Methods: Six glasses were synthesized using a melt-quench route; compositions were based on the following system SiO2, CaO, Na2O, K2O, P2O5, ZnO and MgO. The ratio of these compounds was kept constant along the glass series. Fluoride (CaF2) was added in increasing concentration (2.44, 4.77, 9.11, 10.33, 11.53 and 13 mol %). All glasses were characterized using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and dilatometery. Glass density was measured according to Archimedes method and apatite formation was tested in simulated body fluid (SBF) and Tris-buffer solution. After 1 week immersion, solid particles were analysed using XRD and Fourier transform infrared (FTIR) spectroscopy, whereas filtrate was analysed using inductively coupled plasma (ICP) spectroscopy and fluoride electrode.
Results: XRD results show that all glasses were amorphous. Sintering window, glass transition and softening temperatures decrease with CaF2 content. In contrast, TEC and glass density increase with CaF2 content. After 1 week immersion in SBF and Tris, XRD and FTIR showed that all glasses underwent structural changes with evidence of apatite formation. ICP spectroscopy indicates that fluoride has a substantial effect on ions released and the amount of fluoride released was proportional to the CaF2 content.
Conclusion: The ability of the glass to form apatite in biological fluids was induced by addition of fluoride. However, CaF2 has a negative effect on TEC.