Three-dimensional changes of the mandibular arch after total arch distalization in skeletal Class III malocclusion

Abstract

Objectives: To assess three-dimensional (3D) changes in tooth position, arch dimensions, and gingival levels after mandibular total arch distalization in skeletal Class III malocclusion. Materials and Methods: Skeletal Class III patients treated with mandibular total arch distalization using interradicular temporary anchorage devices were analyzed using stepwise 3D superimposition and reorientation of serial cone beam computed tomography (CBCT) and digital casts (N = 19). After mandibular regional superimposition of pre-(T0) and post-treatment (T1) CBCTs, the mandibles were segmented and merged with the corresponding digital casts, generating reoriented, superimposed T0 and T1 digital casts. Changes in individual tooth position, arch dimensions, occlusal plane, and clinical crown height (CCH) were measured. Results: Mandibular teeth exhibited posterior movement ranging from 1.74 to 2.50 mm with significant lateral movement of the premolars and increase of inter-premolar width by 2.15-2.66 mm (P < .05). Extrusive movement of the entire dentition excluding the second molar was noted (P < .05), inducing changes of the occlusal plane. The overall changes in CCH were limited to-0.23 to 0.16 mm. CCH significantly increased in the premolars and decreased in the first molar (P < .05). Conclusions: Based on a stepwise digital superimposition, mandibular total arch distalization induced complex 3D changes in the mandibular arch, including distalization, extrusion, and increase of interpremolar width. Gingival margins generally were maintained, though mild-to-moderate recession was suggested in around 20% of the premolars, which may require attention.