Dimensional stability of contemporary irreversible hydrocolloids: humidor versus wet tissue storage

The storage time and conditions of irreversible hydrocolloid impressions affect their accuracy and in turn the precision of the definitive cast. Recommendations for proper storage are, however, based on theoretical assumptions rather than facts.

The purpose of this study was to assess the influence of the 2 most common storage conditions on the dimensional stability of 7 contemporary irreversible hydrocolloids (IH) for a period of up to 7 days.

Twelve specimens per material (Blueprint, Cavex CA37, Cavex ColorChange, Jeltrate, Orthoprint, Cavex Orthotrace, and Tetrachrom) were fabricated according to ISO/CD 21563. The specimens were either stored in a humidor (n=6) or wrapped in a wet tissue (n=6) inside a plastic bag (bag/tissue). The linear dimensional change of the specimens was calculated (Δ| [%]) at baseline and after a storage time of 1, 2, 4, 24, 48, 72, 120, and 168 hours. Data were subjected to a repeated measures ANOVA, followed by post hoc comparisons (Tukey HSD Test, Games-Howell Test) at α=.05.

For specimens stored in the humidor, Δ| ranged from 0.33% to -2.35% and in the bag/tissue from 2.89% to -2.8%. Storage in the bag/tissue resulted in the most unpredictable results. The color-changing IH showed a pronounced expansion when stored in the bag/tissue.

If humidor storage is used, IH impressions should be poured within 4 hours. If bag/tissue storage is used, noncolor-change IH impressions should, preferably, be poured within 2 hours. In general, the color-change IHs studied had higher dimensional change values. For optimum dimensional stability, IH impressions should be poured as soon as possible.