| ObjectiveThe incidence of Skeletal Class III(SCIII) in Mongoloid Race is relative higher than that of other Races. The Skeletal ClassⅢis often accompanied by facial asymmetry. In this study cone-beam computerized tomography (CBCT) was used to investigate three-dimensional maxillofacial morphological characteristics and spacial position characteristics of facial asymmetry in adult Skeletal Class III malocclusion patients.MethodsForty-six Chinese adult patients with SCIII, who had a three-dimensional cone-beam CT taken before orthognathic surgical surgery, were assigned to experimental group(asymmetry,8 men; 10 women; mean age,21.8years) and control group (symmetry,14 men; 14 women; mean age,23.2years)according to the amount of Menton Deviation (MD) from facial midline. CT data accorded with Dicom3.0 were reconstructed into 3D models by using medical image processing software Mimics 10.01. Nasi-maxillary complex and mandibular variables were measured and statistically analyzed.The study consists of two parts:1.An analysis of three-dimensional maxillofacial skeletal morphological characteristics in adult Skeletal Class III with facial asymmetry.In this study, we divided mandible into condylar unit, body unit, coronoid unit, angular unit, and chin unit according to mandibular foramen and mental foramen. The lines and angulars to represent condylar, coronoid, angular, body and chin units were used, we analysed the results with paired t-test between bilateral measurements and independent-samples t test between the control and experimental groups by using software SPSS 13.0.2. An analysis of three-dimensional special position of maxillofacial skeletal structure in adult Skeletal Class III with facial asymmetry.Three-dimensional coordinate and anatomical landmarks were designated on the reconstructed 3-dimensional models. The distances between each anatomical landmark and the 3 reference planes were measured in millimeters and defined as x, y, z coordinate values. We analysed the results with paired t-test between bilateral measurements and independent-samples t test between the control and experimental groups by using software SPSS 13.0. The asymmetry index of each point was defined and calculated. A diagrammatic chart with a baseline indicating the mean asymmetry indices plus the standard deviation in the control group was designed.Results:1.In the experimental group, coronoid unit length, external ramal inclination, mandibular angle and mandibular plane angle were significantly smaller on the nondeviated side than on the deviated side(P<0.05); ramal and body inclination angulars, condylar and body unit lengths were significantly larger on the nondeviated side than on the deviated side(P<0.05). Condylar unit length, remal length, ramal inclination angular and mandibular plane angle was significantly correlated with Menton Deviation (MD)(P<0.05).2. The experimental group showed more superior positioning of the upper canine and first molar on the deviated side of nasi-maxillary complex; more superior-posterior-lateral positioning of most mandibular landmarks on the deviated side. In control group, the gonion emerged as the most asymmetrical point and the anterior nasal spine showed least deviation.Conclusion:1. Both condylar and body units appeared to contribute to facial asymmetry, with a more capital role of the condylar unit.2. Except the alveolar process appeared compensation for the asymmetry, other parts of nasi-maxillary complex were basically symmetry.3. Mandible appeared not only asymmetry in shape but also displaced and rotated in spacial position. Ramus on the deviate side had the tendency of superior-posterior-lateral displacement. Mandible rotated around y and z axis to deviate side.4. Asymmetry was observed most frequently in the mandible. The extent of maxillofacial deformity increased from top to bottom in adults with facial asymmetry. The statistics bar chart about asymmetry index can be used to evaluated the degree of deformity in facial asymmetry patients. |
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