title: Effect of large incisor retraction on upper airway morphology in adult bimaxillary protrusion patients.
abstract: OBJECTIVE
  To evaluate, using multislice computed tomography (MSCT), the morphologic changes in the upper airway after large incisor retraction in adult bimaxillary protrusion patients.
  
  
  METHODS
  Thirty adult patients with bimaxillary protrusion had four first premolars extracted, and then miniscrews were placed to provide anchorage. A CT scan was performed before incisor retraction and again posttreatment. Three-dimensional (3D) reconstruction of the pre- (T1) and post- (T2) CT data was used to assess for morphological changes of the upper airway. A paired t-test was used to compare changes from T1 to T2. The relationship among the three variables (upper incisor retraction amount, upper airway size, and hyoid position) was analyzed by Pearson correlation coefficient.
  
  
  RESULTS
  The amounts of upper incisor retraction at the incisal edge and apex were 7.64 ± 1.68 mm and 3.91 ± 2.10 mm, respectively. The hyoid was retracted 2.96 ± 0.54 mm and 9.87 ± 2.92 mm, respectively, in the horizontal and vertical directions. No significant difference was observed in the mean cross-sectional area of the nasopharynx (P > .05) between T1 and T2, while significant differences between T1 and T2 were found in the mean cross-sectional areas of the palatopharynx, glossopharynx, and hypopharynx (P < .05); these mean cross-sectional areas were decreased by 21.02% ± 7.89%, 25.18% ± 13.51%, and 38.19% ± 5.51%, respectively. The largest change in the cross-sectional area is always noted in the hypopharynx. There was a significant correlation among the retraction distance of the upper incisor at its edge, the retraction distance of the hyoid in the horizontal direction, and the decrease of the hypopharynx.
  
  
  CONCLUSIONS
  Large incisor retraction leads to narrowing of the upper airway in adult bimaxillary protrusion patients.
authors.affiliation: Department of Orthodontics, School of Dentistry, Shandong University, Jinan City, China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Chen
authors.forename: Liu
authors.initials: L
authors.lastname: Hong
authors.forename: Chun-ling
authors.initials: CL
authors.lastname: Wang
authors.forename: Shi-jie
authors.initials: SJ
authors.lastname: Zhang
authors.forename: Cong
authors.initials: C
authors.lastname: Cao
authors.forename: Fulan
authors.initials: F
authors.lastname: Wei
authors.forename: Tao
authors.initials: T
authors.lastname: Lv
authors.forename: Fan
authors.initials: F
authors.lastname: Zhang
authors.forename: Dong-xu
authors.initials: DX
authors.lastname: Liu
mesh_terms: D000328:Adult; D001641:Bicuspid / Q000601:surgery*; D001863:Bone Screws; D005260:Female; D006801:Humans; D006928:Hyoid Bone / Q000033:anatomy & histology; D007091:Image Processing, Computer-Assisted; D008297:Male; D008310:Malocclusion / Q000601:surgery*; D008437:Maxilla / Q000033:anatomy & histology / Q000601:surgery; D061330:Multidetector Computed Tomography; D052280:Orthodontic Anchorage Procedures / Q000379:methods; D009971:Orthodontics, Corrective / Q000379:methods; D010614:Pharynx / Q000033:anatomy & histology*; D014081:Tooth Extraction / Q000009:adverse effects*; D014087:Tooth Movement Techniques / Q000009:adverse effects* / Q000379:methods