Three-dimensional evaluation of extended pour alginate impression materials following variable storage time intervals...

The purpose of this study was to assess and compare the dimensional accuracy of the stone casts made of three extended pour alginate impressions materials (Cavex Colorchange, Kromopan, and Neocolloid) following storage under different storage conditions and pouring at different time intervals.

A maxillary Frasaco (dentulous) model was selected as a standard model. Index holes of 1 mm depth and 1 mm diameter were made on the palatal cusp tips of right and left first premolars, mesiopalatal cusp tips of right and left third molars and in the midline of the palate, perpendicular to a line joining the index holes made on cusp tips of the first premolars as reference points for measurement. A single uniformly spaced custom tray was fabricated with heat-cure acrylic resin and used to make impressions for the entire study. A total of 210 impressions of the master model were made, seventy impressions were made from each of the alginate material brands and were subjected to three storage conditions (open air, uncontrolled humidity, and 100% controlled humidity) for three different storage time intervals (0, 1, 6 h). Since no storage was done in the immediate-pour group, it contained 10 specimens from each brand. Following the designated storage time interval, all impressions were poured in type IV gypsum. Measurements of stone casts were done in three dimensions, anteroposterior, lateral using Measuroscope and vertical by Dial Gauge. Data were organized in tables and statistical analyses were performed. Three-way ANOVAs were used to check if the material brands, storage time intervals, and conditions affect the measurements. Tukey HSD post hoc tests were used for the multiple comparisons if ANOVA is significant. One sample t-test was used to compare between the casts made of alginate brands and the master model. Significance level was set to α < 0.05 for all tests.

Results showed that the material brands, storage time intervals, and conditions do affect the measurements in all three dimensions (all P < 0.05). In addition, all two-way and three-way interactions were significant for all measurements except the interaction of storage time intervals and conditions for B-C (lateral) measurements, and interaction of material brands and storage time intervals for C-D (anteroposteriorly) measurements. When stone casts were compared to the master model, immediate pour, and storage for 1 h in 100% controlled humidity resulted in statistically insignificant changes among all three alginate impression brands. In addition, the specimens made of Cavex Colorchange and Kromopan following storage in uncontrolled humidity condition for 1 h showed statistical insignificance when compared to the master model.

Within the limitations of this study, it can be extrapolated that, although this class of alginate impression materials was manufactured for extended pour purposes, clinicians should avoid storage of the studied brands for 6 h. Whenever 1 h to pour is necessary, 100% controlled humidity is the ideal and standardized environment for all three alginate brands. Perhaps, Cavex Colorchange, and Kromopan can be safely stored in uncontrolled humidity condition while maintaining their optimal dimensional accuracy.