Purpose: To compare the 24-h microtensile bond strength of a microfilled hybrid composite to the same material after mechanical and/or chemical treatment and assess the effect of oxygen inhibition on the composite-composite bond. Materials and Methods: Forty composite cylinders of Gradia Direct Anterior (GC) were prepared and stored 24 h prior to the following surface treatments: 50-µm aluminum oxide air abrasion and 37% phosphoric acid etching (group 1); hydrochloric acid and 6.9% hydrofluoric acid etching (group 2); diamond bur roughening and 37% phosphoric acid etching (group 3); diamond bur roughening (group 4). In all groups, Prime & Bond NT (Dentsply De Trey) was applied and light cured in air or under a nitrogen atmosphere, prior to layering a buildup of the repairing resin composite. Microtensile bond strength measurements were performed. Data were statistically analyzed with two-way ANOVA and Tukey's test (α = 0.05). Results: The curing atmosphere did not significantly influence the interfacial strength (p 0.05). Surface treatment significantly affected the composite-composite bond (p > 0.05). Air abrasion, regardless of curing atmosphere, resulted in the strongest bond (p 0.05). The other treatments were comparable. Conclusion: Air abrasion and the application of a bonding agent offer satisfactory bond strengths for composite repair. The oxygen inhibition layer on a light-cured adhesive is not crucial to the success of the 24-h composite-composite bond. Keywords: composite repair, surface treatment, oxygen-inhibited layer, microtensile bond strength.