Rheological Behavior, Slumping, and Polymerization Shrinkage of Bulk-Fill Flowable Composites

Objectives: The aim of this study was to evaluate the rheological properties, slumping resistance, and polymerization shrinkage of bulk-fill flowable composites.
Methods: Eight brands of bulk-fill flowable composites [Any-Com (ABF), Beautifil (BBF), Charisma (CBF), DenFil (DBF), Filtek Fill and Core (FFC), G-aenial Bulk Injectable (GBI), SDR, Tetric N-Flow (TBF)] were used. The complex viscosity was measured at an angular frequency of 0.1-100 rad/s using the AR2000 rotational rheometer (TA instruments, USA) with a parallel plate geometry (n=3). To evaluate the slumping resistance, composites were extruded through a needle (0.8 mm in diameter) with a 1-ml syringe on a glass slide by pressing 1 mm at a speed of 0.2 mm/s using a lab-made loading device. The extruded composites (17.3 mm³) were allowed to slump for 10s before being light cured. The aspect ratios (height/diameter) of the slumped composites were measured (n=5). Axial polymerization shrinkage was evaluated using a modified bonded disc method. Composite discs (0.5 mm thick, 5-6 mm in diameter) were light cured for 20s. Measurements were recorded on a computer at 10 data/s for 600s (n=3). Data were analyzed using one-way ANOVA and Tukey’s test.
Results: GBI showed the highest complex viscosity for all frequencies and pseudoplastic behavior, whereas SDR showed Newtonian. The aspect ratio of GBI exhibited the highest (1.37), while DBF the lowest (0.34). The polymerization shrinkage (%) of composites ranged from 2.77 (TBF) to 4.21 (ABF). Peak shrinkage rate (%/s) and peak time (s) ranged 0.55 - 1.01 and 0.7 - 1.5, respectively. BBF showed the highest peak shrinkage rate. GBI exhibited the lowest peak shrinkage rate with the most delayed peak time.
Conclusions: The rheological properties and slumping tendencies of bulk-fill flowable composites are closely related to their handling characteristics. Clinicians should also consider the polymerization shrinkage of bulk-fill flowable composites, as they are used in large quantities.