Method: Glasses with and without 2 mol% of ZnO were synthesised and studied. Glass degradation and apatite formation was followed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and magic angle spinning nuclear magnetic resonance (MAS-NMR). The ions in solution following immersion in Tris buffer were determined by inductively coupled plasma – optical emission spectroscopy (ICP-OES) and by a fluoride-ion selective electrode.
Result: The zinc free glass formed a fluorapatite (FAP) phase in under two hours that was evident in both the XRD patterns and FTIR spectra. The zinc containing glass however did not show sharp XRD peaks of the apatite phase until 24 hours immersion and did not show the characteristic n(PO4) peaks of a crystalline orthophosphate in the FTIR spectra. The 31P and 19F MAS-NMR spectra showed that the zinc free glass formed FAP in under two hours and the dissolution of the glass was complete in <6 hours. The zinc containing glass also formed a FAP, but the apatite formed was in smaller amounts and the broader peaks indicate a more disordered apatite. The dissolution of the glass in terms of its fluorine and phosphate content was not complete in 24 hours.
Conclusion: Zinc oxide substitution in bioactive glass slows down rapid degradation of the bioactive glass and formation of the apatite phase. Thus, the studied composition of a zinc containing bioactive glass can be incorporated as a desensitiser into a remineralising toothpaste and it is therefore suggested that the sustained release of both fluoride and zinc ions from the bioactive glass in a toothpaste formulation may deliver a therapeutic effect in vivo.