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Comparison of Radiographic Visualization of Retromolar Foramina and Canals


Kyoko Fujii, DH – Dent-oral Science Institute

Shigeo Osato, DDS, PhD

Tadakazu Miyao, DDS

Iwao Kuroyama, DDS, PhD

Irika Miyao, DDS

Yukari Osato, DDS


Purpose of the Study: The surgical and anesthetic procedures used for the mandibular molars and retromolar areas may lead to anesthetic failures, injuries, and complications affecting the neurovascular bundles running through the retromolar foramina (RMFs) and the retromolar canals (RMCs). The purpose of this study was to compare the macroscopic photographic findings with those obtained from dental panoramic radiography (DPR) and cone-beam computed tomography (CBCT), in terms of the number, distribution, and dimensions of RMFs in the retromolar areas of the dentate mandibles; the occurrence of RMCs; and the course of RMCs.

Methods: 27 human dried mandibles (54 sides) were evaluated on photographs and radiographic images (2×). The longest diameters of the RMFs were measured using digital vernier calipers. The foramina and canals in the mandibles, in which a wire of 0.25 mm diameter could be inserted at ≥ 2 mm depth, were defined as RMF and RMC, respectively. The DPR and CBCT radiographic images of the mandibles were obtained using a Veraviewepocs 3Df (Morita). The data were statistically analyzed using StatView software.

Results: A total of 61 openings in the retromolar area were observed, but only 14 (22.95%) fulfilled the criteria of RMF. The 14 RMFs were observed in 13 sides (24.07%) involving 11 (40.74%) of 27 mandibles (54 sides). The RMFs were found bilaterally and unilaterally in 2 (18.18%) and 9 (81.82%) mandibles, respectively, with a significant difference (P = 0.0007). There was no significant difference with respect to sides (6 vs. 7) in 27 mandibles. Of the 14 RMFs observed on macroscopic photographs, 5 (35.71%) were large sized (35.71%) and 9 (64.29%) were medium and small sized. The mean length of the long axis of the RMFs was 0.94 ± 0.40 mm (range, 0.50−1.70). DPR detected 3 out of 14 RMFs (21.43%) and 3 out of 14 RMCs (21.43%), and CBCT detected 10 out of 14 RMFs (71.43%) and 10 out of 14 RMCs (71.43%), with significant differences in the distribution (DPR: P = 0.0008 and CBCT: P = 0.0134). The number of RMFs and RMCs detected using CBCT (detected: 10 each and undetected: 4 each) was significantly higher than that detected using DPR (detected: 3 each and undetected: 11 each; P = 0.0107). Three courses of RMCs on the CBCT images were type A (30.00%) and seven were type B (70.00%), with a significant difference (P = 0.0480), according to the classifications of Jamalpour, et al. (2016). The mean angle of inclination between the mandibular canal (MC) and the mandibular plane on the DPR image was 39.00 ± 3.23°, which was significantly larger by 3.41° compared to that in the mandibles without RMCs (P = 0.0245).

Conclusion: These results revealed that CBCT was more useful than DPR to detect RMFs and RMCs in the retromolar areas despite their sizes; however, it was difficult to precisely detect the RMFs of size ≤ 0.9 mm and the corresponding RMCs. It was also suggested that the angles of inclination of the MCs on DPR images, in the mandibles with RMCs as determined by CBCT images, were significantly increased. In clinical practice, particularly when undertaking anesthetic and surgical procedures in the mandibular molar and retromolar areas, RMFs and RMCs, which are not detected by CBCT images, should be taken into careful consideration.

Articles: 1. Moreno Rabie C, Vranckx M, Rusque MI, Deambrosi C, Ockerman A, Politis C, Jacobs R. Anatomical relation of third molars and the retromolar canal. Br J Oral Maxillofac Surg. 2019 Jul 23. doi: 10.1016/j.bjoms.2019.07.006. 2. Kikuta S, Iwanaga J, Nakamura K, Hino K, Nakamura M, Kusukawa J. The retromolar canals and foramina: Radiographic observation and application to oral surgery. Surg Radiol Anat. 2018; 40: 647–652. 3. Truong MK, He P, Adeeb N, Oskouian RJ, Tubbs RS, Iwanaga J. Clinical anatomy and significance of the retromolar foramina and their canals: A literature review. Cureus. 2017; 9: e1781. 4. Park MK, Jung W, Bae JH, Kwak HH. Anatomical and radiographic study of the mandibular retromolar canal. J Dent Sci. 2016; 11: 370–376. 5. Muinelo-Lorenzo J, Suárez-Quintanilla JA, Fernández-Alonso A, Marsillas-Rascado S, Suárez-Cunqueiro MM. Descriptive study of the bifid mandibular canals and retromolar foramina: Cone beam CT vs panoramic radiography. Dentomaxillofac Radiol. 2014; 43: 20140090.

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