A new method for the evaluation of the accuracy of full-arch digital impressions in vitro.

OBJECTIVES: Introducing a new approach to evaluate the accuracy of digital impression methods for full-arch scans, avoiding "best-fit alignment."
MATERIALS AND METHODS: A lower jaw model with a straight metal bar between the second molars of both quadrants was directly digitized using an intraoral scanner (True Definition, TRD, n = 12) and indirectly digitized (D810, CON, n = 12) after impression and plaster cast. A dataset of the bar from a coordinate measuring machine served as reference (REF). Datasets obtained from test groups were analyzed using inspection software to determine the aberration of the bar length, the linear shift (in X-, Y-, Z-axis) and the angle deviation (α overall, α coronal, α horizontal) caused by the digitalization method. Mann-Whitney U and unpaired two-sample Student's t test were implemented to detect differences. The level of significance was set at 5 %.
RESULTS: Concerning the bar length, no significant differences were found between groups. In view of the linear shift, CON showed significantly higher values than TRD in Y-axis (p = 0.003) and in Z-axis (p = 0.040). Regarding the angle measurement, TRD showed significant smaller values than CON for α overall (p = 0.006) and for α coronal (p = 0.005).
CONCLUSIONS: This in vitro study shows that intraoral scanning systems seem to show the same or even higher accuracy than the conventional impression with subsequent indirect digitalization. CLINICAL RELEVANCE: Intraoral scanners have proven excellent accuracy for single teeth or small spans. However, insufficient data is available about their accuracy for full-arch scans. The presented new approach seems to be suitable to precisely analyze differences in the accuracy of different digitalization methods without using best-fit alignment.