|Year : 2013 | Volume
| Issue : 2 | Page : 86-89
Retromolar canal as observed on cone-beam computed tomography: Report of two cases with clinical importance
Ahmet Ercan Sekerci, Yildiray Sisman, Mehtap Arikan Payveren
Department of Maxillofacial Radiology, Faculty of Dentistry, Erciyes University, Kayseri, Turkey
|Date of Web Publication||21-Oct-2013|
Ahmet Ercan Sekerci
Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Erciyes University, 38039, Kayseri
Source of Support: None, Conflict of Interest: None
The retromolar canal (RMC) is an anatomical structure of the mandible with the clinical importance for surgical procedures such as impacted molar extraction and sagittal split ramus osteotomy. Since the RMC has omitted in anatomical textbooks and has rarely been reported in the dental literature, awareness of this condition is important. The aim of this study was to describe two cases of RMC and foramen on the basis of cone beam computed tomography images: One in a 53-year-old female and the other in a 64-year-old female. The authors believe that the present study will aid to the confirmation of the "RMC;" thus, permitting the planning of surgery with a lower risk of surgical damage.
Keywords: Accessory innervation, mandibular anatomy, retromolar canal, retromolar foramen
|How to cite this article:|
Sekerci AE, Sisman Y, Payveren MA. Retromolar canal as observed on cone-beam computed tomography: Report of two cases with clinical importance. J Oral Maxillofac Radiol 2013;1:86-9
|How to cite this URL:|
Sekerci AE, Sisman Y, Payveren MA. Retromolar canal as observed on cone-beam computed tomography: Report of two cases with clinical importance. J Oral Maxillofac Radiol [serial online] 2013 [cited 2020 Feb 23];1:86-9. Available from: http://www.joomr.org/text.asp?2013/1/2/86/120130
| Introduction|| |
The retromolar canal (RMC) is a rare anatomic variation found in the retromolar triangle, a small triangular-shaped region posterior to the third molar tooth in the mandible.  Identifying the position and configuration of mandibular canal variations are important in surgical procedures including sagittal split osteotomy, removal of impacted third molars and implant placement.  The neurovascular content of the mandibular RMC is very important for surgical procedures involving the retromolar area. 
The clinical significance of the existence of a RMC and of its neurovascular content is not yet clear. There have been limited articles about both anatomy and the description of RMC in anatomy or surgery textbooks until recent research in this area. Knowledge of this anatomical variation may prevent in this area and serve as an anatomical landmark for ethnic identification. 
Cone beam computed tomography (CBCT) technology is a substantial impact on maxillofacial imaging that has been used in several areas of dentistry because it shows 3D images of dental structures in addition to providing clear structural images with high contrast.  It has enabled us better to visualize the anatomy of the mandibular canal and ramified canals.  Recently, CBCT helped to detect the presence of RMCs and to distinguish five different morphologies and courses of this structure. 
This study reports of two female patients who referred to pre-surgical evaluation of mandible for dental implant placement. A limited CBCT scan was made and revealed RMC in the mandible.
| Case Reports|| |
A 64-year-old female patient was referred to Department of Oral and Maxillofacial Radiology for prosthetic restoration. Patient stated in his anamnesis that he wanted an implant treatment, since he had problems with accepting a removable lower denture. Preliminary assessment of the implant to patient for the treatment of panoramic radiographs. On the panoramic radiograph, the presence of a unilateral, RMC was suspected [Figure 1]. To evaluate the mandibular for dental implant surgery and to identify the RMC computed tomography (CT) scans with axial, sagittal and coronal cross-sectional cuts perpendicular to the alveolar ridge were performed with CBCT (Newtom 5G, QR, Verona, Italy) and confirmed the presence of an RMC, branching from the mandibular canal and running posterosuperiorly toward the retromolar fossa [Figure 1]b-d.
|Figure 1: Cropped panoramic radiograph of Patient I (a), sagittal cone beam computed tomography (CBCT) cut shows a curved retromolar canal (RMC) (arrows) behind the right mandibular third molar branching from the mandibular canal (b) and three-dimensional (c, d) CBCT image shows RMC (arrows) and running posterosuperiorly toward the retromolar fossa|
Click here to view
A 53-year-old female patient was referred to our department for implant treatment of mandibular edentulous region. Dental check-up a panoramic radiograph was obtained as routine evaluation [Figure 2]a. The panoramic radiograph revealed at the right side a RMC seemed to be related to the distal region of mandibular third molar. For implant planning, detailed radiographic examination of the distance between alveolar crest and the mandibular canal using, CBCT (Newtom 5G, QR, Verona, Italy) scan was performed. CT findings confirmed RMC branching from the mandibular canal and running posterosuperiorly toward the retromolar fossa [Figure 2]b-d.
