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Year : 2017  |  Volume : 20  |  Issue : 12  |  Page : 1550-1554

Evaluation of accessory mental foramina morphology with cone-beam computed tomography

1 Ministry of Health Topraklik Oral and Dental Health Center, Ankara, Turkey
2 Department of Dentomaxillofacial Radiology, Gazi University, Ankara, Turkey
3 Department of Periodontology, Faculty of Dentistry, Gazi University, Ankara, Turkey

Date of Acceptance21-Mar-2016
Date of Web Publication29-Jan-2018

Correspondence Address:
Dr. M Gumusok
Ministry of Health Topraklik Oral and Dental Health Center, Ankara
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/1119-3077.187329

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Background: Accessory mental foramen (AMF) is the extra mental foramen (MF) located in the mandible. The recognition of AMF is important to avoid complications during surgical procedures involving MF and cheeks. Aim: This study aimed to determine the prevalence, localization, and size of AMF by using cone-beam computed tomography (CBCT). Materials and Methods: CBCT images of 645 patients over 13-14 years (male 281; female 364) were retrospectively evaluated. The CBCT images were obtained using Promax 3D® (Planmeca, Helsinki, Finland) device with automated exposure parameters varying depending on the cases. Statistical analysis was performed using descriptive statistics, chi-square test and t-test. Results: AMF was detected in 75 (11.6%) patients. There was no significant difference between the presence of AMF and gender (P = 0.57, P > 0.05). Majority of the cases (n = 67, 88.8%) consisted of single AMF, while double AMF was observed in 6 (10%) and triple AMF in 2 (1.2%) patients. The most common location of AMF with respect to MF was posterio-inferior (n = 57, 67.1%), and AMF placed at the root line of first molar tooth in 45 cases (52.9%). Conclusion: AMF can be seen in the mandible one in every ten patients being single in most cases. Considering the high prevalence and present morphological features, AMF should be detected by CBCT before surgical operations, particularly in implant planning for the prevention of possible complications.

Keywords: Cone-beam computed tomography, dentistry, mandible, mental foramen

How to cite this article:
Gumusok M, Akarslan Z Z, Basman A, Ucok O. Evaluation of accessory mental foramina morphology with cone-beam computed tomography. Niger J Clin Pract 2017;20:1550-4

How to cite this URL:
Gumusok M, Akarslan Z Z, Basman A, Ucok O. Evaluation of accessory mental foramina morphology with cone-beam computed tomography. Niger J Clin Pract [serial online] 2017 [cited 2021 Mar 3];20:1550-4. Available from:

   Introduction Top

Mental foremen (MF) is an important anatomical structure. It is round or oval and is usually located apical to the second mandibular premolar or between the apices of the first or second premolars. However, it can be located in the mandibular canine region and the first molar rarely.[1] While one MF occurs each on the right and the left sides of the mandible, multiple MF may rarely occur.[2] In case there is more than one MF, one of these formations is called the MF and the other(s) is/are called accessory mental foramen (AMF).[3] AMF includes an accessory mental nerve branch separated before exiting from the MF.[4],[5] The mental nerve exiting from AMF distributed in the mucous membranes, the skin at the corner of the mouth, and the inner surface of lip could be related to the branches of buccal and facial nerves.[5]

The AMF is an important anatomical structure in local anesthesia and surgical procedures involving this area, such as genioplasty, mandibular rehabilitation after trauma, bone harvesting from the chin, root resection of mandibular premolars, and particularly placement of dental implants.[6],[7],[8],[9] The recognition of the AMF is important to avoid complications during surgical procedures involving the MF and cheeks, such as nerve damage and hemorrhage.[10],[11] This may allow adequate anesthesia and correct diagnosis of bone lesions.[12]

Although traditional two-dimensional (2D) imaging methods are frequently used in dentistry, they are generally unsuccessful in the diagnosis of MF's anatomical variations.[13] However, cone-beam computed tomography (CBCT) technique provides three-dimensional (3D) imaging of the structures in the maxillofacial region without superimposition of surrounding structures [14] and is able to form images having higher spatial resolution with lower radiation dose compared to CT,[15] thus is more successful in diagnosing MF location and its variations than conventional 2D radiographic techniques.[13] Although CBCT has been shown to be effective in detecting AMF,[13],[14],[15] its structural details have not been reported.

The purpose of this study was to determine the prevalence, location with respect to MF, and dimension of AMF by retrospectively assessing the CBCT images.

