• Hill, R. G.
• Mneimne, M.
• Karpukhina, N.
• Shah, P.
• Chen, Xiaohui

Abstract

INTRODUCTION<br/>Fluoride containing bioactive glasses are attractive for incorporation into remineralising toothpastes for three reasons: (i) they form fluorapatite which is much more acid durable than hydroxycarbonated apatite; (ii) they release fluoride that is known to inhibit apatite dissolution and caries formation; and (iii) they have a more disrupted glass network with lower glass transition temperatures and should be softer and are therefore less abrasive towards enamel. <br/>Fluoride containing bioactive glasses were originally studied by Spilman and Hench1 in the 1970s but there has been increased interest in fluoride containing glasses in recent years including glasses with high phosphate2.<br/>Zinc Oxide has been incorporated into bioactive glasses3 and it is potentially attractive for use in toothpastes, since zinc salts are added to existing toothpastes where the zinc has a bacteriocidal action, an anti-caries action and an anti-gingivitis action.<br/>This study examines the influence of ZnO incorporation on the dissolution and apatite forming ability of a high phosphate fluoride containing bioactive glass. Since ZnO is thought to act as an intermediate oxide it has been substituted for SiO2 with additional CaO and Na2O to charge balance the ZnO4 tetrahedra and maintain a fixed network connectivity.<br/><br/>EXPERIMENTAL METHODS<br/>Bioactive 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.<br/><br/>RESULTS AND DISCUSSION<br/>The zinc free glass formed a fluorapatite (FAP) like phase in under two hours that was evident in the XRD patterns and FTIR spectra. The zinc containing glass did not show sharp XRD peaks of the apatite phase until 24 hours immersion and did not show the characteristic (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 less than 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 fluoride and phosphate content was not complete in 24 hours.<br/><br/>CONCLUSION<br/>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 the zinc containing bioactive glass can be incorporated as a desensitiser into remineralising toothpaste. Sustained release of both fluoride and zinc ions from the bioactive glass can deliver therapeutic effect via toothpaste.<br/><br/>REFERENCES<br/>1. Hench L.L. et al., US patent 4775646. 1988.<br/>2. Mneimne M. et al., Acta Biomater. 7:1827-1834, 2011.<br/>3. Linati L. et al., J Phys Chem B, 109:4989-4998, 2005.<br/><br/>ACKNOWLEDGMENTS<br/>Authors would like to acknowledge Dr Rory Wilson for XRD measurements, Dr Andy Bushby, Dr David Gillam and Dr Jonathan Earl for useful discussions.<br/>

Topics

• impedance spectroscopy
• phase
• x-ray diffraction
• zinc
• glass
• glass
• laser emission spectroscopy
• glass transition temperature
• Nuclear Magnetic Resonance spectroscopy
• atomic emission spectroscopy
• spinning