The Er: YAG laser system is applied either as a more comfortable alternative to conventional mechanical cavity preparation, or as an adjunctive method performed at the same time. However, discoloration of the dentin margin of the cervical cavity could be a problem. The purpose of this study was to evaluate the improvement of resin bond strength to Er: YAG laser-irradiated dentin with mechanical processing. Extracted bovine dentins were cut at the cervix, ground the exposed coronal dentins from 180-up to 600-grid SiC paper disc, and the ground surfaces were then uniformly irradiated with the Er: YAG laser. The laser-treated surface was then stained with a caries detector. The stained region was removed with mechanical dentin-surface processing (with a hand excavator, an ultrasonic scaler, and a dental polishing brush). After processing, the surface was etched with an aqueous solution of 10% citric acid/3% ferric chloride (10-3). A PMMA rod was bonded to the etched dentins with 4-META/MMA-TBB resin (Super Bond C & B). The bonded teeth were then cross-sectioned to make 2.0-mm-thick bonded dentin slabs, which were trimmed to prepare a miniaturized dumbbell-shaped specimens. After storage in water at 37°C for one day, the tensile bond strength was measured, and we evaluated the fracture mode after the tensile testing, by scanning electron microscopy (SEM). All of the teeth from which the stained region detected by the caries detector had been removed, had superior bond strength compared with non-processed teeth in which the stained region was left intact. In particular, cohesive failure in resin was observed in the groups in which the stained region was removed with the dental polishing brush or the ultrasonic scaler, by SEM evaluation. These results suggested that removal of the Er: YAG laser-affected dentin surface with a dental polishing brush or an ultrasonic scaler can resultin a good dentin surface for resin bonding.
