Slumping tendency and rheological properties of flowable composites

Objectives: The aim of this study was to develop a method for measuring the slumping tendency of flowable resin composites and to correlate the results with those obtained from standard rheological methods. Methods: Five commercial flowable composites (Aeliteflo: AF, Filtek flow: FF, DenFil flow: DF, Tetric flow: TF and Revolution: RV) were used. A fixed volume of each composite was extruded from a syringe onto a glass slide using a custom-made loading device. The composite was allowed to slump for 10 s at 25 °C and light cured. The aspect ratio (height/diameter) of the cone or dome shaped specimen was measured to estimate the slumping tendency of the composites. In order to investigate the relationship between the slumping tendency and the rheological properties of the composites, the complex viscosity η* of each composite was measured by a dynamic oscillatory shear test over a range of angular frequency ω = 0.1-100 rad/s using a rheometer. The aspect ratios of the composites were compared by one-way ANOVA and Tukey's post hoc test at the 5% significance level. Regression analysis was performed to investigate the relationship between the aspect ratio and the complex viscosity. Results: Slumping tendency based on the aspect ratio varied among the five materials (AF < FF < DF < TF < RV). Flowable composites exhibited pseudoplasticity in which the complex viscosity decreased with increasing frequency. Slumping resistance increased with increase in the complex modulus. Significance: The slumping tendency could be quantified by measuring the aspect ratio of slumped flowable composites. This method may be applicable to evaluate the clinical handling characteristics of these materials.