Effect of Second Wash in One and Two Step Impression Techniques on Dimensional Accuracy of Stone Models

The most common impression techniques used in fixed prosthodontics are one and two step with spacer. Sometimes impression details are not registered and as a result, use of second wash would be necessary. The aim of this study was to evaluate the effect of second wash of speedex impression material on dimensional accuracy of stone model in one and two stage impression techniques. In this experimental study, two metallic dies (with and without undercut) were used. Impressions were made using four techniques (one step, one step with second wash, two steps, and two steps with second wash). For each technique the impression taking was repeated 15 times and totally 60 impressions were provided. Impressions were poured with Vel-mix stone. Height and diameter for each die as well as distances between the dies were measured by sterio microscope and data were analyzed using ANOVA and T-tests.This study showed that in all four techniques height of dies with undercut was increased, but in the two step technique, the difference was not statistically significant (p= 0.282). In one step and two step with second wash technique, heights of dies without undercut were increased, while in the other two techniques they were decreased. In two step technique, diameters of the two dies were increased, while in other techniques they were decreased. In the two step technique, the distance between the dies was decreased, mean while other techniques did not show any increase and the differences were not statistically significant (p<0.05).The two step technique was more accurate than the other techniques. The one step with second wash technique was more accurate than one step technique. The use of two step with second wash technique is not recommended in fixed partial dentures, but in single crowns it can be used only with special considerations.