To evaluate the bond strength of a self-etching (Clearfil SE Bond) and a single-bottle (Excite) adhesive system using two cavity configurations (C-factors 5 and 1). Class I cavities (3 x 4 x 2.5 mm) were prepared in 28 extracted human molars using diamond burs under water cooling. Teeth were divided into 4 groups: G1: Excite, C-factor 5; G2: Excite, C-factor 1; G3: Clearfil, C-factor 5; G4: Clearfil, C-factor 1. To determine C-factor 5, systems were applied to all cavity walls according to the manufacturers' instructions (5 bonded, 1 unbonded). For C-factor 1, lateral walls were isolated using nail varnish, and adhesive systems were only applied to the pulpal floor (5 unbonded, 1 bonded). Cavities were restored using Tetric Ceram composite resin (Ivoclar/Vivadent), and bulk light cured for 40 s (500 mW/cm2). Teeth were stored in distilled water for 24 h at 37°C, and then sectioned using a diamond disk, yielding stick-shaped specimens with a bonded area of approximately 0.8 mm2. Specimens were submitted to the microtensile bond test at a rate of 1 mm/min speed in a universal testing machine. Resin-dentin bond strengths (MPa) were submitted to ANOVA and Tukey's tests (p 0.05) [number of specimens]: G1 = 35.8b [43]; G2 = 48.9a [55]; G3 = 45.9a [60]; G4 = 49.0a [53]. There was no statistically significant difference between adhesive systems for C-factor 1. For C-factor 5, Clearfil SE Bond produced higher values when compared to the other group. Changes in C-factor only affected the total-etch adhesive system tested. This may be a result of the different filler volume in the self-etching system, and not of the bonding technique itself.