An in vitro study of salivary film formation at solid/liquid interfaces

The aim of this study was to use the technique of in situ null ellipsometry to study some aspects of salivary film formation at solid/liquid interfaces. Experiments were performed in a fused quartz cell, and hydrophilic plasma cleaned silica and methylated hydrophobic silica surfaces were used as substrates. Samples of unstimulated whole saliva were allowed to adsorb on the test surfaces for 30 min. After the adsorption period, rinsing was performed for 5 min. Recordings were continued for another 30 min, and then new saliva samples were added in the cell. The results showed that statistically significant higher amounts were adsorbed on the hydrophobic than on the hydrophilic surfaces. The adsorbed films on both types of tested substrates consisted of loosely associated parts which were removed after rinsing and of more tightly adsorbed fractions. A significantly larger fraction was desorbed from the films adsorbed on the hydrophobic than on the hydrophilic surfaces. When saliva was introduced again in the cell, it was shown that the amounts adsorbed attained the values obtained before the rinsings. Increase in the concentration of saliva in the cell without previous rinsing did not cause any further increase in the mass of the adsorbed film.