The rheology of silicone rubber impression materials

A selection of silicone rubber impression materials were studied for their rheological properties prior to and following mixing. The techniques used were a cone and plate viscometer and a capillary viscometer. All the impression materials were found to show pseudoplastic behaviour which is readily described by a power law function. For the mixed materials the onset of molecular entanglement, whilst theoretically establishing the absolute end of the working time, gave a gross overestimate of the clinical working time. The capillary viscometer is more useful than the cone and plate viscometer in providing information on the clinical working time.