Recently, manufactures are trying to increase the storage time of hydrocolloid impression materials. Due to clinical limitations, in the majority of cases, the impressions are poured after a time delay longer than the recommended period. Some studies show that it is possible to store a hydrocolloid impression for up to 1, 2 and even 4 hours. Numerous studies have evaluated the dimensional accuracy of conventional alginates. However, some have claimed that it is possible to store the impression in a humid environment for up to one hour. ![]() Researchers have recommended that in order to maintain dimensional accuracy, hydrocolloid impressions should be poured immediately or maximally within 12 minutes. ![]() Syneresis also leads to considerable shrinkage. However, minor dimensional changes have been reported as the result of storage in 100% relative humidity. Irreversible hydrocolloid impressions undergo shrinkage if stored exposed to air whereas, water storage leads to swelling of the impression and distortion as the result of imbibition. Dimensions of the impression are affected by several factors including the composition of the irreversible hydrocolloid material, conditions under which the impressions are stored and the duration of storage before pouring. ![]() Irreversible hydrocolloids suffer one major drawback, namely the dimensional change of impressions that have set. ĭue to differences in formulations, products of different manufacturing companies have variable characteristics and properties in terms of consistency, setting time, dimensional stability, elasticity and strength. Because of their acceptable accuracy, availability, reasonable price and facile handling, this type of impression material is used for many purposes such as preparation of a study cast for diagnosis, fabrication of provisional prosthesis, custom trays, appliances and a definitive cast for fabrication of complete dentures in cases with undercut areas, partial denture and for maxillofacial prostheses. Irreversible hydrocolloids (alginates) are among the most commonly used impression materials.
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