|Figure 2: Cropped panoramic radiograph of Patient II (a), sagittal (b) and three-dimensional (c, d) CBCT image shows the mandibular retromolar canal (arrows) branching from the mandibular canal distal to third molar area and running posterosuperiorly toward the retromolar fossa|
Click here to view
| Discussion|| |
The RMC is an anatomic variant, which normally arises from the mandibular canal behind the third molar and travels anterosuperiorly to the retromolar foramen (RMF), which is located in the retromolar fossa.  Carter et al. demonstrated that a neural branch to the mandibular molars arises from the inferior alveolar nerve (IAN) or from the retromolar branch that travels through the RMC.  However, Jablonski et al.  have shown an aberrant buccal nerve originating from the IAN within the ramus of the mandible, traversing through the RMC, emerging through the RMF and then passing forward and upward to penetrate the buccinator muscle.
Boronat and Penarrocha reported the importance of the RMF and canal with accessory innervation, but also with failure of locoregional anesthesia in dentistry.  A cadaver study performed by Schejtman et al.  assessed the course of the neurovascular bundle originating from the RMF. After leaving the foramen, these elements were distributed mostly to the temporal tendon, the buccinator muscle, the most posterior zone of the alveolar process, and the third mandibular molar. Ikeda et al. suggested that branches of the mandibular division of the IAN can arise high in the infratemporal fossa and extend to the base of the coronoid process to enter the mandible in the retromolar fossa and to allow sensory fibers to innervate the mandibular molars. 
The incidence of RMCs in osseous and CBCT studies has been found to a range between 6.1% and 72%  among different populations. The few cadaver studies that have evaluated the existence of the RMF have reported great variability, with a frequency of up to 72% depending on the study design, i.e., the minimum size required for an opening in the bony surface to be defined as a foramen. ,,, In Patil et al.'s study,  an incidence of 65% was found and this was found to be higher than the incidence rates reported in previous CBCT studies. ,,
As the present case report has shown, the ability to detect a RMC with panoramic radiography is limited. von Arx et al.  studied in 100 patients were evaluated (100 unilateral and 21 bilateral cases) using CBCT, of 31 RMCs seen with CBCT, only seven were visible on corresponding panoramic radiographs. One explanation might be that the RMC is too thin to be detected (mean width, 0.99 mm; range: 0.5-1.75 mm). There have been studies, which have included only those RMCs with a diameter equal to or more than 0.5 mm  and 1 mm.  Kaufman et al.  detected bilateral accessory canals, 1-2 mm in diameter, slightly anterior to the ascending ramus of the mandible. Bilecenoglu and Tuncer  studied 80 sides of 40 dry adult mandibles and reported mean distances of 4.2 mm and 11.9 mm from the RMF to the distal aspect of the alveolar socket of the third and second molars, respectively.
There was no difference in the occurrence of RMCs with regard to sex and sides of the mandible.  However, Sawyer and Kiely  found a positive correlation with the accessory mandibular foramen, regarding the same-side occurrence. In the present report, patients were female and RMCs were at the right side.
Most of studies ,,,,, have reported that RMCs mostly occur unilaterally. On the contrary, a by Sagne et al.  where in a high frequency of bilateral occurrence was found in a section of the study sample.
The contents of the RMC have been reported to consist of branches of inferior alveolar vessels and nerves. , Histopathological surveys confirm the presence of myelinated nerve fibers associated with numerous venules and an artery.  Schejtman et al.  performed the dissection of RMC in cadavers during his autopsy, they found that the most constant element is a myelinated nerve (present in eight of the nine cases that were studied under a microscope). Bilecenoglu and Tuncer mentioned that their histopathologic investigation showed that the contents of the neurovascular bundle were striated muscle fibers and thin myelinated nerve fibers, numerous venules and a muscular artery having a lumen of 120-130 μm. Anderson et al. reported that myelinated nerve fibers innervate part of the temporalis muscle, part of the buccinator muscle, the most posterior part of the alveolar processes called the retromolar trigone and the pulp of the third molar tooth.  In Bilecenoglu and Tuncer  have found that there was no statistical correlation between the presence of the RMF and the last tooth of the arch. They suggested that the results of their study support the assertion that the elements in the RMC innervate and supply a part of the third molar.
