title: Evaluation of x-ray projection angulation for successful radix entomolaris diagnosis in mandibular first molars in vitro.
abstract: BACKGROUND
  The aim of this study was to evaluate the radiographic features of permanent three-rooted mandibular first molars with radix entomolaris (RE), investigate the correlation between anatomical classification and radiographic type of RE, and to determine the most effective horizontal beam angulation for the diagnosis of RE.
  
  
  METHODS
  Twenty-five extracted mandibular first permanent molars with RE were selected for taking radiographs in 7 horizontal angulations. By using set criteria, 3 evaluators assessed morphologic and radiographic features of the RE and optimum beam angulation for RE diagnosis. Intraexaminer variability was analyzed with Cohen kappa test.
  
  
  RESULTS
  Three types of curvature of RE presented with 3 distinct types of typical radiographic appearance on orthoradial radiographs. We classified the radiographic features of RE into 3 types, as follows: type i, type ii, and type iii. Seven teeth showed type i radiographic features. Zero-degree, 5-degree, 15-degree, and 25-degree radiographs were significantly better than the mesially angulated -15-degree and -25-degree images for detecting the type i RE images (P < .05). Fifteen-degree, 25-degree, and -25-degree horizontal beam angulations showed significantly more accurate diagnoses of RE in 8 type ii images (P < .05). Only 25-degree-angled radiographs were found to have a high diagnostic yield of type iii RE images (P < .05). A significant correlation was found between morphologic and radiographic types of RE (P < .05, contingency coefficient = 0.473). Intraexaminer variability was low, with kappa = 0.68 (P < .05).
  
  
  CONCLUSIONS
  RE presents 3 types of typical radiographic features on orthoradial radiographs. Additional 25-degree mesial horizontal-angled radiographs are essential for preoperative identification and evaluation of RE, especially types ii and iii.
authors.affiliation: State Key Laboratory of Oral Diseases (Sichuan University), Chengdu, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.forename: Gang
authors.initials: G
authors.lastname: Yu
authors.forename: Xue-dong
authors.initials: XD
authors.lastname: Zhou
authors.forename: Ove A
authors.initials: OA
authors.lastname: Peters
authors.forename: Qing-hua
authors.initials: QH
authors.lastname: Zheng
authors.forename: Ding-ming
authors.initials: DM
authors.lastname: Huang
mesh_terms: D044466:Asian People; D002681:China; D003786:Dental Pulp Cavity / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*; D006801:Humans; D008334:Mandible; D008963:Molar / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D015588:Observer Variation; D011861:Radiography, Dental / Q000379:methods*; D014092:Tooth Root / Q000033:anatomy & histology* / Q000000981:diagnostic imaging*