Introduction: In order to increase the bonding strength of the composite resin cements to the indirect composites, experiments such as the creation of surface roughness with sandblasting, acid-etching, silane application, laser, etc. have been carried out. However, there is no consensus about the results. Therefore, the purpose of this study was to investigate the effect of Er: YAG and Nd: YAG lasers and acid etching on microshear bond strength of an indirect composite resin. Methods: After making 30 blocks of Gradia indirect composite (GC/Japan), three groups were considered (10 each): A(Er:YAG), B(Nd:YAG) and C (control, without interfering laser). Phosphoric acid (40%) was applied on half of the subjects in each group. Thereafter, 4 columns of the Panavia F2 resin cement were made on top of each block of composite. The micro-shear bond strength rates were examined by MTD-500(SD Mechatronik-Germany )with the cross head speed of 1mm/min). The data were analyzed by the t-test, one way /two-way ANOVA and the Post-Hoc analyses. Results: There was a significant increase in the bond strength in the laser groups, Er:YAG(P: 0.01) and Nd: YAG(P: 0.01), compared with the control group(P:0.94). The lasers alone (P<0.001) and the combination of the laser and acid-etching (P: 0.001) had significant effects. Overall, the effect of Er:YAG without acid-etching was more than all the other groups. Conclusion: The two Er:YAG and Nd: YAG lasers increased the bond strength. Though etching alone had no significant effect, the application of the laser Nd:YAG with etching increased the bond strength.

Keywords: Acid-Etching; Er:YAG laser; Indirect composite; Nd:YAG laser; Micro shear bond strength

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