title: Prevalence of 3-rooted first permanent molars among a Shanghai Chinese population.
abstract: OBJECTIVE
  This study aimed to assess the prevalence of 3-rooted mandibular first molars among a Shanghai Chinese population by using periapical radiographs.
  
  
  METHODS
  A total of 510 patients possessing both mandibular first molars were selected. The radiographs of these cases were evaluated under optimal conditions using double magnifying glasses. The incidence of 3-rooted mandibular first molars and the correlation between occurrences in males and females and between the left and right sides were recorded and analyzed. A total of 1020 mandibular first molars were evaluated.
  
  
  RESULTS
  A total of 165 patients were found to have a 3-rooted mandibular first molar: 92 males and 73 females (P = .106). The overall incidence of patients with 3-rooted mandibular first molars was 32.35%. Of all the patients with 3-rooted molars, 67.27% (111/165) of cases occurred bilaterally. The incidence of teeth showing an extra root was 27.06%. The occurrence of such permanent 3-rooted mandibular first molars also did not differ significantly between the right side (n = 142, 13.92%) and the left side (n = 134, 13.14%; P = .573).
  
  
  CONCLUSIONS
  The prevalence and bilateral incidence of 3-rooted mandibular first molars among the Shanghai Chinese population was high and such variation varied among Chinese populations living in different areas.
authors.affiliation: Department of General Dentistry, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai, China.
authors.forename: Ya
authors.initials: Y
authors.lastname: Yang
authors.forename: Lu-Dong
authors.initials: LD
authors.lastname: Zhang
authors.forename: Jian-ping
authors.initials: JP
authors.lastname: Ge
authors.forename: Ya-qin
authors.initials: YQ
authors.lastname: Zhu
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002681:China / Q000453:epidemiology; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008334:Mandible / Q000000981:diagnostic imaging; D008875:Middle Aged; D008963:Molar / Q000002:abnormalities* / Q000000981:diagnostic imaging; D015995:Prevalence; D016300:Radiography, Bitewing; D012737:Sex Factors; D014092:Tooth Root / Q000002:abnormalities* / Q000000981:diagnostic imaging; D055815:Young Adult