A novel measurement method for the morphology of the mandibular ramus using homologous modelling

Abstract

Objectives: It is important to assess the mandibular morphology when orthognathic surgery, especially mandibular ramus osteotomy, is performed. Several studies on three-dimensional (3D) facial asymmetry have reported differences in linear and angle measurements between the deviated and contralateral sides in asymmetric mandibles. However, methods used in these studies cannot analyse the 3D morphology of the ramus. In this study, we aimed to evaluate the differences in mandibular ramus between the deviated and contralateral sides in asymmetric mandibles using traditional measurements as well as 3D shape analysis. Methods: 15 Japanese females with jaw deformities treated by orthodontic surgery were enrolled. 3D CT images were reconstructed, and 14 landmarks were identified on the model surface. Ten linear and four angle measurements were calculated using these landmarks. Homologous ramus models were constructed for each sample, and after converting all homologous models to the right side, 30 homologous models of the ramus were analysed using principal component analysis. Results: Firstly, eight principal components explained .80% of the total variance. Differences between the deviated and contralateral sides in measurements and scores of the eight principal components were tested. Significant difference at the 5% level between the deviated and contralateral sides was observed in five linear measurements, three angle measurements and the third principal component. The variance of the deviated side was significantly larger in the diameter between the mandibular notch and coronoid process, horizontal dilated angle of the mandibular ramus and vertical dilated angle of the mandibular ramus. The variance of the contralateral side was significantly larger in the height of mandibular ramus, height of posterior of mandibular ramus, condylar width, height of condylar head and mandibular angle. The squared multiple correlation coefficient adjusted for the degrees of freedom was 0.815. The third principal component showed the difference between the deviated and contralateral sides. Shape variation represented by the third principal component visually indicated that the contralateral side was larger and had inwardly directed coronoid process and the deviated side had a mandibular angle that was turned inwards to a greater extent. Conclusions: In conclusion, we successfully created a homologous model of the mandibular ramus and demonstrated the effectiveness of this model in the 3D comparison of the ramus morphology between the contralateral and deviated sides in asymmetric mandibles.

Evaluation of natural mandibular shape asymmetry: an approach by using elliptical Fourier analysis

“…12 Nevertheless, for the main purpose of the present study, EFA allowed to statistically reach a deeper search of differences in shape morphology that cannot be accomplished in some studies that used only linear and angular measurements, even if they are using CT scans. 6,18 Such results are found not only in sexual difference, in general or specific asymmetry, but also in the differentiation of skeletal patterns.…”

Global patterns of the cranial form of modern human populations described by analysis of a 3D surface homologous model

“…HBM-Rugle incorporates mHBM software and has additional functions for user convenience, including setting coordinate systems and size adjustment of input data. The robustness of the fitting accuracy of this software has been verified in several studies 52,[54][55][56][57][58][59][60] .…”

“…By analyzing the coordinate values of the vertices that make up the mesh models using a multivariate analysis method, such as principal component analysis (PCA), variations in the entire surface shape can be analyzed, and virtual shapes at arbitrary positions in the distribution can be calculated and visualized 53 . Nowadays, mesh models created using template fitting have been widely used for shape analyses in various fields 52,[54][55][56][57][58][59][60] .…”

Average Models and 3-dimensional Growth Patterns of the Healthy Infant Cranium

“…This technology was originally developed in the industrial field, and recently, it has been applied to the analysis of the human body in the medical field. 12 , 13 …”