In conclusion, knowledge of this anatomical variance and its assessment before surgery involving the posterior mandible like extraction of an impacted third molar, bone harvesting as a donor site for bone graft surgery and sagittal split osteotomy may warn the clinician about possible inadequate pre-surgical anesthesia, unexpected bleeding or local altered sensation post-operatively through damage to the vessels and nerves through the RMC/RMF. It is, therefore, important to confirm the course of the RMC and the location of the RMF prior to these surgical procedures.
| References|| |
|1.||Patil S, Matsuda Y, Nakajima K, Araki K, Okano T. Retromolar canals as observed on cone-beam computed tomography: Their incidence, course, and characteristics. Oral Surg Oral Med Oral Pathol Oral Radiol 2013;115:692-9. |
|2.||Naitoh M, Hiraiwa Y, Aimiya H, Ariji E. Observation of bifid mandibular canal using cone-beam computerized tomography. Int J Oral Maxillofac Implants 2009;24:155-9. |
|3.||Bilecenoglu B, Tuncer N. Clinical and anatomical study of retromolar foramen and canal. J Oral Maxillofac Surg 2006;64:1493-7. |
|4.||von Arx T, Hänni A, Sendi P, Buser D, Bornstein MM. Radiographic study of the mandibular retromolar canal: An anatomic structure with clinical importance. J Endod 2011;37:1630-5. |
|5.||Neves FS, Souza TC, Almeida SM, Haiter-Neto F, Freitas DQ, Bóscolo FN. Correlation of panoramic radiography and cone beam CT findings in the assessment of the relationship between impacted mandibular third molars and the mandibular canal. Dentomaxillofac Radiol 2012;41:553-7. |
|6.||Ossenberg NS. Retromolar foramen of the human mandible. Am J Phys Anthropol 1987;73:119-28. |
|7.||Carter RB, Keen EN. The intramandibular course of the inferior alveolar nerve. J Anat 1971;108:433-40. |
|8.||Jablonski NG, Cheng CM, Cheng LC, Cheung HM. Unusual origins of the buccal and mylohyoid nerves. Oral Surg Oral Med Oral Pathol 1985;60:487-8. |
|9.||Boronat López A, Peñarrocha Diago M. Failure of locoregional anesthesia in dental practice. Review of the literature. Med Oral Patol Oral Cir Bucal 2006;11:E510-3. |
|10.||Schejtman R, Devoto FC, Arias NH. The origin and distribution of the elements of the human mandibular retromolar canal. Arch Oral Biol 1967;12:1261-8. |
|11.||Ikeda K, Ho KC, Nowicki BH, Haughton VM. Multiplanar MR and anatomic study of the mandibular canal. AJNR Am J Neuroradiol 1996;17:579-84. |
|12.||Pyle MA, Jasinevicius TR, Lalumandier JA, Kohrs KJ, Sawyer DR. Prevalence and implications of accessory retromolar foramina in clinical dentistry. Gen Dent 1999;47:500-3. |
|13.||Narayana K, Nayak UA, Ahmed WN, Bhat JG, Devaiah BA. The retromolar foramen and canal in south Indian dry mandibles. Eur J Anat 2002;6:141-6. |
|14.||Kawai T, Asaumi R, Sato I, Kumazawa Y, Yosue T. Observation of the retromolar foramen and canal of the mandible: A CBCT and macroscopic study. Oral Radiol 2012;28:10-4. |
|15.||Lizio G, Pelliccioni GA, Ghigi G, Fanelli A, Marchetti C. Radiographic assessment of the mandibular retromolar canal using cone-beam computed tomography. Acta Odontol Scand 2013;71:650-5. |
|16.||Kaufman E, Serman NJ, Wang PD. Bilateral mandibular accessory foramina and canals: A case report and review of the literature. Dentomaxillofac Radiol 2000;29:170-5. |
|17.||Sawyer DR, Kiely ML. Retromolar foramen: A mandibular variant important to dentistry. Ann Dent 1991;50:16-8. |
|18.||Priya R, Manjunath KY, Balasubramanyam V. Retromolar foramen. Indian J Dent Res 2005;16:15-6. |
|19.||Sagne S, Olsson G, Hollender L. Retromolar foramina and canals in the human mandible. Studies in a medieval skull material. Dentomaxillofac Radiol 1977;6:41-5. |
|20.||Kodera H, Hashimoto I. A case of mandibular retromolar canal: Elements of nerves and arteries in this canal. Kaibogaku Zasshi 1995;70:23-30. |
|21.||Anderson LC, Kosinski TF, Mentag PJ. A review of the intraosseous course of the nerves of the mandible. J Oral Implantol 1991;17:394-403. |
[Figure 1], [Figure 2]