Properties of heterogeneous apatites containing magnesium, fluoride, and carbonate.
Biological apatites present in the mineral phases of normal and pathological calcifications contain magnesium, Mg, and carbonate, CO3. As a consequence of fluctuations in the composition of the micro-environment, these apatites may sometimes form by heterogeneous precipitation. The purpose of this study was to investigate the properties of (Mg, CO3)-apatites formed heterogeneously in the presence of fluoride, F. Two types of fluoridated (Mg, CO3)-apatites formed from solutions with low and high levels of Mg were prepared at 80 degrees C, pH 7.4. We prepared FMgCO3-MgCO3AP (Type 1) by adding the F-containing solution to those containing calcium, Mg, and phosphate ions during the first half of the precipitation period. We prepared MgCO3-FMgCO3Ap (Type 2) by adding the F-containing solution during the final half of the period. The apatites were analyzed by x-ray diffraction (XRD), infrared absorption spectroscopy, and scanning electron microscopy (SEM). SEM and XRD analyses showed evidence of mixed crystals in the heterogeneous apatites. The presence of Mg inhibits, while F promotes, apatite crystal growth. In addition, Mg incorporation increased with increasing fluoride concentration. The extent of dissolution in acid buffer of both types of heterogeneous apatites increased with Mg: Type 1 > Type 2. These results suggest that the crystal and dissolution properties of heterogeneous fluoridated (Mg, CO3)-apatites are greatly affected by the mode of F incorporation and Mg concentrations in the environment.
Okazaki
M
M
Osaka University Faculty of Dentistry, Japan.
LeGeros
R Z
RZ
D001031:Apatites / Q000138:chemical synthesis / Q000737:chemistry*; D002021:Buffers; D002254:Carbonates / Q000032:analysis / Q000737:chemistry; D003460:Crystallization; D018360:Crystallography, X-Ray; D005459:Fluorides / Q000032:analysis / Q000737:chemistry; D008274:Magnesium / Q000032:analysis / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D012995:Solubility; D013054:Spectrophotometry, Atomic
D001031:Apatites; D002021:Buffers; D002254:Carbonates; D008274:Magnesium; C025105:fluorapatite; D005459:Fluorides