Load dependency of the coefficient of friction of oral mucosa

Frictional conditions in the mouth are thought by food scientists to be critical to the perception of important food attributes such as astringency, smoothness, roughness, slipperiness, etc. This ability to detect friction probably evolved to avoid foods that could wear the teeth excessively. In modern humans, sensations related to friction and lubrication affect consumer responses to food products and are therefore commercially important. In this study, the coefficient of friction between two mucosal surfaces was measured using stimulated and unstimulated saliva at loads varying from 0.34 to 2.20 N and at speeds varying from 0.1 to 700 mm s−1. The coefficient of friction decreased with increasing load and speed for both types of saliva. Lubrication with stimulated saliva resulted in higher friction than with unstimulated saliva. Stimulated saliva has a higher protein content and lower viscosity than unstimulated saliva, which may explain the friction differences found between the two types of saliva. The reduction in friction with load is attributed to deformation of the mucosal surfaces, leading to a reduction in surface roughness.