ABSTRACT
The bond strength of composite resins (CRs) to dentin is influenced by the interfacial microstructure of the hybrid layer (HL) and the resin tags (TAG). The contemporary self-etching primer adhesive systems overcame the inconvenient of the etch-and-rinse protocol. Studies, however, have demonstrated that HL thickness and TAG length vary according to the wetting time and additional use of acid-etching prior to self-etching primers. This study investigated the localized stress distribution in the HL and the dentin/adhesive interface. Two HL thicknesses (3 or 6 mum), two TAG lengths (13 or 17 mum) and two loading conditions (perpendicular and oblique-25°) were investigated by the finite element (FE) analysis. Five two-dimensional FE models (M) of a dentin specimen restored with CR (38 x 64 mum) were constructed: M1 - no HL and no TAG; M2 - 3 mum of HL and 13 ìm of TAG; M3 - 3 mum of HL and 17 mum of TAG; M4 - 6 mum of HL and 13 mum of TAG; and M5 - 6 mum of HL and 17 mum of TAG. Two distributed loadings (L) (20N) were applied on CR surface: L1 - perpendicular, and L2 - oblique (25°). Fixed interfacial conditions were assigned on the border of the dentin specimen. Ansys 10.0 (Ansys®, Houston, PA, USA) software was used to calculate the stress fields. The peak of von Mises (sigmavM) and maximum principal stress (sigmamax) was higher in L2 than in L1. Microstructures (HL and TAG) had no effect on local stresses for L1. Decreasing HL decreased sigmavM and sigmamax in all structures for L2, but the TAG length had influence only on the peributular dentin. The thickness of HL had more influence on the sigmavM and sigmamax than TAG length. The peritubular dentin and its adjacent structures showed the highest sigmavM and sigmamax, mainly in the oblique loading.