Effect of saliva flow rate on the adsorption kinetics and lubrication of salivary pellicle on human tooth enamel surface

Abstract

The adsorption and lubrication of salivary pellicle is closely associated with saliva secretion, while the relationship between saliva flow rate and salivary pellicle lubrication is still unclear. In this study, the adsorption kinetics and lubrication behavior of salivary pellicle on human tooth enamel surface has been investigated in vitro at different salivary flow rates using quartz crystal microbalance with dissipation (QCM-D) and nano-indentation/scratch technique. Human whole saliva was collected from healthy donors. Regardless of flow rates, salivary protein adsorption on the enamel surface experiences initially rapid saturated adsorption to form a stable multi-layer structure of salivary pellicle and then slow oversaturated adsorption of some proteins with weak bonding. With the flow rate increasing, the saturated adsorption process is expedited, but the oversaturated adsorption is decelerated. Hence, the pellicle has decreased roughness, thickness, viscoelasticity, and normal load-bearing capability at high flow rates than at low flow rates. Its anti-wear properties are slightly weakened but its friction-reducing properties are enhanced. In sum, there exists a coupling effect of flow rate and adsorption time on the adsorption of salivary proteins. Saliva lubrication mainly depends on the saturated adsorption of salivary proteins on enamel surface.