Third Palatal Rugae — Accurate Radiation-Free Reference for Digital Orthodontic Superimposition

Objective: To evaluate the validity of using third palatal rugae as reference landmarks for superimposition of maxillary intraoral digital models in orthodontic extraction cases. Design: Retrospective cohort study. Methods: Included were 22 skeletally mature patients who underwent bilateral maxillary first premolar extraction followed by incisor retraction. Intraoral scans and cone-beam CT (CBCT) images were obtained at baseline (T0) and after approximately 4 months (T1). Digital models were superimposed using a 3-point and surface-based registration method at the third palatal rugae. CBCT scans were superimposed using voxel-based registration at the cranial base as the gold standard. Tooth displacements of maxillary central incisors and cuspids were measured in both horizontal and combined 2-dimensional (2D) directions. Results: Excellent intra-examiner reliability (intra-class correlation coefficients, 0.92 to 0.99) and minimal measurement error were demonstrated. Mean differences more...