| Summary: | 碩士 === 國立臺灣大學 === 臨床牙醫學研究所 === 100 === Objective: The prevalence of Class III malocclusion is higher in Asians than in Caucasians. To improve the occlusal function and facial esthetics, orthodontic treatment combined with orthognathic surgery is often indicated in Class III malocclusion with severe skeletal discrepancy. The objectives of this research were to investigate the three-dimensional (3D) morphological changes of the soft and hard tissues in Class III facial asymmetry patients who were corrected with surgical orthodontic treatment.
Method: The subjects included 15 adult skeletal Class III patients who had 3D cone beam computerized tomography (CBCT) taken before full mouth orthodontic treatment (T1) and within one month after debanding and debonding (T2). They were treated with orthodontic treatment combined with one-jaw surgery to setback mandible (bilateral sagittal split osteotomy, BSSO) or two-jaw surgery (Le Fort I maxillary advancement and BSSO mandibular setback). The 3D CBCT images were superimposed on the cranial base in Dolphin imaging system (best fit of cranial base). After superimposition, 3D changes of the soft and hard tissues were measured from the vertical, anteroposterior, and transverse directions, respectively. In addition, the soft to hard tissue movement ratios were calculated.
Result: Asymmetry was more evident in the lower face in comparison with the middle face. Chin deviation was found in 13 of 15 subjects and 5 of them were deviated to the right side. Moreover, the mean deviation of bony pogonion at T1 was 4.32 mm. The mandibular prognathism were successfully corrected and facial asymmetry improved, but not fully corrected. In the vertical evaluation, the average occlusal plane canting changed from 1.73 mm to 1.04 mm. The vertical discrepancy of bilateral mandibular inferior border changed from 1.87 mm (T1) to 2.08 mm (T2). In the evaluations either before or after treatment, the vertical asymmetry of bilateral mandibular inferior borders was coincident with the direction of occlusal plane canting. In the anteroposterior (AP) evaluation of two-jaw surgery patients, the soft-to-hard tissue movement ratios (S/H ratios) of the maxilla gradually increased from midsagittal to paranasal area (0.295, 0.745, 1.19). The S/H ratios of the mandible were gradually increased from L1 CEJ to pogonion. Furthermore, marked individual variation of S/H ratios in transverse direction is noted.
Conclusion: The CBCT 3D image is useful to evaluate the treatment effects of surgical orthodontic treatment in patients with mandibular prognathism and facial asymmetry. The S/H ratios of maxilla in AP direction gradually increased from midsagittal to paranasal area. The S/H ratios in mandible were close to one. The transverse movement of the soft tissue seemed difficult to predict from hard tissue because of marked individual variation.
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