title: [Establishment of normal value of posterior arch length of adolescence in Chengdu].
abstract: OBJECTIVE
  To investigate the development of third molar embryo and establish the normal value of posterior arch length of adolescence in Chengdu.
  
  
  METHODS
  The samples consisted of 40 males and 41 females with Class 1 dentitions, normal second molar occlusion, no history of orthodontic treatment, and good facial balance. Cephalometry and statistic analysis were conducted for all the subject.
  
  
  RESULTS
  The normal value of posterior arch length of maxilla in male was(16.52 +/- 2.35) mm and in female was(16.42 +/- 2.55) mm. The normal length of mandible was(13.00 +/- 2.44) mm in male and(12.43 +/- 2.18) mm in female. But statistic analysis showed no gender difference. Most of the third molar embryo had been formed and their tooth crowns had been calcified, the occurrence ratio was 84.0% in maxilla and 85.2% in mandible. Most of them located in the middle and inclined mesially.
  
  
  CONCLUSIONS
  The data obtained in this study will be valuable for our clinical practice and be helpful for the study concerning dento-facial growth and development.
authors.affiliation: Department of Orthodontics, West China College of Stomatology, Sichuan University, Chengdu 610041, China.
authors.forename: Chufeng
authors.initials: C
authors.lastname: Liu
authors.forename: Yang
authors.initials: Y
authors.lastname: Cao
authors.forename: Zhihe
authors.initials: Z
authors.lastname: Zhao
mesh_terms: D000293:Adolescent; D000539:Alveolar Process / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D002508:Cephalometry; D002648:Child; D003724:Dental Arch / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D003766:Dental Occlusion; D003817:Dentition; D005260:Female; D006801:Humans; D008297:Male; D008334:Mandible / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D008437:Maxilla / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D008964:Molar, Third / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D011859:Radiography; D012016:Reference Values; D014085:Tooth Migration