Objectives: To evaluate the microtensile bond strength (µTBS) to dentin of 4 adhesive systems, the micromorphology of the adhesive/dentin interface and to compare the results to the µTS (cohesive strength) of sound dentin and resin composite. Methods: Occlusal surfaces of 24 extracted caries-free human molars were cut flat to expose the dentin surface. They were randomly assigned to 4 groups (n=6): Adper Scotchbond Multi Purpose Plus (MP), Adper Single Bond (SB), Clearfil Protect Bond (CP) and Adper Prompt (AP). Adhesive systems were applied and “crowns” were built using Z100. Other 5 human molars were sectioned to obtain square-shaped dentin blocks and 5 resin blocks were built using a composite resin, Z100. After storage in distilled water at 37oC for 24h, stick-shaped specimens were obtained for all groups (n=5) with 0.8 mm2 and subjected to µTBS e µTS test. Results were analysed using One-Way ANOVA and Tukey's test at p<0.05. The remaining bonded teeth were cut in two halves perpendicularly to the bonded interface and prepared for SEM analyses. Results: No significant differences were found among CP (45.6 ± 7.4 MPa), SB (43.3 ± 6.5 MPa) and MP (35.1 ± 5.9 MPa) (p>0.05). The lowest result was found for AP (27.4 ± 4.7 MPa), although not statistically from MP. Most specimens (89.4%) showed predominant adhesive failure. None of the systems tested reached the µTS values of dentin (108.5 ± 9.4 MPa) and Z100 (86.5 ±6.6 MPa). Conclusion: Bonded interfaces showed lower µTBS than those µTS of dentin and resin composite blocks. The all-in-one self-etching adhesive had the lowest µTBS.

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