ABILITY OF VARIOUS IMPRESSION MATERIALS TO PRODUCE DUPLICATE DIES FROM SUCCESSIVE IMPRESSIONS

This in vitro study evaluated the ability of five different impression techniques to make duplicate dies of two different types of tooth pre paration. One mandibular second premolar Ivorine tooth was prepared fo r a complete crown and one for an onlay. A master impression was made of each tooth preparation with the use of five impression techniques f or a total of 10 master impressions, and a master die was made from ea ch of these impressions. Castings were made on these master dies, and the fit of each casting was verified on the respective Ivorine tooth. Marginal openings of the castings on the master dies were recorded und er magnification at four predetermined points. Five successive impress ions, with the use of each impression material, were then made of each tooth preparation for a total of 50 test impressions, and 50 test die s were made from these impressions. The fit of the respective casting was evaluated under magnification for each test die at the four predet ermined points, and marginal openings were recorded. Differences betwe en the marginal discrepancies of the casting on the master die and on the test die were tabulated and the results were statistically analyze d. Results indicated that none of the impression materials was capable of producing exact replicas. Polysulfide rubber performed significant ly better than two materials for the production of duplicate dies with the complete crown preparation; and polyvinyl siloxane used with a pu tty-light body, single-stage technique produced mean marginal discrepa ncies that were significantly greater than the other four techniques w hen used for the onlay preparation. Mean marginal discrepancies were l ess than 25 mu m for all techniques except for the single-stage polyvi nyl siloxane impression of the onlay preparation where the mean margin al opening was 48.18 mu m +/- 15.28 mu m.