Performance of an Experimental Dental Composite Functionalized With a low Sodium Bioactive Glass.

Objectives: Conventional bioactive glass contains relatively high levels of sodium (24.5 mol% Na₂O) which compromises the primary function of bioactive restorative materials through water sorption during function leading to poor mechanical properties. This study aimed to evaluate ion release and flexural strength of an experimental composite functionalised with low-sodium bioactive glass fillers.
Methods: A low-sodium bioactive glass (G6), composed of (SiO2, P2O5, CaCO3, Na2O, CaF2, SrO, and MgO) with the following percentages respectively; (36.5, 5.5, 30, 4, 10, 10, and 4 mol%) was prepared using melt-quench technique and milled to <32 µm particles. A high sodium equivalent (G6-Na) was also prepared for comparison which contains 24.5 mol% Na2O. Both compositions were silanated (2%) and mixed with Bis-GMA/TEGDMA resin in 60:40 by weight. Standardised composite discs were prepared and immersed into three different solutions (Tris-Buffer (TB), Artificial Saliva (AS4), and (AS7) for eight timepoints (up to 12 weeks). At each time point, the discs were removed and assessed using Fourier-transform infrared spectroscopy (FTIR), X-Ray diffraction analysis (XRD) and the supernatant solutions were evaluated for ion release using ion-selective electrodes (ISE). Flexural strength testing was also performed after immersion in AS7 for 24 hours, 2 weeks and 1 month.
Results: Calcium and fluoride release was higher in acidic solution compared to neutral solutions throughout the study. A pH rise was noted within the first hour for all three solutions with a consistent rise in calcium and fluoride release. An opaque white precipitate indicated apatite formation as shown with FTIR and XRD. For G6-Na group, the reduction in flexural strength after immersion was statistically significant compared to G6 (p=0.031) using paired t-test.
Conclusions: A low-sodium bioactive glass filler has the potential to release calcium and fluoride ions which induce apatite formation while maintaining the flexural strength thereby prolonging the lifetime of the restoration.