RESUMO
Aim: The objective of this in vitro study was to evaluate the bond strength of universal adhesive systems in self-etch and etch-and-rinse modes at the repair interface between aged and new composite resins. Materials and Methods: Composite resin (Filtek Z250) was thermocycled to represent aged composite resin to be repaired. New composite resin was placed over the aged substrate after surface conditioning: NC (negative control, no surface treatment), A (adhesive only), SBM (Scotchbond Multi-Purpose in etch-and-rinse mode), CSE (Clearfil SE Bond in self-etch mode), SBU (Single Bond Universal), ABU (All Bond Universal), and TBU (Tetric N-Bond Universal). Universal adhesives (SBU, ABU, and TBU) were applied both in etch-and-rinse and self-etch modes. 1 mm × 1 mm × 8 mm beams were sectioned, and microtensile bond strength was measured after 24 hours of water storage and 10,000 thermocycling processes (n = 20/group). The fracture surfaces were observed with a scanning electron microscope to evaluate the failure pattern. Results: The repair bond strength between the old and new composite resins was material-dependent. Universal adhesives significantly improved the repair bond strength (p < 0.05), while no significant difference was observed between the etch modes (self-etch or etch-and-rinse) for each universal adhesive (p > 0.05). Thermocycling significantly reduced the bond strength in all groups (p < 0.05). Conclusion: Universal adhesives in both etch-and-rinse and self-etch modes outperformed the conventional 3-step etch-and-rinse and 2-step self-etch adhesive systems in terms of resin repair bond strength.