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.

Automated summary

The effect of span lengths and total occlusal convergence (TOC) on the accuracy of intraoral scanners was assessed. The results showed that scanner type, TOC, and scan spans all had an impact on the intraoral scan results, but the accuracy of different scanners was still within clinically acceptable range.