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 Table of Contents  
Year : 2022  |  Volume : 9  |  Issue : 1  |  Page : 14-18

Evaluation of mandibular canal and mental foramen variations on cone-beam computed tomography images

Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Kirikkale University, Kirikkale, Turkey

Date of Submission20-Jan-2021
Date of Decision02-Oct-2021
Date of Acceptance22-Feb-2021
Date of Web Publication06-Apr-2022

Correspondence Address:
Merve Aydogdu
Department of Oral and Maxillofacial Radiology,Faculty of Dentistry, Kirikkale University, Kirikkale
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jdrr.jdrr_9_21

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Aim: The aim of the study was to evaluate the prevalence of mandibular canal (MC) and mental foramen (MF) variations using cone-beam computed tomography (CBCT). Materials and Methods: CBCT images (n = 459) were retrospectively evaluated. The final sample consisted of 362 CBCT images of 152 men and 210 women between the ages of 10–87. MC and MF variations were evaluated according to presence and localizations. Data were analyzed using SPSS version 20. Results: Participants had a mean age of 38.79 ± 16.45 years. Fifty-seven images (15.7%) showed MC and MF variations. Forty-seven images (13%) showed bifid MCs (BMCs), 14 (3.9%) accessory mental foramen (AMF), and only five (1.4%) trifid MCs. MF was absent in one image (0.3%). The prevalence of AMF was statistically found to be higher among younger patients (7.9%). BMCs and AMF were more common in men than in women. Images with AMF presented unilateral placement, particularly on the right side. Conclusion: Variations were more common in men, and involvement was more frequent on the right side. Early identification of high-risk patients and variations can help prevent neurosensory complications such as bleeding, traumatic neuroma, paraesthesia, and paralysis.

Keywords: Accessory mental foramen, anatomical variation, cone-beam computed tomography, mandibular canal

How to cite this article:
Adisen MZ, Aydogdu M. Evaluation of mandibular canal and mental foramen variations on cone-beam computed tomography images. J Dent Res Rev 2022;9:14-8

How to cite this URL:
Adisen MZ, Aydogdu M. Evaluation of mandibular canal and mental foramen variations on cone-beam computed tomography images. J Dent Res Rev [serial online] 2022 [cited 2022 Dec 2];9:14-8. Available from: https://www.jdrr.org/text.asp?2022/9/1/14/342712

  Introduction Top

The mandibular canal (MC) containing the inferior alveolar nerve, artery, and the vein, and the mental foramen (MF) located on the lateral aspect of the MC should be detected for dental implant applications, endodontic treatments, and surgical interventions.[1]

Anatomical and radiological studies show that the MC has a significantly different path of expansion.[2] According to Chávez-Lomeli et al., three inferior dental nerves resulting in the innervation of the mandibular teeth during embryonic maturation are fused together in the later stages.[3] Aberrations during the fusion of those nerves account for bifid MCs (BMCs) and trifid MCs (TMCs). Anatomical variations can also be observed in the MF. There may be more than one MF. Any foramen other than the MF is referred to as accessory MF (AMF).[4] In some situations, no MF is observed. No MF has been observed only in four cases so far.

Panoramic and periapical radiographs routinely used in dentistry are often not good enough to image variations.[5] Cone-beam computed tomography (CBCT) has been popular in dentistry in recent years because it uses less radiation than most computed tomography (CT) scans for imaging and takes up less space than them.[6] Numerous studies use CBCT to evaluate the variations in the MC and report that it yields results different from those of conventional two-dimensional radiography. Many researchers recommend that CBCT be used to detect variations in the MC.

This study examined CBCT images to investigate MC and MF variations.

