Novel fluoride and strontium-containing bioactive glasses for dental varnishes-design and bioactivity in Tris buffer solution

Abstract Objective The objective of this study was to establish the overall remineralizing potential of bioactive glasses which were specifically designed to be incorporated in dental varnishes. This study evaluates the in vitro ability of bioactive glasses (BAGs) to release ions including: fluoride, calcium, strontium and phosphate and to form apatite when immersed in Tris buffer solution, and also investigates the effect of increasing strontium substitution for calcium on remineralization potential. Materials and methods A melt-derived bioactive glass series was formulated (SiO2–Na2O–CaO–P2O5-CaF2) with progressive (0–100%) replacement of calcium (Ca) with strontium (Sr) and prepared. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) were utilised before and after immersion for specific time periods (0, 3, 6, 24, 72, 168 h) in 50 ml Tris buffer solution at 37 °C. A fluoride-ISE was used to measure the concentration of fluoride, whilst inductively coupled plasma–optical emission spectroscopy (ICP-OES) was used to measure the concentration of phosphorus, calcium and strontium in the solutions. Results The FTIR and XRD data indicated the amorphous nature of all unreacted bioactive glasses, except for the high Sr-substituted glasses, which crystallised to fluorapatite. Degradation of all the glass powders resulted in fluoride, phosphate and calcium/strontium ion release. All the glasses formed apatite on immersion. Ion release enhanced significantly in the three compositions with 50% SrO substituted for CaO, while calcium ion release was greater for low SrO substitutions. Conclusion Ion release data obtained for the new compositions of novel bioactive glasses to be incorporated into varnishes have promise in the prevent and/or treatment of white spot lesions through the release of fluoride, phosphate and calcium/strontium.