Performance of Universal Adhesives in Composite Resin Repair

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. $1\text{mm}\times 1\text{mm}\times 8\text{mm}$ 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.