Effects of inorganic orthophosphate and pyrophosphate on dissolution of calcium fluoride in water.

Calcium and fluoride release from excess solid calcium fluoride was monitored for 15-30 min in aqueous solutions containing various concentrations of inorganic orthophosphate and pyrophosphate. Low concentrations of these ions (1-10 mumol/L) considerably inhibited the rate of dissolution of calcium fluoride. This inhibition was pH-dependent, being reduced at pH values below 5. It is suggested that a reduced calcium fluoride dissolution rate, in the presence of phosphate, can account for the relatively slow loss of calcium fluoride from dental enamel observed in recent clinical studies. It also appears that calcium fluoride coated with phosphate may provide a pH-controlled slow release of fluoride that may be of clinical significance and a major component of the cariostatic mechanism of topically applied fluoride.