Adsorption of whole saliva onto hydrophilic and hydrophobic solid surfaces: influence of concentration, ionic strength and pH.

The influence of the concentration of salivary proteinaceous material from solutions of whole saliva on the kinetics of in vitro pellicle formation were studied together with the effects of ionic strength, pH and certain substrate characteristics. The pellicle formation was monitored by an automated Rudolph ellipsometer, equipped with a He-Ne laser (wavelength 632.8 nm). The substrates compared in the study were hydrophilic negatively charged silica surfaces and hydrophobic methylated silica surfaces. The results show that the adsorption of salivary proteins is a very rapid process on both types of surfaces. Part of the formed biofilm, however, desorbed upon rinsing, indicating that the proteinaceous material was adsorbed with varying binding strengths. Larger adsorbed amounts were recorded on hydrophobic than on hydrophilic surfaces. Increase of ionic strength caused larger amounts to be adsorbed on both types of surfaces but change of pH did not affect the adsorption on either of the studied surfaces. Ellipsometry was found to be a suitable technique to monitor the adsorption of salivary proteins at solid/liquid interfaces.