On the dissolution/reaction of small-grain Bioglass 45S5 and F-modified bioactive glasses in artificial saliva (AS)

The reaction of small-grain Bioglass^® 45S5 in artificial saliva (AS), to produce a layer of hydroxy-apatite (HA) and/or hydroxy-carbonate apatite (HCA), has been studied and compared to the results obtained in a simple buffered solution (TRIS). Some potentially bioactive glasses based on the composition of Bioglass^® and containing CaF₂ (HCaCaF₂ 5% and HNaCaF₂ 5%) have also been studied, in order to analyze the effects/changes produced when a F-containing glass surface is contacted with AS. The insertion of fluorine has been proposed to improve bioactive glass bone-bonding ability, and to parallel fluorine-containing glass-ceramics currently used in dentistry. ICP-OES analysis of the solution, and FTIR spectroscopy of the solid samples provided compositional information on the stages of reaction. These data were integrated with XRD and the textural and morphological data, obtained by specific surface areas determination and TEM-EDS measurements. In the case of Bioglass^® 45S5, a comparison at corresponding reaction times indicates that the precipitation of an amorphous Ca-phosphate phase is faster in AS, but the crystallization of HA/HCA is delayed in AS with respect to the TRIS solution. For fluoride-containing glasses, the sample HCaCaF₂ 5%, in which CaF₂ replaces part of CaO, possesses the fastest rate for HA/HCA crystallization (1 week) in AS. Some lines of interpretation for these results are proposed.