effect of storage time on the accuracy and dimensional stability of two irreversible hydrocolloid impression materials

ABSTRACT

It has been stated that hydrocolloid impression materials [Alginate] should be poured immediately to gain maximum dimensional stability. With modem formulations of these materials, it is possible store the impression at 100% humidity for varying periods. The purpose of this study was to evaluate the effect storage time on dimensional stability of casts poured from two types of alginate impression materials. A metal model [CK steel] composed of two metal plates, one holding the impression tray and the other holding two dies, was used to make the impressions. Five impressions were taken with the Iranian [Golchai] and foreign [Alginoplast] alginates for each tested time interval. The impressions were stored in l00% humidity 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 the groups using two-way ANOVA and Tukey tests. A statistically significant difference was encountered between the dimensions of the casts poured from the two alginates at the tested time intervals [p=0.027]. No significant difference was observed between the experimental casts' dimensions and the master model at the different storage times [p=0.0230]. A 0.06 mm and 0.01 mm difference was found between the master model and the mean height of dye no.2 in the Iranian and foreign groups, respectively. The results of this study show that the studied hydrocolIoid materials can be stored in a humid environment for 3 hours, without undergoing significant changes