Abstract: Objective: To investigate the influence of different concentrations and time of sodium hypochlorite (NaClO) solution on the resin-dentin bonding interface. Methods: Fifty human molars were selected to remove the tooth root and occlusal enamel, and exposed the dentin layer. A 4mm thick composite resin block was piled on the bonding surface. Teeth were sectioned vertically along two perpendicular directions into beams of approximately 1.0 mm² in cross-section. Fifty specimens were randomly divided into five groups: Group C (control), Group A1 (2.5%NaClO solution for 1 hour), Group A2 (2.5%NaClO solution for 2 hours), Group B1 (5.25%NaClO solution for 1 hour), and Group B2 (5.25%NaClO solution for 2 hours). The microtensile bond strength (μTBS) of five groups was tested. The stereomicroscope and SEM images of the fractured areas were used to determine the fracture mode of specimens. Results: The microtensile strength values of four experimental groups were significantly reduced compared to the control group with the increase of the concentration and the action time of NaClO solution. The action time of NaClO solution had no significant effects on the resin dentin bonding strength (P>0.05). The concentration of NaClO solution had no significant effects on the dentin bonding strength of the resin (P>0.05). However, there was an interaction effect between the concentration and action time of NaClO solution (P<0.05). Scanning electron microscope and stereo microscope showed that five groups of samples mainly fractured at the bonding interface. Conclusion: The micro-tensile bonding strength of the adhesion interface between dentin and resin can be reduced with the increase of concentration and action time of NaClO solution.

Key words: dentine bonding, sodium hypochlorite, microtensile bond strength, adhesive interface, two-way ANOVA