Purpose: To assess microtensile bond strength of two universal adhesives with/without acid etching to enamel compared to Two-step self-etch system after thermocycling.
Materials and Methods: Fifty freshly extracted sound human third molars were disinfected, decoronated and sectioned mesiodistally to get 100 buccal and lingual halves. Enamel surface was ground by a diamond grit and smoothed with 600-grit silicon-carbide paper. Specimens were assigned into Five groups (n=20): G-Premio bond with/without etching, Single Bond Universal with/without etching and OptiBond XTR. Etching was done by phosphoric acid 37% for 20 seconds followed by rinsing and drying. Each adhesive was applied and then, a block of resin composite was built up. After storage in distilled water into incubator (24 hour /37˚C), half of the specimens of each group (n=10) was thermocycled. All specimens were sectioned into beams 0.9 mm2 to be tested until failure using universal testing machine. Failure mode was assessed with Stereomicroscope. Data were subjected to statistical analysis (p˃0.05).
Results: Universal adhesives with prior etching and Two-step self-etch system revealed microtensile bond strength mean values significantly higher than that of universal adhesives without etching (P0.05). All adhesives showed reduced microtensile bond strength after thermocycling. Mixed failure was predominant in universal adhesives with prior etching and Two-step self-etch system, however adhesive failure was observed with universal adhesives without prior etching.
Conclusions: Universal adhesives with prior etching had considerable improvements on Microtensile bond strength to enamel. Thermocycling negatively affected the bonding performance of universal adhesives to enamel.