Compatibility of Self-etch Adhesives with Chemical/Dual-cured Composites – Two-step vs.Single-Step systems

Self-etch adhesives are classified into two-step, self-etching primers that require the use of a bonding resin to couple composites to the primed dentin, and single-step systems that etch, prime and bond simultaneously. Microtensile bond strengths (ETBSs) produced by single-step, self-etch adhesive-bonded dentin to chemical-cured (cc) composites were inferior to light-cured (lc) composites. Objectives: This study tested the null hypothesis that two-step, self-etch adhesives exhibit no difference in ETBS when a chemical/dual-cured (c/d-c) composite is activated using lc or cc mode. Methods: Flat hydrated dentin from human third molars were bonded using two two-step systems (Clearfil SE Bond [SE], Kuraray; and Tyrian/One-Step Plus [TO], Bisco) and two single-step system (Xeno CF2 Bond [CF], Dentsply-Sankin; Experimental RZII [RZ], Sun Medical). For ETBS evaluation, a c/d-c composite (Bis-Core, Bisco) was coupled to bonded hydrated dentin using lc or cc mode, with the former hand-mixed in the same manner as the latter. For TEM, a lc microfilled composite (Metafil CX, Sun Medical) and an experimental cc composite of the same composition (Sun Medical) were used. Specimens were immersed in an ammoniacal silver nitrate tracer before TEM processing and examination of unstained, undemineralized sections . Results: One-way ANOVA and Tukey's test of the ETBS results (MPa; P<0.001) were: SE-lc (54.9±8.0)^A; SE-cc (55.0±5.7)^A; TO-lc (53.0±7.7)^A; TO-cc (49.8±7.4)^A; CF-lc (48.8±9.3)^A; CF-cc (7.1±7.0)^D; RZ-lc (41.6±4.4)^B and RZ-cc (21.0±4.8)^C. Premature failures were only observed in X2-cc during beam preparation for ETBS testing. TEM revealed the presence of water trees and silver deposits along the adhesive-composite interface that were responsible for the low bond strength in X2-cc. Conclusion: Unlike single-step systems, two-step, self-etch adhesives are compatible with c/d-c composites, due to the presence of a thicker coupling bonding resin layer that is probably less permeable and comparatively more hydrophobic than interfaces bonded with a single-step system.