Objective: To assess the impact of horizontal intraoral scan bodies (H-ISBs) on the trueness of complete-arch digital impressions compared to vertical ISBs (V-ISBs). To evaluate trueness among four intraoral scanners (IOS) and inter-operator variability across different ISB × IOS combinations.

Materials and methods: Digital impressions were made from a dental cast with four multi-unit analogs using four H-ISBs: H-NB, H-NS, H-M6, H-SF, and a V-ISB (V-EA) as a comparison. Two operators performed 10 scans per ISB with four IOS devices (i5D, PS, T3, T4), generating 400 impressions. Reference scans were obtained with a desktop scanner, and trueness was analyzed using root-mean-square (RMS) error calculations (α = 0.05).

Results: H-NS and H-SF exhibited the highest trueness across IOSs, whereas H-NB and H-M6 showed lower trueness. V-EA outperformed H-NB and H-M6 but not H-NS and H-SF. Significant IOS-ISB interaction effects (p < 0.01) indicated H-SF as the most accurate, especially with PS. T4 and i5D displayed greater variability, particularly with H-NB. V-ISBs exhibited higher inter-operator variability compared to H-ISBs.

Conclusions: H-ISBs did not perform better than V-ISBs in all scenarios. The interactions among ISB design, IOS type, and operator significantly affect the digital impression trueness. The discrepancies measured among the systems remain well below the currently accepted threshold for clinically relevant misfit, supporting the suitability of the horizontal configuration for complete-arch impressions.