Effect of the Nd:YAG and the Er:YAG Laser on the Adhesive–Dentin Interface: A Scanning Electron Microscopy Study

Abstract

This study analyzed the adhesive-dentin interface when Nd:YAG and Er:YAG lasers were applied to dentin. Lasers applied to dentin cause morphological changes of this tissue. Because adhesive systems bond to dentin through the hybrid layer, it is important to investigate the adhesive-dentin interface when dentin is irradiated with lasers. The occlusal dentin of 12 human molars was exposed and polished with 400 and 600 grit silicon carbide abrasive paper. Teeth were randomly divided into six groups: Group 1, adhesive system Adper Single Bond 2 (SB); Group 2, adhesive system Clearfil SE Bond (CSB); Group 3, Nd:YAG laser (60 mJ, 15 Hz, 0.9 W) and SB; Group 4, Nd:YAG laser (60 mJ, 15 Hz, 0.9 W) and CSB; Group 5, Er:YAG (200 mJ, 4 Hz, 0.8 W) and SB; Group 6, Er:YAG (200 mJ, 4 Hz, 0.8 W) and CSB. Blocks of composite resin were built upon the adhesive system. Tooth-resin sets were cut in a mesio-distal direction, resulting in four samples for each group. Surfaces were polished until 1200 grit silicon carbide abrasive paper, followed by diamond pastes. Samples were demineralized, deproteinized, dried, metalized, and evaluated by scanning electron microscopy. SB formed a thicker hybrid layer, with resin tags longer than CSB. Nd:YAG laser application on the dentin surface, prior to the adhesive procedures, resulted in a thinner hybrid layer with fewer resin tags. Er:YAG laser application on the dentin surface, prior to the adhesive procedures, did not allow the formation of a hybrid layer but formed resin tags. Nd:YAG and Er:YAG laser changed the adhesive-dentin interface.