Abstract
To compare the three-dimensional accuracy of an open-tray and two snap on impression techniques (with and without connecting the plastic caps of the snap on impression transfers) in a full arch 6-implant model, a reference acrylic resin model of the maxilla with six implants was fabricated. Prominent geometrical triangles, in the palate area, served as reference points for a digital overlap between scans. Three impression transfer techniques were evaluated and compared: open-tray direct impression (DI), snap on impression (SpO), and connected snap on impression (SpOC). Polyether impression material was used to make 30 impressions (n = 10), and the master model and all casts were digitally scanned with a laboratory optical scanner. The obtained 3D data were converted and recorded as STL files, which were imported to a 3D inspection software program. Angular deviations (buccal, occlusal and interproximal planes) between the study casts and the reference model were measured. Data were analyzed using one-way analysis of variance (ANOVA) and Tukey post hoc test, with 0.05 used as the level of significance. The 3D angular deviations from the master model revealed no significant differences between the DI and SpO impression groups, but there were significant differences in the SpOC impression group, particularly in the buccal and occlusal planes. In all groups, the 3D angular deviation between the most distal scan abutments on each side of the model was significantly different from all other areas when compared to the master model. Within the limits of this study, it is possible to conclude that the indirect closed tray snap on impression technique with unconnected plastic caps exhibited the same three-dimensional accuracies as the direct open tray technique. The indirect closed tray snap on impression technique with connected plastic caps was less accurate than either the indirect closed tray snap on impression technique with unconnected plastic caps or the direct open tray technique. In the case of full arch implant supported prostheses, inaccuracies may be expected in the most distal implants for all the three impression techniques evaluated in this study. Further in vitro and in vivo research is required.
Highlights
The procedure of making an impression is a crucial stage in the implant prosthodontic treatment process, as it directly affects the accuracy of the definitive cast and the passive fit of the implant supported superstructure [1]
The objective of this study was to evaluate the three-dimensional accuracy of open-tray (DI) and two closed-tray snap on impression techniques, namely with (SpOC)
We found no significant differences between the SpO group and the direct impression (DI) groups in the angles of any of the three surfaces, but the results in the Snap On Impression Connect (SpOC) group were significantly different from the other two groups
Summary
The procedure of making an impression is a crucial stage in the implant prosthodontic treatment process, as it directly affects the accuracy of the definitive cast and the passive fit of the implant supported superstructure [1]. Practically speaking, the achievement of a perfect passive fit is almost impossible, aspiring to diminish impression errors and improve the outcome of the impression procedure is an important part of implant prosthodontic treatment. A number of studies have investigated the clinical factors that affect the precision of implant supported impressions. These include studies comparing open and closed-tray impression techniques [5], or the use of different impression materials [6]. Other studies have examined the effect of connecting the implant transfers on the accuracy of the impressions [7,8], as well as the effect of implant angulation or the design of different prosthetic parts [9]
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