Effect of thermocycling on the bond strength of composite resin to bur and laser treated composite resin

The objective of this study was to investigate the effect of two different surface treatments (Er:YAG laser and bur) and three different numbers of thermal cycling (no aging, 1,000, 5,000, and 10,000 cycles) on the micro-shear bond strength of repaired composite resin. Ninety-six composite blocks (4 mm × 4 mm × 1 mm) obtained with a micromatrix hybrid composite were prepared. The composite blocks were then randomly divided into four groups ( n = 24), according to the thermal cycling procedure: (1) stored in distilled water at 37°C for 24 h (control group), (2) 1,000 cycles, (3) 5,000 cycles, and (4) 10,000 cycles. After aging, the blocks were further subdivided into two subgroups ( n = 12), according to surface treatment. Bur and laser-treated composite surfaces were treated with an etch&rinse adhesive system. In addition, a microhybrid composite resin was bonded to the surfaces via polyethylene tubing. Specimens were subjected to micro-shear bond strength test by a universal testing machine with a crosshead speed of 0 and 5 mm/min. The data were analyzed using one-way analysis of variance and Tukey tests (α = 0.05) for micro-shear bond strengths. After conducting a bond strength test, it was found that the laser and bur-treated specimens had similar results. Aging with 10,000 thermocycles significantly affected the repair bond strength of composite resins.