Rheological properties of elastomers during setting.

A controlled stress rheometer has been used to monitor the changes in rheological properties occurring in five elastomeric impression materials during setting. The rheometer differs from conventional rotary viscometers in that the torque is the controlled variable, and the resulting deformation is measured. The use of such an instrument in oscillatory mode enables a range of rheological parameters--including viscosity, rigidity, and elasticity--to be monitored during setting. The polyvinylsiloxane impression materials develop elasticity at a rate that would not be apparent from measurements of viscosity or rigidity alone. This highlights the potential danger of basing the evaluation of clinically important properties, such as working time, on simple measurements of viscosity or rigidity.