|Year : 2019 | Volume
| Issue : 2 | Page : 134-139
Evaluation of morphometric variations in mental foramen and prevalence of anterior loop in South Indian population – A CBCT study
Vani Chappidi1, LA Swapna2, Voulligonda Dheeraj1, GR Nikitha1, Madhuri Kanakagiri1
1 Department of Oral Medicine and Radiology, Sri Sai College of Dental Surgery, Vikarabad, Telangana, India
2 Department of Surgical and Diagnostic Sciences, Dar Al Uloom University, Riyadh, Saudi Arabia
|Date of Submission||29-Dec-2018|
|Date of Acceptance||05-Jun-2019|
|Date of Web Publication||24-Jun-2019|
Prof. Vani Chappidi
Department of Oral Medicine and Radiology, Sri Sai College of Dental Surgery, Vikarabad, Telangana - 501 102
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Introduction: The mental foramen (MF) opens on the lateral aspect of the mandible near premolar region on both sides of the mandible. The portion of inferior alveolar nerve present anterior to the MF, prior to exiting the canal, is referred to as the anterior loop (AL) of the inferior alveolar nerve. These anatomical variations cannot be evaluated by conventional imaging techniques. Cone beam computed tomography (CBCT) provides three-dimensional reliable images of maxilla–mandibular region. Hence, it plays an important role to detect and evaluate these anatomical variations and to prevent intra- and postoperative complications. Materials and Methods: This retrospective observational study includes 500 CBCT images of the mandible. The average size, location, shape of MF, and presence of AL were assessed in sagittal, tangential, and axial sections. Results: Out of 250 CBCT scans analyzed, 132 scans (52.8%) were of males and 118 scans (47.2%) belonged to females. The mean size of MF as measured in the sagittal sections was found to be 3.36 mm in height and 2.54 mm in length. The most common position for the MF related to the mandibular teeth in this study was between first and second premolars in 310 CBCT images (62%). A majority of the MF were oval in shape (n = 346, 69.2%) followed by round shape (n = 154, 30.8%). The presence of AL of inferior alveolar nerve was found in only 20% (n = 100) of cases in this study. Conclusion: Considering these variations in MF and AL, the use of CBCT seems necessary for better evaluation and treatment planning.
Keywords: Anterior loop, cone beam computed tomography, mental foramen
|How to cite this article:|
Chappidi V, Swapna L A, Dheeraj V, Nikitha G R, Kanakagiri M. Evaluation of morphometric variations in mental foramen and prevalence of anterior loop in South Indian population – A CBCT study. J Indian Acad Oral Med Radiol 2019;31:134-9
|How to cite this URL:|
Chappidi V, Swapna L A, Dheeraj V, Nikitha G R, Kanakagiri M. Evaluation of morphometric variations in mental foramen and prevalence of anterior loop in South Indian population – A CBCT study. J Indian Acad Oral Med Radiol [serial online] 2019 [cited 2020 Aug 8];31:134-9. Available from: http://www.jiaomr.in/text.asp?2019/31/2/134/261083
| Introduction|| |
The mental foramen (MF) opens on the lateral aspect of the mandible near premolar region on both sides of the mandible. It carries mental nerve and associated blood vessels. It signifies the anterior end of the inferior alveolar canal. It is the topographic landmark for the mental anesthesia in dentistry.
The morphometric evaluation of MF has gained interest in the recent years in endodontics, implantology, and surgery because correct localization and dimensions of the MF are important for procedures such as periapical surgery, administration of local anesthesia, fixation of fractures, orthognathic surgeries, and dental implant placement.,,,,
The portion of the inferior alveolar nerve present anterior to the MF, prior to exiting the canal, is referred to as the anterior loop (AL) of the inferior alveolar nerve. The presence of AL is important to determine a safe interforaminal area when placing implants in the mandible, genioplasty procedures, and reduction of mandibular fractures.
Inadvertent damage to the mental nerve may lead to complications such as temporary or permanent paresthesia of lip and chin region, hemorrhage, and postoperative pain. Presurgical evaluation of the anatomical variations in the MF and AL prevents these complications. These variations cannot be evaluated by conventional imaging techniques because of their magnification and image distortion. Cone beam computed tomography (CBCT) provides three-dimensional (3D) reliable images of maxilla–mandibular region. Hence, it plays an important role to detect and evaluate these anatomical variations.
Therefore, the objectives of this study were to evaluate the variations in MF with respect to its position and dimensions and also to evaluate the prevalence of AL of the inferior alveolar nerve using CBCT.
| Materials and Methods|| |
This retrospective observational study includes 500 CBCT images which were collected from various CBCT centers in Hyderabad during the period from August 2018 to March 2019. All the CBCT scans were obtained from centers with CS9000 3D CBCT machine with exposure parameters of 120 kV, 15 mA, and 12 inches field of view. The images were reconstructed using CS 3D Imaging software and required measurements were performed.
