Enhancement of bonding to enamel and dentin prepared by Er,Cr:YSGG laser

Background and Objective: Erbium lasers are potential tools to remove caries and dental hard tissue but bond strengths of composites to those preparations are reported to be lower than conventional methods. The purpose of this study was to evaluate the effect of mechanical excavation and/or chemical alteration on bond strength of composites to laser irradiated enamel and dentin. Materials and Methods: Seventy-two premolars were ground to obtain flat enamel (E, n = 36) or dentin (D, n = 36) surfaces in both buccal and lingual cusps, divided into: LaserExcavation (LEx), LaserNo-excavation (LNex), and Bur (B) groups. The laser groups were irradiated for 10 seconds by Er,Cr:YSGG laser [4.5 W, 60% air, 80% water (enamel) 3W, 60% air, 70% water (dentin)]. Irradiated surfaces in the excavation groups (Ex) were then mechanically smoothed with a dental excavator, prepared surfaces were then etched (37%H₃PO ₄) for 20 or 40 seconds (enamel) and 15 or 30 seconds (dentin), washed (20 seconds), adhesive was applied(Single Bond Plus), and light cured (20 seconds). A composite cylinder (Filtek Supreme Plus) formed, placed and light cured (40 seconds). The specimens were stored (37°C,48 hours), shear bond tested (1 mm/minute), and statistically analyzed (P < 0.05). Results: Mixed-model ANOVA showed significant differences between enamel (P = 0.0091) and between dentin groups (P = 0.0035). Tukey/Kramer showed mean shear bond strength (SBS ± SE) of EB40 (27.01 ± 2.38 MPa) was significantly higher than ELNoExc20 (14.39 ± 2.5 MPa) and ELExc40 (14.90 ± 2.28 MPa). Also DB30 (17.57 ± 1.67 MPa) and DLExc30 (18.6 ± 1.74 MPa) were significantly higher than DLNoExc15 (9.56 ± 1.86 MPa). Conclusion: Increasing the etching time up to 40 seconds or excavation of the laser prepared surface (but not the combination) may increase the bond strength to the level of conventional methods in enamel but excavation has a greater influence in dentin. Also the combination of both methods [excavation+longer etching time (30 seconds)] exhibit significantly better results in dentin. Mode of failure study showed mechanical excavation in both enamel and dentin can significantly reduce the cohesive failure in tooth structure.