title: Root canal morphology of permanent three-rooted mandibular first molars--part I: pulp floor and root canal system.
abstract: BACKGROUND
  Racial variations in root form and canal anatomy present endodontic challenges for clinicians. This study examined root canal morphology of three-rooted mandibular first molars by micro-computed tomography scans.
  
  
  METHODS
  A total of 122 extracted mandibular first molars were collected from a native Chinese population. After calculating the frequency of occurrence, 20 three-rooted (experimental group) and 25 two-rooted first molars (control group) were scanned and reconstructed three-dimensionally.
  
  
  RESULTS
  The frequency of three-rooted mandibular first molars was 31.97% (39/122). The mean interorifice distances from the distolingual (DL) canal to the distobuccal (DB) and mesiolingual canal were 2.93 mm and 2.86 mm, respectively. The mesial root predominately contained a type 2-2 root canal, with an incidence of 65% in the experimental group and 64% in the control group. Type 1-1 canals were seen more frequently in the DL and DB roots of the three-rooted first molars as well as in the distal roots of the two-rooted first molars. The incidences were 100% (20/20), 95% (19/20), and 72% (18/25), respectively. Accessory and lateral canals rarely occurred in the extra DL roots. The incidence was only 10% (2/20). A furcation canal extending from the floor to the furcation region was not observed.
  
  
  CONCLUSIONS
  Three-rooted mandibular first molars commonly have 4 separate canals with high incidences of accessory canals in the mesial and DB root. The geometric data of pulp floors are useful for locating the extra DL canal.
authors.affiliation: Department of Operative Dentistry & Endodontics, School of Stomatology, Fourth Military Medical University, Xi'an, China.
authors.forename: Yongchun
authors.initials: Y
authors.lastname: Gu
authors.forename: Qun
authors.initials: Q
authors.lastname: Lu
authors.forename: Hanguo
authors.initials: H
authors.lastname: Wang
authors.forename: Yuefeng
authors.initials: Y
authors.lastname: Ding
authors.forename: Ping
authors.initials: P
authors.lastname: Wang
authors.forename: Longxing
authors.initials: L
authors.lastname: Ni
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D002681:China; D003782:Dental Pulp / Q000033:anatomy & histology*; D003786:Dental Pulp Cavity / Q000033:anatomy & histology*; D003809:Dentin, Secondary / Q000033:anatomy & histology; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008297:Male; D008334:Mandible / Q000033:anatomy & histology*; D008875:Middle Aged; D008963:Molar / Q000033:anatomy & histology*; D014092:Tooth Root / Q000033:anatomy & histology*; D055114:X-Ray Microtomography / Q000379:methods; D055815:Young Adult