Inhibition of enamel erosion by in vitro salivary pellicles

Objectives: Enamel erosion is the focus of considerable, predominantly in vitro, research. Many such studies neglect the effects of a salivary pellicle. The aim of this study was to investigate the effect of salivary pellicles formed by short-term exposure to human saliva on enamel erosion in vitro. Methods: Polished human enamel specimens (n=102; 6 per category) were exposed to stimulated, pooled, whole saliva at 36ºC for 0, 30, 60, 90 or 120 min then rinsed gently in distilled water. The edges of the specimen were masked with adhesive tape to provide a central area which was exposed to acid and two adjacent, reference areas. Specimens were attached to an overhead, quantified stirrer such that all specimens were subject to the same stirring conditions with an equivalent linear velocity of 0.15 m.s-1. Enamel erosion was investigated in 14.4 mM citric acid at pH 3.20 (0, 30, 60, 90, 120 min pellicle formation) and in citric acid at pH 2.80 and 3.80 and three commercially available soft drinks (Capri Sun Orange, Robinson's Apple Fruitshoot, Tropicana Orange Juice) (0, 120 min pellicle formation only). Erosion was measured using non-contact optical profilometry. Results: Enamel erosion was reduced by the presence of a salivary pellicle. The degree of protection increased with increasing time of pellicle formation (p = 0.0008). There was a linear relationship between pellicle formation time and reduction in erosion. After formation of a 120 min pellicle, erosion was reduced by ~20% in citric acid at pH 2.8, 3.2 and 3.8 and in the soft drinks. Conclusions: 120 min salivary pellicles formed in vitro reduced enamel erosion by approximately 20% in citric acid solutions and soft drinks. There was a linear relationship between time of pellicle formation and erosion reduction over the range of times investigated in this study.