Background: Certain studies have been conducted on the effects of mechanical and thermal loadcycling on the microtensile bond strength (microTBS) of composites to dentin, but the resultswere different. The authors therefore decided to evaluate these effects on the bonding of ClearfilSE bond to superficial dentin.

 Materials and Methods: Flat dentinal surface of 42 molar teeth were bonded to Filtek‑Z250 resincomposite by Clearfil SE bond. The teeth were randomly divided into 7 groups and exposed to differentmechanical and thermal load cycling. Thermocycling was at 5‑55‹C and mechanical load cycling wascreated with a force of 125 N and 0.5 Hz. Then, the teeth were sectioned and shaped to hour glass formand subjected to microTBS testing at a speed of 0.5 mm/min. The results were statistically analyzed bycomputer with three‑way analysis of variance and T‑test at P < 0.05 significant. To evaluate the locationand mode of failure, the specimens were observed under the stereomicroscope. Then, one of thespecimens in each group was evaluated under Scanning Electron Microscopy (SEM) for mode of failure.

 Results: All of the study groups had a significantly lower microTBS as compared to the control group (P < 0.001). There was no statistically significant difference between mechanical cycling with50K (kilo = 1000) cycles, and 50K mechanical cycles plus 1K thermal cycles. Most of the fracturesin the control group were of adhesive type and this type of fracture increased after exposure tomechanical and thermal load cycling.

 Conclusion: Thermal and mechanical load cycling had significant negative effects on microTBS andthe significant effects of mechanical load cycling started to be significant at 100K cycles.

 Source: Dental Research Journal

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