RELATIONSHIP BETWEEN pH, AGE, AND CONCENTRATION OF SOLUTIONS OF STANNOUS FLUORIDE AND SODIUM FLUORIDE IN DECREASING ENAMEL SOLUBILITY AND AFFECTING THE UPTAKE OF FLUORINE

¹ Chemical Laboratories of Indiana University, Bloomington, Ind.

The marked effectiveness of freshly prepared stannous fluoride solutions in reducing the solubility of powdered dental enamel decreases over a period of a few days, but the effectiveness of sodium fluoride solutions is not decreased. Enamel takes up larger amounts of fluorine from stannous fluoride regardless of the age of the solutions, and the uptake is greater from old stannous fluoride solutions than from those which are freshly prepared. The uptake of fluorine from sodium fluoride is not affected by age. These changes appear to be related to the pH of the solutions. The pH of the stannous compound decreases, through hydrolysis of the salt, but the pH of the sodium salt remains unchanged. Aged dilute solutions are decidedly less effective than those freshly prepared in reducing the solubility of dental enamel.