|Year : 2016 | Volume
| Issue : 4 | Page : 209-213
Panoramic radiographic study of mandibular canal and mental foramen in a selected Iranian population
Sara Soheilifar1, Mohsen Bidgoli1, Abbas Shokri2, Javad Faradmal3, Samareh Kafilzadeh4, Parisa Eyvazi5, Masoumeh Nikkhah6
1 Department of Periodontology, Faculty of Dentistry, Hamedan University of Medical Sciences, Hamedan, Iran
2 Department of Radiology, Faculty of Dentistry, Hamedan University of Medical Sciences, Hamedan, Iran
3 Department of Epidemiology and Biostatistics, Research Center for Health Sciences, School of Public Health, Hamadan University of Medical Sciences, Hamedan, Iran
4 Department of Periodontology, Faculty of Dentistry, Zanjan University of Medical Sciences, Zanjan, Iran
5 Private Dentist, Hamedan, Iran
6 Department of Periodontology, Faculty of Dentistry, Gilan University of Medical Sciences, Gilan, Iran
|Date of Web Publication||13-Dec-2016|
Department of Periodontology, Faculty of Dentistry, Zanjan University of Medical Sciences, Zanjan
Source of Support: None, Conflict of Interest: None
Background and Aim: The mandibular canal and mental foramen are two important anatomic landmarks that should be noted before dental surgeries in the posterior region of the mandible. The aim of this study was to evaluate the accuracy of digital panoramic images in visualizing the mandibular canal and mental foramen. The horizontal location of mental foramen among Iranians was also investigated. Materials and Methods: In this cross-sectional study, 150 digital panoramic images acquired from the radiology database at the Dental Faculty of Hamedan University of Medical Sciences were analyzed. All the panoramic radiographs were shot by a digital panoramic machine, CRANEX ® Tome Ceph (Soredex, Helsinki, Finland), considering standard exposure parameters. The visibility of mandibular canal and mental foramen and the horizontal location of mental foramen were assessed by three examiners independently. Results: The visibility of mandibular canal and mental foramen on both left and right sides was 96.6% and 79.7%, respectively. The most frequent horizontal position of mental foramen was in line with the second premolar on the right (48%) and left (51.3%) sides, followed by the area between the first and second premolar. The mean distance between two mental foramina was 49.23 mm and 46.89 mm in males and females, respectively. Conclusion: Although panoramic images showed a satisfactory accuracy in identifying mandibular canal and mental foramen, caution should be taken, especially when identifying mental foramen.
Keywords: Mandibular canal, mental foramen, panoramic radiography, visibility
|How to cite this article:|
Soheilifar S, Bidgoli M, Shokri A, Faradmal J, Kafilzadeh S, Eyvazi P, Nikkhah M. Panoramic radiographic study of mandibular canal and mental foramen in a selected Iranian population. SRM J Res Dent Sci 2016;7:209-13
|How to cite this URL:|
Soheilifar S, Bidgoli M, Shokri A, Faradmal J, Kafilzadeh S, Eyvazi P, Nikkhah M. Panoramic radiographic study of mandibular canal and mental foramen in a selected Iranian population. SRM J Res Dent Sci [serial online] 2016 [cited 2022 Aug 18];7:209-13. Available from: https://www.srmjrds.in/text.asp?2016/7/4/209/195617
| Introduction|| |
Knowledge of accurate anatomical locations of the mandibular canal and mental foramen is an important factor in the surgical management of any patient. The mandibular canal contains the inferior alveolar neurovascular (IAN) bundle and crosses the mental foramen anteriorly where it splits into the mental and incisive canals.  Injury to the inferior alveolar nerve is one of the most serious complications of mandibular surgery.
Extraction of mandibular third molars, implant surgeries, orthognathic surgeries, and reduction and fixation of fractures in the different regions of the jaw are examples of the procedures that can be done close to the mandibular canal, increasing the risks inferior alveolar nerve injury. , The other important anatomical structure located in the body of the mandible is mental foramen. The mental bundle passes through mental foramen and supplies sensory innervations and nutrition to the chin, lower lip, facial gingiva, and mucosa in the anterior mandible. 
Its position is generally described as being below the second premolar, but it has also been reported to vary in its appearance, size, and locations according to the ethnic group studied. ,,
Mental nerve injury can cause transitory or permanent sensitive, thermal and tactile changes. 
The interest in the mental foramen localization further increased after the development of implant techniques.
