Capillary rheology of two composite resin systems

The rheological properties of two commercial resin systems, Isopast and Cosmic, were studied in the shear rate range 0.65-65 s-1 by capillary techniques. Isopast represents a low inorganic filled composite, whereas Cosmic is a conventionally filled system whose resin matrix resembles that of Isopast. All components of both systems obeyed power law dependence of shear stress as a function of shear rate according to the relation 1n tau = 1n K + n 1n gamma; values of n for Cosmic catalyst and paste and Isopast paste were of the order of 0.6 whereas Isopast catalyst was of the order of 0.3. Setting systems obeyed a power law relationship during the working time with an exponent n congruent to 0.7-1.0. Accordingly the systems appear pseudoplastic in component form and slightly pseudoplastic to near Newtonian after mixing.