Dissolution of calcium fluoride in human saliva

The dissolution behavior of calcium fluoride in saliva was investigated. Chemically pure calcium fluoride (200 mg) was equilibrated in 10 ml of either saliva or distilled water for 3 weeks or repeatedly exposed, at 15-min intervals, to 10 ml of fresh solutions of saliva, distilled water, or phosphate- or calcium-containing solutions. Calcium fluoride dissolved more readily in water than in saliva. The study confirmed that exposure to saliva caused formation of a dissolution-limiting layer and that this layer consists of surface-adsorbed phosphates and showed in addition that the dissolution rate was continuously reduced with time of exposure to saliva or phosphate buffer. Calcium fluoride-like material, formed on enamel by treatment with 2% NaF solution, was shown by scanning electron microscopy to have higher stability in saliva than in water after 3 weeks' incubation.