STL Triangle Count and Trueness in Prepared Tooth Regions: Effects of Scanner System and Scanning Mode Across Intraoral, Laboratory, and Industrial Scanners.

OBJECTIVES: To evaluate the effects of different scanning modes of intraoral scanners (scan-only versus restoration type selected) on STL triangle counts and to assess the influence of STL triangle counts on trueness across different scanner systems. METHODS: A typodont model with 3 prepared teeth was scanned with 15 scanners (11 intraoral, 2 laboratory, and 2 industrial). Intraoral scanners were used in scan-only and restoration type selected modes (n=10 each); the other scanners were used in a standard workflow (n=10). Triangle counts were measured in MeshLab within 3 predefined prepared tooth regions. Trueness of intraoral and laboratory datasets was assessed against an ATOS reference scan with best-fit superimposition and root mean square (RMS) deviations. Triangle counts were analyzed with linear mixed-effects models, and RMS deviations with Friedman, post hoc pairwise, and Wilcoxon signed-rank tests (p<.05). RESULTS: STL triangle counts and trueness differed significantly among scanners (p<.001). Triangle counts showed a significant scanner-by-mode interaction, with marked increases for Trios 3 and Trios 5 in restoration type selected mode (p<.001). Among intraoral scanners, the lowest mean RMS values were observed for iTero Lumina in scan-only mode (24 ± 8 µm) and for iTero Lumina and Trios 6 in restoration type selected mode (24 ± 5 µm and 24 ± 9 µm, respectively). CONCLUSIONS: Scanner system and scanning mode affected STL triangle count, whereas trueness was influenced primarily by scanner system. Because restoration type selected mode improved trueness only in selected scanners, STL triangle count should be regarded as a complementary descriptor of mesh representation rather than a direct indicator of trueness. CLINICAL SIGNIFICANCE: Scanning mode may influence not only STL triangle counts but also trueness; however, this effect appears to be scanner-dependent rather than universally applicable. Therefore, clinicians should be aware that the potential benefit of the restoration type selection mode over the scan-only mode may vary depending on the intraoral scanner system used.