  Materials and Methods Top

CBCT images (n = 459) from the Oral and Maxillofacial Radiology Archive of the Faculty of Dentistry of Kirikkale University were retrospectively analyzed by a specialist radiologist. Images were taken by an X-ray technician with 10 years of experience using an I-CAT (Imaging Sciences International, Hatfield, PA, USA) (irradiation parameters: 23 cm × 17 cm FOV, 18.54 mAn, 120 kVp, 8.9 s) CBCT device. The ethical approval of the study was given by the Noninterventional Research Ethics Committee of Kirikkale University (Decision No: 2020/10-17). Images of 97 patients without MC and MF were excluded. The sample consisted of 362 images of 152 men and 210 women 10–87 years of age. A panoramic imaging mode was used to examine the images sectionally in order to determine the absence of BMC, TMC, AMF, and MF [Figure 1]. Images with variations were further analyzed to localize those variations and determine whether or not they were on both sides. Only a maximum of 25 tomography images were examined per day to avoid errors due to fatigue. All images were evaluated on a 21' liquid crystal display monitor under appropriate light conditions. For intraobserver agreement, fifty randomly selected images were re-examined. Data were analyzed using the Statistical Package for the Social Sciences (SPSS Statistics for Windows, Version 20.0, Released 2011, IBM Corp, Armonk, NY, USA.) at a significance level of 0.05. The sex difference in the prevalence of MC and MF variations was compared using Chi-square test. Intraobserver agreement was evaluated using Cronbach's alpha test.
Figure 1: Variations in cone-beam computed tomography Images; (a) bifid mandibular canal, (b) trifid mandibular canal, (c) accessory mental foramen, (d) no mental foramen

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  Results Top

The mean age of participants was (n = 362) 38.79 ± 16.45 years. Fifty-seven images (15.7%) showed MC and MF variations. The intraobserver agreement was high (alpha >0.90). The variations were BMCs (13%), AMF (3.9%), and TMCs (1.4%) and a lack of MF (0.3%) [Table 1]. BMCs and AMF were more common in male participants than in females (P < 0.05) [Table 2]. The distribution of variations by age was examined in three groups as 10–29, 30–59, and >60 years old. Statistically no significant difference was found between the age groups according to the prevalence of BMC, TMC, and absence of MF. However, the prevalence of BMC found to be higher in older age group above 60 years old. The prevalence of AMF was statistically found to be higher among younger patients (P = 0.004) [Table 3]. AMF were located on one side, mostly on the right side [Table 4].
Table 1: Prevalence of variations

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Table 2: Comparison of variations prevalence according to gender

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Table 2: Comparison of variations prevalence according to gender

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Table 4: Distribution of variations by side of mandible

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  Discussion Top

Distortions and superpositions in two-dimensional radiographic imaging methods make localization of MC challenging. Radiographic signs of condensation or the elevation of the insertion of the mylohyoid muscle parallel to the internal surface of the mandible may also prevent the detection of mandibular boundary contour, and hence, MC variations.[7] Research also shows that panoramic radiography is not good at detecting many MC variations. For example, the prevalence of BMC ranges from 0.08% to 0.95% in panoramic radiographs, while it ranges from 10% to 65% in CT.[8] Besides, there is only one reported case with TMC detected on panoramic radiography.[9] Adisen et al. reported that what they considered to be BMC on the panoramic radiography of a patient turned out to be a third AMF on his CBCT images.[8]

In the literature, it is reported that CT and CBCT presented similar results in the diagnosis of maxillomandibular region and also CBCT presented various advantages compared to CT such as low radiation dose, more accessible equipment, and higher quality imaging of bone tissue.[7] Forty-seven images showed BMCs, which is consistent with what has been reported by CT studies. In several studies with CBCT, the prevalence of BMCs was reported as 19% in Belgium, 16.2% in Korea, 22.8%–36.8% in Spain, 18,4%–46.5% in Turkey, and 15%–56.5% in Japan.[10],[11] In this study, the prevalence of BMC (13%) was found to be lower in the Turkish population than in previous studies using CBCT. This result may be due to the regional differences and different population sizes.

TMC has a much lower prevalence than BMC and has been reported in only a handful of cases. Rashsuren et al. detected seven cases of TMC out of CBCT images of 500 patients.[12] There are only two more cases of TMC detected on CBCT images.[8],[13] In this study, TMC was observed only in five patients [Figure 2].
Figure 2: Cases of trifid mandibular canal in cone-beam computed tomography images

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BMCs are classified in different ways. Orhan et al.[14] categorize BMCs on CBCT sections as follows:

  1. Forward canals originate from the superior wall of the main canal
  2. Buccolingual canals originate from the buccal or lingual wall of the main canal
  3. Dental canals reach the end of the root apexes of the bifurcated canals
  4. Retromolar canals originate from the main canal and open at the retromolar foramen.

Forward and retromolar canals are the most common BMCs. However, Rashsuren et al. mostly observed retromolar canals.[12] It is clinically significant to classify the BMCs, especially the retromolar and dental canal type. According to Naitoh et al.,[15] the retromolar region is a potential donor of bone block, and therefore, the retromolar canal should be determined to achieve safe harvest. The dental canal should also be identified for extraction and root canal treatment.[16] The images in this study mostly presented retromolar canals as well.

