title: [Stability of teeth alignment after orthodontic treatment].
abstract: OBJECTIVE
  To investigate the relapse of incisor alignment after orthodontic treatment and possible factors which may related to its stability.
  
  
  METHODS
  72 finished cases with full records selected from orthodontic clinic of Peking University School of Stomatology composed the sample. The follow-up lateral head films and study casts were taken at least 2 years after orthodontic treatment. The cephalograms were measured by computerized program and the study casts measured by caliper.
  
  
  RESULTS
  The upper Irregularity Index decreased from (11.5 +/- 5.02) mm before treatment to (2.01 +/- 1.39) mm after treatment and then increased to (3.46 +/- 1.69) mm in the follow-up stage. The lower Irregularity Index decreased from (7.24 +/- 44.35) mm before treatment to (1.75 +/- 1.04) mm after treatment and then increased to (3.39 +/- 1.78) mm in the follow-up stage. The changes are significant statistically. The changes of jaw in the sagittal and vertical directions as well as the related changes of the position of lower incisors, the decrease of the lower canine arch width, Bolton Index and sex all have statistically significant relation with the changes of the lower Irregularity Index after retention.
  
  
  CONCLUSIONS
  Compared with lower arch, the alignment in upper arch is more stable in the follow-up stage. The results suggest that some possible factors may have correlations with the change of lower arch crowding during the follow-up stage.
authors.affiliation: Department of Orthodontics, Peking University School of Stomatology, Beijing 100081, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Liu
authors.forename: Tian-min
authors.initials: TM
authors.lastname: Xu
authors.forename: Jiu-xiang
authors.initials: JX
authors.lastname: Lin
mesh_terms: D000293:Adolescent; D002648:Child; D003724:Dental Arch / Q000473:pathology*; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D009971:Orthodontics, Corrective; D012008:Recurrence; D014085:Tooth Migration