title: [Evaluation of X-ray beam angulation for successful four canals identification in the mandibular first molars].
abstract: OBJECTIVE
  This study was aimed to determine the most effective horizontal beam angulation to identify 4 canals in the mandibular first molars, so as to provide full and accurate information for the clinic.
  
  
  METHODS
  One hundred and twenty mandibular first molars with four canals that needed endodontic treatment in vivo were selected. Radiographs were taken at horizontal angles of 0,10,20 degrees from distal direction and 0,10,20,30 degrees from mesial direction of the tooth. The numbers of root canal and the degree of resolution were identified and recorded by 3 independent observers. Data were analyzed using SPSS10.0 software package or Chi-square test.
  
  
  RESULTS
  At 30 and 20 degrees from mesial direction, 93.3% and 90.0% of all the 120 teeth were correctly identified as 4 canals, compared with 0 degree of 40.0%(P<0.01). Of them, 71.5% and 89.7% could be classified as with high resolution, respectively. The latter was not significantly lower than 0 degree of 95.0% (P>0.05).
  
  
  CONCLUSIONS
  Twenty degrees from mesial direction is the most effective X-ray beam angle in diagnosing 4 canals of the first mandibular molars. Supported by Research Fund of Science and Technology Commission of Shanghai Municipality (Grant No.08DZ2271100).
authors.affiliation: Department of General Dentistry, College of Stomatology, Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai Key Laboratory of Stomatology, Shanghai 200011, China. muduproject@yahoo.com.cn
authors.forename: Lu-dong
authors.initials: LD
authors.lastname: Zhang
authors.forename: Xiang-wei
authors.initials: XW
authors.lastname: Chen
authors.forename: Yan
authors.initials: Y
authors.lastname: He
authors.forename: Jun-li
authors.initials: JL
authors.lastname: Han
authors.forename: Hai-ning
authors.initials: HN
authors.lastname: Wang
mesh_terms: D001641:Bicuspid; D003786:Dental Pulp Cavity; D006801:Humans; D008334:Mandible; D008963:Molar; D012390:Root Canal Therapy; D014965:X-Rays