Method: Dentin-composite disks (f5mm×2mm) were prepared with bovine incisors and the composites Z100TM or FiltekTMLS (3M-ESPE); n = 6 per group. All disk surfaces, except one side of the composite, were covered with nail varnish to prevent large-scale dentin demineralization while allowing the composite-dentin interface to be challenged. A Basal Mucin Medium (BMM) containing hog gastric mucin was used as the medium and its pH was adjusted by 1N HCl. Previously, the disks were subjected to biofilm challenge in a CDC bioreactor with sucrose pulsing (5 times/day, pH 4.5) to simulate the oral environment. In this work, they were first incubated at pH 7.0 for 48h at 37 °C, and then subjected to pH 4.5 for 24h to simulate the biofilm challenge with equivalent duration. A control group was run at pH 7.0 for 72h. All the disks were then fractured under diametral compression. Fracture surfaces were examined using SEM/EDS to assess interfacial degradation. ANOVA was used to assess the significance of differences in fracture loads.
Results: Both the LS and Z100 groups showed demineralization of up to 40 µm deep. Under load, Z100 specimens predominantly failed at the adhesive-composite interface, while LS specimens exhibited both adhesive-composite and adhesive-dentin interfacial failures. Significant bond strength reduction (10%, p<0.05) was observed in disks restored with Z100 compared to the control. The degree of dentin demineralization and bond strength reduction were similar to those obtained with biofilm challenges.
Conclusion: The static chemical model produced similar interfacial degradation, in terms of demineralization and bond strength reduction, in dentin-composite specimens as the more representative biofilm model.