Objective: To portray and assess the interfacial morphology achieved with self-etching systems in dentin under observation by scanning electron microscopy. Method and Materials: Ten caries-free extracted erupted human third molars were used in this study. The occlusal enamel was removed, and 10 dentin disks with a thickness of 800 ± 200 µm were obtained by slow-speed sectioning with a diamond saw parallel to the occlusal surface. A standard smear layer was created on the occlusal surface by wet sanding with 600-grit sandpaper for 60 seconds. The dentin disks were randomly assigned to one of the systems: AdheSE (Ivoclar Vivadent), Optibond Solo Plus—Self-Etch (Kerr), Tyrian SPE (Bisco) as self-etching primers, and Adper Prompt Self-Etch (3M Espe) and One-Up Bond F (Tokuyama) as self-etching adhesives. All systems were applied according to the manufacturers’ instructions. After application of the adhesive systems, a 1.0-mm-thick layer of a flowable composite resin (Filtek Flow; 3M Espe) was applied to the treated dentin surface and light cured for 40 seconds. The specimens were then processed for observation by scanning electron microscopy. Results: All self-etching systems achieved the formation of sealed interfaces and hybridized areas with variable extents except for the self-etching adhesive One-Up Bond F, which showed some gap formation and poor hybridization. Optibond Solo Plus—Self-Etch presented a more consistent adhesive interface with thicker hybrid layers, numerous resin tags, and lateral branches. Conclusion: Regarding the micromorphology aspect, Optibond Solo Plus—Self-Etch showed the finest result, while One-Up Bond F was not able to produce a satisfactory ultrastructural morphology. (Quintessence Int 2007;38:92.e112–119)

Key words: adhesive, dentin, hybrid layer, interfacial morphology, scanning electron microscopy, self-etching primers