Internal and marginal adaptation of high-viscosity bulk-fill composites in class II cavities placed with different adhesive strategies

The aim of this study was to evaluate internal and marginal adaptation of high-viscosity bulk-fill composites to enamel and dentin with a self-etch (SE) and an etch-and-rinse adhesive (ER) without and with artificial aging. 128 MOD cavities in extracted human molars were prepared, randomly assigned to 8 groups ( n = 16), bonded with either OptiBond FL (OFL, ER) or Xeno V+ (X, SE), and restored in 4 mm horizontal bulk layers with SonicFill (SF), Tetric EvoCeram Bulk fill (TEC), and x-tra fil (XF). Incremental layering technique with Premise (P) served as control. Half of the specimens each ( n = 8) were subjected either to water storage (1 day, 37 °C) or prolonged storage (180 days) and thereafter thermocycling. Replicas were analyzed for marginal gap formation. After sectioning, interfacial adhesive defects were assessed. Results were statistical analyzed. (1) Internal adaptation: Except for TEC/OFL at enamel without artificial aging, no significant differences between bulk-fill composites and the control were observed. All groups at dentin with OFL showed less internal adhesive defects than that with X ( p < 0.05). (2) Marginal adaptation: No significant differences were observed between bulk-fill composites and control except for P after artificial aging ( p > 0.05). All other composites, regardless of artificial aging, formed significantly more marginal gaps at enamel with X compared to with OFL ( p ≤ 0.05). Simplified restorations with high-viscosity bulk-fill composite showed comparable internal and marginal adaptation to incrementally placed fillings. A superiority of the 3-step ER approach was seen compared to the 1-step SE adhesive irrespective of the bulk-fill composite used.