SEM evaluation of resin-carious dentin interfaces formed by two dentin adhesive systems

Objectives: We investigated the influence of dentin tubule direction and identifiable zone of carious dentin on the microstructure and the thickness of the hybrid-like layer (HL) formed by self-etch and etch-rinse adhesive systems.Methods: An etch-rinse and a self-etching adhesive were bonded to dentin carious zones divided into groups with parallel or perpendicular orientation relative to the dentin tubules at the resin-carious dentin interface (N = 5/variable). Bonds were prepared to each of the four zones of carious dentin apparent after staining with Caries Detector: pink, light pink, transparent and apparently normal; six non-carious third molars were controls. The microstructure and thickness of the HL were determined by SEM and compared using three-way ANOVA and Tukey's multiple comparisons (p < 0.05).Results: Etch-rinse controls gave thicker HLs than self-etching systems; orientation did not affect thickness for the self-etch system. Perpendicular orientations gave thicker HLs than parallel for the pink zone bonded with the etch-rinse system. For both adhesives, HL thickness in the pink zone was significantly greater than in light pink for the perpendicular group, but no significant differences were found among other variables. HL microstructure was more granular and rougher for the etch-rinse than for the self-etching system. Pores and cracks were obvious in the more demineralized zones. Resin tags were shorter and irregular in the transparent zone and often were completely absent in the outer demineralized zones (pink, light pink).Significance: Microstructure of bonded interfaces varies markedly depending on adhesive system, tubule orientation and carious zone.