Microtensile bond strength of bulk-fill resin composite restorations in high C-factor cavities

Abstract

Aim: To evaluate the microtensile bond strength (μTBS) and the fracture modes of four bulk-fill resin composites (Tetric EvoCeram Bulk Fill/ Ivoclar Vivadent, Filtek Bulk Fill/3M ESPE, Venus Bulk Fill/Heraus Kulzer, and Filtek Bulk Fill Flow/3M ESPE) and one conventional incrementally filled resin composite (Filtek Z250/3M ESPE) inserted in class I cavities, after 24 hours and 6 months of water storage. Materials and methods: In all, 30 sound human extracted molars were divided into five restorative groups. Standardized class I cavities were prepared and restored following the manufacturer's instructions. The restored teeth were then assigned into one of the storage times (24 hours or 6 months). The molars were then cut into 1 mm2 sticks and submitted to μTBS. All fractured specimens were analyzed under a stereomicroscope (40x). Data were submitted to analysis of variance (ANOVA) and the Tukey post hoc test was applied for comparison between groups; and paired t test for comparison within storage times (p = 0.05). Results: After 24 hours of storage, statistically significant differences were observed between Filtek Z250 and Filtek Bulk Fill Flow groups. However, after 6 months, no statistical differences were observed between groups. Additionally, no differences were observed for the μTBS between the storage times. Adhesive failures were the most frequent fracture mode after 24 hours (54%) and 6 months (43%), the resin cohesive fracture mode showed 16% for 24 hours and 14% for 6 months, the dentin cohesive fracture mode showed 14% for 24 hours and 26% for 6 months, and the mixed fracture mode showed 16% for 24 hours and 17% for 6 months. Conclusion: Bulk-fill resin composites obtained similar μTBS in high C-factor cavities as conventional incrementally filled resin composites. No bond strength reduction was observed after 6 months of storage. Clinical significance: Single increment restorations in high C-factor cavities with bulk-fill resin composites did not reduce μTBS after 24 hours or 6 months of storage. The comparable results to the conventional incrementally filled resin composites and the reduction in the operative time, make the bulk-fill resin composites a restorative option for posterior teeth restorations.