Are self-adhesive resin cements a valid alternative to conventional resin cements? A laboratory study of the long-term bond strength

OBJECTIVES: The aim of the study was to test whether or not the shear bond strengths of six self-adhesive resin cements to dentin and to glass-ceramic, 24h and long-term-aged, are similar to the one of a conventional resin cement. METHODS: Human molars (N=168, n=12 per group) and silicabased glass-ceramic specimens (N=168, n=12 per group) were embedded in acrylic resin and randomly divided into 28 groups. The following resin cements were luted according to the manufacturers' instructions: Clearfil SA (CSA), G-Cem (GCM), SmartCem2 (SMC), SpeedCEM (SPC), RelyX Unicem (RXU), RelyX Unicem2 (RXU2) and Panavia21 (control group, PAN). Shear bond strength was measured initially (24h of water storage 37°C) and after aging (24,000 thermal cycles, 5/55°C). The failure types (adhesive, and cohesive) were evaluated after debonding. The shear bond strength values were analyzed using three-way and one-way ANOVA, followed by a post hoc Scheffé and two-sample Student's t-tests. RESULTS: RXU, RXU2 and GCM showed similar after 24h and aged shear bond strength to dentin as the control group. CSA, SMC and SPC exhibited significantly lower values. Before aging, none of the bond strength values to glass-ceramic differed significantly from the other. After thermocycling, GCM showed higher results to glass-ceramic than CSA, SMC, RXU2 and the control group. Analyzing failure types after spontaneous debonding and shear bond test at dentin, solely adhesive failures were found, while at glass-ceramic only cohesive failures occurred. CONCLUSION: Not all self-adhesive resin cements can be a valid alternative to conventional resin cements in order to bond silica-based glass-ceramics to human dentin