OBJECTIVES: The aim of this study was to compare the interaction of dentin with 2 different self-etch resin bonding systems, as well as with a total-etch resin bonding system. METHOD AND MATERIALS: Nine recently extracted, unerupted third molars, roots, and occlusal thirds were used. A standardized smear layer was produced on the occlusal dentin surface exposed. The specimens were split into 3 groups of 3 specimens each, 1 group for each bonding agent: Clearfil Liner Bond 2, Prime & Bond 2.1, and Scotchbond Multipurpose (control group). After the tooth was briefly sprayed with an air/water mixture, 1 of the experimental adhesive systems was applied on the dentin surface. A 2-mm layer of composite was applied over the adhesive system layer. After 7 days in distilled water at 37 degrees C, the specimens were cross-sectioned perpendicular to the resin-dentin interface. The crosssections were mounted on aluminum stubs, etched with 2% hydrochloridric acid, and studied using scanning electron microscopy. A descriptive analysis of the images of the interdiffusion zone characteristics was done first. Afterwards, statistical analyses of the measurements of the interdiffusion zone structures-hybrid layer thickness, resin tags penetration, and adhesive layer thickness using analysis of variance, followed by "post hoc" test-were carried out to compare the bonding systems' interactions. RESULTS: The descriptive analysis of the self-etch bonding systems studied showed a good interlocking of Clearfil Liner Bond 2 with dentin, similar to Scotchbond Multipurpose and better than Prime & Bond 2.1. The analysis of variance, followed by the "post hoc" test, identified statistical differences just for the adhesive layer thickness that was thicker for Scotchbond than for Prime & Bond (P = .020). The "post hoc" test also showed a strong tendency to identify differences between the Scotchbond and the Prime & Bond groups (P = .062), and the Clearfil and the Prime & Bond groups (P = .069). CONCLUSION: Within the limitations of this study, Clearfil Liner Bond 2 produced the thickest hybrid layer with deepest tag formation and good interlocking with dentin, similar to the control. Statistical differences among the interdiffusion zone of the 3 bonding systems studied were identified just for the adhesive layer thickness, which was thicker for Scotchbond than for Prime & Bond.