Effect of Storage Time on Accuracy of Alginate Impression Materials

Background and Aim: It is traditionally believed that hydrocolloid impression materials (Alginate) should be poured immediately to gain maximum dimensional stability. With recent improvements in manufacturing dental materials, it is possible to store the impression of hydrocolloids in 100% humidity environment for a few hours. The purpose of this study was to evaluate the effect of storage time on dimensional stability of casts poured from alginate impressions. Materials and Methods: A metal model (CK steel) composed of two metal plate; one holding the impression tray and the other holding two dies, was used to make impressions. Using this model, for each time interval, 5 impressions were made of Iranian (Golchai) and the foreign (Alginoplast) alginate. The impressions were kept in 100% humidity environment for 0, 15, 30, 60 and 180 minutes and then poured with type III dental stone. The stone casts were measured with a digital caliper and the results were compared between groups with two way ANOVA and Tuky tests. Results: Comparing the dimensions of casts poured from two alginates at different storage times showed statistically significant difference between groups (P=0.027). But in comparing the cast dimensions with the master model, there was no statistical significant difference at varying storage times (P=0.230). The mean height of die No. 2 in Iranian groups had 0.06 mm and in foreign groups had 0.01 mm difference with master model. Conclusions: The results of this study show that these two types of hydrocolloid can be stored in humidity for 3 hours without significant changes.