[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.

[Influence of the arch-wire deformation on movement of the maxillary anterior teeth in the lingual retraction force system with micro-implant anchorage using 3-D finite element analysis].

PURPOSE: To evaluate the biomechanical effect of arch wire deformation, height of micro-implant and lever-arm on movement of the maxillary anterior teeth in the lingual retraction force system. METHODS: Nonlinear 3-D finite element model of lingual orthodontic force system with micro-implant was constructed. When the arch-wire was set to be flexible body and rigid body, lingual retraction force system using sliding mechanism, the height of micro-implant and lever-arm was 0, 3, 5, 7 mm to alveolar ridge crest of the middle point of maxillary second premolars and maxillary first molars. The initial movement and hydrostatic pressure of anterior teeth were calculated. RESULTS: In the lingual retraction force system with micro-implant using sliding mechanism, when the wire was set to be flexible body, retroclination primary displacements of maxillary anterior teeth were found because of wire deformation. The maxillary lateral incisor's primary displacement became larger with the height of micro-implant increased. When the wire was set to be rigid body, the teeth tended to be slightly tipping, and with the increase of height of micro-implant, the change of movement tendency was not obvious. High value of periodontal ligament hydrostatic pressure was observed in the lingual retraction force system of maxillary anterior teeth with micro-implant when the wire was flexible, exceeding the capillary pressure. When the wire was rigid, the value of periodontal ligament hydrostatic pressure was small within the upper limit value of capillary pressure. CONCLUSIONS: Deformation of wire has a great influence on initial teeth movement and periodontal hydrostatic pressure. In clinic, using more rigid wire and reducing the initial force may reduce the risk of orthodontic root absorption.