Rheology of Dental Composition (Impression Compound)

¹ Dental School of The London Hospital Medical College, University of London, London, England

Impression compounds have near-Newtonian viscosity characteristics at shear stresses between 10⁴ and 10⁷ dyne/cm². The viscosity of these materials is highly dependent on temperature; a 5°C. temperature change causes a tenfold change in viscosity, or more. At 60°C., the viscosity of the materials studied was at least that of a heavy-bodied polysulfide impression paste, and often considerably more.

Results from a plastimeter gave viscosity values in reasonable agreement with those from a capilliary-type viscometer. The ADA flow tests for impression compound can be expressed in terms of minimum coefficients of viscosity (for example, 2.8 X 10⁶ poise at 45°C.).