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ORIGINAL ARTICLE
Year : 2013  |  Volume : 1  |  Issue : 1  |  Page : 2-7

Morphometric analysis of the mental foramen in a Turkish population based on multi-slice computed tomography


1 Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Erciyes University, Kayseri, Turkey
2 Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Abant Izzet Baysal University, Bolu, Turkey
3 Department of Radiology, School of Medicine, Erciyes University, Kayseri, Turkey

Date of Web Publication3-May-2013

Correspondence Address:
Ahmet Ercan Sekerci
Department of Maxillofacial Radiology, Faculty of Dentistry, Erciyes University, 38039, Kayseri
Turkey
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Source of Support: None, Conflict of Interest: None


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  Abstract 

Purpose : The aim of this study was to determine the location, orientation, shape, appearance, and area of the mental foramen (MF), as seen on CT images, and to compare our findings with international values. Materials and Methods : CT records were randomly selected from the collection of 550 Turkish patients and were evaluated morphometric analysis of the MF. Results : The most common anterior-posterior position of the MF was bilaterally symmetrical and located on the same vertical line with the long axis of the lower second premolar. The majority of foramina were round in shape, and the most frequent appearance was the continuous type. The most frequent (76%) superior-inferior position was situated below the level of the apices of mandibular premolar roots. Conclusions : The results of this study may assist surgeons to localize important maxillofacial neurovascular bundles passing through the MF in avoiding complication from local anesthetic, surgical, and other invasive procedures.

Keywords: Anatomy, computed tomography, mandible, mental foramen, Turkish population


How to cite this article:
Sekerci AE, Sahman H, Sisman Y, Aksu Y. Morphometric analysis of the mental foramen in a Turkish population based on multi-slice computed tomography. J Oral Maxillofac Radiol 2013;1:2-7

How to cite this URL:
Sekerci AE, Sahman H, Sisman Y, Aksu Y. Morphometric analysis of the mental foramen in a Turkish population based on multi-slice computed tomography. J Oral Maxillofac Radiol [serial online] 2013 [cited 2018 Feb 17];1:2-7. Available from: http://www.joomr.org/text.asp?2013/1/1/2/111341


  Introduction Top


The great development of surgical techniques in the mandible and the progress of radiological imaging procedures have brought much interest in the clinical anatomy of the mental foramen (MF). The mental nerve is a terminal branch of the inferior alveolar nerve that passes through the MF, providing sensory innervations to the lower lip, mucous membrane, and gingiva as far posterior as the second mandibular premolar tooth. [1],[2] Anatomically, the MF on each side of the mandible is normally single; however, double or even multiple foramina have been reported, but some of these which were termed as accessory mental foramina by most authorities are now considered as possibly part of the mental-incisive foramen complex. [3],[4],[5] On rare occasions, the MF may be absent. [5] The accuracy the MF identification is quite important in clinical dentistry, for instance in the administration of local anesthesia and surgical procedures such as performing periapical surgery, dental implant placement in terms of achieving effective mandibular nerve blocks, and avoiding injuries to the neurovascular bundles. [1],[2],[3]

Many studies have reported the position of the MF by examining collections of dried skulls, [2],[5],[6],[7] human cadavers [2] and clinical radiographs. [8],[9] In the literature, the MF is frequently described as situated below the apex of the second premolar or between the apices of the first and second premolars, but individual variations occur occasionally. Examples of sexual and racial osteologic differences are fairly common. [2]

It is well known that conventional radiography has shown limitations in acquiring images of the maxillofacial complex; thus, computed tomography (CT) scanning is the best option to the present date for the diagnosis, surgical planning, and treatment of bone lesions, owing to its specific properties. Therefore, three-dimensional computed tomography images (3D CT), dry skulls, and human cadavers studies allow for a more accurate localization of the MF.

According to a review of the literature, the present report is the first study to investigate the location, orientation shape, appearance, and symmetry of the MF as seen on CT images. The aim of this study was, therefore, to investigate the mentioned features of the MF as seen on the CT images of Turkish population as compared to international findings.


