title: Connecting the new with the old: modifying the combined application of Procrustes superimposition and principal component analysis, to allow for comparison with traditional lateral cephalometric variables.
abstract: The combination of generalized Procrustes superimposition (GPS) and principal component analysis (PCA) has been hypothesized to solve some of the problems plaguing traditional cephalometry. This study demonstrates how to establish the currently unclear relationship between the shape space defined by the first two principal components to the ANB angle, Wits appraisal, and GoGnSN angle, and to elucidate possible clinical applications thereof.
  
  
  
  Digitized landmarks of 200 lateral cephalograms were subjected to GPS and PCA, after which the sample mean shape was deformed along/parallel to principal components (PC) 1 and 2, recording the ANB, Wits, and GoGnSN value at each location. Trajectories were then calculated through the PC1-PC2 space connecting locations with the same values. These were finally utilized to renormalize the PC1-PC2 space.
  
  
  
  The trajectories for the Wits appraisal were almost straight and parallel to PC1.Those for the ANB angle were angled approximately 20degrees downward relative to PC1, with a more accentuated curvature. The GoGnSN curves were mildly angled relative to the PC2 axis, their curvature increasing slightly with increasing PC1 scores. By combining the aforementioned trajectories, it was possible to delineate the region of the PC1-PC2 shape space which would be regarded as normodivergent and skeletal Class I in traditional cephalometry. Geometric distortion could be avoided by assigning patients the ANB, Wits, or GoGnSN value of the sample mean shape, deformed to the patient's position within the PC1-PC2 plot.
  
  
  
  The methodology successfully relates the shape space resulting from the GPS-PCA results with traditional cephalometric variables.
authors.affiliation: Department of Orthodontics and Craniofacial Biology, Radboud University Nijmegen Medical Centre, The Netherlands wellens.hans@telenet.be.
authors.forename: Hans L L
authors.initials: HL
authors.lastname: Wellens
authors.affiliation: Department of Orthodontics and Craniofacial Biology, Radboud University Nijmegen Medical Centre, The Netherlands.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Kuijpers-Jagtman
mesh_terms: D000293:Adolescent; D000465:Algorithms; D059925:Anatomic Landmarks; D002508:Cephalometry / Q000379:methods*; D002648:Child; D005260:Female; D006801:Humans; D008297:Male; D008334:Mandible / Q000033:anatomy & histology; D008437:Maxilla / Q000033:anatomy & histology; D025341:Principal Component Analysis; D000075082:Proof of Concept Study; D011861:Radiography, Dental / Q000379:methods; D055815:Young Adult