title: [Three-dimension model analysis for physiological drift of the mandibular dentition after extraction of mandibular second premolars of Angle class II patients].
abstract: OBJECTIVE
  To observe the self-adjustment of the mandibular dental arch after extraction of the second mandibular premolars.
  
  
  METHODS
  Mandibular dental casts of 20 Angle class II patients treated with extraction of lower second premolars and upper first premolars, bonded with Alexander  appliance,were taken before (T1) and after self-adjustment (T2). All the casts were laser scanned, Little index, curve of Spee, arch width, arch length and  extraction spaces of casts were digitally measured and analyzed with SPSS 16.0.
  
  
  RESULTS
  Little index,lower molar width, lower arch length and  extraction spaces were reduced [(12.70±3.28) mm vs.(8.82±2.69) mm, P<0.001;(41.21±2.48) mm vs.(40.54±2.23) mm, P<0.001; (24.63±3.19) mm  vs.(22.12±2.97) mm, P<0.001;(8.06±0.48) mm vs.(4.17±1.51) mm, P<0.001;(8.13±0.95) mm vs.(4.14±1.98) mm, P<0.001],while the curve of  Spee and anterior lower arch length were increased significantly[(2.14±0.75) mm vs.(2.65±0.88) mm, P<0.05; (15.88±2.86) mm vs.(17.55±2.33) mm, P<0.05]. Width between lower canines remained the same[(27.25±2.69) mm vs.(27.26±1.73) mm, P>0 .05].
  
  
  CONCLUSIONS
  Severe crowding and  Angle class II molar relationship could be successfully relived with lower second premolar extraction followed by self-adjustment.
authors: Department of Orthodontics, Peking University School, Beijing, China. drsongwei@yahoo.com
authors: Song
authors: S
authors: Wei
authors: Jing
authors: J
authors: Li
authors: Yan-heng
authors: YH
authors: Zhou
mesh_terms: D000293:Adolescent; D001641:Bicuspid / Q000601:surgery*; D002648:Child; D003724:Dental Arch / Q000033:anatomy & histology; D005260:Female; D006801:Humans; D008297:Male; D008312:Malocclusion, Angle Class II / Q000503:physiopathology / Q000628:therapy*; D003765:Models, Dental; D009971:Orthodontics, Corrective / Q000379:methods; D014081:Tooth Extraction; D014085:Tooth Migration / Q000503:physiopathology*; D055815:Young Adult