In Vivo Accuracy and Precision in Prosthodontics

Abstract: Background: There has been a dramatic increase in commercially available intraoral scanners (IOS) in the last decade, offering to replace indirect digitization of models (MOD) fabricated from impressions (IMPR). IOS has benefits of less patient discomfort and a faster workflow to fabricate fixed dental prosthesis (FDP), and implant-supported prostheses (IFD). However, in vivo evidence is lacking not only for IOS, but also for MOD, FDP and IFD fit.Aims: Paper I: to evaluate in vitro finish line distinction and accuracy in seven IOS and one MOD. To assess parameters of resolution, tessellation, topography, and color. Paper II: to evaluate a method of acquiring an in vivo reference measurement in dentate subjects and analyse accuracy and precision of IOS and MOD. Paper III: to evaluate an in vivo reference-measurement method in fully edentulous maxillae with full-arch implant treatments and to analyse accuracy of MOD and fit of existing IFD. Paper IV: to analyse precision and accuracy of IOS using different acquisition protocols compared to the reference-measurement in Paper III.Material and Methods: Paper I: A model with a crown preparation was reference-scanned with an industrial scanner, (ATOS), scanned with seven IOS and the MOD of an IMPR was digitized. Best-fit Alignment and 3D Compare Analysis was followed by descriptive analysis. Paper II: A reference-scan was acquired with ATOS. Subjects were scanned with IOS and one MOD of an IMPR was digitized. Accuracy and precision were evaluated after Best-Fit Alignment and 3D Compare Analysis. Paper III: A reference-measurement of implant positions was acquired with ATOS. MOD from IMPR was digitized and IFD scanned. Datum and Relative Point System Alignment was followed by accuracy and precision analysis. Paper IV: Subjects in Paper III were scanned with IOS using three different protocols, followed by accuracy and precision analysis.Results: Paper I: There were considerable differences between IOS depiction of finish line and finish line accuracy. Paper II: IOS presented varying results for impressions in up to ten units. No differences were found for MOD. Paper III: IFD was significantly less accurate than MOD. Paper IV: Differences were found between scanning protocols. Compared to Paper III, IFD was less accurate. No differences were found for MOD.Conclusion: There are relevant differences between IOS when scanning subgingival preparations. Some IOS are better suited for long-span scans. Some IOS can be used for full-arch impressions for IFD in the maxilla, however, adequate soft-tissue management is crucial.