Influence of Superimposition Strategies and Landmark Distribution on the Full‐Arch Trueness of Orthodontic Digital Models

Objective To evaluate the influence of superimposition protocols and landmark distribution on deviation outcomes in orthodontic full‐arch models. Materials and Methods Twenty plaster models were scanned using an intraoral and desktop scanner. Ten models were evaluated for landmark suitability and inter‐scanner coordinate agreement. All models were superimposed using automatic global best‐fit (AGB), three‐point landmark (3PL) alignment with two different triads, and area‐specific alignment (ASA). Deviation metrics were root mean square (RMS), absolute average (Abs. Avg.), and (90–10)/2. Mixed‐effects models were utilized for analysis. Results The alignment protocol significantly affected all metrics ( p < 0.001). The protocol × arch interaction was significant for RMS ( p < 0.001) and (90–10)/2 ( p = 0.046), but not Abs. Avg. ( p = 0.484). AGB and both 3PL triads produced comparable outcomes ( p > 0.05), whereas ASA yielded higher deviations ( p < 0.01), particularly in the mandible (RMS increased by approximately 27 μm relative to AGB). Conclusions AGB and 3PL protocols yield comparable reference‐based trueness, whereas ASA produced higher deviations. This effect is strongly arch‐dependent, suggesting the unreliability of restricted‐region registration in mandibular datasets. Clinical Significance Digital superimposition trueness depends heavily on the alignment protocol. Standardizing registration is essential, as minor positional differences impact symmetry and finishing decisions.