Effects of Water/Powder Ratio of Irreversible Hydrocolloid on Dimensional Stability of Impressions

Background and Aim: Water/powder ratio is effective on some properties of irreversible hydrocolloid impression materials. This study aimed to determine the ef-fects of water/powder ratio of irreversible hydrocolloid impression materials on di-mensional stability of impressions. Materials and Methods: In this in vitro experimental study, a metal model with two abutments as anchoring support for a three-unit dental bridge was used. Sixty alginate impressions were made with different water/powder ratios (control group and test group with 50% extra water). The impressions were made by acrylic trays. Alginate impressions were poured with dental stone after 15, 60 and 240 min of removal from the model. The diagonals and heights of the small and large dies as well as the outer space between the two dies were measured trice using a digital caliper with 0.01 mm accuracy, and the mean values were reported. The obtained dimensions were com-pared with each other and with the model. Data were analyzed by one-way ANOVA, one-sample t-test, and independent samples t-test (α=0.05). Results: In the majority of dimensions in both the control and test groups, there was a significant difference in comparison with the metal model. The mean dimensions of casts did not show any significant difference between the two groups after 240 min (P>0.1). Conclusion: Increasing the water added to alginate powder by 50% affected the di-mensional stability of the resulted casts. The time interval before pouring the cast had a significant effect on dimensional accuracy of the casts.