Purpose: To evaluate the effect of different silane agents and air-drying temperatures on the repair strength of a microfilled hybrid composite. Materials and Methods: Composite cylinders (8 x 4 mm) of Gradia Direct Anterior (GC, N = 36), stored in a saline solution at 37°C for 1 month, were sandblasted (50-μm aluminium oxide), cleaned (35% phosphoric acid) and randomly divided into six groups (n = 6). Two prehydrolyzed silane primers (Monobond-S, Ivoclar-Vivadent, Porcelain Primer, Bisco), a non prehydrolyzed silane primer (Porcelain Liner M, Sun Medical) and three silane/adhesive coupling agents (Porcelain Bond Activator-PBA/Clearfil New Bond, PBA/Clearfil SE Bond, PBA/Clearfil Tri-S Bond, Kuraray) were investigated. Silane-coated surfaces were air dried at two different temperatures (23°C and 38°C) and repairs (8 x 8mm) were fabricated (Gradia Direct Anterior). Unrepaired composite cylinders (8 x 8 mm, n = 6) were used as control to evaluate the cohesive strength of the material. Microtensile bond strength measurements (μTBS) were performed. Results: The silane agent applied (p < 0.001), the airdrying temperature (p < 0.001) and their interaction (p < 0.001) were significant factors (two-way ANOVA, Tukey test; p < 0.05). Silane primers achieved inferior μTBS when air dried at 23°C as compared to silane/adhesive blends. Warm air-drying was significantly beneficial to composite repairs mediated by silane primers. Comparable results were achieved by silane/adhesive couplings at 23°C and 38°C. At 38°C all the intermediate agents resulted in repair μTBS that were comparable to the 24-h cohesive strength of the composite (one-way ANOVA, Dunnett t-tests; p < 0.05). Conclusion: The chemical interactions between silane primers and compozite substrate may be optimized through warm airdrying. Silane/adhesive couplings were not influenced by the air drying temperature.

Keywords: silane, adhesive resin, warm air drying, composite repair, microtensile bond strength