Objectives: Various adhesive systems have been developed, such as phosphoric acid, self-etching, and dental laser-treatment, to use to modify the complex dentinal structures. Laser irradiation has been recognized as a promising method in dental applications of caries prevention. The aim of this study was to investigate the effect of different treatment methods on shear bond strength between resin composite and dentin. Methods: Freshly extracted human molars were sectioned to expose dentin surface, followed by polishing up to 600-grit SiC sandpaper. Four different treatments including phosphoric acid (Scotch Bond, 3M), Liner Bond II (Kuraray, Osaka, Japan), SE Bond (Kuraray) and Nd:YAP laser irradiation (Lokki, France) were carried out. Some specimens were assigned into three groups, NaOCl, EDTA, and phosphoric acid when laser irradiation was conducted previously. All specimens were evaluated using shear bond strength test (EZ test, Shimadzu, Japan) at 0.5 mm/min until failure. Fracture surfaces were examined by scanning electron microscope. Results: The morphologies of dentin surfaces essentially depended on the surface techniques. Laser irradiation could seal the dentinal tubule openings. After conventional phosphoric acid processing, the diameter of the tubules on the dentin surface were opened and enlarged to approximately 5 micro twice more than those for untreated dentin. Shear strengths of phosphoric acid, Liner Bond II, SE Bond, and Nd:YAP laser-treatment dentins were 18.9, 11.5, 15.1, and 13.5 MPa, respectively. Secondary-treatment groups with NaOCl, EDTA, and phosphoric acid after laser irradiation became 13.9, 14.9, and 16.7 MPa of bond strength, respectively, without statistical difference (p > 0.05). There were not significantly different among laser and self-etching groups (p > 0.05). Fracture observation indicated that failure mostly appeared at the interface between composite resin and dental specimen. Conclusions: Laser irradiation can effectively seal the dentinal tubules with a comparable shear strength to those acquired using the self-etching system.

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