Evaluation of X-Ray Projection Angulation for Successful Radix Entomolaris Diagnosis in Mandibular First Molars In Vitro

By Wang Q, Yu G, Zhou XD, Peters OA, Zheng QH, and Huang DM

Date: 12/2011
Journal: JOE


•Purpose: To evaluate the radiographic features of RE at various horizontal angulations, to investigate possible correlation between anatomical classification and radiographic type of RE, and to determine the most effective horizontal angulation for successful RE diagnosis in mandibular first molars.

•N= 25 mandibular 1st molars 12 right &13 left with radix entomolaris & intact contour (Chinese patients)


  • A commercial angulometer with a point was fixed on the base of rotating part of the jig to indicate the horizontal angle of the x-ray beam.
  • Exposure in various horizontal angulations (–25o, –15o, –5o, 0o, 5o, 15o, 25o); positive angles at mesial horizontal angulation and negative angles at distal angulation.
  • Radiographs were assessed by 3 dentists. The criteria to diagnose the presence of RE was a clear distinction from a distobuccal root with distinct apex and continuous periodontal space on radiographs.

Most highlighted Results:

  •   table 2
  • All REs were categorized into 3 groups according to their morphologic features Type I, II and III. Fig 1
  • RE were classified on the basis of the radiographic overlapped degree between DL &DB root , type I, ii and iii Fig 2.
  • A significant association between the radiographic and morphologic types; especially morphologic type III RE was detected most frequently in radiographic type i samples.
  • 25o mesial radiographs were significantly better than 25o distal radiographs. (Table 3)

Clinical significance:

Additional 25-degree mesial horizontal angulation radiographs are essential for the preoperative identification and evaluation of RE.