Effect of different span lengths with different total occlusal convergences on the accuracy of intraoral scanners

Purpose: The aim was to assess the effect of span lengths and total occlusal convergence (TOC) on the accuracy of intraoral scanners. Materials and methods: Two typodont acrylic teeth models were prepared to receive fixed dental prostheses with three different span lengths. Span 1: between maxillary canines; span 2: between maxillary second premolars; and span 3: between maxillary second molars. In the first model, prepared teeth had a TOC of 12 degrees, whereas, in the second model, teeth had a TOC of 20 degrees. Each model was scanned 10 times using 4 different intraoral scanners (Omnicam, Primescan, Trios 4, and Medit i500). The STL files from the scans were compared to the reference models (trueness) and within each test group (precision) using a 3D comparison software. Data were then statistically analyzed. Results: Regarding trueness, no significant differences were found among Primescan (32.58 +/- 13.08), Trios 4 (32.33 +/- 12.19), and Medit i500 (32.26 +/- 9.57). However, all showed significantly better trueness than Omnicam (35.70 +/- 8.35) (p < 0.001). The highest values were found in scans between the second molars (47.42 +/- 3.94), followed by scans between second premolars (28.42 +/- 3.78), and the highest trueness was found in scans between the canines (23.80 +/- 3.85). For TOC, 12 degrees had a significantly higher value than 20 degrees (p < 0.001). Regarding precision, the highest values were found with Omnicam (29.84 +/- 3.89), followed by Medit i500 (28.04 +/- 2.94), then Trios 4 (25.64 +/- 3.11), and Primescan (24.69 +/- 5.25). The highest values and least precision were found in scans between the second molars (28.97 +/- 5.27) and scans between second premolars (27.59 +/- 3.97), whereas the highest precision was found in scans between the canines (24.60 +/- 2.04). For TOC, 12 degrees had significantly higher values than 20 degrees (p < 0.001). Conclusions: Intraoral scans are directly affected by scanner type, TOC, and scan spans. All tested scanners showed clinically acceptable results even for long-span restorations.