Accuracy of 2 Impression Techniques for ITI Implants

Purpose: The aim of this study was to compare the accuracy of casts produced by 2 impression techniques and elastomeric impression materials commonly used for the fabrication of implant-supported fixed prostheses. Materials and Methods: A master model with 4 synOcta ITI implants placed unilaterally in place of the mandibular right central incisor, canine, first premolar, and first molar was constructed. Implant-level impressions were made by direct and indirect techniques. In the direct technique, synOcta impression caps with integral guide screws were used to transfer the implants using a custom-made acrylic resin tray and a polyether impression material (the PE direct technique). In the indirect technique, synOcta plastic positioning cylinders with impression caps were used to transfer the implants with either a custom-made acrylic resin tray and polyether impression material (the PE indirect technique) or with a stock tray with a vinylpolysiloxane impression material (the VPS indirect technique). After impression making, all casts (n = 21) were poured in type IV dental stone. Linear changes in -x or -y direction and numeric and descriptive angular changes between the implants were quantified using a coordinate measuring machine. Results: Seven of 12 distance measurements (6 for -x direction, 6 for -y direction) showed differences between groups (P .05). Of these, 5 were associated with the PE direct versus PE indirect and PE indirect versus VPS indirect, and 3 were associated with PE direct versus VPS indirect. Two implants also showed angular changes but only for the PE indirect technique versus the VPS indirect technique (P .05). Conclusion: The snap-on VPS indirect impression technique using a stock tray, which has the advantages of being clinically convenient and eliminating repositioning after removal of the impression, resulted in dimensional accuracy similar to that achieved with the PE direct technique.