Open-Tray vs. Snap-on Impression Techniques- in Vitro 3D Study

Objectives: The aim of this study was to compare the three-dimensional accuracy of open-tray and 2 snap-on impression techniques (with and without connecting the snap-on) in a full arch 6-implant model. Three impression transfer techniques were evaluated and compared: open-tray direct impression (DI), snap-on impression (SpO) and connected snap-on impression (SpOC).
Methods: A reference acrylic resin model of the maxilla with 6 implants was fabricated. Geometrical prominent triangles were made in the palate area as reference points for digital overlap between scans. Polyether impression materail was used to make 30 impressions (n=10 for each impression technique). The master model and all casts were digitally scanned with a laboratory optical scanner using scan abutments. The obtained 3D data was converted and recorded as STL files, which were imported to a 3D inspection software program. Angular deviations (buccal, occlusal, interproximal planes) between the study casts and the reference model were measured. Data was analyzed using one-way analysis of variance (ANOVA) and Tukey post hoc test and 0.05 was used as the level of significance.
Results: The 3D angular deviations from the master model revealed no significant differences in the DI and SpO impression groups, while in the SpOC impression group, significant differences were found, especially, in the buccal, and occlusal planes. In all groups, the 3D angular deviation between the most distal scan abutment on each side of the model, was significantly different from all other areas, when compared to the master model.
Conclusions: Within the limits of this study, it is possible to assume that: 1. The SpO impression technique exhibits a three-dimensional accuracy as the DI technique; 2. The SpOC impression technique is less accurate then the DI and the SpO impression techniques; 3. In case of full arch implant supported prosthesis, inaccuracies between the most distally implants are expected.