RESUMEN
Dimensional stability of die plays very important role in fixed prosthodontic treatments. Different impression taking techniques may be the main source of die dimensional changes. However, in this regards, contradictory results have been reported in the literature. This study was designed to assess the dimensional accuracy of master casts prepared by means of three impression techniques using Speedex silicone impression material. This quasi-experimental study was carried out using laboratory stainless steel master models that contained three complete crown abutment preparations. The one-step, two-step with and without relief methods were the three putty-wash impression techniques used in this investigation. Fifteen impressions were taken for each technique and velmix casting material was used to prepare stone models. Profile Projector and micrometer were used to measure the final die's height, diameter and different dimensions in order to compare them with laboratory model. ANOVA and paired samples t-test were used for data analyses. The two step technique with spacer was the most accurate method with zero LC distance [distance between left and middle abutment]. However, in the other two techniques, the mean difference was 0.22 [ +/- 0.01], [P<0.05]. Regarding the distances between abutments, there was no significant difference when comparing one-stage and two-stage technique without spacer. Although, the height of abutment was more accurate in two-stage technique without spacer than one-stage. The two-step technique with spacer was the most accurate technique when using Speedex impression material