Dimensional accuracy in multiple casting with three different elastomeric impression materials

The ability to produce multiple accurate casts from a single impression has been evaluated in a few impression materials. The aim of this study was to evaluate the effect of multiple casting in specific time intervals with three different elastomeric impression materials, on the dimensional accuracy. A stainless steel model composed of two dies with precut molar and premolar teeth were used in this study. The bigger die had a notch to reproduce undercut in order to study the elastic recovery. Seven impressions were made from this model by each of the following impression materials: Correct plus, Panasil (addition–cured silicones) and Speedex (condensation–cured silicone) according to manufacturer’s instructions. The 21 impressions were poured in 30, 90, 150 minutes and 24 hours after impression taking. The stone casts were measured in six dimensions by an optical traveling, high precision (0.001 millimeter) microscope. The mean dimensions were compared with each other and the stainless steel model. For statistical analysis, Two-way ANOVA and Post Hoc tests were used to determine the significance levels. There were significant changes in most of the dimensions between the metal model and the first cast, but these changes were within the acceptable limits, according to ANSI/ADA Specification No.19 for impression materials. No significant difference was observed between almost all of the dimensions of the second, third and fourth casts when compared with the first cast of each impression material (P>0.05). The only significant difference was detected between the fourth cast and the first cast of Speedex in one dimension. Based on these results, four casts from Correct plus and Panasil as well as three casts from Speedex could be considered as acceptable from clinical stand points.