Effect of thermal cycling on enamel bond strength of single-step self-etch systems

This study investigated the influence of thermal cycling on the enamel bond strength of single-step self-etch adhesive systems. The systems used were Absolute, Clearfil tri-S Bond, G-Bond and One-Up Bond F Plus. Bovine mandibular incisors were mounted in self-curing resin, and the facial surfaces were wet ground with #600 SiC paper. Adhesives were applied on the prepared enamel surfaces and light irradiated according to each manufacturer's instructions. Resin composites were condensed into a mold (o4x2 mm) and light irradiated for 30 seconds. Thirty specimens per adhesive systems were divided into 1 of 3 test groups (n=10) following storage in water at 37 degrees C for 24 hours. The specimens were then stored in 37 degrees C water for 24 hours, followed by thermal cycling 10,000 and 20,000 times between 5 degrees C and 60 degrees C. After each storage condition, the specimens were tested in shear mode at a crosshead speed of 1.0-mm/minute. One-way ANOVAs and Tukey HSD test at a level of 0.05 were conducted. After 24 hours of water storage, the mean enamel bond strengths ranged from 11.3 to 16.9 MPa, and Clearfil tri-S Bond showed significantly higher bond strength. After thermal cycling, the mean bond strengths ranged from 8.3 to 20.7 MPa. The changes in enamel bond strengths were different among the adhesive systems tested. Failure modes after the test were commonly adhesive failure associated with partial cohesive failure adhesive in resin. With a careful choice of adhesive systems, the benefit to using single-step self-etch systems in terms of simplifying the clinical procedure might be acceptable, even after thermal stresses.