Influence of edentulous span length on complete-arch intraoral scanner accuracy: a comparative in vitro study.

Statement of problem: While intraoral scanners (IOS) demonstrate high accuracy in single-tooth and partial-arch applications, their reliability in full-arch scans with varying edentulous spans remains uncertain. Increasing span length may compromise scanning accuracy and prosthetic outcomes.

Objectives: To assess the influence of edentulous span length on the accuracy of two IOS devices Primescan (Dentsply Sirona) and Trios 3 (3Shape) in complete-arch scenarios. The hypothesis was that accuracy would decline with increasing span length, with performance differences between scanners.

Material and methods: An in vitro study was conducted using a maxillary complete-arch model with a central incisor implant. Twelve span-length scenarios (FA1-FA12) were created by sequentially removing adjacent teeth. Each condition was scanned 10 times using both IOS devices (n = 240). A laboratory scanner (Identica blue, MEDIT) provided reference scans. Trueness (vs. reference) and precision (intra-group) were evaluated using root mean square (RMS) error. Scans were aligned via automatic and local best-fit in Medit Design. Statistical analysis included two-way mixed ANOVA, repeated measures ANOVA, and linear regression with Bonferroni correction (α = 0.004).

Results: Trios 3 demonstrated lower overall RMS values (0.296 ± 0.043 mm) than Primescan (0.338 ± 0.049 mm), with significant differences in 9 of 12 scenarios (p < 0.001). Correlation with span length was stronger for Primescan (R² = 0.892) than Trios 3 (R² = 0.674). Both devices showed high reliability.

Conclusions: Increasing edentulous span length negatively impacts scanner accuracy. Devices demonstrating consistent performance are preferable for reliable full-arch digital workflows.