Effect of Er:YAG laser pulse duration on the shear bond strength of bleached dentin

The influence of different Er:YAG laser pulse durations on the shear bond strength (SBS) of bleached dentin was investigated in this study. In total, 176 crowns of extracted human premolars were cut horizontally, embedded and ground to expose the sound dentin. Of these, 132 specimens were bleached with 12% hydrogen peroxide (HP) and divided into three groups, irradiated by an Er:YAG laser with different pulse lengths of 50 µs super short pulse (SSP), 100 µs moderate short pulse (MSP) and 300 µs short pulse (SP), respectively. The energy density of the three groups was the same at about 15.73 J cm−2 for each. Then, each group was further divided into two subgroups according to whether it had been etched with 37% phosphoric acid or not. The control group (N = 22) was bleached and etched with acid while the blank group (N = 22) was just etched with acid. The surface morphology of the dentin was observed using scanning electron microscopy (SEM). The SBS of the composite resin to the conditioned dentin was tested with a universal testing machine. It was found that the SBS of the dentin significantly decreased after bleaching treatment, while it was possible to restore it using Er:YAG laser irradiation. Lasers with various pulse durations led to different surface morphologies but had no effect on the SBS. The SSP laser was more suitable on account of it resulting in less thermal damage, and additional acid etching was not necessary for the irradiated bleached dentin in the clinic because it could not further improve the SBS value.