ABSTRACT
<p><b>OBJECTIVE</b>To observe the microscopic characteristic of the bonding interface between resin cement and dentin before and after using Nd: YAG laser, and evaluate the effects of the Nd: YAG laser on the shear bond strength of 3 resin cements to dentin.</p><p><b>METHODS</b>30 human premolars were cut into nearly equal halves, prepared to expose the dentin and randomly divided into two groups: Laser group and control group. The teeth in the laser group were processed with pulse Nd: YAG laser (0.8 W, 10 Hz) for 25 s, and then the teeth were bonded using 3 resin cements (RelyX ARC, Panavia F and RelyX Unicem) to dentin. All teeth in the control group were directly filled with 3 cements. The shear bond strength of specimens was measured. Each fractured specimen was examined under dental microscope. And 6 new human premolars were prepared into standard bonding specimens. After 3 teeth processed with pulse Nd: YAG laser, all teeth were bonded using 3 resin cements. To observe the microscopic characteristics of the bonding interface between resin cements and dentin.</p><p><b>RESULTS</b>Nd: YAG laser on dentin surface could increase bond strength of Panavia F and RelyX Unicem (P < 0.05). And the laser could decrease bond strength of RelyX ARC (P < 0.05). Most of the fractured adhesive dentin surfaces were adhesive failure modes. Scanning electron microscope (SEM) observation demonstrated that Nd: YAG laser irradiation on dentin surface could decrease the hybrid layer and resin tags between the resin cements (RelyX ARC and Panavia F) and dentin. The interface between RelyX Unicem and dentin showed no obvious change, and resin tags were not observed.</p><p><b>CONCLUSION</b>Nd: YAG laser on dentin surface can increase bond strength of Panavia F and RelyX Unicem. Therefore, they can be used together in clinic.</p>