles was higher than that obtained with pure saliva. Two regions with different tribological behaviour of enamel were observed in relation to saliva viscosity; the region with stable and low values of the tribological parameters beyond some threshold value, and the other with higher mean values of tribological parameters and their scattering. The author suggests that different concentrations of proteins are possible at the same low saliva viscosity, thus there are qualitatively different interactions between enamel surface and saliva components resulting in different lubrication regimes.