The consumption of BisGMA biodegradation products by oral bacteria

Background: In vitro work has shown that the composite resin monomer, bisphenylglycidyl dimethacrylate (BisGMA) biodegrades into methacrylic acid (MA) and bishydroxypropoxyphenylpropane (BisHPPP) by human saliva-derived esterases (HSDE), and these products can modulate bacterial growth rates. Objectives: To determine the effect of BisHPPP and MA on cell viability and the relative consumption of these products by S. mutans NG8 at bacterial levels characteristic of high caries risk patients. Methods: Mid-log phase S. mutans were centrifuged, the pellet washed in D-PBS (pH 7.0) and reconstituted in D-PBS to 10⁶ CFU/ml. 2.0mL aliquots of S. mutans solutions were prepared with no products (control), 0.1mM MA or 0.1mM BisHPPP, corresponding to in vitro degradation product levels produced in human saliva incubations with composites. After 0, 2, 4, 6, 8, 10, and 20 hours incubation (37°C, 5% CO₂), samples were removed for bacteria counting and high performance liquid chromatography analysis of MA and BisHPPP. Results: A 50.6% reduction in S. mutans counts was observed with MA within minutes. After 2 hours, a 98.8% and 65.5% reduction in cell counts was demonstrated in MA and BisHPPP groups, respectively, versus control. The longer survival time for BisHPPP, might suggest that MA is more readily consumed, possibly due to the difference in molecular size and solubility. However, BisHPPP and MA levels in all the incubation solutions showed no significant change over time, indicating that the degradation product levels saturated bacteria interactions. Conclusion: Biodegradation products formed at degrading composite surfaces showed an inhibitory effect on S. mutans viability, and the relative amounts of product required to induce this effect was lower than 0.1mM. These findings are relevant to clinical practice, as the group’s recent work demonstrates degradation of commercial composite resins by HSDE at the composite-tooth interface – a major site of recurrent decay in such restorations. Acknowledgements: CIHR