A male 45 years old wants his missing teeth to be replaced. Intraoral examination reveals Kennedy class 4 edentulous maxillary arch. Impression is made with hydrocolloid impression material. The impression is placed in which of the following storage medium to prevent dimensional change?

Dimensional Stability Once the hydrocolloid impression is removed from the mouth and exposed to air at room temperature, some shrinkage associated with syneresis and evaporation will occur. Conversely, if the impression is immersed in water, swelling caused by imbibition can occur. The storage medium, such as 2% potassium sulfate solution, or 100% relative humidity in a storage chamber, is suggested to reduce the dimensional change of agar impressions.  100% relative humidity is the best storage environment to preserve the normal water content of the impression.