Dimensional Stability of Elastomeric Impression Materials

Objectives: The present study investigated the ability of elastomeric impression materials to preserve their dimensions and weight after setting and until their pouring with gypsum. Methods: A recently introduced addition silicone product (Honigum, DMG), was tested along with representative elastomeric materials, including a condensation silicone, an addition silicone and a polyether. Dimensional stability was assessed by calculating the linear changes observed on long specimens of rectangular cross section. Water imbibition and loss of components was evaluated by estimating weight alterations after the disk-shaped specimens had been kept in air or immersed in distilled water. Measurements were conducted 1, 24 and 48 hours after mixing, for a sample size of 6 specimens. The statistical analysis of the results was performed by 2- and 1-way ANOVA and the differences between individual samples were evaluated with Scheffè and Dunnet c multiple comparison tests (p = 0.05). Results: All tested materials exhibited linear dimensional changes, which were occasionally statistically significant; in all cases, however, the changes were within the limits of the corresponding ADA specification. The weight of the materials declined, by up to 0,50%, after storage in dry environment, except for the new product, whose weight increased slightly. Following immersion in distilled water all materials gained weight by up to 2,08%. Conclusion: The recently introduced elastomer exhibited exceptional stability, similar to that of the other addition-type silicone tested. Greater, yet clinically acceptable, changes were noticed for the polyether and the condensation silicone materials. The study of weight changes occurring on storage in dry and wet environment can be helpful in exploring the mechanism of dimensional alteration of elastomers after setting.