Apatite Formation on Resin-Modified Bioactive Glass Ionomer Cement

Bioactive bonding agents may help prevent decalcification of tooth surfaces during orthodontic treatment in patients with poor oral hygiene. Objective: We examined apatite growth on resin-modified bioactive glass ionomer cement(RMBGIC)containing various amounts and types of bioactive glass(BAG). Methods: BAG was prepared by sol-gel methods with three compositions: 65%SiO₂-31%CaO-4%P₂O₅(BAG-1); 75%SiO₂-21%CaO-4%P₂O₅(BAG-2); and 85%SiO₂-11%CaO-4%P₂O₅(BAG-3). Glasses were ground, micronized, and mixed with Fuji ORTHO LC powder in volume ratios of 1:1; 1:2; and 1:3. They were combined with standard RMGIC liquid and cured in cylindrical molds(5x2mm) pressed between two glass slides. Each disc was light cured for 40 seconds per side. Resulting RMBGIC was immersed in Simulated Body Fluid (SBF) for times of 1, 3, and 7 days with continuous agitation at 37°C. Apatite formation at each time point was assessed using powder KBr pellet FT-IR spectroscopy. Peaks near 565 and 603 cm^-1 were considered to be characteristic for apatite formation. Pure RMGIC discs were used as controls. Results: The FT-IR data show the initial development of PO₄^-3 on all of the RMBGICs at the day one time point. However, significant differences appear in the materials after 3 and 7 days of immersion. Specifically, BAG-3 at 1:1 and 1:2 ratios develops both peaks characteristic for CaP at day 3 of immersion. The other BAG mixtures do not result in these peaks until day 7, and then only with the 1:1 ratios. By day 7, all samples except 1:1 ratios had no detectable peaks. Scanning electron microscopy confirmed the altered appearance of these materials Conclusion: Our data suggests that there is an initial interaction between SBF and all of the RMBGICs. However, this initial deposition of phosphate is not stable and undergoes dissolution by day 7, except for in those samples with higher amounts of BAG. Acknowledgement: Funded in part by A.D. Williams Trust.