Purpose: The aim of this study was to evaluate the marginal quality and wear of bulk-fill composite resins (BFs) for Class-II restorations of primary and permanent molars in comparison to a conventionally layered composite resin (RC) and to compare the results of the two dentitions.
Materials and Methods: Eighty (40 primary and 40 permanent) extracted molars received standardized Class-II cavity preparations and were restored with either one of two flowable BFs, one of two high viscous BFs, or a composite resin (RC). Thermomechanical loading (TML; 2,500 cycles +5°C/+55°C; 100,000 cycles, 50N, 1.67Hz) followed. A quantitative marginal analysis using SEM images and a profilometric quantification of two-body wear were carried out using replicas. ANOVA, Kruskal–Wallis, Mann–Whitney U, and Wilcoxon signed-rank tests were used for statistical analysis (P < 0.05).
Results: For both dentitions, a significant reduction of perfect margins was observed after TML (P < 0.02). For the primary dentition, the flowable BFs showed significantly less perfect margins than all high viscous materials (P < 0.005). For the permanent dentition, RC showed significantly fewer gaps than the flowable BFs (P < 0.04). Regarding wear, within the dentitions, no significant differences could be computed between groups with regard to the maximum height loss (P < 0.05).
Conclusion: All of the investigated bulk-fill composite resins showed satisfactory in-vitro results for both tested parameters in primary and permanent teeth, with a superiority of the high-viscosity materials in terms of marginal quality.