title: Clinical relevance of third permanent molars in relation to crowding after orthodontic treatment.
abstract: OBJECTIVE
  The purpose of this study was to determine the relationship between dental crowding and the clinical presence or absence of third permanent molar teeth.
  
  
  METHODS
  Ninety-nine patients were analysed before and after orthodontic treatment and at least three years after the end of retention. The sample consisted of four groups: subjects whose third permanent molar teeth had erupted into the mouth, were non-erupted, were extracted, and were congenitally absent. Arch Length Discrepancy, Irregularity Index and observer bias were examined. Multivariate analysis of variance with repeated measurements was used to analyse differences between the four groups.
  
  
  RESULTS
  Significant differences in Arch Length Discrepancy during time were shown between the premolar segment and the frontal area. The group with third permanent molar teeth congenitally missing showed a significant higher positive Arch Length Discrepancy in the premolar segment of the upper jaw. No significant differences in Irregularity Index were found between the third molar groups.
  
  
  CONCLUSIONS
  It can be concluded that there is no relation between crowding and the presence or absence of third permanent molar teeth.
authors.affiliation: Department of Orthodontics, Academic Centre for Dentistry Amsterdam (ACTA), The Netherlands.
authors.forename: E A
authors.initials: EA
authors.lastname: van der Schoot
authors.forename: R B
authors.initials: RB
authors.lastname: Kuitert
authors.forename: F C
authors.initials: FC
authors.lastname: van Ginkel
authors.forename: B
authors.initials: B
authors.lastname: Prahl-Andersen
mesh_terms: D000293:Adolescent; D000328:Adult; D000848:Anodontia / Q000503:physiopathology; D015982:Bias; D001641:Bicuspid / Q000473:pathology; D002648:Child; D003724:Dental Arch / Q000473:pathology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008310:Malocclusion / Q000209:etiology* / Q000473:pathology / Q000628:therapy; D008437:Maxilla / Q000473:pathology; D008964:Molar, Third / Q000002:abnormalities / Q000503:physiopathology* / Q000601:surgery; D015999:Multivariate Analysis; D015588:Observer Variation; D009971:Orthodontics, Corrective; D012008:Recurrence; D014078:Tooth Eruption; D014081:Tooth Extraction; D014097:Tooth, Unerupted / Q000503:physiopathology