Bonding of mild self-etching primers/adhesives to dentin with thick smear layers

Purpose: To compare the microtensile bond strength (μTBS) and the ultrastructure of resin-dentin interfaces of four self-etching systems that were applied to dentin with thick smear layers. Methods: Human third molars were ground with 180-grit silicon carbide papers to expose deep coronal dentin. A 3-mm vertical slit was made along the diameter of each tooth to fit a glass cover slip, dividing each tooth into two bonding surfaces. Two 2-step, self-etching primers (ABF experimental system and Imperva Fluoro Bond) and two single-step, self-etching adhesives (One-Up Bond F and AQ Bond) were examined. Adhesives were applied to one side of the teeth passively, and to the other side with continuous agitation for the same self-etching period. Incremental composite buildups were performed and beams with cross-sectional areas of 0.81 mm² were prepared for μTBS evaluation. Demineralized, bonded specimens were processed for TEM examination. Results: Two-way ANOVA showed that both the adhesive type and the application mode significantly affected μTBS results. However, the interaction of these two factors was not statistically significant (P> 0.05). For each adhesive, agitation produced significantly higher μTBS than passive application. With passive application, all systems diffused through thick smear layers and formed thin hybrid layers in intact dentin. With continuous agitation, smear layers were completely dispersed or dissolved, and thicker hybrid layers with upstanding collagen fibrils were observed.