Tehran University of Medical Sciences Frontiers in Dentistry 2676-296X 11 6 2014 12 15 655 64 Ahmad Rohanian Dental Research Center Dentistry Research Institute, Department of Prosthodontics, Faculty of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. Ghasem Ommati Shabestari Dental Research Center Dentistry Research Institute, Department of Prosthodontics, Faculty of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. Somayeh Zeighami Dental Research Center Dentistry Research Institute, Department of Prosthodontics, Faculty of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. Mohammad Javad Samadi Dentist, Private Practice, Tehran, Iran. Ahmad Reza Shamshiri Dental Research Center Dentistry Research Institute, Department of Prosthodontics, Faculty of Dentistry, Tehran University of Medical Sciences, Tehran, Iran. 2015 10 16 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.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 https://fid.tums.ac.ir/index.php/fid/article/view/403 https://fid.tums.ac.ir/index.php/fid/article/download/403/379