title: Mandibular changes secondary to serial extractions compared with late premolar extractions and controls.
abstract: BACKGROUND
  Variations in treatment times for serial extraction and late premolar extraction patients may be due to differences in the time needed to flatten the occlusal curves. In this study, we compared tooth tipping and occlusal curves in patients treated by serial extractions or late premolar extractions with untreated controls.
  
  
  METHODS
  Mandibular dental casts and cephalometric radiographs were collected from 90 subjects (30 Class I control subjects, 30 patients with serial extractions, and 30 with late premolar extractions) at 3 time points: T0, baseline for the controls and serial extraction patients; T1, after natural drift and preorthodontics for the controls and the serial extraction patients, and pretreatment for the late premolar extraction patients; and T2, after comprehensive orthodontic treatment for the serial extraction and the late premolar extraction groups. The long axes of the central incisor, canine, and first molar to the palatal plane were measured on digitized headfilms to determine the direction and the amount of tipping between the time points. Three occlusal curves were measured by sphere fitting cusp-tip landmarks on digitized mandibular casts.
  
  
  RESULTS
  From T0 to T1, incisors and canines in the patients with serial extractions tipped distally. Molars at T1 in the patients with serial extractions were tipped forward more than in the late premolar extraction patients and the controls. From T1 to T2, canines and molars in the patients with serial extractions were uprighted.
  
  
  CONCLUSIONS
  Serial extractions produce steeper occlusal curves and distal tipping of the incisors and canines after drift (T1). Posttreatment (T2) occlusal curves in the patients with serial extractions are steeper than in the late premolar extraction patients and controls (except for the curve of Spee). After the serial extractions, orthodontic treatment included incisor and canine proclination, with molar uprighting and occlusal curve flattening.
authors.affiliation: Formerly, graduate student, Department of Orthodontics, Faculty of Dentistry, University of British Columbia, Vancouver, British Columbia, Canada; private practice, Los Angeles, Calif. Electronic address: estherfeldman@gmail.com.
authors.forename: Esther
authors.initials: E
authors.lastname: Feldman
authors.affiliation: Clinical professor, Department of Orthodontics, Faculty of Dentistry, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: David B
authors.initials: DB
authors.lastname: Kennedy
authors.affiliation: Assistant professor, Department of Orthodontics, Faculty of Dentistry, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Jolanta
authors.initials: J
authors.lastname: Aleksejuniene
authors.affiliation: Professor emeritus, Department of Orthodontics, Faculty of Dentistry, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Alan G
authors.initials: AG
authors.lastname: Hannam
authors.affiliation: Program director and dean emeritus, Department of Orthodontics, Faculty of Dentistry, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: Edwin H
authors.initials: EH
authors.lastname: Yen
mesh_terms: D059925:Anatomic Landmarks / Q000473:pathology; D001641:Bicuspid / Q000601:surgery*; D016022:Case-Control Studies; D002508:Cephalometry / Q000379:methods; D003481:Cuspid / Q000473:pathology; D003724:Dental Arch / Q000473:pathology*; D005500:Follow-Up Studies; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D007180:Incisor / Q000473:pathology; D008334:Mandible / Q000473:pathology*; D003765:Models, Dental; D008963:Molar / Q000473:pathology; D012690:Serial Extraction / Q000379:methods*; D014081:Tooth Extraction / Q000379:methods*; D014087:Tooth Movement Techniques / Q000379:methods