The effect of temperature on linear dimensional stability of elastomers

Objectives: The objective of this study was to investigate the effect of temperature on dimensional stability of elastomeric impression materials. Materials and Methods: Polyether and polyvinyl siloxane impressions of an International Organization for Standardization-specified test-block were photographed at two temperatures and 3 time intervals. This resulted in 12 groups (n = 10). Images were digitally calibrated and measured. Mean percentage dimensional change (%DC) was analyzed using the Variance Estimation and Precision module of Statistica 10 (Statsoft®, Southern Africa) (95% confidence), with Fisher least significant difference correction for multiple pairwise comparisons. Results: For silicone, dimensional accuracy was highest when stored at 21°C for 14 days (%DC = 0.006). This was significantly better than all other silicone groups (P < 0.05). Dimensional accuracy was worst when stored at 21°C for 8 h (%DC = 0.237) and after cooling-off from 66°C (%DC = 0.300), with no difference between latter groups (P = 0.187). For polyether, dimensional accuracy was highest when stored at 21°C for 14 days (%DC = −0.272). This was significantly better than all other polyether groups (P < 0.05). Dimensional accuracy was worst when stored at 21°C for 8 h (%DC = 0.364) and after cooling-off from 66°C (%DC = 0.306), with no difference between latter groups (P = 0.199). Comparing polyether with silicone, %DC did not differ between the two materials when kept at 21°C for 14 days and when cooled-off after heat exposure for 8 h. At all other instances, the %DC between the two materials differed, with silicone always closest to zero %DC. Conclusions: Exposing silicone and polyether to high temperature doesn′t lead to higher dimensional inaccuracy on the short-term compared to keeping them at 21°C. However, heat has an effect on shelf-life (14 days) of impressions, decreasing accuracy. This effect is worse for polyether.