Comparison of Different Impression Techniques When Using the All-on-Four Implant Treatment Protocol.

Purpose: The aim of this in vitro study was to compare the accuracy of two different impression techniques for the All-on-Four implant therapy protocol.
Materials and Methods: An acrylic resin analog for an edentulous maxilla with four internal connection implants (Replace Select, Nobel Biocare) was fabricated according to the All-on-Four protocol. A total of 40 impressions were made with different techniques (open and closed tray) at abutment and implant levels and poured in type IV dental stone. A coordinate measuring machine was used to record the x, y, and z coordinates and angular displacement. The measurements were compared with those obtained from the reference model. Data were analyzed with analysis of variance and t test at α = .05.
Results: There was less linear and rotational displacement for the open-tray technique when compared with the closed-tray technique (P = .02 and P < .001, respectively). Impressions made at abutment level produced fewer linear and rotational displacements when compared with implant level impressions using the open-tray technique for straight and angulated implants (P = .04 and P < .001, respectively). However, less rotational dislocation was observed for impressions made with the closed-tray technique when compared with the open-tray technique at implant level (P < .001).
Conclusion: Choice of impression technique affected the accuracy of impressions, and less displacement was observed with the open-tray method. Abutment-level impressions with an open-tray technique were more accurate, while implant-level impressions were more accurate when a closed-tray technique was used.