Accuracy of second pour casts using dual-arch impressions

This study compared the accuracy of the second pour of addition silicone impressions made using custom acrylic resin complete-arch trays and two types of dual-arch trays. Thirty impressions were made of a typodont using metal dual-arch, plastic dual-arch and acrylic resin complete-arch custom trays (10 impressions/group). Tooth #30 (first molar) and tooth #32 (third molar) in the typodont were custom metal dies made in the shape of complete crown preparations. On the metal dies were scribed reference marks permitting measurements to be made in the mesial-distal, buccal-lingual and occlusal-gingival dimensions. In addition, an inter-tooth measurement between tooth #30 and #32 was made. Following impression procedures, gypsum casts were poured. The casts were removed from the impression and, 24-hours later, second pours were completed. The distances between reference marks on each cast were measured using a measuring microscope. The measurements from each second pour cast were used to compute a group mean, with values expressed as a percent deviation from the master model. A two way analysis of variance was used to compare the groups. No statistically significant differences were found in accuracy among the three type trays except in the inter-tooth measurement where the metal dual-arch tray was more accurate than the other trays.