title: Three-dimensional analysis of the change in the curvature of the smiling line following orthodontic treatment in incisor class II division 1 malocclusion.
abstract: OBJECTIVE
  To investigate the different effects of changes in the occlusal plane, incisors inclination, and maxillary intercanine width on the curvature of the smiling line.
  
  
  METHODS
  Records of 46 subjects (28 females and 18 males, mean age 16.6 ± 4.2 years) with incisor class II division 1 malocclusions were selected. All subjects had four premolar extractions and were treated with preadjusted edgewise appliances.
  
  
  METHODS
  Pre- and post-treatment maxillary dental digital models were virtually aligned via corresponding landmarks to the respective lateral cephalograms. Subsequent two-dimensional superimposition of the aligned cephalograms facilitated the three-dimensional superimposition of the pre- and post-treatment models. This process allowed the quantification of the curvature from a frontal perspective of the models. The change in curvature was then correlated with changes in the cephalometric inclination of the anterior occlusal plane (AOP), functional occlusal plane (FOP), maxillary central incisor (U1), and the intercanine width.
  
  
  RESULTS
  Orthodontic correction in this sample resulted in the clockwise rotation of the anterior occlusal plane (5.84 degrees), reduction in proclination of the incisors (-14.39 degrees), increase in intercanine width (2.48mm), and a corresponding increase in the curvature of the smiling line (6.83 degrees).
  
  
  CONCLUSIONS
  The change in curvature of the smiling line in these subjects was found to be related more significantly to the magnitude of difference in the inclination between the pre-treatment AOP and FOP than to the change in the inclination of the maxillary incisors. With orthodontic treatment, the smiling line can be correlated with cephalometric data to improve or maintain the curvature.
authors.affiliation: *Discipline of Orthodontics, Faculty of Dentistry, National University of Singapore, michaelmah@nus.edu.sg.
authors.forename: Michael
authors.initials: M
authors.lastname: Mah
authors.affiliation: **Department of Electrical and Computer Engineering, National University of Singapore, and.
authors.forename: Wei Chuan
authors.initials: WC
authors.lastname: Tan
authors.affiliation: **Department of Electrical and Computer Engineering, National University of Singapore, and.
authors.forename: Sim Heng
authors.initials: SH
authors.lastname: Ong
authors.affiliation: ***Biostatistics Unit, Faculty of Medicine, National University of Singapore, Singapore.
authors.forename: Yiong Huak
authors.initials: YH
authors.lastname: Chan
authors.affiliation: *Discipline of Orthodontics, Faculty of Dentistry, National University of Singapore.
authors.forename: Kelvin
authors.initials: K
authors.lastname: Foong
mesh_terms: D000293:Adolescent; D000328:Adult; D001641:Bicuspid / Q000601:surgery; D002508:Cephalometry / Q000379:methods; D003766:Dental Occlusion; D005260:Female; D006801:Humans; D007180:Incisor / Q000473:pathology*; D008297:Male; D008312:Malocclusion, Angle Class II / Q000473:pathology / Q000628:therapy*; D008437:Maxilla / Q000473:pathology; D003765:Models, Dental; D009971:Orthodontics, Corrective / Q000379:methods*; D012904:Smiling; D055815:Young Adult