title: Prevalence of three-rooted primary mandibular first molars in Taiwan.
abstract: OBJECTIVE
  Knowledge of root canal anatomy is important for dental practice and for identifying features of anthropological significance. Three-rooted permanent mandibular molars are considered an anatomical variant of the Mongoloid race. This study aimed to determine the prevalence of three-rooted primary mandibular first molars in Taiwanese subjects.
  
  
  METHODS
  Vertical bite-wing radiographs of 227 subjects, which had been obtained previously in the Department of Pediatric Dentistry, Taichung Veterans General Hospital, Taichung, Taiwan, from January 2004 to December 2007, were screened retrospectively. Images of 121 subjects [54 boys and 67 girls; mean age (range), 5.8 (2.4-10.4) years] who had bilateral primary mandibular first molars were studied. The sex, symmetry and frequency of occurrence of three-rooted primary mandibular first molars were recorded and statistically analyzed.
  
  
  RESULTS
  The overall prevalence of subjects with three-rooted primary mandibular first molars was 5.0% (6/121), and 83.0% of the molars were unilateral. The prevalence of teeth that showed an extra root among all teeth examined was 2.9% (7/242). Such prevalence did not differ significantly between the right and left sides of the mandible, bilateral and unilateral, or with sex.
  
  
  CONCLUSIONS
  The data presented here indicate that approximately 5% of Taiwanese subjects had a threerooted mandibular primary first molar and 80% of such teeth occurred unilaterally. Dentists should take into account the prevalence of these three-rooted variants in primary mandibular first molars among Taiwanese patients during their daily endodontic and exodontic procedures.
authors.affiliation: School of Dentistry, College of Medicine, China Medical University, and Department of Dentistry, China Medical University Hospital, Taichung, Taiwan. mgtu@mail.cmu.edu.tw
authors.forename: Ming-Gene
authors.initials: MG
authors.lastname: Tu
authors.forename: Jeng-Fen
authors.initials: JF
authors.lastname: Liu
authors.forename: Pei-Wei
authors.initials: PW
authors.lastname: Dai
authors.forename: San-Yue
authors.initials: SY
authors.lastname: Chen
authors.forename: Jui-Ting
authors.initials: JT
authors.lastname: Hsu
authors.forename: Heng-Li
authors.initials: HL
authors.lastname: Huang
mesh_terms: D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D008297:Male; D008334:Mandible; D008963:Molar / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D015995:Prevalence; D016300:Radiography, Bitewing; D012189:Retrospective Studies; D012737:Sex Factors; D013624:Taiwan / Q000453:epidemiology; D014092:Tooth Root / Q000033:anatomy & histology* / Q000000981:diagnostic imaging