Researchers at the Tehran University of Medical Sciences in Iran evaluated the 3-dimensional accuracy of a digital implant impression technique using a 3Shape TRIOS intraoral scanner (IOS) compared to the conventional pickup and transfer implant impression techniques in clinical situations.
The study involved 36 patients who had two implants (Implantium, internal connection) ranging in diameter between 3.8 and 4.8 mm in posterior regions of the mouth. Thirty-six reference models (RMs) were fabricated by attaching 2 impression copings intraorally, splinted with autopolymerizing acrylic resin, verified by sectioning through the middle of the index, and rejoined again with freshly mixed autopolymerizing acrylic resin pattern (Pattern Resin) with the brush bead method.
Then, the splinted assemblies were attached to implant analogs (DANSE) and impressed with type III dental stone (Gypsum Microstone) in standard plastic die lock trays. Thirty-six working casts were fabricated for each conventional impression technique (ie, pickup and transfer). Thirty-six digital impressions were made with a TRIOS 3Shape IOS.
Eight of the digitally scanned files were damaged; 28 digital scan files were retrieved to STL format. A coordinate-measuring machine (CMM) was used to record linear displacement measurements (x, y, and z coordinates), interimplant distances, and angular displacements for the RMs and conventionally fabricated working casts.
CATIA 3D evaluation software was used to assess the digital STL files for the same variables as the CMM measurements. CMM measurements made on the RMs, and conventionally fabricated working casts were compared with 3-D software measurements made on the digitally scanned files.
The study showed significant differences between the pickup and digital groups in all of the measured variables (p < 0.001). Concerning the transfer and digital groups, the results were statistically significant in angular displacement (p < 0.001), distance measurements (p = 0.01), and linear displacement (p = 0.03). However, between the pickup and transfer groups, there was no statistical significance in all of the measured variables.
The digital implant impression technique had the least accuracy. Distance and angulation errors associated with the intraoral digital implant impressions were too large to fabricate well-fitting restorations for partially edentulous patients. The pickup implant impression technique was the most accurate, and the transfer technique revealed comparable accuracy to it.
The study, “A Clinical Comparative Study of 3-Dimensional Accuracy between Digital and Conventional Implant Impression Techniques,” was published by the Journal of Prosthodontics.
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