Comparison of reproducibility of dual-arch impression with conventional impressions

Purpose: This study compared the reproducibility of dual-arch impression technique with conventional impression techniques. Materials and Methods: Full-crown preparation was completed on posterior teeth of fresh porcine upper jaws. Dual-arch impression was made immediately after the preparation without gingival retraction cord or triple-tray (experimental group), followed by conventional 1-step and 2-step impressions (control groups). Sub-marginal impression lengths were measured at the center of mesial, distal, buccal and palatal surfaces and compared among three groups. The accuracy was compared by calculating the ratios of the widths among stone casts generated from each impression for mesial-distal and buccal-palatal measurements. Differences among the groups were analyzed by Wilcoxon signed-ranks test at 95% confidence level. Results: Regarding sub-marginal lengths, there were no significant differences among three groups (p>0.05) at buccal site. However, dual-arch impression was significantly smaller than control groups at mesial site (p<0.05), smaller than 1-step impression group at distal site (p<0.05), and smaller than 2-step impression group at palatal site (p<0.05). There were no significant differences among three groups (p>0.05) for mesial-distal widths, however, buccal-palatal widths of the dual-arch impression was significantly smaller than the control groups (p<0.05); 99.1 % of 1-step group and 99.20 % of 2-step group. Conclusion: Sub-marginal lengths of dual-arch impression without using retraction cord seemed to be clinically sufficient. However, the use of triple-tray is recommended when the dual-arch impression techniques are employed. (Int Chin J Dent 2006; 6: 9-16.)