  Materials and Methods Top


Five hundred and fifty CT images were randomly selected from the Radiology Department collection of the Medical Faculty in Erciyes University (between January 2007 and December 2010). All CT (MSCT (GE Light Speed 16 Milwakee, WI)) images were of dentate Turkish patients, with erupted first and second premolars and first molars. The images were chosen according to the following criteria:

  1. High quality with respect to angulation and contrast.
  2. All mandibular teeth from the right first molar to the left first molar were present.
  3. The images must be free from any radiolucent or radiopaque lesion in the lower arch and showed no radiographic exposure or processing artifacts.


Of the 825 CT images, 275 were excluded from the study due to various reasons like;

  1. Ct images in which the lower teeth (between 36 and 46) were missing, had deep caries, root canal treatment, or various restorations were eliminated because of possible associated periapical radiolucency.
  2. Ct images in which the MF could not be identified were excluded,
  3. Incomplete eruption of permanent teeth.
  4. Patient with previous orthodontic treatment.
  5. Presence of crowding and spacing in the lower arch.
  6. Radiographs that showed the lower canine was missing were excluded because of the possibility of mesial premolar drift.
  7. Unerupted or missing mandibular premolar teeth.
  8. Jaw lesions in the mandibular premolar area.


The CT images of the 550 subjects were examined twice by two observers. Each image was assessed by using direct inspection and computerized imaging analysis. Observations were repeated with a random sample of 55 radiographs which were re-examined.

The remaining 550 radiographs were analyzed according to location, the orientation, and the size of the two sides and according to variables depicted in [Table 1]. The orientation of exit of each mental canal on the buccal cortical plate of the mandible was visually determined.
Table 1: Features of mental foramen studied on CT images

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The anterior-posterior position of the MF relative to the lower teeth was graded as either in line with the longitudinal axis of a tooth or as lying between two adjacent teeth as shown [Figure 1]. This method was first reported by Green, [10] later by Neo, [11] Santini, [7] Jasser and Nwoku. [8] When there appeared to be multiple foramina, it was considered, according to Yosue and Brooks, the correct radiographic MF was considered to be the upper most one, nearest the mandibular canal. We used the edge of a ruler to identify the longitudinal axis of the nearest tooth and the position of the MF was recorded in relation to this. If the MF was too large or was situated between two teeth, the position of the foramen was established after drawing an imaginary line parallel to the long axis of the teeth. The maximum transverse and vertical diameters of the MF were measured. The superior-inferior position of MF in relation to the apices of mandibular premolar teeth was shown [Figure 2].
Figure 1: Determining of the anterior-posterior position of mental foramen. An image of a longitudinal section of the buccal surface bone was reconstructed using CT image

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Figure 2: The superior– inferior position of mental foramen in relation to the apices of mandibular premolar teeth

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Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS), 15 th version.


  Results Top


The appearance and location of the mental foramina were determined on the CT images of 550 patients. Of the 550 patients included in the study, there were 335 males (mean age 36.6 ± 6.32) and 215 females (mean age 37.1 ± 5.71), with a female-to-male ratio of 1:1.55. Age ranged from 12 to 77 years with a mean of 36.8 ± 6.10 years; 42 (7%) of the 550 cases were below 18 years of age.

The most common position of the MF relative to the lower teeth in the Turkish sample was in the same vertical line with the long axis of the second premolar (43.5%), followed by that between the lower first and second premolars (42.5%) [Table 2]. There was no significant difference between males and females in the anterior-posterior relationship between the center of the MF and the premolar in both measurements (P > 0.05).
Table 2: The anterior-posterior position of the mental foramen (in relation to the long axes of teeth and interdental spaces on the CT of 550 Turk patients)

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The position of the MF was symmetric in 318 (57.8%) images with the remaining 232 (42.2%) being asymmetric cases [Table 3]. Asymmetrical mental foramina were found most commonly on the right side, with the highest frequency at position 4 (n = 125, 53.9%), followed by position 3 (n = 60, 25.9%) [Table 3].
Table 3: Distribution of symmetrical and asymmetrical mental foramina in relation to the long axes of teeth and interdental spaces on the CT of 550 Turk patients

