An evaluation of elastomeric impression materials based on surface compressive strength

The setting times of seven commercially available elastomeric impression ma terials were determined using Wilson's reciprocating rheometer at temperatu res 23 +/- 0.5 or 32 +/- 0.5 degreesC. The surface compressive strength and depression of these materials after setting time were measured using a rhe ometer (Fudoh). Each material was mixed according to the mixing proportion (base/accelerator or catalyst ratio) recommended by the manufacturer. The s urface compressive strength and the depression of each material were measur ed by using a method which pressed the material to the edge of a sensitive rod (2.0 mm in diameter) connected to a load cell. In the case of silicone impression materials (additional type) at a temperature of 23 +/- 0.5 degre esC, the surface compressive strength and the depression of these materials were extremely stable after the setting time. However, the surface compres sive strength of other materials except additional type materials increased markedly after setting time and the depression corresponding to the surfac e compressive strength decreased. These increased largely with the increase , in pressing speed to the sensitive rod. At 450 s from the setting time of all materials, there was an adequate correlation (r = 0.84) between measur ed values and theoretical values derived using the theory of elasticity.