Abstract

  Background and Aim: Dimensional stability of die is very important factor in fixed prosthodontic treatments and different impression techniques is one of the most factors in this specify, the aim of this study was comparison of three impression.

  Techniques: one step and two step with out spacer and two step with spacer on die dimensional variation.

  Materials and methods: This experimental study, was carried out using laboratory stainless steel master models that contained three complete crown abutment preparations with 22 mm distance, 7 mm diameter 7.5 mm height and
3 ° convergence. To prepare master casts three impression techniques was done by using president silicone impression material. Twelve impression were taken for each technique and Elite Rock tip IV casting material was used to prepare stone models. Profile projector and micrometer were used to measure different dimensions of laboratory model. Anova test were used for data analysis.

  Results: The study was carried out on 36 impressions in three groups . The measurement location for crowns distances and height of the main model to the impression methods (p<0.4) and in HC distance is similar. The results in main model was 7.4+0.06, in one step 7.37+0.04 , in two steps 7.31+0.03 and in 2 steps with space was 7.33+0.05 micrometers (p<0.6).

  Conclusions: It seems the impressions methods do not affect on the dimensional changes of die and their dimensional changes are not significant. The study on other related  factors on dimentional changes of die is recommended.

  Key words: Dimensional accuracy, impression technique, Silicone