Effect of bulk/incremental fill on internal gap formation of bulk-fill composites

To examine the effects of composite type (bulk-fill/conventional) and placement (4-mm bulk/2-mm increments) on internal marginal adaptation of Class I preparations.

Cylindrical, Class I, 4-mm×4-mm preparations were made on 50 recently extracted human molars and restored using either a bulk-fill (SureFil SDR Flow (SDR), Quixx (QX), SonicFill (SF), Tetric EvoCeram Bulk (TEC)) or a conventional composite designed for 2-mm increments (Filtek Supreme Ultra (FSU)). Restorations were placed in 1 or 2 increments using the manufacturer's bonding agent and curing light (n=5). Teeth were sectioned occluso-gingivally and dye was placed on the internal margin and visually examined by 3 observers. Gap-free marginal lengths were analysed within three different regions of the sectioned tooth: enamel, mid-dentine, and pulpal floor.

Marginal integrity was unaffected by placement method. Bulk-placement demonstrated significantly fewer gap-free margins at the pulpal floor than in enamel, for all materials except SDR. Greater percentages of gap-free margins were found within the mid-dentine than at the pulpal floor for FSU. QX had more gap-free margins in enamel compared with the mid-dentine. Proportion of gap-free margins within enamel and mid-dentine was not significantly different for any incrementally placed product. Excluding FSU, gap-free margins within enamel were significantly greater than at the pulpal floor. Notably, significantly more gap-free margins were found within mid-dentine than at the pulpal floor for SF.

No significant differences in gap-free margins were found between placement methods within a given product per location. Except for SDR, percentage of gap-free margins was significantly lower at the pulpal floor interface than at the enamel interface for bulk-fill.