KEY WORDS Sodium hypochlorite; Condensation silicone; Disinfection; Dimensional changes

Statement of the Problem: Impression materials are concerned as a significant source of cross-contamination because of exposure to blood and saliva. Purpose: Considering the importance of infection control in the dental environments, this study is performed to investigate the dimensional changes of two condensation silicone impression materials, Speedex and Irasil, after immersion in 0.5 % sodium hypochlorite. Materials and Method: In this in-vitro study, two condensation silicone impression materials, Speedex and Irasil, were used on a prefabricated metal model having two dies, one with and the other without undercut. Each impression material was used to prepare 30 impressions; half of each group was immersed in 0.5 % sodium hypochlorite for 20 min. The casts were prepared and a profile projector was used to measure the casts in terms of height and diameter of the die without undercut, distance between the two dies, die diameter below the undercut, and the height of the die above the undercut. The results were statistically analyzed using Student t-test