Abstract: Objective: To investigate the bonding strength of different resin composites.  Methods: Methacrylate-based resin APX and silorane-based resin composite P90 were chosen in this study, with their corresponding adhesives Clearfil SE Bond (SE) and Filtek P90 System Adhesive (SA). The specimens were divided into three groups: (1) bulk group, filling each block with the same composite, then curing; (2) direct filling group, curing and polishing one composite, then filling a new composite directly; (3) bonding group, after curing and polishing one composite, conditioning the surface with adhesives, then filling a new composite. Cut each resin blocks into 1 mm×1 mm×14 mm each piece, detecting the microtensile strength, and analyzing by One-Way ANOVA and LSD. Results: (1) The microtensile strength of the bulk group was the highest. (2) In direct filling group, the microtensile strength of 4 subgroups showed no statistical significance with each other but lower than that of the bulk group. (3) In bonding group, the microtensile strength of repairing with APX was higher than that with P90. When repairing with same composite, the microtensile strength was higher if the resin type of substrates was same with restorations than that was different. The microtensile strength of adhesives SE was higher than that of SA. (4) The sorting of the microtensile strength: bulk>SE bonding APX>SA bonding APX>SE bonding P90=direct filling>SA bonding P90. Conclusion: Retention force is higher when substrates are repaired with methacrylate-based resins and corresponding adhesives. Retention force is lower when repaired with silorane-based composites and corresponding adhesives. Types of the substrate composites show no influence on the bonding strength.

Key words: Composite resins, Dental bonding, Dental stress analysis