title: Statistical shape analysis-based determination of optimal midsagittal reference plane for evaluation of facial asymmetry.
abstract: BACKGROUND
  The purpose of this study was to determine, by statistical shape analysis of original and mirrored skeletal landmarks, the optimal landmark-based midsagittal reference plane for evaluation of facial asymmetry.
  
  
  METHODS
  The study sample comprised 69 patients with facial asymmetry (36 men, 33 women; mean age, 23.0 ± 4.1 years). All landmarks were obtained with cone-beam computed tomography using a 3-dimensional coordinate system. For identifying the landmark-based midsagittal reference plane, the 3 landmarks nearest to the symmetric midsagittal reference plane were selected by ordinary and generalized Procrustes analyses. To verify the 3-landmark-based midsagittal reference plane's compatibility with the symmetric midsagittal reference plane, asymmetry measurements were calculated and tested for each.
  
  
  RESULTS
  The 3 nearest landmarks (nasion, anterior nasal spine, and posterior nasal spine) were selected for the 3-landmark-based midsagittal reference plane. The averages of the sums of the squared Euclidean distance and the squared Procrustes distance differences between the 2 configurations and shapes fabricated by the symmetric and landmark-based midsagittal reference planes, respectively, were calculated as 0.121 ± 0.241 mm and 1.69 × 10(-6) ± 3.25 × 10(-6). The testing results for the symmetric and landmark-based midsagittal reference planes were almost the same.
  
  
  CONCLUSIONS
  The results indicated that a 3-dimensional midsagittal reference plane constructed of nasion, anterior nasal spine, and posterior nasal spine could be a valuable tool for the evaluation of patients with facial asymmetry.
authors.affiliation: Researcher, Department of Orthodontics, School of Dentistry, Pusan National University, Busan, South Korea; researcher, Department of Statistics, College of Nature, Pusan National University, Busan, South Korea.
authors.forename: Sang Min
authors.initials: SM
authors.lastname: Shin
authors.affiliation: Resident, Department of Orthodontics, Pusan National University Dental Hospital, Yangsan, South Korea.
authors.forename: You-Min
authors.initials: YM
authors.lastname: Kim
authors.affiliation: Postgraduate student, Department of Orthodontics, Pusan National University Dental Hospital, Yangsan, South Korea.
authors.forename: Na-Ri
authors.initials: NR
authors.lastname: Kim
authors.affiliation: Professor, Department of Statistics, College of Nature, Pusan National University, Busan, South Korea.
authors.forename: Yong-Seok
authors.initials: YS
authors.lastname: Choi
authors.affiliation: Professor, Department of Orthodontics, Dental Research Institute, Pusan National University Dental Hospital, Yangsan, South Korea.
authors.forename: Soo-Byung
authors.initials: SB
authors.lastname: Park
authors.affiliation: Assistant professor, Department of Orthodontics, Institute of Translational Dental Sciences, School of Dentistry, Pusan National University, Yangsan, South Korea; assistant professor, Biomedical Research Institute, Pusan National University Hospital, Busan, South Korea. Electronic address: kimyongil@pusan.ac.kr.
authors.forename: Yong-Il
authors.initials: YI
authors.lastname: Kim
mesh_terms: D059925:Anatomic Landmarks; D002508:Cephalometry; D054893:Cone-Beam Computed Tomography; D005146:Facial Asymmetry / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D015233:Models, Statistical; D011857:Radiographic Image Interpretation, Computer-Assisted; D056910:Republic of Korea; D012189:Retrospective Studies; D055815:Young Adult