|Year : 2014 | Volume
| Issue : 1 | Page : 101-104
Bilateral accessory mental foramina and canals: Report of an extremely rare anatomical variation
Ahmet Ercan Sekerci, Yildiray Sisman
Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Erciyes University, Kayseri, Turkey
|Date of Web Publication||19-Apr-2014|
Ahmet Ercan Sekerci
Department of Maxillofacial Radiology, Faculty of Dentistry, Erciyes University, 38039, Kayseri
Source of Support: None, Conflict of Interest: None
| Abstract|| |
The mental nerve is a somatic afferent sensory nerve of the mandibular nerve that emerges from the mental foramen and which presents as a single circular, or elliptical, bilateral radiolucent area in the premolar region. The mental foramen is an important anatomical structure of particular importance in local anesthesia and surgical procedures in terms of achieving effective mandibular nerve blocks and avoiding injuries to the neurovascular bundles. Accessory mental foramen is a rare anatomical variation. Even so, in order to avoid neurovascular complications, particular attention should be paid to the possible occurrence of one or more mental foramen during surgical procedures involving the mandible. The purpose of the present report was to present a case the bilateral accessory mental foramina observed on cone-beam computed tomography and review the relevant literature.
Keywords: Accessory mental foramen, anatomy, buccal foramen, cone beam computed tomography, mental foramen, mandible
|How to cite this article:|
Sekerci AE, Sisman Y. Bilateral accessory mental foramina and canals: Report of an extremely rare anatomical variation. J Dent Implant 2014;4:101-4
|How to cite this URL:|
Sekerci AE, Sisman Y. Bilateral accessory mental foramina and canals: Report of an extremely rare anatomical variation. J Dent Implant [serial online] 2014 [cited 2021 Jan 28];4:101-4. Available from: https://www.jdionline.org/text.asp?2014/4/1/101/131016
| Introduction|| |
Confirmation of the mandibular canal, also called the inferior alveolar canal, course, which carries the inferior alveolar nerve, artery, vein, sympathetic autonomous nerve fibers, and lymphatic vessels, is clinically important to avoid local injury to the nerve during surgical and endodontic procedures.  Especially, it is crucial to identify the anatomic location of the mental foramen. The mental nerve is a somatic afferent sensory nerve of the mandibular nerve that emerges from the mental foramen and which presents as a single circular, or elliptical, bilateral radiolucent area in the premolar region.  On the perimandibular surface, the presence of small foramina identified as accessory mental foramina (AMFs) in the surrounding area of the mental foramen has been reported in the literature. 
The evaluations of accessory foramina that relate to the mandibular canal are clinically important in endodontic treatments and surgical procedures such as dental implant insertion, implant-related bone grafting, genioplasty and mandibular anterior segmented osteotomy.  Recently, some studies investigating the presence of small foramina in the perimandibular region have been carried out.  In CT-based studies, Naitoh et al.  and Katakami et al.  classified accessory foramina according to their continuity with the mandibular canal. According to these reports, an accessory foramen showing a connection with the mandibular canal was defined as accessory mental foramen (AMF), and an accessory foramen showing no connection with the mandibular canal was defined as a nutrient foramen. , However, in a cadaveric study, Fuakami et al.  stated that neurovascularization of these foramina is more complex than was previously thought. Thus, in that report, all the detected accessory foramina on the buccal mandibular surface were defined as accessory buccal foramina (ABFs), regardless of location and course. In this study, we have termed the accessory foramina on the buccal surface of the mandible as AMF because they originate from the mental foramen.
AMFs are rarely observed with conventional radiography techniques, such as periapical and panoramic radiographs, because the long axis of an AMF is generally less than 1.5 mm, and it is difficult to recognize this structure with two-dimensional techniques. ,,, Three-dimensional (3D) evaluation with CT and cone-beam CT (CBCT) could demonstrate the presence and course of AMFs. The detection of AMFs may reduce the rates of hemorrhage, post-operative pain and paralysis in surgical procedures. 
This report clearly demonstrates the advantage of CBCT over panoramic radiography in identification of anatomical variations and is the first to demonstrate these important anatomical variations in this way in Turkish population.
| Case Report|| |
A 42-year-old systemically healthy man was referred to Department of Maxillofacial Radiology, Dentistry Faculty at Erciyes University for routine dental examination and possible implant surgery in a partially edentulous mandible. Intraoral examination revealed clinical signs of periodontal disease and several restorations. He was referred for CBCT of the mandible prior to possible provision of dental implants. Axial, sagittal and coronal slices (0.1-mm slice thickness each) were reformatted and 3D reconstruction was performed. Reconstructed panoramic CBCT image of the mandible demonstrated two openings leading to the mandibular canal that were found on both right and left side [Figure 1]a. On the right side, two AMFs are evident on the sagittal image [Figure 1]b and 3D reconstruction image [Figure 2]a. The AMFs are located on the postero-superior and postero-inferior aspect of the mental foramen as shown in the 3D reconstruction image. On the left side, one AMF is evident on the sagittal image [Figure 1]c and 3D reconstruction image [Figure 2]b. The AMF are located on the postero-superior and postero-inferior aspect of the mental foramen as shown in the 3D reconstruction image. Both on the right and left side, the canal of the accessory foramen was at its widest at the point of communication with the mental foramen and the diameter of the accessory canal decreased as the distance from the mandibular canal increased. Both in the left and right premolar-molar regions, bifurcation of the mandibular canal between the premolars were evident, producing buccal exit. The location of AMF in relation to the MF in two sides was posteriorly located to the MF. Courses of the canals are illustrated in [Figure 2]c. Planning for dental implant placement was performed considering the anatomical variation mentioned, in order to avoid neurovascular bundle damage.
