Effect of Er:YAG Laser Irradiation with Various Power Levels on Shear Bond Strength of Repair to Aged Nanofilled Composite Resin

<b>Objectives:</b> The increasing applications of composite resins and the need for correction of defects developed over time call for strategies to increase the bond strength of new repair composite resin to old (aged) composite resin. Thus, this study aimed to assess the effect of erbium-doped yttrium aluminum garnet (Er:YAG) laser irradiation with various power levels on shear bond strength (SBS) of repair to aged nanofilled composite resin. <b>Materials and Methods:</b> Thermocycled disc-shaped (4.0×7.0mm) nanofilled composite resin specimens were randomly assigned to 4 groups (n=15): bur abrasion and 35% phosphoric acid (control group), irradiation of 1 W Er:YAG laser, irradiation of 2W Er:YAG laser, and irradiation of 4.5W Er:YAG laser. The SBS was measured after the application of repair composite and thermocycling. Specimens were observed under a stereomicroscope to determine the mode of failure. Atomic force microscopy (AFM) was used to assess the surface topography. Data were analyzed with one-way ANOVA, Games-Howell, and Fisher's exact tests (α=0.05). <b>Results:</b> The mean SBS in the 1W and 2W laser groups was significantly lower than that in the 4.5W laser and control groups (P<0.05). The difference in SBS of the 1W and 2W laser (P=0.999), and the 4.5W laser and control (P=0.999) groups was not significant. <b>Conclusion:</b> Er:YAG laser irradiation with 4.5W power yielded a SBS comparable to that of the control group and significantly higher than that of the 1W and 2W laser groups.