Cuspal flexure, depth-of-cure, and bond integrity of bulk-fill composites.

Purpose: Evaluate cuspal flexure caused by polymerization shrinkage stress, bond integrity, and depth-of-cure of bulk-fill composites.
Methods: Twenty-eight extracted permanent molars were mounted in stainless steel rings. Slot-shaped Class II mesio-occlusal-distal preparations (four mm deep) were restored with Filtek Supreme Ultra (control; two two-mm increments) and bulk-fill composites (Tetric EvoCeram, Venus, Filtek Bulk Fill). The teeth were digitized using a 3D scanner before and after restoration. Before- and after-restoration scans were aligned, and cuspal flexure was calculated. Bond integrity along occlusal interfaces was assessed by dye penetration and measured after overnight immersion in basic fuchsin dye and cross-sectioning. Depth-of-cure was determined on the cross-sections using Vickers hardness. Statistical analysis was performed with one-way analysis of variance.
Results: All composites caused inward cuspal flexure (10.4 to 13.6 μm). No statistical difference in flexure was found among the composites (P=.07). No significant difference in microhardness at any restoration depths was found for any composite (.35<P<.99). Dye penetration showed comparable bonding along occlusal interfaces for the tested composites.
Conclusions: Bulk-fill composites cured all the way through four-mm restoration depths. Cuspal flexure, caused by polymerization shrinkage, and bond integrity were not different between teeth restored with the bulk-fill and conventional incrementally placed restorative composites.