title: Impaction of permanent mandibular second molars in ethnic Chinese schoolchildren.
abstract: OBJECTIVE
  To investigate the prevalence of impaction of permanent mandibular second molars and associated dental and radiographic characteristics of Chinese children in Hong Kong.
  
  
  METHODS
  Dental and radiographic records of a group of Chinese schoolchildren were studied retrospectively. Cases of impaction of 1 or both permanent mandibular second molars were selected. Demographic data and dental and radiographic findings were recorded and analyzed. The angle of the impacted second molars was measured on panoramic radiographs.
  
  
  RESULTS
  Among the 3,053 records reviewed, 32 cases of impaction of permanent mandibular second molars were identified and studied. Mesial impaction was found in all but 1 case. The angle of the mesially impacted teeth ranged from 13 degrees to 75 degrees . Mandibular crowding and the presence of third molars were common. Dens evaginatus, taurodontism and Class III malocclusions were significantly more prevalent in the study group than in the general population of Chinese children of similar age.
  
  
  CONCLUSIONS
  The prevalence of impaction of permanent mandibular second molars in Chinese children was estimated to be 1%. Thorough and regular examination of the child"s developing dentition is recommended to diagnose dental impaction promptly.
authors.affiliation: dental service, department of health, Hong Kong. rony_cho@dh.gov.hk
authors.forename: Shiu-yin
authors.initials: SY
authors.lastname: Cho
authors.forename: Yung
authors.initials: Y
authors.lastname: Ki
authors.forename: Vanessa
authors.initials: V
authors.lastname: Chu
authors.forename: Joseph
authors.initials: J
authors.lastname: Chan
mesh_terms: D000293:Adolescent; D002648:Child; D002681:China / Q000208:ethnology; D003719:Dens in Dente / Q000453:epidemiology; D003786:Dental Pulp Cavity / Q000002:abnormalities; D005006:Ethnicity / Q000706:statistics & numerical data*; D005260:Female; D005500:Follow-Up Studies; D006723:Hong Kong; D006801:Humans; D008297:Male; D008310:Malocclusion / Q000453:epidemiology; D008313:Malocclusion, Angle Class III / Q000453:epidemiology; D008334:Mandible; D008963:Molar / Q000473:pathology*; D015995:Prevalence; D011862:Radiography, Panoramic / Q000706:statistics & numerical data; D012189:Retrospective Studies; D014095:Tooth, Impacted / Q000453:epidemiology*