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Published on: February 23, 2024
Influence of Superimposition Strategies and Landmark Distribution on the Full-Arch Trueness of Orthodontic Digital
Ezgi Cansu Firinciogullari1, Edanur Dark2, Genta Agani Sabah3
1Department of Applied Craniofacial Sciences, Medical University of South Carolina, Charleston, South Carolina, USA.
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.
