Effect of storage time on dimensional stability of Extended-pour irreversible hydrocolloid impression material

When there is no immediate access to dental laboratory for pouring dental impressions, impression materials with dimensional stability over time should be used. The aim of this study was to evaluate the effect of storage time on dimensional stability of casts poured from alginate impressions. In this experimental-laboratory study, a metal model containing two dies and acrylic impression trays were used to make five alginate impressions at each time interval using three different alginate brands [Hydrogum5 (Zhermack), Elastic Cromo (Spofadental), and Alginmax (Major)]. The impressions were kept in a humid environment for 0, 24, 48, 72, and 120 hours and then poured with Type III dental stone. Five dimensions were measured in each cast with a digital caliper: ED (distance between the two dies), H1 (height of the smaller die), H2 (height of the larger die), D1 (diameter of the smaller die), D2 (diameter of the larger die). The results were compared among groups with two-way ANOVA and a post hoc Tukey test (α=0.05). Dimensional stability of alginate impressions was dependent on both the material and time (p value < 0.05); however, their reciprocal interaction did not exhibit any significant relationship at the same interval (p value > 0.05). After 24 hours, dimensions of Elastic Cromo alginate only did not exhibit any statistically significant differences with the model (p value > 0.05). After 48 and 72 hours Hydrogum5 alginate only did not demonstrate any significant dimensional differences with the model (p value > 0.05). After 120 hours, Hydrogum5 alginate exhibited a significant difference with the model in H2 dimension. The results showed that Alginmax impressions must be poured immediately. Elastic Cromo impressions can be poured after 24 hours. The impression of these three kinds of impression materials did not exhibit any significant dimensional differences before 120 hours; however, they are not reliable for five-day usage.