Crystallographic and chemical properties of Mg-containing apatites before and after suspension in solutions.

Mg-containing synthetic apatites were prepared and then incubated in unbuffered 0.9% NaCl solution and in buffered 0.1 M CH3COOK solution (pH 7.4) at 37 degrees C to examine the changes in their crystallographic and chemical properties after suspension in these solutions. After one month of incubation, the magnesium (Mg) content in the samples decreased greatly, especially in samples with higher Mg content. The a and c axis dimensions of the samples changed with the decrease of Mg content. On the other hand, Mg concentrations in both solutions increased more than the Ca concentrations. Mg-substituted beta-tricalcium phosphate (beta-TCP), or whitlockite, formed from solutions with high Mg concentration. These results show that Mg-containing apatites dissolve to a greater extent than Mg-free apatites with the subsequent reprecipitation of Mg-poor apatites. In addition, the high Mg/Ca in solution favoured the reprecipitation of Mg-containing beta-TCP.