Abstract: Objective To investigate the effects of different energies of Er: YAG laser pretreatment on the shear bond strength of self-adhesive resin cement .Methods Seventy extracted human molars collected in accordance with the inclusion criteria were randomly divided into 7 groups according to the different Er:YAG laser energy pretreatments on the dentin surface :Group A (control), GroupB(50 mJ,10 Hz),GroupC(100 mJ,10 Hz),GroupD(150 mJ,10 Hz),GroupE(200 mJ,10 Hz),GroupF(250 mJ,10 Hz),GroupG(300 mJ,10 Hz).Two teeth were selected randomly from each group and 3mm thick dentin slices cut from the teeth were observed under scanning electron microscopy after being pretreated according to the respective requirements .The remaining eight teeth were prepared into the consistent standards dentin surface after being embedded ,and then bonded with the self-adhesive resin cement RelyXTM Unicem and Everest ZS zirconia ceramic after pretreatment according to the respective requirements. 24h later, the shear bond strength was tested and a statistical analysis was performed. Result Scanning electron microscopy showed that the dentin surface morphology pretreated by Er：YAG laser changed into tough irregular one significantly, and the dentinal tubules became open without the smear layer. Peritubular dentin and intertubular dentin suggested demineralization and presented a better bonding surface in a appropriate energy range. The results showed that the Er：YAG laser pretreatment could enhance the bong strength of RelyXTM Unicem self-adhesive resin （P<0.01);there was significant difference between Group C、D、E and Group A（P<0.05).Conclusions The study shows that bond strength is closely related to the dentin bonding surface, and suitable energy of Er：YAG laser pretreatment can obtain better dentin bonding surface, improve the shear bond strength of the self-adhesive resin and dentin and zirconia ceramic.

Key words: Er：YAG laser , self-adhesive resin, SEM, shear bond strength