Slumping tendency and rheological property of flowable composites / 대한치과보존학회지

The aim of this study was to develop a method for measuring the slumping resistance of flowable resin composites and to evaluate the efficacy using rheological methodology. Five commercial flowable composites (Aelitefil flow:AF, Filtek flow:FF, DenFil flow:DF, Tetric flow:TF and Revolution:RV) were used. Same volume of composites in a syringe was extruded on a glass slide using a custom-made loading device. The resin composites were allowed to slump for 10 seconds at 25degrees C and light cured. The aspect ratio (height/diameter) of cone or dome shaped specimen was measured for estimating the slumping tendency of composites. The complex viscosity of each composite was measured by a dynamic oscillatory shear test as a function of angular frequency using a rheometer. To compare the slumping tendency of composites, one way-ANOVA and Turkey's post hoc test was performed for the aspect ratio at 95% confidence level. Regression analysis was performed to investigate the relationship between the complex viscosity and the aspect ratio. The results were as follows. 1. Slumping tendency based on the aspect ratio varied among the five materials (AF < FF < DF < TF < RV). 2. Flowable composites exhibited pseudoplasticity in which the complex viscosity decreased with increasing frequency (shear rate). AF was the most significant, RV the least. 3. The slumping tendency was strongly related with the complex viscosity. Slumping resistance increased with increasing the complex viscosity. 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 flowable composites.

Rheological properties of resin composites according to the change of monomer and filler compositions / 대한치과보존학회지

OBJECTIVES: The aim of this study was to investigate the effect of monomer and filler compositions on the rheological properties related to the handling characteristics of resin composites. METHODS: Resin matrices that Bis-GMA as base monomer was blended with TEGDMA as diluent at various ratio were mixed with the Barium glass (0.7 um and 1.0 um), 0.04 um fumed silica and 0.5 um round silica. All used fillers were silane treated. In order to vary the viscosity of experimental composites, the type and content of incorporated fillers were changed. Using a rheometer, a steady shear test and a dynamic oscillatory shear test were used to evaluate the viscosity (eta) of resin matrix, and the storage shear modulus (G'), the loss shear modulus (G"), the loss tangent (tandelta) and the complex viscosity (eta*) of the composites as a function of frequency omega = 0.1-100 rad/s. To investigate the effect of temperature on the viscosity of composites, a temperature sweep test was also undertaken. RESULTS: Resin matrices were Newtonian fluid regardless of diluent concentration and all experimental composites exhibited pseudoplastic behavior with increasing shear rate. The viscosity of composites was exponentially increased with increasing filler volume%. In the same filler volume, the smaller the fillers were used, the higher the viscosities were. The effect of filler size on the viscosity was increased with increasing filler content. Increasing filler content reduced tandelta by increasing the G' further than the G". The viscosity of composites was decreased exponentially with increasing temperature.