title: A biometric study of C-shaped root canal systems in mandibular second molars using cone-beam computed tomography.
abstract: OBJECTIVE
  To investigate the configuration of C-shaped canals in mandibular second molars, canal wall thickness and the orientation of the thinnest area at 1-mm intervals from the canal orifice to the apex by using cone-beam computed tomographic (CBCT) images.
  
  
  METHODS
  Three-dimensional CBCT images of 92 Korean mandibular second molars having C-shaped root canals were analysed to determine their configuration using a modification of Melton's classification, as well as the thinnest walls and their location. Associations between configuration type and distance from the canal orifice to the apex, as well as associations between the directional orientation of the thinnest root wall and distance from the canal orifice to the apex, were assessed by Fisher's exact test. Because serial measurements of minimum wall thicknesses were correlated with individual teeth, a mixed-effects analysis was applied.
  
  
  RESULTS
  The most common configuration types were Melton's type I in the coronal region and Melton's type III in the apical region. Mean thicknesses of the thinnest root canal walls were 1.39 ± 0.38, 0.85 ± 0.25 and 0.77 ± 0.20 mm in the coronal, middle and apical regions, respectively. The thicker the root canal walls at the orifice region, the greater the decrease in thickness towards the apical region (P < 0.05), with the linguo-central root area being the thinnest. The pattern of decreasing thickness from the orifice to the apex formed a nonlinear cubic curve.
  
  
  CONCLUSIONS
  The most prevalent configuration types were Melton's type I (coronal region) and type III (apical region). The linguo-central root area was the thinnest in C-shaped root canals of Korean mandibular second molars. These anatomical variations should be considered during surgical or nonsurgical endodontic procedures.
authors.affiliation: Department of Conservative Dentistry and Dental Research Institute, Seoul National University Dental Hospital, Seoul National University School of Dentistry, Seoul, Korea.
authors.forename: D-G
authors.initials: DG
authors.lastname: Seo
authors.forename: Y
authors.initials: Y
authors.lastname: Gu
authors.forename: Y-A
authors.initials: YA
authors.lastname: Yi
authors.forename: S-J
authors.initials: SJ
authors.lastname: Lee
authors.forename: J-S
authors.initials: JS
authors.lastname: Jeong
authors.forename: Y
authors.initials: Y
authors.lastname: Lee
authors.forename: S-W
authors.initials: SW
authors.lastname: Chang
authors.forename: J-K
authors.initials: JK
authors.lastname: Lee
authors.forename: W
authors.initials: W
authors.lastname: Park
authors.forename: K-D
authors.initials: KD
authors.lastname: Kim
authors.forename: K-Y
authors.initials: KY
authors.lastname: Kum
mesh_terms: D000328:Adult; D063405:Anatomic Variation; D019412:Anatomy, Cross-Sectional / Q000706:statistics & numerical data; D001699:Biometry; D054893:Cone-Beam Computed Tomography / Q000706:statistics & numerical data*; D003786:Dental Pulp Cavity / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D008334:Mandible / Q000000981:diagnostic imaging; D008875:Middle Aged; D008963:Molar / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D009811:Odontometry / Q000706:statistics & numerical data; D056910:Republic of Korea; D012189:Retrospective Studies; D019227:Tooth Apex / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D019228:Tooth Crown / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D014092:Tooth Root / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D055815:Young Adult