Characterisation of a Bioactive SiO2-CaO-CaF2-Na2O Glass Used in Composites

Abstract

Objectives: To characterise the ion release, pH changes and apatite formation of a phosphate free bioactive glass.

Methods: A SiO₂-CaO-CaF₂-Na₂O glass was synthesized by a melt route with a composition close to the reactive glass in the commercial Cention N® composite. The glass was characterized after immersion in three media: Artificial Saliva pH4 (AS4) Artificial Saliva pH7 (AS7) and in a high phosphate artificial saliva at pH6.5 (AS6.5). The pH and fluoride release were measured using a pH meter and an ion selective electrode. The concentration of Ca, P, Na and Si were measured by ICP-OES. The glass powders after immersion were characterized by FTIR, X-ray powder diffraction and ¹⁹F MAS-NMR.

Results: The glass increased the pH in all three media. Fluoride was detected in all three media but was much higher in AS 6.5. Calcium fluoride formed in AS4 with a small amount of fluorapatite at long immersion times. Fluorapatite and calcium fluoride formed in AS7, whilst in AS6.5 fluorapatite formed. The ion concentrations in solution after immersion reflected the glass composition and the immersion media with fluorapatite being favoured by higher pHs and phosphate contents in the media.

Significance: The results demonstrated the ability of the glass to increase the pH and to form fluorapatite in phosphate containing media. This may explain the low incidence of secondary caries found in the commercial composite. Unlike the commercial composite evidence was found for the precipitation of fluorite, which will act to reduce the release of fluoride for preventing secondary caries.

Keywords: Bioactive Glass; Composite; Fluorapatite; Fluoride; Ion Release.