Accuracy of different impression techniques for multiunit implant restoration: A qualitative in vitro study

Statement of problem. Displacement of impression copings and/or implant replicas during impression making and dimensional changes that occur during clinical and laboratory phases of making multiunit implant prostheses may affect the accuracy and fit of the prostheses. Purpose. The purpose of this qualitative study was to investigate and compare 3 different impression techniques for osseointegrated dental implant transfer procedures. Material and methods. Three impression transfer approaches were evaluated and compared: closed-tray impression technique (CTT), impression with plastic snap-fit impression copings; open-tray impression technique (OTT), impression with independent square copings; and OTT joining the impression copings with a photo-polymerized resin (PPT). A reference acrylic resin model with 4 implants was fabricated. Polyvinyl siloxane with a stock tray was used to make 45 impressions (n=15 for each impression technique), and 45 die definitive stone casts. A computer-aided design and computer-aided manufacturing (CAD-CAM) titanium framework was fabricated on the reference model. Three blinded operators evaluated the fit of the CAD-CAM titanium framework on each model to find clinically acceptable fit. The Kappa test was used for the agreement between the examiners (alpha=.05). Results. Agreement was found among the 3 examiners on 44 of 45 specimens (Kappa value = 0.939; P<.001). In the CTT group, 14 casts were found to be acceptable. In the OTT group, nearly half of the specimens produced unacceptable fitting casts, whereas in the PPT group, 13 casts were found acceptable. Conclusions. CTT and PPT produced more accurate casts than the OTT technique, which yielded inferior results.