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The accuracy and dimensional stability of impression materials are one of the most important factors for successful prosthodontic treatment. The purpose of this study was to evaluate the accuracy of several dental elastomeric impression materials used widely and clinically；Impregum-F??, Permlastic??, Silascon??, Perfect??, Xantopren??. There have been many studies to evaluate the accuracy of impression materials. But it has not been decided yet, which method was most suitable for the evaluation of the accuracy. In this study, two resin teeth, ＃15 ＆ 25, were prepared with rounded shoulder margin and 90 degree cavosurface angle. For the polysulfide rubber and polyether, the custom tray was made at least 24 hours prior to impression taking. For the silicone rubber materials, putty/wash impression technique was applied in taking impressions. Marginal openings of the castings on the master dies and prepared reisn teeth were measured under stereomicroscope. The results were statistically analyzed and compared between tested impression materials. The results were as follows； 1. In the overall accuracy of impression materials, polyether was the most accurate one, followed by polysulfide, additional silicone and condensation silicone. 2. On the first model pouring, condensation silicone had the largest discrepancies and there was significant difference compared to the other impression miterials. 3. Polysulfide had the least discrepancies in the first model pouring, but showed larger discrepancies in the immediate second pouring than the first pouring. 4. On the immediate second pouring, the discrepancy of polyether was shown to be the smallest, while the largest one was additional silicone.
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