Biodegradation of the Composite Resin -Dentin Interface Contributes to Bacterial Microleakage

Objectives: Bis-GMA containing resins undergo biodegradation in human saliva, yielding Bis-hydroxy-propoxy-phenol propane (Bis-HPPP). The objective was to simulate this biodegradation at the composite resin-dentin marginal interface and to quantify that marginal breakdown through assessment of bacterial microleakage. Methods: Human dentin blocks were bonded (Scotchbond MP, 3M) to composite resin (Z250, 3M) under sterile conditions, producing standardized resin-dentin specimens. Samples were randomly assigned to three experimental conditions; no incubation, incubation in buffer, or incubation in a mixed pseudo-cholinesterase/cholesterol esterase enzyme solution (PCE-CE) in activity levels and profiles that match that of human saliva, for 7, 14, 30, and 90 days (pH=7.0, 37°C). Incubation solutions were analyzed for resin degradation products using high performance liquid chromatography combined with ultraviolet spectroscopy and mass spectrometry. Following incubation, specimens from all experimental conditions were suspended in a chemostat-based biofilm fermentor (CBBF). A mono-culture Streptococcus mutans NG8 biofilm was established on the specimens through continuous flow of medium (supplemented Todd Hewitt yeast extract, 4X diluted) for 7 days. Assessment of bacterial penetration along the resin-dentin interface was conducted through confocal laser scanning microscopy (CLSM) analysis combined with fluorescence staining. Results: Significantly higher amounts of Bis-HPPP were produced from resin-dentin specimens incubated for 30 (P<0.02) and 90 (P<0.01) days with PCE-CE solution, as compared to those incubated with buffer. Cumulative bacterial count and maximum depth of bacterial penetration along the interface was also found to be significantly higher among 30 day (P<0.05) and 90 day (P<0.001) PCE-CE incubated specimens, as compared to buffer-incubated groups. CLSM images taken of 30 and 90 day PCE-CE samples revealed progressive enhancement of regionally exposed zones of demineralized dentin and hybrid layer interruption. Conclusion: Human saliva-like esterase activities caused a decline in resin-dentin marginal integrity as indicated by the increase of bacterial microleakage along the resin-dentin marginal interface Acknowledgements: CIHR