Multi-component SiO2-P2O5-Na2O-K2O-CaO-SrO-ZnO-CaF2-SrF2 bioactive glass with lower fluoride content can form strontium-containing fluorapatite: a 19F MAS-NMR analysis

This study aimed to reproduce multi-component glasses with varying concentrations of fluoride [F] and to investigate if Sr-containing apatite (Sr-Ap) or SrF2 would be formed when the glasses were immersed in Tris buffer for 24 h and one week. Multi-component SiO2-P2O5-Na2O-K2O-CaO-SrO-ZnO-CaF2-SrF2 glasses with 9, 13, 17 and 32 mol% of [F] (named F9, F13, F17, F32 and F32sq) were prepared, and their degradation and Ap formation were investigated using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and 19F magic angle spinning-nuclear magnetic resonance (MAS-NMR) analysis before and after immersion in Tris buffer for 24 h and one week. The pH changes and the [F] released were also measured. Only F9, F13 and F17 produced Ap detected by FTIR spectroscopy. After one week, Ap and CaF2 diffraction peaks were detected for F9, F13 and F17; F32 and F32sq presented Ca0.5Sr0.5F2 peaks. By 19F MAS-NMR analysis, fluorapatite (FAp) and Sr-FAp were detected for F9, F13 and F17. For F32, only Ca0.5Sr0.5F2 was detected after one week. F32sq presented the same species before and after immersion with varying intensities. All glasses increased the pH of the solution and released [F] proportionally to their composition. In conclusion, despite all multi-component bioactive glasses increasing the pH of Tris buffer and releasing [F], only those with lower [F] formed Sr-FAp instead of SrF2 or Ca0.5Sr0.5F2, which could guide synthesis of formulations to be used in dental materials with enhanced properties.