The effect of ionic surfactants on salivary proteins adsorbed on silica surfaces

The adsorption onto silicon oxide surfaces from water and 0.1 M acetate buffer containing 10% parotid saliva at 25 degrees C and 35 degrees C and at pH 6 was monitored in situ using ellipsometry. The silicon oxide surface was used as a model for dental enamel. The adsorption kinetics and the reversibility on rinsing were determined, and the desorbable fraction was found not to change after either 30 or 120 min of adsorption. Addition of sodium dodecyl sulfate after 30 or 120 min of saliva adsorption caused strong desorption. Rinsing 30 min after surfactant addition caused some redeposition if saliva was present, whereas continued desorption occurred in the absence of saliva. Cetyltrimethylammonium bromide caused either an increase or a slight decrease in the amount adsorbed when added after 30 min and 120 min, respectively. For both times, rinsing caused desorption, left the same amount adsorbed, and was not affected by the presence or absence of saliva in solution. No major effect from temperature and ionic strength was found.