Observation of retromolar canals on cone beam computed tomography

  • Yunwen Hou
  • Guanying Feng
  • Wen Lin
  • Ruixia WangEmail author
  • Hua YuanEmail author
Original Article



To evaluate the incidence and location of retromolar canal (RMC) in an eastern Chinese population using cone beam computed tomography (CBCT) images.


Six hundred and fifty-seven patients (276 males and 381 females, 19–49 years old) from east China were enrolled. Both right and left sides of the mandible were examined (n = 1314). Two-dimensional (2D) images of various planes in the mandibular ramus region and reconstructed three-dimensional (3D) images were reviewed. The course of the RMC and the location of the retromolar foramina (RMF) were observed.


Retromolar canal (RMC) was observed in 25.9% (170/657) of patients and 15.7% of sides (206/1314). 20.4% patients had unilateral RMC (134/657) and 5.5% had bilaterally RMC (36/657). Most RMC are horizontally curved course (Type B, 45.6%), followed by vertically curved course (Type A, 44.2%). Type C RMC, which run independently from separate foramina in the mandibular ramus, were relatively rare (10.2%). The distance from the middle of the RMF to the distal end of the second molar ranged from 4.56 to 24.01 mm and the mean distance was 11.97 mm.


RMC is not a rare anatomical structure in the eastern Chinese population. CBCT should be applied as a diagnostic tool to provide detailed information involving the retromolar area.


Cone beam CT(CBCT) Retromolar canal (RMC) Retromolar foramina (RMF) Incidence Oral surgery 



This work was supported in part by a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD, 2018–87). The Project of Invigorating Health Care through Science, Technology and Education (Jiangsu Provincial Medical Youth Talent QNRC2016852), Jiangsu Provincial Medical Innovation Team (CXTDA2017036) and sponsored by Qing Lan Project.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflicts of interest.

Ethical approval

All procedures followed were in accordance with the ethical standards of the responsible committee on human experimentation (institutional and national) and with the Helsinki Declaration of 1975, as revised in 2008.

Informed consent

Informed consent was obtained from all patients for being included in the study.


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Copyright information

© Japanese Society for Oral and Maxillofacial Radiology and Springer Nature Singapore Pte Ltd. 2019

Authors and Affiliations

  1. 1.Jiangsu Key Laboratory of Oral DiseasesNanjing Medical UniversityNanjingPeople’s Republic of China
  2. 2.Department of Oral and Maxillofacial Surgery, Affiliated Hospital of StomatologyNanjing Medical UniversityNanjingChina

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