Measured accuracy of intraoral scanners is highly dependent on methodical factors.

PURPOSE: The accuracy of intraoral and model scanners has been widely investigated with heterogeneous results, but the impact of the applied diversity of measurement methods on the outcomes remains unknown. This study aimed to evaluate the influence of methodological factors on the measurement result when comparing full-arch scans. METHODS: The evaluation referred to a 5M model to analyze whether accuracy measurements are affected by (1) the reference geometry, (2) mesh density of the standard tessellation language (STL) datasets, (3) operator, (4) inspection software, and (5) alignment procedure. STL datasets of full-arch reference models were measured with 29 different combinations of these factors. For each combination, 10 repeated measurements of the intermolar width were performed. Trueness was statistically analyzed with one-way ANOVA and T-tests, repeatability with Levene tests, and reproducibility with interclass correlation coefficients. RESULTS: Measurement method variations affected the intermolar width by up to 186 microm. The alignment algorithm had a significant effect on the measurement outcome (p = 0.001). Likewise, reference geometry influenced trueness and repeatability significantly (p = 0.001), whereas mesh density affected the repeatability only in some cases. The operator had no impact on the measurement result. The inspection software affected the repeatability but not the trueness. CONCLUSION: The factors reference geometry and alignment algorithm highly affected the measurement outcome, while the operator, inspection software, and mesh density showed no impact on the trueness of the outcome. Cylindrical reference geometries showed fewer differences than bar-shaped ones and best-fit alignments fewer variations than alignments based on boundary parameters.