Conventional open-tray impression versus intraoral digital scan for implant-level complete-arch impression

Abstract

STATEMENT OF PROBLEM:

The best-fit method is frequently used to evaluate the accuracy of different implant impression techniques. However, the method includes inherent superimposition errors, which may accumulate and become more exaggerated in complete-arch impressions.

PURPOSE:

The purpose of this in vitro study was to evaluate and compare the trueness and precision of conventional open-tray impressions and intraoral digital scans at the implant level in an edentulous maxillary model with 6 implant replicas without superimposition.

MATERIAL AND METHODS:

A master model was fabricated using epoxy resin by duplicating a maxillary edentulous cast that had 6 implant replicas in the right first molar, right first premolar, right lateral incisor, left lateral incisor, left first premolar, and left first molar positions. The conventional open-tray, splinted-coping impression technique was used to fabricate 10 definitive casts (group CI). Intraoral digital scans were performed, after which scan bodies were connected to each implant replica to fabricate 10 digital models (group IOS). For the master model and group CI, a computerized coordinate-measuring machine was used to determine the 3D spatial orientation of the implant replicas. For group IOS, the scan bodies were converted to implant replicas using a digital library, and an inspection software program was used to measure the implant replicas. To compare the accuracies of different impression techniques, a 3D part coordinate system was set to compute the centroid and projection angles of each implant replica. The changes in the centroid coordinates (linear displacement: Δx, Δy, Δz, and ΔD; ΔD=Δx2+Δy2+Δz2) and projection angles onto XY and ZX planes (angular displacement: ΔθXY and ΔθZX) were statistically compared (α=.05).

RESULTS:

Group CI gave more accurate trueness values than group IOS for overall Δx (P<.001), Δy (P =.029), Δz (P<.001), and ΔD (P<.001). Furthermore, group CI had more accurate precision values for Δx, Δy, and Δz. Group IOS exhibited a statistically greater angular displacement in the ZX plane (P=.002), but the difference was only 0.24 degrees. No differences were found between the 2 groups for the angular displacement in the XY plane (P=.529).

CONCLUSIONS:

Conventional open-tray impressions produced significantly smaller linear displacements than the digital scan obtained using an intraoral scanner at the implant level in a complete-arch model.