Effect of storage time on dimensional changes of irreversible hydrocolloid impression material

AbstractIntroduction: Storage time influences some characteristics of irreversible hydrocolloid impression material. The aim of this study was to evaluate the effect of storage time on dimensional changes of alginate irreversible hydrocolloid impression material.Materials and Methods: In this experimental study, a metal pattern was used with two abutments for a 3-unit bridge. Thirty alginate impressions with standard water-to-powder ratios were provided. The impressions were poured after 15, 60 and 240 minutes with stone gypsum within 10 seconds and the casts were removed after 45 minutes. Then the diameter and height of small and large dies and external distance between the two dies were measured three times by means of digital calipers and the mean values were reported. One-way ANOVA and independent sample t-test were used for data analysis (α = 0.05).Results: The diameter of the large die and the height of the small die exhibited statistically significant differences between 15- and 60-minute time intervals (p value ≤ 0.001 and p value ≤ 0.01, respectively). Comparison of dimensions between 15- and 240-minute time intervals revealed significant differences in the heights of large and small dies (p value ≤ 0.001 and p value ≤ 0.026, respectively). There were no significant differences between 60- and 240-minute intervals in any of the dimensions.Conclusion: Under the limitations of the present study increasing storage time from 15 to 60 minutes led to dimensional instability only in the height of small die, with no effect on other dimensions. Key words: Impression materials, Dental, Alginate, Time factors