title: A novel measurement method for the morphology of the mandibular ramus using homologous modelling.
abstract: OBJECTIVE
  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.
authors.affiliation: 1 Section of Oral and Maxillofacial Surgery, Division of Maxillofacial Diagnostic and Surgical Sciences, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Inoue
authors.affiliation: 1 Section of Oral and Maxillofacial Surgery, Division of Maxillofacial Diagnostic and Surgical Sciences, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Nakano
authors.affiliation: 1 Section of Oral and Maxillofacial Surgery, Division of Maxillofacial Diagnostic and Surgical Sciences, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Sumida
authors.affiliation: 1 Section of Oral and Maxillofacial Surgery, Division of Maxillofacial Diagnostic and Surgical Sciences, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Yamada
authors.affiliation: 1 Section of Oral and Maxillofacial Surgery, Division of Maxillofacial Diagnostic and Surgical Sciences, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Otawa
authors.affiliation: 1 Section of Oral and Maxillofacial Surgery, Division of Maxillofacial Diagnostic and Surgical Sciences, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Fukuda
authors.affiliation: 1 Section of Oral and Maxillofacial Surgery, Division of Maxillofacial Diagnostic and Surgical Sciences, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Nakajima
authors.affiliation: 1 Section of Oral and Maxillofacial Surgery, Division of Maxillofacial Diagnostic and Surgical Sciences, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
authors.forename: W
authors.initials: W
authors.lastname: Kumamaru
authors.affiliation: 2 Department of Oral and Maxillofacial Surgery, Yamaguchi University Graduate School of Medicine, Yamaguchi, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Mishima
authors.affiliation: 3 Digital Human Research Center, National Institute of Advanced Industrial Science and Technology, Tokyo, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kouchi
authors.affiliation: 4 Section of Orthodontics and Dentofacial Orthopedics, Graduate School of Dental Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: I
authors.initials: I
authors.lastname: Takahashi
authors.affiliation: 1 Section of Oral and Maxillofacial Surgery, Division of Maxillofacial Diagnostic and Surgical Sciences, Faculty of Dental Science, Kyushu University, Fukuoka, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Mori
mesh_terms: D000293:Adolescent; D000328:Adult; D059925:Anatomic Landmarks / Q000000981:diagnostic imaging; D002508:Cephalometry / Q000379:methods* / Q000706:statistics & numerical data; D017076:Computer-Aided Design; D005146:Facial Asymmetry / Q000000981:diagnostic imaging; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods* / Q000706:statistics & numerical data; D021621:Imaging, Three-Dimensional / Q000379:methods* / Q000706:statistics & numerical data; D008334:Mandible / Q000000981:diagnostic imaging*; D008335:Mandibular Condyle / Q000000981:diagnostic imaging; D008953:Models, Anatomic; D025341:Principal Component Analysis; D011378:Prognathism / Q000000981:diagnostic imaging; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed / Q000379:methods* / Q000706:statistics & numerical data; D055815:Young Adult
keywords: facial asymmetry; homologous model; mandible; three-dimensional imaging