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

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 degrees C and pH 7.4. The alpha-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 degrees 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.