the effect of disinfection with sodium hypochlorite 0.5% on dimensional stability of condensation silicone impression materials of speedex and irasil

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. results: in speedex group, an increase was detected in the height of die without undercut and the height of the die above the undercut, but other dimensions have decreased. no significant change was observed in dimensions of speedex group except for the distance between the two dies and die height above the undercut. in irasil group, the height of the die without undercut, the distance between the two dies and the height of the die above the undercut have increased; while decrease was observed in other dimensions. compared with the original sample, no significant difference was observed in dimensions except for the height of the die above the undercut. conclusion: these changes for speedex group include changes in distance between the two dies and the height above the undercut which can impede proper placement of prosthesis, particularly fixed partial dentures in which the accuracy of the distance between the two dies are of utmost importance. in irasil group, the height of above the undercut was altered and this negative effect is highlighted in registering the reduced single tooth with an undercut. key words: sodium hypochlorite; condensation silicone; disinfection; dimensional changes