Microtensile bond strength of dual-polymerizing cementing systems to dentin using different polymerizing modes

Statement of the problem: The effectiveness of bond strength using dual-polymerizing cementing systems ([DCSs] defined as the combination of dual-polymerizing bonding agents and resin cements) used with indirect restorations has not been evaluated when used solely with the autopolymerizing mode. Purpose: This study evaluated the in vitro microtensile bond strength (MTBS) of fourth- and fifth-generation DCSs with indirect composite restorations either light polymerized or autopolymerized. Material and methods: Occlusal dentin surfaces of 48 human third molars were exposed and flattened. Teeth were assigned to 8 groups (n = 6) according to the DCS and polymerizing modes: All-Bond2/Duolink (AB2), Optibond/Nexus2 (OPT), Bond1/Lute-it (B1), and Optibond Solo Dual Cure/Nexus2 (SOLO). Bonding agents were applied to dentin surfaces and left in the unpolymerized state. Resin cements were applied to prepolymerized resin discs (2 mm thick/Z250), which were subsequently bonded to the dentin surfaces. The restored teeth were light polymerized according to manufacturers' instructions (PP/XL 3000) or allowed to autopolymerize (AP). Restored teeth were stored in water at 37°C for 24 hours and were both mesio-distally and bucco-lingually sectioned to obtain multiple bonded beams (1.2 mm² of cross-sectional area). Each specimen was tested in tension at a crosshead speed of 0.6 mm/min until failure. Data (MPa) were analyzed by 2-way analysis of variance and the Tukey post hoc test (α = .05). Failure patterns of tested specimens were analyzed using scanning electron microscopy. Results: The mean (SD) MTBS values (MPa) were: AB2/PP: 36.9 (6.5); AB2/AP: 32.7 (7.3); B1/PP: 38.2 (7.0); B1/AP: 13.0 (4.2); SOLO/PP: 33.2 (7.2); SOLO/AP: 23.4 (3.4); OPT/PP: 30.8 (7.5); OPT/AP: 13.1 (5.8). The AP groups showed significantly lower MTBS than the PP groups (P<.0001), except for AB2, which showed no difference between polymerization modes (P=.2608). Conclusion: The autopolymerizing mode of some dual-polymerizing cement systems may not be effective in promoting bond strength.