title: Root canal morphology of permanent three-rooted mandibular first molars: Part II--measurement of root canal curvatures.
abstract: BACKGROUND
  The distolingual (DL) roots of three-rooted mandibular molars often challenge clinicians during root canal therapy. This study investigated canal curvatures in permanent three-rooted mandibular first molars by using micro-computed tomography (micro-CT) scans.
  
  
  METHODS
  Twenty three-rooted (group 1) and twenty-five two-rooted mandibular first molars (group 2) were scanned by micro-CT. The specimens were reconstructed 3-dimensionally by the software Mimics 10.01 and shown in a parallel projection mode. The images of the root canals in clinical view (CV) and proximal view (PV) were analyzed by the software Image-Pro Plus. Schneider method and a modified Pruett method were used to measure the angles and radius of canal curvatures.
  
  
  RESULTS
  In the three-rooted molar group in a CV, the average angles of primary curvatures were 24.34 degrees for the mesiobuccal, 22.39 degrees for the mesiolingual, 13.71 degrees for the distobuccal (DB), and 13.81 degrees for the DL canal. In a PV, the average angles were 16.60 degrees for the DB and 36.06 degrees for the DL canal, respectively. Secondary curvatures were frequently seen in a CV (60%) for the DB canals, with an average angle of 26.94 degrees. In a PV, the average central angle of curvature was 59.04 degrees for the DL canal, and the average radius and curve length were 6.17 and 5.73 mm, respectively. In general, no statistically significant difference was found for canal curvatures in the mesial roots between the three-rooted and two-rooted molar groups (P > .05).
  
  
  CONCLUSIONS
  A better understanding of the canal curvatures is essential for successful endodontic treatment of three-rooted mandibular first molars.
authors.affiliation: Department of Operative Dentistry & Endodontics, School of Stomatology, Fourth Military Medical University, Xi'an 710032, China.
authors.forename: Yongchun
authors.initials: Y
authors.lastname: Gu
authors.forename: Qun
authors.initials: Q
authors.lastname: Lu
authors.forename: Ping
authors.initials: P
authors.lastname: Wang
authors.forename: Longxing
authors.initials: L
authors.lastname: Ni
mesh_terms: D003786:Dental Pulp Cavity / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D021621:Imaging, Three-Dimensional / Q000379:methods; D008334:Mandible; D008963:Molar / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D009811:Odontometry / Q000379:methods / Q000706:statistics & numerical data; D014092:Tooth Root / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D055114:X-Ray Microtomography / Q000379:methods