Abstract
Background: Facial asymmetry can be evaluated by analyzing some facial lines. The spherical coordinate system is useful to analyze the surgical change to facial lines. This study aims to analyze the amount of asymmetry of facial lines before and after orthognathic surgery using spherical coordinate system from three-dimensional computed tomography (CT). Methods: A retrospective study was carried out on 14 CT scans which were taken from 7 subjects before and after orthognathic surgery (3 males, 4 females, average age of 24 yrs±3 mns). Four bilateral 3D facial lines, ramal height, ramal lateral, ramal posterior and mandibular body lines, were established on each CT scan, and the spherical coordinates (length, midsagittal inclination angle, coronal inclination angle) of each facial line were statistically compared before and after orthognathic surgery. Statistical analysis was done for comparing between before and after surgery in the mental deviation and amount of asymmetry. Results: The menton deviation was statistically significantly reduced by surgery (preoperative 7.67mm±4.46mm, postoperative 2.17 mm±1.58 mm, p <.05). The amount of asymmetry of the facial lines changed after surgery in all subjects, but only the amount of asymmetry of midsagittal inclination angle of mandibular body line was significantly different between before and after surgery (presurgical –7.65±5.67°, postsurgical -1.19±4.64°, p<.05). Conclusion: Facial asymmetry may remain after surgery even with attempts to correct asymmetry by reducing the menton deviation.
Highlights
Orthognathic surgery is required for many cases of class III malocclusion for improving function and establishing a symmetric aesthetic face [1,2,3,4,5,6]
This study aims to analyze the amount of asymmetry of facial lines before and after orthognathic surgery using spherical coordinate system from three-dimensional computed tomography (CT)
Three-dimensional analysis of facial asymmetry can be effectively achieved by using a spherical coordinate system(v,θ,φ) of 3D facial lines, where v is length, θ midsagittal inclination angle, and φ coronal inclination angle
Summary
Orthognathic surgery is required for many cases of class III malocclusion for improving function and establishing a symmetric aesthetic face [1,2,3,4,5,6]. There have been many studies for developing the evaluation methods of facial asymmetry using 3D CT. The evaluation method of facial asymmetry has not yet been established [8,9,10,11,12,13]. Facial asymmetry can be evaluated by analyzing some facial lines [10]. An alternative spherical coordinate system was developed from the geographic coordinate system for analyzing facial lines and asymmetry [12,13,14]. Three-dimensional analysis of facial asymmetry can be effectively achieved by using a spherical coordinate system(v,θ,φ) of 3D facial lines, where v is length, θ midsagittal inclination angle, and φ coronal inclination angle. The alternative spherical coordinates can be calculated from rectangular coordinates(x,y, z) of landmarks which compose the facial lines. The rectangular coordinates are obtained from three orthogonal planes, midsagittal, coronal and horizontal reference planes
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