   Materials and Methods Top

Study design and patients

The CBCT images of 645 patients over 13–14 years (281 [43.57%] male, 364 [56.43%] female; mean age 41 years), showing the entire mandible and stored in the archive center of the Department of Oral and Maxillofacial Radiology in Gazi University were used in this study. The images of patients with incomplete root apices, artifacts and pathologies such as fracture, lesion, bone disease, and skeletal anomaly, which impaired the quality of the mandibular view, were not evaluated.

The study was approved by the Ethics Committee of Ankara University Faculty of Dentistry (No. 12/9).

Cone-beam computed tomography technique

The CBCT images were obtained using Promax 3D ® (Planmeca, Helsinki, Finland) device with automated exposure parameters varying depending on the cases. The images were assessed by an oral and maxillofacial radiologist on a computer screen (22 inch; resolution 1920 × 1080) in a low light setting from a distance of 50 cm. The mandible was examined in axial, sagittal, coronal planes and 3D images, through which MFs were detected on the right and left sides and the presence of the AMF was identified. The AMF was defined as the foramen that was smaller than the MF and expanded into the mandibular cortex showing continuity with the sub-branch of the mandibular canal.[10],[16],[17]

Parameters evaluated

The AMF was classified as located in the dentate or edentulous mandibles. The numbers of AMF, its horizontal and vertical diameters, location with respect to the MF, and distance to the MF were determined. The horizontal and vertical diameters of MF were also measured. Moreover, in dentate cases, the positions of the teeth in the neighborhood of AMF were evaluated considering their root(s).

Statistical analysis

Statistical analysis was performed using descriptive statistics, chi-square test and t-test. Each of multi-AMF was statistically assessed as an independent case. Data were analyzed with SPSS Software Package for Windows (Statistical Package for Social Sciences, version 15.0, SPSS Inc., Chicago, Illinois, USA). Statistical level of significance was defined as P < 0.05.

   Results Top

Of the CBCT images, 75 (11.6%) were diagnosed with AMF. Single AMF was found in 67 (88.8%) patients while double AMF was detected in 6 (10%) and three AMF in 2 (1.2%) patients. Of the patients with double AMF, formations were bilateral in 5 patients while they were unilateral in 1 patient. Among the patients with three AMF, the third AMF was on the right in 1 patient, and on the left in the other patient. Examples of images of AMF are given in [Figure 1] and [Figure 2].
Figure 1: Cone-beam computed tomography three-dimensional image of accessory mental foramen (black arrow) localized posterior to the right mental foremen (white arrow) (a). Anastomosis of accessory mental foramen (black arrows in b-d) with mandibular canal (red arrows in b and c) and mental foremen and its relationship with mandibular canal (white arrow in e) were seen in sagittal sections

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Figure 2: Cone-beam computed tomography three-dimensional image of accessory mental foramen (black arrow) localized in the posterior-inferior region of mental foremen (white arrow) (a). The relationship of mental foremen (white arrow) and accessory mental foramen (black arrow) with the mandibular canal (red arrow) was seen in axial sections (b and c) and coronal sections (d-f). White, red and black arrows in d-f represent mental foremen, mandibular canal, and accessory mental foramen, respectively

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AMF was detected in 75 (11.6%) patients being more common in females (50/364, 13.7%) than males (25/281, 8.8%). There was no significant difference between the presence of AMF and gender (P = 0.57; P > 0.05).

When the location of AMF in the mandible with respect to MF and dental roots was evaluated, the AMF was observed to be mostly located in the posterio-inferior region of MF (n = 57, 67.1%) and at the root line of the first molar tooth (n = 45, 52.9%) [Table 1] and [Table 2]. No significant difference was found between the female and male patients regarding location according to the dental roots (P = 0.209).
Table 1: AMF localizations according to MF

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Table 2: AMF localization according to the dental roots in edentulous and dentate mandibles

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The mean distance between MF and AMF was 2.84 ± 2.14 mm. No statistically significant difference was found between the female and male patients with regard to the distance [P = 0.127, [Table 3]. The mean vertical diameter of MF was 3.11 ± 0.89 mm and horizontal diameter 2.80 ± 0.99 mm. On the other hand, the vertical and horizontal diameters of AMF were 1.50 ± 0.63 mm and 1.27 ± 0.40 mm, respectively. There was no statistically significant difference between the female and male patients regarding the diameters of MF and AMF [P > 0.05, [Table 3].
Table 3: Diameters of AMF and MF and MF-AMF distance

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   Discussion Top

In this retrospective series of 645 patients, AMF were found in the mandible in approximately one in every ten patients (11.6%) being single in most cases. The prevalence of AMF was higher than the rates reported by previous studies on Turkish population. Kalender et al.[17] reported the incidence rate of AMF as 6.5% in 386 CBCT images and Goregen et al.[12] also reported this rate as 6.3% in 315 images. Similarly, Orhan et al.[18] found AMF in 6.3% of 63 pediatric patients. It is thought that the higher prevalence rate of AMF in our study might have resulted from the larger sample size and also from the fact that the device used for acquiring images was different from the ones used in the other studies.

