ABSTRACT
Recently, a homologous modeling method was developed to simulate 3D human body forms, which can visualize principal component analysis (PCA) results and facilitate its detailed comparison with results of previous method. Herein, we aimed to construct a homologous model of the face to identify differences between a straight face and a posed smile. Thirty-eight volunteers (19 males and 19 females, 38 straight faces and 38 posed smiles) with no medical history associated with a posed smile were enrolled. Three-dimensional images were constructed using the Homologous Body Modeling software and the HBM-Rugle; 9 landmarks were identified on the 3D-model surfaces. The template model automatically fitted into an individually scanned point cloud of the face by minimizing external and internal energy functions. Faces were analyzed using PCA; differences between straight faces and posed smiles were analyzed using paired t tests. Contribution of the most important principal component was 23.8%; 8 principal components explained >75% of the total variance. A significant difference between a straight face and a posed smile was observed in the second and the fourth principal components. The second principal component images revealed differences between a straight face and a posed smile and changes around the chin area with regard to length, shape, and anteroposterior position. Such changes were inclusive of individual differences. However, the fourth principal component image only revealed differences between a straight face and a posed smile; observed differences included simultaneous shortening of upper and lower eyelid length, evaluation of the nasal ala ase, swelling of the cheek area, and elevation of the mouth angle. Although these results were clinically apparent, we believe that this article is the first to statistically verify the same.Consequently, the homologous model technique and PCA are useful for evaluation of the facial soft-tissue changes.
Subject(s)
Smiling , Face , Female , Humans , Imaging, Three-Dimensional , Male , Principal Component AnalysisABSTRACT
PURPOSE: This study was conducted to determine the best design of biodegradable plates for providing rigidity when used for fixation of sagittal split ramus osteotomy. METHODS: A computerized tomography image of a patient was used to generate a 3D model of a hemi-mandible. Four plate designs were merged with the hemi-mandible. They were (1) straight plate, (2) double straight plate, (3) T-shaped plate, and (4) double Y-shaped plate. Four finite element models were analyzed using the properties of biodegradable materials for the plates, and four additional models were analyzed using titanium alloy properties. RESULTS: The models predicted that rigidity of fixation would be noticeably less among biodegradable plates than titanium plates. They also predicted that the most rigid design among the titanium plates would be the straight plate, but among the biodegradable plates, it would be the double Y-shaped plate. CONCLUSION: The double Y-shaped design is recommended when using biodegradable plates in fixation of sagittal split ramus osteotomy.
