title: [A micro-computed tomographic study of the isthmus in the root canal system of mandibular first molar].
abstract: OBJECTIVE
  To investigate the prevalence and configuration of the isthmuses in the apical 6 mm of the mesial and distal roots of Chinese mandibular first molar by means of micro-computed tomography.
  
  
  METHODS
  Thirty-six extracted human mandibular first molars were selected. Specimens were subject to micro-CT and a slice thickness of 30 microm was obtained in the apical 6 mm of the roots examined. The number of sections showing isthmuses at each apical level was recorded. Three-dimensional images of isthmuses of mandibular first molars were reconstructed and observed.
  
  
  RESULTS
  The mesial roots of human mandibular first molars had a high incidence of isthmus. The isthmus incidence was greatest 4-6 mm from the apex in human mandibular first molar, with prevalence figures of 49.5%-66.1% and 17.3%-17.8% in mesial and distal roots, respectively. The chi-square test indicated a significant difference in the distribution of isthmuses between the two roots (P < 0.01).
  
  
  CONCLUSIONS
  The mesial roots of human mandibular first molars have a high incidence of isthmus, which may have clinical implications especially when surgical endodontics is performed on the mesial roots of mandibular molars.
authors.affiliation: Department of Cariology and EndodonTology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou 510055, China.
authors.forename: Li-Sha
authors.initials: LS
authors.lastname: Gu
authors.forename: Jun-Qi
authors.initials: JQ
authors.lastname: Ling
authors.forename: Xiang-Ya
authors.initials: XY
authors.lastname: Huang
authors.forename: Xi
authors.initials: X
authors.lastname: Wei
authors.forename: Qiong
authors.initials: Q
authors.lastname: Xu
mesh_terms: D000328:Adult; D003786:Dental Pulp Cavity / Q000000981:diagnostic imaging*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008334:Mandible / Q000000981:diagnostic imaging; D008963:Molar / Q000000981:diagnostic imaging*; D012390:Root Canal Therapy; D014092:Tooth Root / Q000000981:diagnostic imaging*; D055114:X-Ray Microtomography