Accuracy of one-and two-stage impression techniques –A randomized controlled trial

Objectives: The determination of complex three-dimensional alterations of the reproduction of prepared teeth by different impression techniques in-vivo is possible by a procedure using extraoral digitizing of master casts. This method overcomes the limitations of common methods, which are limited to a two-dimensional analysis. The aim of this study was to determine the three-dimensional accuracy of the reproduction of teeth prepared for single crowns by different dental impressions techniques (monophase, one-stage, two-stage) taken in a private dental office. Methods: For 61 patients with teeth prepared for single crowns a monophase- (MP), one-stage- (OS) and two-stage-impression (TS) were taken in a randomized order. Master-casts were manufactured according to the Zeiser-technique using a type IV die stone for any impression and then optically digitized. The digitized data sets of the MP- and TS-impression were compared with the CAD-surface model of the OS-impression chosen as the reference. Differences between the CAD-surface-model and the digitized data set were analyzed quantitatively and qualitatively using Surfacer® (Imageware Inc., USA). The statistical analysis was performed descriptively by calculating means and SD. Results: The mean positive/ negative deviation (SD) between the reference and the MP- and TS-impression was 0,016mm (0,021mm)/ -0,017mm (0,020mm) for MP and 0,020mm (0,021mm)/ -0,020mm (0,023) for TS. The maximum positive/ negative deviation between the reference and the MP- and TS-impression was 0,251mm/ -0,197mm for MP and 0,193mm / -0,240mm for TS. The finishing line was reproduced more completely by the OS-impression followed by the TS- (0,229mm) and the MP-impression (0,267mm) Conclusion: The one-stage impression showed superior accuracy regarding precision and reproduction of the finishing line. This study was supported in part by the 3M ESPE AG, Seefeld, Germany.