Dimentional Accuracy of Multiple Pour Full-Arch Stone Casts

Abstract

Dimensional accuracy of multiple pour full-arch stone casts made from non-aqueous elastomeric impression materials, namely Permlastic and President, was studied. A maxillary metal cast, carrying eight reference marks, was employed as the master model. Ten impressions were made of the master model with each impression material under the same conditions. Three consecutively poured full-arch stone casts were fabricated from each impression at pouring times of 5', 40', and 75'. Ten point-to-point distances were determined for each of 60 stone casts; the data obtained from those measurements were compared statistically.
The first pour stone casts from the President impressions were the most accurate. The second and third pour stone casts were only slightly less accurate, a statistically significant difference among pours existing for some of the measured distances but not others. The Permlastic derived stone casts were not as accurate as those from President and showed significant differences in dimensions as the pours progressed. The difference in behavior between the two impression materials studied can be explained, in part, by the greater polymerization and thermal contraction and permanent deformation following strain of the polysulfide.
Although superior dimensional accuracy and stability of the President impression would favor its expanded use rather than the expanded use of Permlastic in the fabrication of fixed restorations, this study did not confirm the definite benefit of the introduction of President impression material for the multiple pour technique.