Effect of Bulk/Incremental Fill on Internal Integrity of Bulk-fill Composites

Objectives: To determine the effect of incremental/bulk placement on internal marginal integrity of commercial, bulk-fill resin composites. Methods: Class I preparations (4mm-dia, 4mm-deep) were made in extracted human molars.  Dentin bonding agent (etch/rinse/bond types, corresponding with respective restorative material) was applied and polymerized. Composite was placed: two separate 2-mm thick increments or as single bulk increment. Composite/bonding agent photocured using an LED-based light from respective composite manufacturer for recommended times. Bulk-fill composites used - Surefil SDR Flow (Caulk/Dentsply), QUIXX (Caulk/Dentsply), SonicFill (Kerr-Sybron), Tetric EvoCeram Bulk (Ivoclar/Vivadent). Incremental-recommended control composite - Filtek Supreme Ultra (3M/ESPE). Restored specimens thermocycled (5-55°C, 1,000X) and water-stored at 37°C. Teeth were sectioned (occluso-gingivally through bucco-lingual axis) and polished. Stain (Sable, Ultradent Products) was applied to sectioned margins. Digital photographs were recorded under a light microscope. Software (Image J) record total lengths of intact margins. Percent leakage at three locations determined: enamel, mid-dentin, pulpal floor.  Data were analyzed using 3-way ANOVA with Tukey's pairwise comparisons at a pre-set alpha of 0.05. Results: ANOVA indicated significant 2-way interactions (restorative material/fill type (p=0.022); restorative material/location (p=0.045).  Two-way ANOVAs (fill type/location) were performed separately for each material. No significant differences were found for fill type. Significant differences were found between locations: enamel>pulpal floor; mid-dentin>pulpal floor for Filtek and SonicFill; enamel>mid-dentin and enamel>pulpal floor for Surefil and QUIXX; enamel>pulpal floor for Tetric EvoCeram.  Differences among materials found for certain fill type/location combinations: Surefil<Filtek, SonicFill, and QUIXX for bulk fill in enamel; Surefil<Filtek for bulk fill in mid-dentin; Filtek<QUIXX for incremental fill in enamel. Conclusions: No significant difference in internal marginal integrity among most commercial bulk-fill resin composites was found, which showed no difference from use of a conventional, incremental-only advocated product. Fill type (incremental/bulk) had no effect. Internal marginal integrity is mostly affected by depth into restoration.