Abstract: Objective：To investigate the marginal microleakage after cavity preparation by Er:YAG laser and conventional bur applying different adhesive systems, conditioning surface with acid etching or not. Methods: In the study, 50 primary teeth were divided into 5 groups. (1) Bur+etch-and-rinse system, (2) Bur+self-etching system， (3) Er:YAG laser+etch-and-rinse system, (4) Er:YAG laser+self-etching system, (5) Er:YAG laser+none-etched.  The class V cavities were all filled with composite resin. The microleakage tests were performed, observed and scored under stereomicroscope. Results: Bur+etchand-rinse group had higher microleakage than Er:YAG laser+etch-and-rinse group, and Bur+self-etching group had higher microleakage than Er:YAG laser+self-etching group（P<0.05）. There was no difference between Er:YAG laser+etch-and-rinse group and Er:YAG laser+self-etching group, while they had significantly lower microleakage than that of Er:YAG+none-etched group. Conclusion: Composite resin restoration showed less marginal microleakage when all-in-one self-etch system was used after irradiation by Er:YAG laser on primary teeth.

Key words: Laser therapy, Dental cavity preparation, Dental microleakage, Tooth, deciduous