Preheated and Injected Bulk-Fill Resin Composites: A Micro-CT Analysis of Internal Voids and Marginal Adaptation in Class II Restorations.

The aim of this study was to evaluate, in vitro, the void formation and marginal adaptation in Class II cavities restored with preheated and injected bulk-fill resin composites. Eighty third molars received Class II cavities on their mesial and distal surfaces and were randomly distributed into eight groups (n = 10) according to material (Filtek Universal-control, incremental technique; Filtek One Bulk-Fill; Admira Fusion X-tra Bulk-Fill; VisCalor Bulk-Fill) and the temperature of the material (24 °C or 68 °C). The restored teeth were scanned using a SkyScan 1173 microtomograph. The percentage of internal voids (%IV) was analyzed using CTan software (version 1.23.02) and the percentages of continuous margins (%CM) in enamel and dentin were analyzed using Dataviewer software (version 1.5.6.2). The data of %IV and %CM were subjected to two-way ANOVA on ranks, followed by Tukey's test (α = 0.05). At 24 °C, Filtek Universal had a greater %IV (1.89%) ( < 0.05), which did not differ significantly from that of Admira Fusion X-tra Bulk-Fill (0.29%) ( > 0.05). Filtek One Bulk-Fill (0.07%) and VisCalor Bulk-Fill (0.07%) had lower %IV ( < 0.05). Preheating resulted in a significantly lower %IV for Admira Fusion X-tra Bulk-Fill ( < 0.05). Temperature did not significantly influence marginal adaptation ( > 0.05). VisCalor Bulk-Fill achieved significantly higher %CM in dentin (98%) at 24 °C ( < 0.05). It was concluded that bulk-fill-injected resin composites tend to have fewer internal voids than conventional resin composites using the incremental technique, and the injection of the resin composite into the cavity seems to be more important for marginal adaptation than the preheating procedure.