Method: Thirty six extracted human molars were flattened to obtain dentin surfaces. The dentin specimens were divided into nine groups according to the surface treatments. The dentin surfaces were irradiated with an Er:YAG laser with the combination of following parameters : (1) energy output: 200 mJ or 120mJ; (2) water cooling: 50 ml/min or 25 ml/min; (3) pulse duration: 100µs MSP (medium short pulse mode) or QSP (Quantum square pulse mode) and one group was not subjected to laser irradiation and served as control. The two-step self-etch adhesive was applied to dentin surfaces and composite resin build-ups were prepared. Two teeth of each group were used for μTBS and the rest was used for SEM examination before bonding agent application and after composite build-up process. Specimens were sectioned into serial 1-mm2 sticks and μTBS was measured in randomly selected ten sticks from each tooth (n=20). Failure modes were determined under a stereomicroscope. Results of μTBS were evaluated with analysis of variance (ANOVA) and post-hoc (Tukey-HSD) tests.
Result: The μTBS between the dentin and adhesive was affected by the output power of the Er:YAG laser (p<0.05), but not affected by the pulse duration or water cooling (p>0.05). The highest μTBS result was recorded for the MSP, 120mj and 25 ml/min water cooling applied group (19.1±4.0 MPa) and the lowest was recorded for the control group (7.3±2.7 MPa).
Conclusion: The Er:YAG laser irradiation increased the μTBS of the adhesive to dentin surface when compared with the results of self-etch adhesive alone. Among the Er:YAG laser irradiated surfaces, the highest μTBS result was achieved in low energy output and low water cooling applied group.