|Figure 1: Reconstructed panoramic CBCT image of the mandible displaying AMF canals (a). Curved two-dimensional image of the buccal bone surface marked the mental (arrow) and accessory mental foramina (asterisk), two openings leading to the mandibular canal were found on the right side (b) and one opening on the left side (c)|
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|Figure 2: Three-dimensional reconstruction (a and b) shows the location of the mental foramen (arrows) and accessory mental foramen (AMF) (asterisks). There are two small foramina on the right side and one small foramen on the left side of the mandible, whereas another accessory foramen in the anterior region on the left side was not identifi ed as an AMF. (c) Courses of the canals and foramina|
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| Discussion|| |
In dental practice, anatomical variations in the mandible can cause surgical complications if not properly identified.  An accessory foramen located in the region surrounding the mental foramen and showing a connection with the mandibular canal is defined as AMF and is believed to relate to the mental nerve. On the other hand, an accessory foramen showing no connection with the mandibular canal is defined as a nutrient foramen, which nourishes the bone with arterial structures. , Ichikawa  reported that the submental, lower lip buccal arteries and branches of the facial artery enter into the mandibular cancellous bone through the nutrient foramina.
AMF is a relevant anatomic structure with endemic importance in surgical procedures involving this region, such as genioplasty, bone harvesting from the chin, root resection of mandibular premolars, mandibular rehabilitation after trauma, and especially the placement of dental implants.  In patients with AMF, an accessory mental nerve may be present as well, considered a branch of the inferior alveolar nerve, which presence can cause anesthesia and surgery failure.  Myelinated nerves, neuro-vascular bundles, one or more arterioles and one or more venules have been found to occupy these canals and foramina.  There are few descriptions of the topographic anatomy of the mental nerve. Toh et al.  reported the distribution of the accessory mental nerve from the AMF to the mucous membranes, the skin of the corner of the mouth, and the median labial region. Hu et al.  categorized the mental nerve into four terminal branches-angular, medial inferior labial, lateral inferior labial, and mental branches, which originated from two or three main branches emerging from the MF. The presence of accessory innervation may explain failures to achieve adequate levels of anesthesia during surgical and routine dental procedures using conventional nerve block techniques. 
However, a clear distinction between AMF and the nutrient foramen has not been identified or supported in previous reports. In a cadaveric study, Fuakami et al.  reported some remarkable findings: (a) a branch of the facial artery coursed beside the mandible and re-entered through an ABF which showed a connection with the mandibular canal; and (b) a branch of the mental nerve re-entered the mandible through an ABF which showed no connection to the mandibular canal. Therefore, neurovascularization of these foramina may be more complex than was previously thought, and we also called the accessory foramina found in the present report "accessory buccal foramina" regardless of location and course.
The reported frequency of AMFs has been reported to range widely from 6.62% to 12.5%.  Bilateral AMFs are rare and have been described in 6-8% of the cases of presence of AMF, corresponding to approximately 0.53% of total population. , The different study designs (CBCT, CT, panoramic radiograph and cadaveric examinations) were compared and analyzed by Chi-square test and an association was found between them (P < 0.001). 
Dentists routinely use panoramic radiographs in dental examinations. These radiographs are generally sufficient for general dental practices, and AMFs in many surgical procedures can be found by appropriate surgical approaches.  However, on panoramic radiographs, visualization of AMF was only possible in 48.6% of the cases observed on CBCT images.  Two-dimensional radiographs can underestimate the presence or extension of this variation and are not entirely reliable for presurgical planning.  Application of tomographic techniques can reduce risk factors and provide considerable information before surgical procedures involving the perimandibular region or other important anatomical structures. In recent years, CBCT applications have become widespread. Thus, in order to avoid excessive radiation, clinicians should prefer CBCT to other tomographic techniques. From among different imaging modalities of tomography, we consider that 3D reformat is the best way to observe the presence of AMF and its location in relation to the mental foramen. However, axial, sagittal and cross-sectional slices are more functional regarding the detection of the course of AMF.
The location of the AMF in relation to the mental foramen has been demonstrated by Katakami et al.  and Naitoh et al.  Both studies reported that the majority of AMFs were located in the distal region of mental foramen. Only 1 of 17 and 3 of 15 AMFs, respectively, were located at the mesial region in their reports. According to the comparison of the inferior and superior regions, the majority of AMFs were located in the inferior region in previous studies.
The mean long axis of the AMF ranged from 1.3 to 1.9 mm in previous CT-based studies. ,, In accordance with previous studies, the mean long axis was found to be 1.7 mm in this report. The mean area of the AMFs was found to be 1.7 and 1.5 mm 2 in different studies performed by Naitoh et al.  Similar to those studies, we found a mean diameter of 1.5 mm 2 . Also, Naitoh et al.  reported that the distance between the mental foramen and the ABF ranged from 4.5 to 9.6 mm, with a mean of 6.3 mm. Also, the area of the mental foramen with an AMF was 70% smaller than that without it. There were no significant differences between the sizes of mental foramina with and without an accessory mental foramen.  In the present report, the distance between the mental foramen and the ABF ranged from 5.4 to 10.9 mm, with a mean of 7.2 mm.
In conclusion, presence and location of accessory mental foramen is important during surgical procedures and dental implant insertion involving the mandibular premolar and molar region. The presence of an arterial branch or accessory mental nerve in the buccal perimandibular region should be considered. This approach may reduce the risk of paralysis, hemorrhage and post-operative pain in this region. In dentoalveolar treatment, limited CBCT is effective as presurgical 3D assessment of the neurovascular structures.
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[Figure 1], [Figure 2]