title: [Anatomic study of canal isthmuses of mandibular permanent incisors by micro-CT].
abstract: OBJECTIVE
  To investigate the anatomic feature of the canal isthmus of mandibular permanent incisors by Micro-CT.
  
  
  METHODS
  Thirty-three mandibular permanent incisors with two canals were selected through the radiograph in proximal view. These teeth were then scanned using Micro-CT and reconstructed. The scanning layer thickness was 20 microm. We observed the apical 6 mm of the 33 roots, and 300 sections were gained each tooth, giving a total of 9900 sections. The numbers of canals at each level in the apical 6 mm were recorded. The numbers of sections showing isthmuses at each level of the root canals were recorded too. Data were analyzed using the Chi-square statistic to test the null hypothesis that location of the sections in each of the apical 6 mm and presence of the isthmus were independent. The minimum root canal wall thickness was measured in each of the apical 6 mm of the roots.
  
  
  RESULTS
  Isthmuses were found to be present at all levels with prevalence from 10.0% to 85.5%. The Chi-square test indicated a significant difference in the distribution of isthmuses with section (P = 0.0O1). The incidence of isthmuses was higher at the apical 3-6 mm level, and the highest incidence (85.5%) was at 5 mm level. There were many more sections containing complete isthmuses (49.7%) than those containing partial isthmuses (4.5%). The thickness of the minimum root canal was less than 0.5 mm.
  
  
  CONCLUSIONS
  The mandibular incisors have a high incidence of isthmus and are narrow in proximal direction. Debridement of the isthmus is a major challenge during surgical and nonsurgical root canal treatment.
authors.affiliation: State Key Laboratory of Oral Diseases, Sichuan University, Chengdu 610041, China.
authors.forename: Cheng-xia
authors.initials: CX
authors.lastname: Liu
authors.forename: Wen
authors.initials: W
authors.lastname: Li
authors.forename: Qing-hua
authors.initials: QH
authors.lastname: Zheng
authors.forename: Ning
authors.initials: N
authors.lastname: Geng
authors.forename: Tuo-qi
authors.initials: TQ
authors.lastname: Sun
authors.forename: Ding-ming
authors.initials: DM
authors.lastname: Huang
mesh_terms: D003786:Dental Pulp Cavity; D006801:Humans; D007180:Incisor; D008334:Mandible; D008963:Molar; D019227:Tooth Apex; D055114:X-Ray Microtomography