Crystallinity, solubility, and dissolution rate behavior of fluoridated CO3 apatites

Abstract

To study the effect of fluoride on the physicochemical properties of carbonate‐containing apatites, two series of fluoridated CO₃ apatites with various fluoride contents were synthesized at 80°C and pH 7.4. The a‐axis dimensions of these apatites decreased with the increase of both fluoride and carbonate contents. The crystallinity of the apatites showed similar patterns of variation with the degree of fluoridation irrespective of carbonate content. These patterns appear analogous to the complex pattern of the fluoridated hydroxyapatites previously reported. In contrast to this unexpected crystallinity phenomena, the apparent solubility of fluoridated CO₃ apatites in acetate buffer solutions at pH 4.0 and 6.0 and 37°C decreased monotonically with increasing degree of fluoridation and approached that of fluoridated hydroxyapatites at high fluoride content. Dissolution rate of fluoridated CO₃ apatite pellets at pH 4.0 also showed a simple decrease with increasing degree of fluoridation and was extremely sensitive to acid at low fluoride content.