Shear Bond Strength of Repaired CAD/CAM Resin-Based Composite Materials Submitted to Er:YAG Laser Treatments at Different Powers

This study aimed to investigate the effects of different powers of Er:YAG laser irradiation on the shear bond strength (SBS) of repaired CAD/CAM resin-based composite materials. A total of 180 CAD/CAM resin-based composite specimens (5 x 5 x 2 mm) were obtained (Shofu Block HC-SB; Grandio Blocs-GB). They were allocated into six groups according to surface pretreatment methods: no surface pretreatment (control), hydrofluoric acid (HF), diamond bur and 3 W, 5 W, and 7 W Er:YAG lasers (20 Hz) (n = 15). Silane and universal adhesive were applied. The repair procedure was completed with nano-ceramic composite resin (Ceram-X Sphere TEC-One). The samples were thermocycled for 10,000 cycles (5-55 degrees C). The SBS was evaluated with a universal test machine (1 mm/min). A 3D optic profilometer was used to assess the surface topography. Statistical analysis was performed with a two-way ANOVA and Bonferroni tests (p < 0.05). For SB samples, HF and diamond bur caused significantly higher SBSs than 3 W and 7 W lasers, while for GB samples, they led to a significantly higher SBS than all laser treatments. For SB samples, the 5 W laser led to the highest SBS, while for GB samples, the 7 W laser caused the highest SBS (p < 0.05). For both blocks, adhesive failure was more common for the 3 W laser, and a decrease in adhesive failures and an increase in mixed failures were observed with increasing laser irradiation. The 3D optic profilometer revealed that smoother surfaces were obtained with the 3 W laser than other laser irradiation at different powers. Pretreatment with increasing Er:YAG laser powers led to similar bond strengths to hydrofluoric-acid- and diamond-bur-treated CAD/CAM resin-based composite materials. A more powerful laser treatment is required to provide a higher bond strength for restorative materials containing a higher inorganic ceramic content.