Quantifying Workflow-Induced Vertical Measurement Variability Between Pre- and Post-Preparation Intraoral Scans on Typodont Models: A Primescan–Exocad Study

Aim: Preoperative intraoral scans are routinely used as baseline references for CAD/CAM restoration design by superimposing them with post-preparation scans. This study quantified the workflow-induced apparent vertical discrepancy between pre- and post-preparation intraoral scan datasets after a clinically common registration approach. Method: Twelve maxillary typodont models were scanned at baseline (T0) with an intraoral scanner. A standardized full-crown preparation was performed on a preselected tooth (FDI 14; maxillary right first premolar), followed by post-preparation scanning (T1). T0 and T1 meshes were aligned in dental CAD software using rigid 3-point registration. Apparent vertical (tooth long-axis) differences (|ΔL|, mm) were measured on non-prepared reference teeth (maxillary central incisor, canine, and first molar) to isolate scan–registration variability. Descriptive statistics and empirical cumulative distribution functions were reported. Tooth-type differences were tested using the Friedman test with Holm-adjusted post hoc comparisons (α=0.05). Results: Across 36 measurements, median (IQR) |ΔL| was 0.039 (0.020–0.049) mm for the central incisor, 0.051 (0.037–0.176) mm for the canine, and 0.021 (0.012–0.102) mm for the first molar. The 95th percentiles were 0.311, 0.382, and 0.164 mm, respectively; maximum values approached 0.4–0.5 mm. Overall differences among tooth types were significant (P=0.039), whereas pairwise comparisons were not significant after adjustment. Conclusion: Pre/post intraoral scan superimposition using rigid 3-point alignment can generate non-zero apparent vertical discrepancies on unchanged teeth, occasionally reaching several tenths of a millimeter. Small pre/post differences—used to guide CAD/CAM design—should therefore be interpreted cautiously as they may reflect workflow variability rather than true morphologic change.