Solution Rate of Hydroxyapatite in Acetate Buffer Containing Low Concentrations of Foreign Ions

¹ Forsyth Dental Infirmary, Boston, Massachusetts

The weight loss of hydroxyapatite on exposure to 0.1 M/1 acetate buffer, pH 4.2, was significantly reduced when certain foreign ions were introduced into the buffer. At concentrations of 0.2 mM/l, fluoride had the greatest influence in depressing the rate of solution, but zinc, lead, stannous tin, molybdate, and cadmium had an appreciable effect. Treated residues retained this protection when recycled in control buffer. Stannous and zinc fluoride failed to produce a summation of the separate effects of the metallic and fluoride ions in reducing the rate of dissolution. The protective effect of fluoride, zinc, and stannous tin developed rapidly and was associated with withdrawal of these ions from the solution. The loss from the buffer of zinc and stannous ions was reduced in the presence of fluoride. The findings suggest that low concentrations of certain ionic species in the fluids surrounding the teeth may decrease acid dissolution of tooth mineral.