Effects of strain rate on the behavior of elastomeric impression.

The effects of strain rate on the ultimate tensile strength, ultimate elongation at fracture, and elastic recovery of five commonly used elastomeric dental impression materials were studied. Each specimen was prepared by standard mixing techniques, placed for setting in a standard ASTM mold, removed, trimmed, and mounted in an Instron testing unit. Tensile load was applied and plotted on a load versus displacement curve as the specimen was stretched axially until rupture. Five specimens of each material were tested, respectively, at strain rates of 100, 200, and 500 mm/min crosshead speed. Specimens were then removed, reassembled, and measured with an electronic caliper to assess the elastic recovery; measurements were repeated after 1 minute, 30 minutes, 1 hour, and 24 hours. Findings of this study indicated that (1) polysulfide materials exhibited the greatest amount of deformation, and the lowest tensile strengths of the materials studied; (2) higher tensile strengths were observed with higher strain rates; and (3) polysulfide materials showed the greatest amount of elongation at rupture, with the highest values occurring at the higher strain rates.