title: Effect of storage time of extended-pour and conventional alginate impressions on dimensional accuracy of casts.
abstract: OBJECTIVE
  Some manufacturers claim to have produced new irreversible hydro-colloids that are able to maintain their dimensional stability during storage. The present study evaluated the effect of storage time on dimensional stability of three alginates: Hydrogum 5, Tropicalgin and Alginoplast.
  
  
  METHODS
  In this experimental in-vitro trial, a total of 90 alginate impressions were made from a Dentoform model using Hydrogum 5, Tropicalgin and Alginoplast alginates. The impressions were stored in a sealed plastic bag without a damp paper towel for 0, 24, 48, 72 and 120 hours and then poured with type III dental stone. Cross-arch (facial of 6 to facial of 6 on the opposite side) and antero-posterior (distal of right first molar to the ipsilateral central incisor) measurements were made with a digital caliper on the casts. Data were analyzed by two-way and one-way ANOVA and Tukey's post-hoc test (P<0.05).
  
  
  RESULTS
  Alginate type and the pouring time significantly affected the dimensional stability of alginate impressions (both Ps<0.001). Pouring of Hydrogum 5 impressions can be delayed for up to 120 hours without significant dimensional changes. Alginoplast impressions may be poured after 72 hours, but Tropicalgin should be poured immediately and the storage time should not be more than 24 hours.
  
  
  CONCLUSIONS
  Immediate pouring of alginate impressions provides the highest accuracy in reproducing the teeth and adjacent tissues; however, this study demonstrated that pouring may be delayed for up to five days using extended-pour (Hydrogum 5) alginates.
authors: Dental Research Center Dentistry Research Institute, Department of Prosthodontics, Faculty of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.
authors: Ahmad
authors: A
authors: Rohanian
authors: Dental Research Center Dentistry Research Institute, Department of Prosthodontics, Faculty of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.
authors: Ghasem
authors: G
authors: Ommati Shabestari
authors: Dental Research Center Dentistry Research Institute, Department of Prosthodontics, Faculty of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.
authors: Somayeh
authors: S
authors: Zeighami
authors: Dentist, Private Practice, Tehran, Iran.
authors: Mohammad Javad
authors: MJ
authors: Samadi
authors: Dental Research Center Dentistry Research Institute, Department of Prosthodontics, Faculty of Dentistry, Tehran University of Medical Sciences, Tehran, Iran.
authors: Ahmad Reza
authors: AR
authors: Shamshiri
keywords: Alginates; Dental Impression Materials; Dimensional Measurement Accuracy; Plaster Cast
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