title: [A cone-beam computed tomography study of changes in canal isthmus of maxillary first premolars before and after instrumentation].
abstract: OBJECTIVE
  To analyze the difference of the incidence and type of root canal isthmus in maxillary first premolars with single root and two canals before and after instrumentation using cone-beam computed tomography(CBCT), and investigate the application and effect of CBCT in analysis of root canal isthmus.
  
  
  METHODS
  Sixty-six extracted maxillary first premolar with single root and two canals were scanned by CBCT before and after instrumentation. The incidence and type of isthmus before and after instrumentation were recorded and compared. The data was subjected to X(2) test and rank sum test with SPSS13.0 software package.
  
  
  RESULTS
  The incidence of isthmus was different at each 1 mm level within apical 0-6 mm in maxillary first premolar with single root and two canals before and after instrumentation (P<0.05), which was lowest at apical 1 mm and highest at apical 6 mm; the proportion of partial isthmus (PI) was significantly higher than complete isthmus (CI) (P<0.05). After instrumentation, the incidence of isthmus in apical 0-6 mm decreased (P<0.05), but the proportion of CI increased.
  
  
  CONCLUSIONS
  The difference of root canal isthmus structure before and after instrumentation can be defined accurately with CBCT. CBCT is an ideal method to evaluate root canal isthmus.
authors.affiliation: Department of VIP Dentistry, Ninth People's Hospital, College of Stomatology, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai 200011, China. nalizhu@yahoo.cn
authors.forename: Li-na
authors.initials: LN
authors.lastname: Zhu
authors.forename: Wen-hao
authors.initials: WH
authors.lastname: Qian
authors.forename: Jin
authors.initials: J
authors.lastname: Hong
mesh_terms: D001641:Bicuspid; D054893:Cone-Beam Computed Tomography; D003786:Dental Pulp Cavity; D006801:Humans; D012390:Root Canal Therapy; D014092:Tooth Root