The Effect of Impression Technique, Connection Type and Implant Angulation on Impression Accuracy

Purpose. To measure the accuracy of implant impression techniques in vitro, using open and closed tray techniques with internal and external connection implants at various angulations.;Materials and methods. Three internal connection implants and three external connection implants were placed in an acrylic master cast as follows from posterior to anterior: 90, 15 and 30 degrees. Twenty-four open tray and closed tray impressions were made and the resulting casts were analyzed using digital photography. The following measurements were performed (1) horizontal displacement; (2) vertical displacement; (3) angulation displacement in the lateral view; (4) angulation displacement in the frontal view. Statistical analysis was completed by using a factorial analysis of variance (three-way ANOVA). A p value ≤0.05 was considered significant. Tukey's HSD test was used to analyze significant differences for the angulation variable.;Results. (1) The results show that there was no difference in the impression accuracy when open vs. closed tray impression techniques were used except in the horizontal plane where the closed tray produced more accurate impressions than the open tray. (2) External connection implants produced a significantly larger horizontal displacement compared to the internal connection implants. (3) The results did not follow a particular pattern for the effect of implant angulation on impression accuracy. (4) The interactions observed between connection type, implant angulation and tray type and the resulting discrepancy in the horizontal plane showed that implants placed at 90 degrees produced the largest horizontal displacement. In the vertical plane, internal connection implants placed at 15 degrees when an open tray technique was used produced the largest vertical displacement.;Conclusion. Clinically, the results from this study suggest that when encountering full arch implant restorations it is most beneficial to have the implants as parallel to each other as possible and to remove the custom tray along the same path as the implant angulation. The splinted open tray technique is time consuming and it might not result in a more accurate master cast. Open or closed tray techniques can be used, however, the master cast should always be verified before fabricating the final prosthesis.