Reactions of Stannous Fluoride with Some Inorganic Compounds

¹ Division of Chemistry, American Dental Association, Chicago, Illinois

In general, a 0.4 per cent aqueous solution of stannous fluoride was more stable and available when no other compound was present. The soluble stannous ion concentration of this solution gradually decreased with age, with approximately 50 per cent being lost in 1 month. The soluble fluoride concentration decreased much less rapidly over this same period.

Compounds providing a soluble cation (such as barium, calcium, and strontium carbonates), which can react with fluoride to form an insoluble fluoride salt, rapidly decreased the soluble fluoride ion concentration of an aqueous solution of 0.4 per cent stannous fluoride. The soluble stannous ion concentration of these mixtures also decreased.

Compounds such as the sodium carbonates, which raised the pH of stannous fluoride solutions, reduced the soluble stannous ion concentration but did not necessarily affect the soluble fluoride ion concentration.

The rates at which changes in soluble ion concentration occur depend primarily on the relative concentrations of the soluble species. Dilute systems may be of some utility in screening certain compounds; however, extrapolation of data to determine reaction rates to other stannous fluoride solutions of different concentrations or to other media, such as ointments, is very difficult.

The chemical determination of the soluble ions is indicative of the gross chemical character of the mixture; however, these determinations in themselves are not a good measure of the clinical availability of those ions.