Multi-component SiO2-P2O5-Na2O-K2O-CaO-SrO-ZnO-CaF2-SrF2 bioactive glass with a 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 Ca_0.5Sr_0.5F₂ peaks. By ¹⁹F MAS-NMR analysis, fluorapatite (FAp) and Sr-FAp were detected for F9, F13 and F17. For F32, only Ca_0.5Sr_0.5F₂ 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 Ca_0.5Sr_0.5F₂, which could guide synthesis of formulations to be used in dental materials with enhanced properties.