The effect of different storage times and storage conditions of two types of alginate impression on accuracy of master cast

The aims of this study were to determine the effect of using different storage time and storage media on the accuracy of two types of alginate impression material,Hydrogum soft and Hydrogum elastic.
One hundred sixty impressions were recorded from a standard acrylic model using perforated trays. These impressions were divided into three main groups. In the first group,(48) impressions were stored at (3) times interval namely (15) minutes,(30) minutes,(60) minutes and left on the bench uncovered. In the second one,(48) impressions were stored in disposable plastic bags at the same time interval mentioned above. In the third one,(48) impressions were divided into (3) subgroups, the first one were only washed with tap water before pouring, the other two subgroups were immersed in Sodium Hypochiorite(0.5%) and ChlorhexidineGluconate(0.5%) disinfectant solutions for (30) minutes before pouring,(16) impression will be taken and poured immediately to be considered as a control for this study.
A three dimensional measuring machine (3D) was used for measuring the dimensional change of stone casts, the results showed that there was no significant differences of casts accuracy produced from the two types of an alginate impression material.
Storage of alginate impression material at (15) and (30) minutes on the bench or inside sealed plastic bags showed no significant differences in dimensional changes compared with control samples that poured immediately, Storage to (60) minutes showed a significant difference,washing alginate with tap water and immersion in chlorhexidine disinfectant solution (0.5%) for (30) minutes showed no significant difference Immersion in sodium hypochlorite (0.5%) for (30) minutes showed significant changes.
It was concluded that alginate impression could be stored for (30) minutes inside bags without significant changes if the pouring of alginate impression will be delayed for any reason.