High C-Factor Cavities: How Do "Snowplow Technique"; Adhesive Application Mode and Aging Influence the Microtensile Bond Strength to Dentin?

Purpose: To investigate the microtensile bond strength (mu TBS) to dentin in class-I cavities using different layering techniques, adhesive application modes, and aging. Materials and Methods: 150 caries-free human molars were randomly assigned to 8 experimental and 2 control groups (n=15 teeth/ group). For each tooth, a standardized class-I cavity was prepared (4x4x4mm) and pretreated with a universal adhesive (self-etch or etch-and-rinse mode). Incrementally layered restorations served as the control. In the experimental groups, either lining with bulk-fill flowable composite and a layering technique, bulk filling, or the snowplow technique with one or two layers of viscous composite were applied. Four microsticks were obtained from each cavity. Half were tested initially and the other half after aging (thermocycling, 15,000 cycles, 5-55degree celsius, n=30 sticks/group). Tobit regression was used for analyzing group differences, including analysis of interactions, Pearson's chi-squared test or Fishers's exact test for fracture analyses (significance level 0.05). Results: Regression analysis showed significant differences in mu TBS between groups initially and after aging. In both etching modes, lining with a bulk-fill flowable composite and layering technique achieved the highest mu TBS both initially and after aging. In contrast to the etching mode (self-etch and-rinse groups. Conclusion: The etch-and-rinse mode achieves higher mu TBS in class-I cavities compared to the self-etch mode. The lining technique with bulk-fill flowable composite as well as the snowplow technique yielded the highest mu TBS after aging, whereas bulk filling and its combination with the snowplow technique resulted in lower mu TBS.