The type of MF depends on its position, origin, and number. It may never form, or there may be two or three MF, which are referred to as AMF. So far, there are only four cases with no MF. For double MF, AMF is observed in about 20–100 cases/1000, while that of three MF is observed in about 7 to 12 cases/1000.[17] The prevalence of AMF is lowest and highest among the French (1.4%) and Japanese (12.5%), respectively, which may be due to racial differences and the method used because distortions and superpositions in two-dimensional radiographic imaging methods can make AMF imaging challenging.[18] Fourteen (3.9%) presented AMF, which is within the range of prevalence values reported in the literature. What is more, MF was missing on one side only in one patient, and no patient had three MF.

In the previous studies, the prevalence of the MC and MF variations according to age was evaluated. Rashsuren et al. and Kang et al. reported that there was no significant difference at the prevalence between among age groups.[12],[15] Zhang et al. and Okumuş and Dumlu reported that the prevalence of BMC in second decade and under was significantly lower than in the other age groups.[19],[20] In contrast, Fuentes et al. found higher of BMCs in younger patients.[21] These various results may be explained by the different study populations, imaging technique quality, and radiographic assessment.[20],[22] In this study, the prevalence of AMF was statistically found to be higher among younger patients and no significant difference between age groups and the BMC, TMC, and absence of MF. However, the prevalance of BMC was found to be higher in older age group.

von Arx and Bornstein categorized BMCs variations by geographical region. They reported higher prevalence of BMC in studies conducted in Asia compared to those in Europe or America.[22] Whereas Yoon et al. stated that ethnicity was not an important predictor for BMC prevalence.[23]

Most studies report no sex difference in MC variations,[14],[24],[25] but some suggest that AMF is more common in men than in women. Aytugar et al. reported AMF variations higher in males on the Turkish population although there was no statistical difference in their study.[26] Laçin et al. reported that the male patients showed a higher prevalence of BMC than the female patients.[11] In this study, BMC and AMF were significantly more prevalent in men than in women.

Some studies comparing right and left sides found no significant difference in the distribution predilection of BMCs[10],[21],[27],[28] Laçin et al. reported a higher prevalence of BMC on the right side.[11] In this study, all variations were more frequent on the right side, and particularly MF variations were on one side.

The knowledge of the morphology and variations of the MC is substantial for the mandible surgical procedures of the dental practice. Detection of MC and MF variations prevents the occurrence of inadequate anesthesia, postmandibular osteotomy and implant complications, and pain and discomfort resulting from implant pressure.[11] Boronat López and Peñarrocha Diago suggested that one of the important factors in the failure of local anesthesia, which occurs in 10%–20% of patients, is the presence of an AMF.[29] Kang et al. suggested that, when conventional inferior alveolar nerve block fails, radiographic evaluation of the presence of multiple MCs carefully and anesthesia techniques that provide high inferior alveolar nerve block such as the Gow-gates or Akinosi technique can be used.[15] Verea Linares et al. was reported a bleeding complication related to a BMC. They suggested that the treatment should be carefully planned and undertaken sectional imaging by CBCT to identify anatomical variants when performing extraction for lower third molars thereby to avoid complications such as hemorrhage.[30] Aljunid et al. reported a case that had persistent pain and paraesthesia due to implant impingement on a branch of TMC.[31] They stated that accessory canals seem like radiopaque lines that may be confused for bony trabeculae, and therefore, CBCT should be preferred as a standard imaging method in implantology in the posterior mandible.

  Conclusion Top

MC and MF variations were more prevalent in men, and involvement was more frequent on the right side. The prevalence of AMF was statistically found to be higher among younger patients. Early identification of high-risk patients and variations can help prevent neurosensory complications such as bleeding, traumatic neuroma, paraesthesia, and paralysis. CBCT is a significantly useful imaging system in the investigation of MC and MF variations. Dentists should be aware of these variations to avoid possible complications. Panoramic imaging used as first imaging may not always be detected of variations. In suspicious cases, CBCT should be used as advanced imaging.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

Ethical considerations

The study was approved by the Noninterventional Research Ethics Committee of Kirikkale University (Decision No: 2020/10-17).

  References Top

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  [Figure 1], [Figure 2]

  [Table 1], [Table 2], [Table 3], [Table 4]


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