Hydrothermal synthesis of fluoride-substituted calcium phosphate in supersaturation condition

Fluoride-substituted calcium phosphate occurs naturally in the hard tissue and is particularly found in the outer layer of teeth namely enamel. The presence of fluoride in teeth has a beneficial effect on caries prevention and reducing tooth decay. In dental application, hydroxyapatite is commonly used due to its bioactivity and similarity with the chemical structure of teeth. Nevertheless, hydroxyapatite has poor mechanical properties as a bulk material following with high solubility in an acid condition. Fluoride, by substituting for OH-ion in hydroxyapatite lattice position, provides higher acid resistance and low solubility. Besides, fluoride ions could encourage the mineralization and formation of calcium phosphate in hard tissue. In this study, the nucleation of fluoride-substituted calcium phosphate had been evaluated by treating with various hydrothermal temperature and supersaturated system. The obtained results from x-ray diffraction (XRD) analysis confirmed the formation of fluorapatite in all samples as well as the presence of the liberation mode of hydroxyl as a characteristic functional group detected by fourier transform infrared (FTIR) results. XRD patterns showed that hydrothermal temperature does not affect fluorapatite nucleation, but it does on crystallite size. It was shown by the similar XRD patterns formed as well as the peak intensities. While the higher hydrothermal temperature tends to decrease the crystallite size. Meanwhile, the supersaturation condition containing a higher concentration of calcium precursor significantly affects the purity of fluorapatite obtained. The presence of calcium hydroxide as the calcium precursor in XRD patterns showed the incomplete nucleation of fluorapatite. The incomplete nucleation of fluorapatite results in a higher Ca/P ratio detected in EDX results. On the other hand, the degree of fluoridation of obtained fluorapatite was relevant to that of theory. Moreover, SEM results showed coral-like morphology with an average particle size of 1.5 µm.