Crystallisation of fluoride-containing bioactive glasses

Fluoride prevents dental cavities, stimulates bone formation and inhibits bone resorption, and fluoride-containing bioactive glasses and glass-ceramics are of great interest for dental and orthopaedic applications. In a series of melt derived bioactive glasses (SiO2-P2O5-CaO-Na2O-CaF2) calcium fluoride was added in increasing amounts (0-32.7 mol% CaF2) while keeping the network connectivity constant. Crystallisation temperatures were determined using differential scanning calorimetry. Glass powder was heat treated to crystallisation temperature at a heating rate of 10 K min(-1) before cooling to room temperature. X-ray diffraction followed by Rietveld analysis showed crystal phases after heat treatment to be combeite, cuspidine and fluorite, with the relative amounts of combeite decreasing with increasing fluoride content in the glass while the relative amounts of the fluoride-containing phases increased. Formation of apatite during heat treatment could not be detected, owing to the low phosphate content (<= 1.07 mol%) and too high a sodium content. As formation of apatite and particularly fluorapatite would be preferable for applications in dentistry and orthopaedics, future research will focus on higher phosphate content and low sodium content glasses.