The accuracy of implant scans captured by using intraoral scanners (IOSs) has been reported to decrease over longer spans, which may compromise the passive fit of implant-supported frameworks. Among the implant scanning techniques described, reverse impression and extraoral photogrammetry (PG) have been introduced to overcome the limitation of direct intraoral acquisition by using IOSs. However, their accuracy remains uncertain. The purpose of this systematic review and meta-analysis was to assess the accuracy of complete arch implant scans recorded by using reverse impression and extraoral PG techniques. A comprehensive literature search of PubMed/Medline, Scopus, Embase, Web of Science, and Cochrane databases, as well as a manual search, was conducted up to the end of August 2025. Studies evaluating the trueness and/or precision of complete arch implant scans obtained by using reverse impression or extraoral PG techniques were included. Two reviewers independently assessed methodological quality using the Joanna Briggs Institute (JBI) critical appraisal tool, with a third reviewer resolving disagreements. Studies reporting the mean and standard deviations of the linear and angular discrepancies of complete arch implant scans recorded by using extraoral PG systems were included in the meta-analysis. Publication bias was identified using the funnel plot and Egger test. A total of 29 studies met the inclusion criteria, 3 examined the accuracy of reverse impression, and 26 assessed the accuracy of extraoral PG. The reverse impression technique yielded variable results, influenced by the scanning technology/system and scanning pattern, although the reported accuracy values generally fell within the clinically acceptable limits. The meta-analysis revealed that extraoral PG techniques have a mean linear discrepancy of 27 µm, a mean angular discrepancy of 0.21 degrees, a mean linear trueness of 69 µm, a mean linear precision of 43 µm, a mean angular trueness of 0.23 degrees, a mean angular precision of 0.15 degrees, a mean RMS trueness of 48 µm, and a mean linear precision of 16 µm. Preliminary in vitro data suggested that the reverse impression technique has promising accuracy; however, the evidence remains limited, and additional well-designed studies are needed before clinical acceptability can be established. Extraoral PG techniques are clinically acceptable for capturing implant positions.
Prasad et al. (Sun,) studied this question.