Different results were achieved on the studies carried out with other populations. Al-Khateeb et al.[19] in his study on 860 panoramic radiographs of a Jordan population, found the incidence of AMF as 10%. In another study from Japan, this incidence was reported as 7.0%.[10] Sawyer et al.[20] studied the skulls of four different populations and reported the prevalence of AMF as 1.4% among White Americans, 1.5% among Asian Indians, 5.7% among African-Americans, and 9% among Nazca natives. Rıesenfeld [21] also studied AMF on the polonaise race and reported its prevalence as 12.5%. On the basis of our results, we suggest that the prevalence of AMF among Turkish population is higher than other populations.

Different results were obtained about whether there is a relation between AMF and gender. Naitoh et al.,[10] Goregen et al.[12] and Kalendar et al.[17] suggested that the prevalence of AMF did not vary depending on gender, but Sawyer et al.[20] reported that AMF was more frequent in African and American male patients. In this study, we found that the AMF was more common in female patients but this difference wasn't statistically significant. Moreover, it was found that all of the multiple AMF cases were female patients.

The location of AMF depends on MF and posterior teeth roots. In this study, AMF was mostly seen in the posterio-inferior region of the MF and at the root line of the 1st molar tooth. No difference was found between the female and male patients regarding the localization according to dental root. Kalender et al.[17] reported that the AMF was frequently located in the anterio-inferior of the MF. Balcıoǧlu et al.[22] presented an AMF case located in the anterior region of the MF and at the root line of a deciduous canine tooth on the 3D CT image of a 6-year-old boy. Similar to our findings, Naitoh et al.[10] suggested that the AMF mostly occurred in the posterio-inferior region of the MF.

In the literature, MF and AMF distance was reported between 2.5 mm and 6.3 mm.[10],[12],[17] Similarly, the mean distance between MF and AMF was 2.85 mm without significant difference between the female and male patients in our study.

Studies have reported MF diameters ranging from 2.38 mm to 2.64 mm [23] while AMF diameters varied between 0.74 mm and 0.89 mm.[5] Thus, the AMF is generally smaller than the MF. Our results are consistent with this finding. We found no significant difference between the females and males regarding the size of the AMF. Our results show similarity with the results of Kalender et al.[17]

The most appropriate method for the diagnosis of AMF is the inspection conducted during the dissection process of dried mandibles. However, this method is not used in clinical practice. Instead, radiographic examination is used for diagnosis. In the past, panoramic radiographs were employed for the diagnosis of AMF. However, the prevalence of these formations was found to be lower compared to the anatomical studies because of reasons such as superimposition and inadequate image resolution. In the following years, CT was reported to be effective in the detection of AMF.[24] On the other hand, the need for high-dose radiation to obtain an image on CT and its cost restricted the use of this technique in dentistry. In parallel with the technological advances, the technology of CBCT has been developed to view the hard tissues in the maxillofacial region. Images with high diagnostic quality can be obtained through this technique, and a smaller dose of radiation is used in single rotation compared to conventional CT.[25],[26]

Considering the widespread use of dental implants, many complications can be avoided particularly in the region of the AMF using appropriate imaging methods before implant procedures and other surgical operations. It has been reported that CBCT is an effective imaging method for monitoring neurovascular structures such as the MF and its variations.[13] On the other hand, since the radiation dose used in this technique is higher than in the conventional technique, its usage should be limited only to the cases in which the radiological data would contribute to the efficiency of the treatment.

The main limitation of this study was its retrospective design, which precludes us from reaching a definitive incidence and morphology of AMF in a Turkish population. However, this was largest series of patients in literature (n = 645) on AMF by using CBCT and thus provides important radiological data on this clinically important anatomical variation.

   Conclusion Top

In the present series in a Turkish population, AMF can be seen in the mandible in one in every ten patients being single in most cases. Thus, the AMF was identified as a common anatomic variation. Understanding of the prevalence and morphological features of AMFs is important to prevent complications such as nerve damage and hemorrhage which occur during surgical procedures including endosseous dental implantation, osteoectomy, and flap surgery. We suggest detection of AMF by CBCT before surgical operations.


The authors would like to thank Enago ( for English language review.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

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  [Figure 1], [Figure 2]

  [Table 1], [Table 2], [Table 3]

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