Effect of salivary factors on the susceptibility of hydroxyapatite to early erosion

Objective: Salivary pellicle is known to reduce the erosion of enamel and differences in the level of protection exist between individual saliva sources, but which parameters or components are important is not known. The focus of this study was to investigate the relationship between saliva parameters and early erosion of hydroxyapatite (HAp) with an in situ grown saliva film. Methods: Twenty-eight volunteers carried two HAp and one porcelain discs in their buccal sulcus for 1.5 h. Next, the discs covered with pellicle and the attached saliva film were exposed extraorally to 50 mM (pH = 3) citric acid for 2 min and unstimulated and stimulated saliva was collected. Calcium loss from HAp after erosive challenge was measured, corrected for calcium loss from pellicle on porcelain discs and averaged. Several salivary parameters were analysed. Pearson's linear correlation and multiple regression analysis were used to study the relation between saliva parameters and HAp erosion. Results: Significant correlations were found between HAp erosion and the concentration of phosphorus in unstimulated saliva (r = 0.40, p = 0.03) and between HAp erosion and the concentration of sodium (r = -0.40, p = 0.03), chloride (r = -0.47, p = 0.01), phosphorus (r = 0.45, p = 0.01) and flow (r = -0.39, p = 0.04) of stimulated saliva. Multivariate analysis revealed a significant role in the HAp erosion for sodium, urea, total protein, albumin, pH and flow of unstimulated saliva and for sodium, potassium, urea, and phosphorus of stimulated saliva. Conclusions: Several salivary parameters are associated with the susceptibility of HAp to erosion.