Crystallographic properties of heterogeneous Mg-containing fluoridated apatites synthesized with a two-step supply system

Mg-containing fluoridated hydroxyapatites (Mg-MgFAp and MgF-MgAp) were synthesized heterogeneously with two different modes of fluoride supply. The expanded (300) reflections of the X-ray diffraction of both apatites were broader than and different from those of the mechanical mixture of the homogeneous apatites (MgAp and MgFAp). Scanning electron microscopy (SEM) showed that the crystal size and shape of Mg-MgFAp and MgF-MgAp were different. Energy dispersive spectroscopy (EDS) indicated that the fluoride intensity of Mg-MgFAp synthesized with the fluoride supply in the latter half of the experimental period was higher than that of MgF-MgAp. The apparent solubility of Mg-MgFAp was lower than that of MgF-MgAp. These results suggested that two different types of Mg-containing fluoridated hydroxyapatites might be formed: surface fluoride-rich apatites (Mg-MgFAp) and inner fluoride-rich apatites (MgF-MgAp).