Flexural Strength With Depth and Shrinkage Stress of Bulk-fill Composites

Objectives: This study evaluated biaxial flexural strength (BFS) and polymerization shrinkage stress (PSS) of one conventional and five bulk-fill composites.
Methods: Bulk-fill composites (Tetric EvoCeram Bulk Fill (TEC), Opus Bulk Fill (OBF), Fill-Up! (FUP), Equia Forte (EQF) and Activa BioActive Restorative (ABR)). Filtek Supreme Ultra (FSU) was used as a negative (bulk-filled) and as a positive (incrementally filled) control. For the BFS test, sets of eight stacked composite discs (0.5-mm thick and 6-mm diameter) were prepared simulating bulk-filling of a 4-mm-thick increment (n=7). PSS was determined using composite bonded to acrylic rods attached to a universal testing machine (n=5). Data were analyzed by two-way ANOVA for BFS and one-way ANOVA for PSS, and Tukey post-hoc test (α = 0.05).
Results: ABR and the negative control showed lowest BFS values at deeper regions. PSS means (MPa) (SD) were: TEC- 5.31(0.55)c; OBF- 7.29(1.11)ab; FUP- 7.94(0.8)a; EQF- 0.34(0.04)d; ABR- 6.25(0.86)bc and FSU- 7.51(1.01)ab. Values identified by similar lower case letters were not significantly different.
Conclusions: Most of bulk-fill composites did not exhibit BFS reduction with an increase in depth. The lowest PSS was observed for the hybrid material (glass ionomer/resin (ABR)). PSS of the conventional composite resin (FSU) did not differ from OBF, FUP, and ABR bulk-fill materials.