Bonding ability of three ethanol-based adhesives after thermal fatigue

Purpose: To study the effect of thermal fatigue on the μTBS and interfacial morphology of three ethanolbased etch-&-rinse 2-bottle adhesives. Methods: μTBS - 24 third molars were randomly assigned to one of three adhesive systems: (1) Adper Single Bond Plus (SBP, 3M ESPE); (2) Ambar (AMB, FGM); (3) Excite (EXC, Ivoclar Vivadent), and restored with a hybrid resin composite. For each adhesive, half of the specimens were thermocycled (TC) for 20,000 cycles (5-55°C) while the other half was kept in distilled water for 24 hours at 37°C (control). Specimens were sectioned in X and Y directions and the resulting sticks were tested to failure in tension mode at a crosshead speed of 1 mm/minute. Statistical analysis was computed using ANOVA and Tukey's post hoc for the μTBS; and non-parametric cross-tabulation with Chi-Square for the pre-testing failures at P< 0.05. Interfacial morphology - The occlusal enamel was removed from 12 extracted molars perpendicular to the long axis of the tooth. Teeth were equally assigned to one of the three adhesives and restored with a 1 mm-thick layer of a hybrid composite resin. A 2 mm-thick disk was sectioned from each specimen and cross-sectioned in two identical halves. Half of the each specimen was TC for 20,000 cycles (5-55°C) while the other half was kept in distilled water for 24 hours at 37°C (control). Specimens were chemically challenged and prepared for FESEM observation to observe the integrity of the hybrid layer before and after thermal fatigue. Micrographs were recorded digitally at standard magnifications and measurements were taken with the microscope embedded image software. Results: μTBS - SBP and AMB resulted in statistically similar mean μTBS regardless of thermal fatigue. EXC resulted in statistically lower mean μTBS than SBP and AMB for the control (P< 0.001) and for the TC specimens (P< 0.0001). Interfacial morphology - The hybrid layers of SBP and AMB were densely infiltrated without interfacial failure. For EXC, extensive areas of debonding were observed between the adhesive layer and the hybrid layer both for the control and the TC groups. Thermal fatigue did not influence the bonding ability of AMB and SBP, but was detrimental for EXC.