Prediction of mandibular movement and center of rotation after total arch intrusion.

BACKGROUND

This study aimed to identify the center of mandibular autorotation (CRo) and evaluate the relationship between the amount of intrusion of the maxillary and mandibular dentition and changes in vertical and sagittal cephalometric parameters after total arch intrusion (TAI).

METHODS

Thirty-four adults (5 men and 29 women; mean age = 24.2 ± 6.2 years) treated with TAI were retrospectively analyzed, including 14 patients in the 4-premolar extraction group and 20 in the nonextraction group. Lateral cephalograms taken pretreatment and posttreatment were used to assess cephalometric changes. The CRo was determined based on positional changes of the gonion and pogonion. Paired-samples and independent-samples t tests were used for within-group (pretreatment vs posttreatment) and between-group (extraction vs nonextraction) comparisons.

RESULTS

After TAI, the mandible rotated counterclockwise, resulting in sagittal improvements-including increased SNB, decreased ANB, overjet, and forward movement of the pogonion, and vertical reductions in anterior facial height and mandibular plane angle (P <0.001). No significant differences were observed between the extraction and nonextraction groups (P >0.05). The amount of posterior intrusion was significantly correlated with decreases in anterior facial height, mandibular plane angle, and forward movement of the pogonion (P <0.001). The mean CRo was located 2.8 mm posterior and 18.9 mm inferior to the condylion, with no intergroup difference.

CONCLUSIONS

TAI provides a practical nonsurgical approach for treating skeletal Class II malocclusion with vertical excess, associated with mandibular counterclockwise rotation and improved vertical and sagittal skeletal relationships. The CRo was consistently positioned posterior-inferior to the condylion, with individual variation.