Implant placement in mandibular premolar region is one of the most complicated surgical procedures due to potential inadvertent complications of neurosensory alterations in the chin and lower lip.  Many advanced radiological exams such as computed tomography have been developed in the recent years. However, since these advanced imaging techniques expose the patient to higher doses of radiation, the conventional radiographs are still commonly used.  Vazquez et al.  proposed that panoramic radiography appears to be sufficient to evaluate available bone height before insertion of posterior mandibular implants.
To avoid nerve injury, a better understanding of the anatomical location and course of the mandibular canal and mental foramen before any surgical procedure is strongly recommended.
The aim of this study was to evaluate the accuracy of digital panoramic images in visualizing the mandibular canal and mental foramen. The horizontal location of mental foramen among Iranians was also investigated.
| Materials and Methods|| |
This cross-sectional descriptive study was carried out on panoramic images acquired from the radiology database at the Dental Faculty of Hamedan University of Medical Sciences. All the panoramic radiographs were shot by a digital panoramic machine, CRANEX ® Tome Ceph (Soredex, Helsinki, Finland), considering standard exposure parameters (66 kv, 10 Ma, 240 mA/s, total filtration 2.7 mm aluminum), and by the same technician.
The images taken from July 2010 to June 2014 were reviewed by three radiologists.
A total of 150 cases were selected who met the following inclusion criteria:
- High quality with respect to angulation and contrast
- Known age and gender
- The films must be free from any radiolucent or radiopaque lesion in the mandibular canal and mental foramen region
- Presence of mandibular posterior teeth from the first premolar to the second molar
- Permanent teeth were fully erupted.
Exclusion criteria were:
- Mixed dentition or incomplete eruption of teeth
- Positioning errors and superimposition of structures
- History of any orthodontic treatment.
The images were evaluated in standard viewing conditions.
Three examiners separately identified the appearance and visibility of mandibular canal. In case the superior and/or inferior border or the course of the canal was clearly identifiable, it was recorded as "visible."
Similarly, if the location of mental foramen was clearly noticeable, it was recorded as "visible."
When the distinction between mental foramen and bone marrow spaces was not possible, the case was considered as "nonvisible."
The final decision to call a case visible or nonvisible was made only when the results of at least two observers were similar.
Location of the mental foramen
To determine the exact horizontal location of mental foramen, perpendicular lines were drowned, using a digital ruler, along the mesial and distal surfaces of each tooth at the crestal bone level.
The location of mental foramen in horizontal plane was classified as follows: 
- In line with the first premolar
- Between the first and second premolar
- In line with the second premolar
- Between the second premolar and first molar
- In line with the first molar.
The distances between the two mental foramina were also measured. The measurement was done from the mesial border of each mental foramen to the midline.
This study was approved by the Ethics Committee of Hamedan University of Medical Sciences and was in accordance with the Helsinki Declaration of 1975.
All assessments were done bilaterally, and the data were compared between two genders and two sides. For each subject, data were analyzed with SPSS software (SPSS version 16.0, SPSS, Chicago, IL, USA) and the level of significance was set at 0.05.
| Results|| |
A total of 150 panoramic radiographs fulfilled the inclusion criteria for this study. The radiographs were those of 50 males and 100 females with the mean age of 25.26 ± 6.91.
In general, 98% of the right mandibular canals were "visible." In only 3 images (2%), mandibular canal was considered "nonvisible" as the borders were not corticated or identifiable on the images. Same results were achieved for the left mandibular canal.
There was no significant difference between two sides of the mandible in canal visibility, and the visibility was not influenced by gender (P > 0.05).
Mental foramen was "visible" in 86.4% of images on the right side and 85.1% of images on the left side.
The visibility of mandibular canal and mental foramen on both left and right sides was 96.6% and 79.7%, respectively.
The most common horizontal location of mental foramen was found to be in line with the second premolar on both right (48%) and left (51.3%) sides, followed by the area between the first and second premolar. Similarly, the most frequent position according to gender was the second premolar area [Table 1].
|Table 1: Horizontal location of mental foramen (in relation to the apices of the teeth) |
Click here to view
The position of mental foramen was symmetrical in 78.6% of cases.
