Facial morphology improvements are obtained following two-jaw surgery in mandibular protrusion patients. Changing external nasal morphology does not always lead to good results in all patients. In this study, using 3-dimentional computed tomography (3D-CT), we examined the changes of external nasal morphology of patients who had undergone two-jaw surgery to correct mandibular protrusion. Seven adult patients (5 male; 2 female) who had been treated by two-jaw surgery associated with upward transposition of the posterior maxilla were enrolled in this study. 3D analysis software superimposed 3D-CTs of the pre-operative and post-operative stages (at least 6 months after surgery) on the hard tissue surfaces. We employed the 3D coordinate system constructed by Frankfort horizontal (FH) plane, the frontal plane incorporating the orbitals on both sides and the sagittal plane intersecting at the midpoint between the orbitals. After superimposition, soft tissue images of 3D-CT were reconstructed and changes in external nasal morphology were three-dimensionally analyzed. 3D geographical analysis, linear and angular measurements were performed for the most inferior points on the nasal alar (LBi, RBi) on bilateral sides, the most anterior point on the nose (Prn), the most anterior point on the columella of the nose (Cm), the most posterior superior point on the nasolabial curvature (Sn) and the most anterior point on the convexity of the upper lip (Vu). Correlation of hard tissue and soft tissue changes were statistically analyzed by Spearman's rank correlation analysis.
LBi and RBi moved anterior according to the anterior movement of point A. Increase in distance of both LBi and RBi and angle of LBi-Prn-RBi were observed. We found significant increase in the area of external nasal aperture. Positive correlation was seen between the anterior movement of point A and the distance of LBi and RBi.
These results imply that our superimposition of CT images using the 3D coordinate system are useful to compare soft tissue changes before and after surgery. Further investigation for more information about the factors that influence facial morphology changes is necessary since the changes may not be uniform due to the individual variety of soft tissue characterization, and the direction and amount of maxillary movement by Le Fort I osteotomy.
