Effect of various impression techniques on marginal fit cast crowns

Objectives: The accuracy of 3 vinylpolysiloxane putty-wash impression techniques was compared by marginal fit assessment using the non-destructive method. Methods: A stainless steel master cast containing 3 abutments with 3 metal crowns matching the 3 preparations was used to make 45 impressions (3 groups, 15 impressions for each technique): group A – 1-step (putty and wash impression materials used simultaneously); group B – 2-step with 2 mm relief (putty as a preliminary impression to create 2 mm wash space followed by the wash stage); group C – 2-step technique with a polyethylene spacer (plastic spacer used with the putty impression followed by the wash stage). Accuracy was assessed by a Toolmaker's microscope, measuring and comparing the marginal gaps between each crown and the finish lines on each abutment of the duplicated stone cast poured from the impressions made from each group. A series of 1-way analysis of variance (ANOVA) was used for statistical analysis. One-way analysis of variance showed significant differences among the 3 impression technique groups in all 3 abutments and at all 3 locations (P<.001). Results: Group B yielded dies with minimal gaps compared to Groups A and C. Conclusions: The two-step impression technique with 2 mm relief was the most accurate regarding the crucial clinical factor of marginal fit.