There was a significant association of age with the horizontal location of mental foramen. The frequency of mental foramen to be below or posterior to the second premolar is 31.8% in 20 years and younger, 60% in 21-25 years, 62.8% in 26 years and older [Figure 1]. With advancing age, there was an increase in the frequency of more posterior locations of the mental foramen.
|Figure 1: Frequency of horizontal location of mental foramen according to age. GrMF_L: Mental foramen is below or posterior to the second premolar on the left side, GrMF_R: Mental foramen is below or posterior to the second premolar on the right side, GrMF: Mental foramen is below or posterior to the second premolar on both left and right sides|
Click here to view
The mean distance between two mental foramina was 49.23 mm and 46.89 mm in males and females, respectively. T-test analysis showed a statistically significant difference between males and females (P = 0.022).
| Discussion|| |
In this study, the first objective to be addressed was the visualization of mandibular canal and mental foramen. The radiographic appearance of the mandibular canal usually involves a well-defined radiolucent zone, lined by radiopaque superior and inferior borders. The outline of mandibular canal is not always corticated and thus not easily detected.
In the current study of 150 digital panoramas, the mandibular canal was identifiable in 96.6% of the cases on both sides, which is a satisfactory visibility on panoramic radiographs.
To localize the IAN, most clinicians use conventional radiography (e.g., panoramic views, periapical), which is sufficient for most cases. Vazquez et al.  concluded that panoramic examination can be considered a safe preoperative evaluation procedure for routine posterior mandibular implant placement.
Angelopoulos et al.  compared cone-beam computed tomography (CBCT) reformatted panoramic and digital panoramic images for identification of mandibular canal. They concluded that although CBCT images found to be superior to digital panoramic, CBCT images should not necessarily replace digital panoramic images due to higher radiation exposure.
Mental foramen visualization was also assessed in this study. Mental foramen was visible in 79.7% of cases in both sides. Muinelo-Lorenzo et al.  reported a mental foramen visualization rate of 83.87% on panoramic images. Al Jasser and Nwoku  demonstrates that the mental foramen can easily be identified on panoramic radiographs.
In the majority of cases, nearly 80%, there was bilateral symmetry in the position of mental foramen. This finding was in agreement with Afkhami et al.  and Al Jasser and Nwoku  which reported similarity in a location in 80% of cases. Other studies by Yosue and Brooks,  Al-Khateeb et al.,  and Parnami et al.  reported similarities in 67%, 84.4%, and 86.8% of cases, respectively.
The next objective addressed the location of mental foramen.
Although the determination of mental foramen has been the subject of many studies, it has been reported to vary in position in a horizontal plane in different ethnic groups. Sufficient local anesthesia and safety of surgical procedures in this area are affected by the clinician's knowledge about the position of mental foramen.
The location of mental foramen can be assessed related to many different references. Relating the foramen to teeth is more appropriate to the clinical situation and has been used in many different studies. 
The most frequent location of mental foramen in a selected Iranian population was in line with the second premolar in both left (50.7%) and right sides (47.3%).
This finding is in agreement with two studies of Iranian population , and with studies of other ethnic and racial groups done by Kim et al.  in Korea, Fabian  in Tanzania, Guo et al.  in China, Agarwal and Gupta  in India, Al Jasser and Nwoku  in Saudi Arabia, and Lorenzo et al.
However, Haghanifar and Rokouei  and Dehghani and Ghanea  in studies on Iranian population and Al-Khateeb et al.  in Jordan found that the most frequent position of the mental foramen was in the area between the long axis of first and second mandibular premolars.
In a Nigerian population, Olasoji et al.  reported that the mental foramen was mostly located between the first and second premolars (34%).
This study revealed that the location of the mental foramen is not gender-dependent which is consistent with other similar studies. ,,,
However, Al-Khateeb et al.  found that the most frequent position of mental foramen was different between males and females. The mental foramen was found to be between the mandibular premolars in males and in line with the second premolar in females
This study consisted of an age range from 13 to 49 years. With the increase in age, the mental foramen position appeared to move distally in the present study. This finding is in accordance with other studies. ,, It is likely that this posterior shift in positioning is related to anterior tooth drift due to age-related attrition of the interproximal surfaces of teeth. 
In the current study, the distance between the two mental foramina was also evaluated. There was a statistically significant difference in the distance between the mental foramen in males (49.23 mm) and females (46.89 mm).
| Conclusion|| |
- Mandibular canal and mental foramen were "visible" on both left and right sides, in 96.6% and 79.7% of cases, respectively. Although panoramic images showed a satisfactory accuracy in identifying theses anatomical landmarks in general, caution should be taken, especially when identifying mental foramen
- The most common horizontal location of mental foramen in this group of Iranian population was in line with the second premolar, followed by the area between the first and second premolars
- In 78.6% of cases, the location of mental foramen was symmetrical on both left and right sides
- The mean distance between the two mental foramina was 49.23 mm and 46.89 mm in men and women, respectively. This is an important finding to be considered before formulating a mandibular overdenture treatment plan.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Figure 1]