Comparison of the reverse scan technique with an intraoral scanner and the traditional impression technique

Intraoral scanners have many advantages but have limited applicability for extensive tooth-supported or implant-supported prostheses because of merging errors.

The purpose of this study was to compare the reverse scan technique (RST) with an intraoral scanner using the traditional impression technique both in vitro and in vivo.

A participant was scanned 10 times with an intraoral scanner. Then, the RST was performed 3 times in the oral cavity. One of the intraoral scans was chosen to make a 3-dimensionally (3D) printed cast. The printed cast was scanned 10 times with a laboratory scanner (Control cast) and 10 times with an intraoral scanner (IOS cast). The RST was performed 10 times (RST cast), and 10 dental impressions were made using the traditional splinted technique on the same cast (Impression cast). A laboratory scanner was used to obtain standard tessellation language (STL) files of the tested methods. A newly developed pyramid replacement method was used to evaluate accuracy. This method uses modified virtual abutments with integrated pyramids that determine the exact measurement points. The obtained data were processed using Procrustes analysis and statistically analyzed (α=.05).

The Procrustes distances were Control cast 0 to 0.4 µm (median 0.3 µm), RST cast 5.6 to 6.9 µm (median 6.2 µm), Impression cast 5.4 to 7.1 µm (median 6.5 µm), and IOS cast group 4.5 to 41.2 µm (median 5.8 µm). In the participant, the Procrustes distance values were RST intraoral 9.5 to 9.6 µm (median 9.5 µm) and IOS intraoral 5.7 to 18.3 µm (median 10.9 µm).

The reverse scan technique is an acceptable fully digital replacement for traditional impression making. Using an IOS to obtain a 3D cast of an implant-supported interim prosthesis with scannable implant analogs is not recommended. It is more beneficial to use laboratory scanners rather than intraoral scanners for the digitization of precision improvement devices such as bonded interim implant-supported prostheses with a scannable implant analog or solid index.