Marginal quality of flowable 4-mm base vs. conventionally layered resin composite

ObjectiveThis study evaluated marginal integrity of bonded posterior resin composite fillings to enamel and dentine with and without 4 mm flowable base, before and after thermo-mechanical loading (TML).Methods80 MOD cavities with one proximal box beneath the CEJ were prepared in extracted human third molars. Direct resin composite restorations (SDR with CeramX mono, Tetric EvoCeram, Filtek Supreme XT, and Venus Diamond or the respective resin composites alone) were bonded with system immanent adhesives XP Bond, Xeno V, Syntac, Adper Prompt L-Pop, and iBond self-etch. Before and after thermomechanical loading (100,000 × 50 N, 2500 thermocycles between 5 and 55 °C), marginal gaps were analysed using SEM of epoxy resin replicas. Results were analysed with Kruskal–Wallis and Mann–Whitney U-tests (p < 0.05). After thermomechanical loading, specimens were cut longitudinally in order to investigate internal dentine adaptation by epoxy replicas under a SEM (200× magnification).ResultsIn enamel, high percentages of gap-free margins were initially identified for all adhesives. After TML, etch-and-rinse adhesives performed better than self-etch adhesives (p < 0.05). Also in dentine, initially high percentages of gap-free margins were found for all adhesives. After TML, etch-and-rinse adhesives again performed better than self-etch adhesives for both marginal and internal adaptation (p < 0.05). The presence of a 4 mm layer of SDR had no negative influence on results in any group (p > 0.05).ConclusionsSDR as 4 mm bulk fill dentine replacement showed an good performance with the material combinations under investigation.