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Decade and location distribution of the MF is shown in [Table 4]. We found that in males the most frequent anterior-posterior position of the MF was between the first and second mandibular premolar teeth, and in females along the line of the second mandibular premolar. We also found that with advancing age there was a decrease in the frequency of more posterior locations of the MF.
Table 4: Decade and location distribution of mental foramen

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The superior-inferior position of MF in relation to the apices of mandibular premolar teeth is shown in [Table 5].
Table 5: The superior-inferior position of mental foramen in relation to the apices of mandibular premolar teeth
(n = 1,100 sides)


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The most frequent (76%) superior-inferior position 1 (SIP3) was situated below the level of the apices of mandibular premolar roots. There was no difference between males and females regarding the more frequent superior-inferior position.

Shape and various appearances of the MF in relation to the mental canal are shown in [Table 6]. The majority (43%) of mental foramina was round in shape. The most frequent (66%) appearance was the continuous type. Accessory mental foramina were seen in 2% of the cases. Symmetrical position was higher in females than in males (P = 0.018).
Table 6: Shape and appearance of the mental foramen (n = 1,100 sides)

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  Discussion Top


When reviewing the literature regarding morphometric analysis of the MF based on multi-slice computed tomography, no detailed data has been found. The present study provides new data on the position of the MF in a Turkish population. When practicing periapical/periodontal/im­plant sur­gery, cyst enucleation, surgical orthodon­tic treatments, maxillofacial trauma, and orthognathic procedures such as a mandibular body osteotomy, in order not to cut or damage the mental nerve, it is impor­tant for the operator to know exactly where the MF is. Know­ing the location of the MF, where the mental neurovascular bundle emerges, allows for the correct delivery of local anes­thesia during dental operations and avoids nerve damage. It also aids in in­terpreting the anatomical landmarks in oral pathology and juridical procedures. [11]

Radiography is the only available non-invasive method for diagnosis and treatment planning of major surgical procedures of the mandible. [12] Panoramic radiographs or dry skulls were used in previous studies to examine the position of the MF for operations, so they could the location of the MF as a reference point. [13] However, comparative studies on dry skulls have shown a close correlation with the radiographic position of the MF. [6],[9]

When panoramic radiographs are taken with the patient in the proper position, there will usually be limited horizontal overlap of teeth. However, variations in the facial characteristics of patients, associated with growth and development as well as errors in patient positioning, can lead to mesial or distal angulation of the X-ray beam. [9] Distortion and magnification factors inherent in orthopantomogram techniques cannot be eliminated if the image is too sharp. In addition, as the bone density increases, the foramen becomes more difficult to identify and may not be seen clearly even with optimal illumination. Therefore, there will be a greater separation between the apex and the MF because of the buccal object rule. [9] In addition, CT has been the first option for diagnosis, surgical planning, and treatment of osseous trauma injuries due to its high specificity and sensitivity. [14] As a result of recent advances in computer hardware and software 3D imaging by CT scans of craniofacial anomalies is routinely used by most medical centers to define the unique individual aspects of complex anatomy, plan interventions and follow results. [15]

Therefore, we utilized CT images because they have certain advantages in diagnostic medicine. In our series of 550 CT images, the location of the MF varied widely, being found at any position between the posterior of the canine and the distal root of the first molar; this is in accordance with previous studies. We found that the most frequent anterior-posterior position of the MF was in the area between the long axes of the first and second mandibular premolar teeth (43.5%), followed closely by the position in line with the long axis of the second mandibular premolar tooth (42.5%), with these two positions making an overall prevalence of 86.5%. This is in agreement with previous Western and Asian studies. [2],[10]

In this study, it was shown that more than 95% of foramina lie either at the second mandibular premolar or immediately anterior or posterior to this position. Consequently, when performing a mental or incisive nerve block, if the needle is placed opposite to the second mandibular premolar, one can expect success in 95% of cases. However, about 5% of foramina are present in other positions. Our results agree with studies on Caucasian populations from different countries, [2],[9] but contrast with studies on Mongoloid and Black populations, from different countries, which reported more posterior positions of the MF. [6],[10],[11] However, studies done in other populations such as Malays, Asian Indians, Kenyan Africans, and Saudis, as well as those done by Phillips et al. have indicated that the MF is most commonly positioned in line with the second premolar tooth. [6],[8]

