The Kinetics of Dissolution of Tooth Enamel — A Constant Composition Study

Abstract

The kinetics of dissolution of powdered bovine enamel and of human enamel, both untreated and extracted with either hypochlorite or chloroform, has been studied using a constant solution composition technique in undersaturated solutions of calcium phosphate (total molar calcium concentration, T_Ca = 0.3 to 13.1 × 10-3 mol L^-1, total molar phosphate, Tp = 0.18 to 7.9 x 10^-3 mol L^-1) at an ionic strength of 0.15 mol L^-1, and pH = 4.5. The kinetic equations describing the dissolution reactions suggest a surface dislocation mechanism, and the presence of fluoride ion markedly retarded the reaction. For human enamel, a fluoride level of only 0.5 ppm reduced the rate of dissolution ten-fold. In contrast, the dissolution of hydroxyapatite, HAP, is best interpreted in terms of a polynucleation process.