Remineralisation of fluorapatite from bioglass by solid-state nuclear magnetic resonance

Objectives: The aim of this study was to provide a structural and kinetic understanding of the formation of biomimetic apatite from the fluoride containing bioactive glasses for remineralising tooth pastes. Methods: The dissolution and fluorapatite formation from fluoride containing glasses in Tris buffer solution with pH 7.4 have been investigated. The time evolution of degradation and remineralisation of apatite have been followed by 31P and 19F solid-state NMR spectroscopy. Results: 31P and 19F solid-state NMR results on the bioactive glasses soaked in Tris buffer solution show the gradual atomic rearrangement around phosphorus and fluorine. Presence of fluoride in glasses leads to formation of fluorapatite instead of hydroxylapatite from the bioactive glass. 19F solid-state NMR is the only technique that allows to detect fluorapatite and distinguish it structurally from hydroxylapatite. Direct quantification of the NMR spectra gives clear information on rate of glass dissolution and fluorapatite formation. Variation in fluoride content in the bioactive glass has an effect on the formation of the fluorapatite. These results are compared with the results for the lower phosphorus containing glasses. The reactions proceed faster when phosphorus present in high concentration in bioactive glass. Conclusions: Fluoride and high phosphorus contents in the bioactive glasses promote the rapid formation of fluorapatite. There is an optimum concentration of fluoride in the glasses promoting rapid remineralisation and fluorapatite formation.