Purpose: The purpose of this study was to evaluate dimensional stability and detail reproduction of a newly introduced addition silicon impression material after disinfection and sterilization.Materials and methods: In this study, an epoxy resin master model was duplicated from a modified dentate mandibular model. Heat resistant addition silicon impression material heavy and light body(Affinis/coltene wholedent/Switzerland) was used for making 30 impressions for the master model using heat resistant plastic stock trays (coltene wholedent/Switzerlan). The 30 impressions were divided into three groups Group 1 : ( n=10) Control group , untreated impressions. (C.G) .Group 2 : ( n=10 ) Impressions were sterilized by the autoclave. (S.G). Group 3 : (n=10) Impressions were chemically disinfected.(D.G). After treatments of all impressions, they were poured with extra hard stone (type IV) to get improved stone casts. Dimensional accuracy and detail reproduction of the impressions were evaluated indirectly through the recovered stone casts from impressions of the master model using the travelling microscope. Distances from the stone casts were compared with those of the epoxy master model as well as those of the control group. Results: Results of the present study showed a statistically significant difference between disinfection and sterilization groups regarding cross arch distance length (A) as well as anteroposterior distance (B) sterilization group showed the greatest dimensional change while control group and disinfection groups showed the lowest changes. As regards finish line thickness and Occluso-gingival height, there was no statistically significant difference between the tested groups. Conclusions: Within the limitations of this study, it could be concluded that:Conventional steam sterilization of the polyvinyl siloxane impression material should be viewed with caution, particularly when making fixed partial dentures.Conventional steam sterilization of the polyvinyl siloxane impression material may be satisfactory if that impression is to be used in making diagnostic casts. Chemical disinfectant of polyvinyl siloxane impression material can be successfully used in making fixed partial dentures.