Accuracy and reliability of palatal superimposition of three-dimensional digital models

Objective: To evaluate the accuracy of the superimposition of three-dimensional (3D) digital models using the palatal surface as a reference for measuring tooth movements. Materials and Methods: Maxillary plaster models were selected from 20 patients. The right and left canines, premolars, and molars were individually cut underneath the gingival margins and set up in wax (plaster model 1 = PM1). The PM1s were scanned to create 3D digital models (digital model 1 = DM1). Teeth on the PM1s were randomly moved (plaster model 2 = PM2) and subsequently scanned to produce another set of 3D digital models (digital model 2 = DM2). DM1s and DM2s were superimposed using the palatal area as reference via surface-to-surface matching software, and the changes in tooth movement were calculated. In the plaster models, the tooth movements were directly measured using the Reference Measurement Instrument. A paired t-test and a correlation analysis were performed to determine whether the two measurement methods differed significantly. Results: The means of the anteroposterior (x-axis), transverse (y-axis), and vertical (z-axis) tooth movements of the plaster models and the digital models did not differ significantly, and very high correlations were found between the plaster models and the digital models. Conclusion: From a technical point of view, the superimposition of 3D digital models using the palatal surface provides accurate and reliable measurements, but it remains to be investigated how stable the palatal surface is longitudinally after growth and/or orthopedic treatment take place. (Angle Orthod. 2010;80:685-691.)