Fluoride Removal by Powdered Dental Enamel from Solutions of Stannous or of Sodium Fluoride

Abstract

IN 1955, Hatton, Nebergall and Muhler¹ described an experiment in which powdered enamel samples were shaken in dilute solutions of stannous fluoride or of sodium fluoride that initially contained equivalent concentrations of fluoride. Much more fluoride was removed (presumably taken up by the enamel) from the stannous fluoride solution; for example, when the final concentrations of fluoride were 17 µgm./ml., 7–8 times as much fluoride was removed from the stannous as from the sodium fluoride solution. Hatton et al. suggested that the greater initial acidity of the stannous fluoride solutions may have been in part responsible². Another important pH effect was overlooked by Hatton et al., namely, shaking with powdered enamel increased the pH of the solutions, markedly for stannous fluoride and detectably for sodium fluoride. Stannous fluoride solutions are not stable when the pH increases and even at acid pH's on standing. Nebergall, Muhler and Day³ described the opalescence, “probably stannous hydroxide” (contained less than 0.01 per cent fluorine), which developed and was ultimately precipitated from a solution of pH 2.38. We found that by increasing the pH of stannous fluoride solutions in the absence of enamel, precipitates were formed which contained larger percentages of fluoride (≫ 0.01 per cent fluoride) that might account at least in part for the greater amount of fluoride removed from stannous fluoride solutions. Amorphous precipitates were seen microscopically along with the centrifuged enamel particles when powdered enamel was shaken with stannous fluoride solutions.