Recently, it was suggested that traits such as localization of the MF might not only differ between populations of different geographic environment but also within the inhabitants of the same geography. [16] It is also interesting to note that the MF is positioned more posteriorly in blacks than in whites. [17] Yosue and Brooks suggested that the reason for the absence of the MF included the inability to distinguish it from the trabecular pattern in complete dentition radiographs and over-exposed radiographs. [9] Lack of the MF was not observed in the present study. The MF is normally single but double, or even multiple, foramina have been reported. [3],[4] Riesenfeld [18] reported the highest frequency of accessory mental foramina (12.5%) in a Polynesian population. He noted that this figure is most likely unreliable because of the small sample size. In a review of the literature, it appears that the frequency of occurrence of accessory foramina falls into two groups: a low-frequency group from 1.4% to 3.6% and a second group with a range in frequency from 5.1% to 12.5%. A low incidence of occurrence is seen in the American White and Asian Indian groups while the African American and Nazca Indian groups show accessory mental foramina in over 5% of the mandibles examined. [19] Kjaer [20] reported an interesting note that during the early prenatal life the MF is located in the alveolar bone between the primary canine and first molar. It is therefore probable that positions other than the two most common described above could be due to a lag in developmental changes in its location during postnatal life. [20] In the developing jaw, there may be a change in the position of the MF in relation to the jaw. [11] The premolar and first molar teeth were erupted in all the radiographs in our series.

In present study, we have shown that the MF demonstrates varied positions in the superior-inferior dimension. Although this could be attributed to variable length of roots in the population sample, age is a major contributing factor. Our results that the most frequent superior-inferior position was situated below the level of apices of mandibular premolar roots support the view that the variation in superior-inferior position of the MF is related to age changes. Our findings also agree with studies from different countries and populations. [6],[8],[9],[21],[22],[23] We found that the majority of mental foramina were round in shape. This contrasts with studies on other populations, [22],[24],[25] which showed that the most frequent shape was oval. The most frequent appearance in our study was the continuous type, in consistence with others. [9]

Most MF exits in our subjects opened posterosuperiorly. This finding corresponded with the general direction of exit of the mental canal reported in Mongoloids, Caucasoids and Negroids, [6],[26],[27],[28],[29] but differed from the posterior direction reported by Montagu. [30] The MF can appear as multiple foramina. The occurrence of multiple MF reported in our study confirms that multiple MF may exist in a minority of the patients and injury to any branch can result in a sensory deficit.

The precise identification of the MF is important in both diagnostic and clinical procedures of the mandible. Clinically, the mental nerve bundle that emerges from the foramen may get injured during surgical procedures with resulting paresthesia or anesthesia along its sensory distribution. Findings of present study suggest that the clinician should expect to find the MF in line with the long axis of the lower second premolar, in the midpoint of the distance between the alveolar bone crest and the lower border of the mandible, and approximately three-fifth of the distance from the buccal cusp tip of this tooth to the lower border of the mandible. If the MF cannot be localized in the position described above or in the patient without a reference tooth, the MF can be estimated at approximately one-third of the distance from the symphysis menti to the posterior border of the mandibular ramus, and approximately 16 mm above the lower border of the mandible.

In conclusion, we have shown that the location, the orientation, and the size of the MF on the CT images of a sample Turks. The knowledge may assist surgeons to localize the MF, avoid injury to the neurovascular bundles, and facilitate surgical, local anesthetic, and other invasive procedures. The data are of direct relevance to clinical teaching and practice.

 
  References Top

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29.Piyawinijwong S, Rojananin J, Pornkuntham U, Pilakasiri K. The mental foramen in Thais. R Thai Air Force Med Gaz 1985;31:141-6.  Back to cited text no. 29
    
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    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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