Understanding the effect of scan spans on the accuracy of intraoral and desktop scanners

Objectives: This study aimed to measure and compare the accuracy (trueness and precision) of intraoral scanners and desktop scanners when scanning different spans. Methods: Three plaster models representing different spans (full arch, half arch, and three teeth) were obtained from conventional silicone impressions of a maxillary typodont and used as the scanning objects. An industrial scanner (ATOS III Triple Scan) was used to scan the three plaster models to obtain reference digital models. The plaster models were then scanned using two intraoral scanners (Trios 3 and Primescan) and two desktop scanners (LS3 and D2000) to obtain test digital models. The reference and test models were imported into professional reverse engineering software for processing and analysis. The root mean square value indicated differences between the reference and test models. Two-way ANOVA and Bonferroni multiple comparison tests were used for statistical analysis. Results: Two-way ANOVA tests revealed significant differences in trueness and precision for different scan spans (p < 0.001) and different scanners (p < 0.001), which indicates that the scanner types and scan spans affect the accuracy of the scanner. There was no significant difference in the accuracy of the D2000 at three different scan spans (trueness: 23.82 +/- 0.22 mu m, 21.53 +/- 0.18 mu m, and 21.02 +/- 0.27 mu m respectively; precision: 7.86 +/- 0.83 mu m, 7.87 +/- 1.11 mu m, and 7.82 +/- 0.84 mu m respectively). For the LS3 and the two intraoral scanners, the accuracy of the full arch scan (LS 3, trueness: 33.35 +/- 0.47 mu m, precision:15.36 +/- 3.10 mu m; Trios 3, trueness: 46.92 +/- 9.23 mu m, precision:20.79 +/- 3.08 mu m; Primescan, trueness: 28.73 +/- 0.77 mu m, precision:15.74 +/- 2.45 mu m) was significantly lower than that of the half arch (LS 3, trueness: 27.27 +/- 0.43 mu m, precision:5.62 +/- 0.88 mu m; trios 3, Trueness: 22.29 +/- 1.50 mu m, precision:14.12 +/- 2.25 mu m; Primescan, trueness: 18.91 +/- 0.70 mu m, precision:7.94 +/- 1.09 mu m) and three teeth scans (LS 3, trueness: 24.68 +/- 0.36 mu m, precision:5.29 +/- 0.62 mu m; Trios 3, trueness: 16.92 +/- 0.78 mu m, precision:11.95 +/- 2.22 mu m; Primescan, trueness: 15.79 +/- 0.65 mu m, precision:7.68 +/- 0.62 mu m). Conclusions: The scan span affected the accuracy of the intraoral scanners, but not necessarily the accuracy of the desktop scanners.