Bond Strength and Interfacial Micromorphology of Etch-and-Rinse and Self-Adhesive Resin Cements to Dentin

Purpose: To evaluate the microtensile bond strength and interfacial micromorphology of indirect composite restorations to dentin using three commercial resin cements after 24 hours and 30 days of water storage. Materials and Methods: The medium dentin of third human molars was exposed (N = 30, n = 10 per group). Three commercial resin cements were used to cement indirect resin composite restorations to dentin: the auto-cured C& B Cement/All Bond 2, the dual-cured RelyX ARC/Adper Single Bond 2, and the self-adhesive dualcured RelyX Unicem. Teeth were sectioned after water storage at 37 degrees C (24 hours and 30 days) to obtain beams with a bonded area of 0.8 mm(2). The specimens were tested in a universal testing machine at a 0.5 mm/min crosshead speed. Scanning electron microscopic fractographic and interfacial micromorphology analyses were performed. Data were analyzed using two-way ANOVA and Tukey's test (alpha = 0.05). Results: Mean bond strength (MPa) after 24 hours: C& B Cement 19.5 +/- 3.8, RelyX ARC 40.8 +/- 9.4, RelyX Unicem 31.3 +/- 7.4; after 30 days: C& B Cement 24.5 +/- 5.1, RelyX ARC 44.2 +/- 8.5, RelyX Unicem 28.3 +/- 7.1. The mean bond strengths of both dual-cure cements were significantly higher than that obtained with C& B Cement after 24 hours. A significant increase in the bond strength of C& B Cement was verified after 30 days, reaching values statistically equivalent to those produced by RelyX Unicem and RelyX ARC. The self-adhesive cement preserved the same level of bond strength after 30 days. Fractographic analysis revealed a prevalence of cohesive fractures in the hybrid layer for C& B Cement, mixed (cohesive in the cement, hybrid layer, and adhesive) for RelyX ARC, and cohesive in the cement for RelyX Unicem. No distinguishable hybrid layer or resin tags were observed in the interaction of RelyX Unicem with dentin. Conclusions: The particular interaction of each cement with dentin results in specific bond strength and failure patterns that varied among groups in both evaluation times. Even though the self-adhesive cement tested exhibited no authentic hybrid layer, it was able to promote reliable adhesion with the underlying dentin.