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[Comparative study of alveolar bone remodeling around the upper incisor area after Twin-block and high-pull headgear-activator functional orthopedic therapy].

PURPOSE
The aim of this clinical study was to evaluate the changes of alveolar bone morphology around the upper incisors before and after functional treatment in adolescents using cone-beam CT(CBCT).


METHODS
Thirty patients with skeletal Class II mandibular retrusion who were successfully treated with high-pull headgear-activator(HGAC) and Twin-block were selected and divided into 2 groups (HGAC and Twin-block groups), 15 in each group. CBCT was performed before and after treatment, to observe upper incisor movement in the alveolar bone and alveolar bone remodeling. Statistical analysis was performed using SPSS 20.0 software package to analyze the changes of alveolar bone thickness, angle of central incisor and alveolar bone before and after treatment.


RESULTS
Horizontally, the edge of the maxillary incisor appeared lingual movement in both groups, while the root apex appeared lingual movement in HGAC group and labial movement in Twin-block group. Vertically, the edge of the maxillary incisor was moved down and the root apex was moved up in all patients, whereas the moving distance was less in the edge and larger in the root apex in HGAC group. The thicknesses of major areas in the alveolar bone significantly increased in HGAC group, while in Twin-block group the labial thickness of the alveolar bone showed significant decrease and the palatal thickness showed significant increase. Moreover, the total thickness of the alveolar bone showed significant increase in both groups, yet Twin-block group showed more increase, and the angle of the alveolar bone showed more decrease in HGAC group.


CONCLUSIONS
Both functional appliances can cause positive alveolar bone remodeling in maxillary incisor area. HGAC can achieve a controlled tilt inward movement of the maxillary incisors, intrude the incisors to a certain extent, and allow certain change in the bending angle of the incisor alveolar bone at the same time, which is conducive to improving ClassⅡcraniofacial pattern. Twin-block can tilt the maxillary incisor inward, suggesting that more attention needs to be paid to the control of the torque of the incisor when retracting anterior teeth in fixed orthodontic treatment after Twin-block functional treatment.