The inclusion criteria for the CBCT scans were presence of first and second premolars on both sides of the mandible and patients older than 18 years whose skeletal growth was completed.
The exclusion criteria for the CBCT scans were presence of any pathology, fracture, supernumerary, or impacted teeth in the mandible.
These CBCT images were analyzed in different sectional planes – sagittal, tangential, and axial. The acquired images were analyzed by two observers.
The parameters evaluated were as follows:
- The average size (length and height) of MF on the right and left sides of the mandible [Figure 1].
- The location of MF in relation to the mandibular premolars [Figure 2].
- Shape of MF.
- Presence of AL of the inferior alveolar nerve canal [Figure 3].
- Variations in the dimensions and location of MF with respect to gender.
The anteroposterior position of MF was recorded as follows:
- Below first premolar,
- Between first and second premolars,
- Below second premolar,
- Between second premolar and first molar.
The dimensions of MF were measured as the length and height of the foramen in the sagittal sections. The prevalence of AL was assessed based on unilateral or bilateral presence of this structure. A descriptive statistical analysis was conducted for the total sample. Interobserver variability was assessed using kappa test.
| Results|| |
Out of 500 CBCT images of the MF, 264 scans (52.8%) were of males and 236 scans (47.2%) belonged to females. The mean size of MF as measured in the sagittal sections was found to be 3.48 mm in height and 2.68 mm in length in males and 3.23 mm in height and 2.40 mm in length in females. The mean size of the foramen [Table 1], [Graph 1] was found to be larger on the right side (length 2.43 mm and height 3.42 mm) compared to the left side (length 2.39 mm and height 3.38 mm).
|Table 1: Morphometric measurements of mental foramen related to side and gender|
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The most common position [Table 2], [Graph 2] for the MF related to the mandibular teeth in this study was between the first and second premolars in 310 CBCT images (62%), followed by below the second premolar in 170 images (34%), below the first premolar in 13 images (1.6%), and was found in 7 images (1.4%) between second premolar and first molar. MF position between first and second premolars was also the most common position among the males (n = 176, 66.7%) and females (n = 134, 56.8%), followed by below the second premolar among the males (n = 77, 29.2%) and females (n = 93, 39.4%).
A majority of the MF were oval [Table 3], [Graph 3] (n = 346, 69.2%) followed by round shape (n = 154, 30.8%). The presence of AL of inferior alveolar nerve was found in only 20% (n = 100) of cases in this study. Males showed a higher incidence of AL (n = 59, 22.3%) when compared with females (n = 41, 17.4%) [Table 4], [Graph 4].
|Table 4: Distribution of male and female subjects based on anterior loop|
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The presence of AL was more commonly seen on the left side of the mandible (n = 62, 24.8%) when compared with the right side (n = 38, 15.2%) [Table 5], [Graph 5].
|Table 5: Distribution of subjects based on anterior loop on right and left sides of the mandible|
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Out of 500 CBCT images, AL was unilateral in 15.2% (n = 76) and bilateral in 4.8% (n = 24) of the scans [Table 6], [Graph 6].
|Table 6: Distribution of subjects based on unilateral and bilateral anterior loops|
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Out of the 500 CBCT images of MF, unilateral AL was found to be more frequent on the left side of the mandible (n = 55, 72.4%) compared with the right side (n = 21, 27.6%) [Table 7], [Graph 7].
|Table 7: Frequency of anterior loop with respect to gender and right/left side of mandible|
Click here to view
In our study, unilateral AL was more commonly seen in males (n = 47, 61.8%) than females (n = 29,38.2%) [Table 7], [Graph 7].
| Discussion|| |
When placing the implants in the foraminal region of the mandibular arch, the important anatomical landmark that should be considered is MF. The AL refers to the extension of the inferior alveolar nerve, anterior to MF, prior to exiting the canal. To prevent the damage of neurovascular bundle during surgical interventions such as implant placement, genioplasty, osteotomy, and open reduction of mandibular condyle, it is essential to evaluate the anatomical structures and variations in the MF region.,,,
In the field of maxillofacial imaging, there is an increasing demand for CBCT because of its good image quality, volumetric analysis, short scan times, and relatively less radiation dose than other conventional medical CT. Hence, the anatomical variations can be evaluated by using CBCT.
Chen et al. considered the buccolingual diameter of the inferior alveolar canal at the site of MF to be similar to MF diameter. The mean diameters in their study were 2.26 mm in the American population and 2.13 mm in Taiwanese population. The majority of MF (56%) were located apically between the two premolars, and another 35.7% of MF were positioned below the second premolar.
The average height and length of the MF in the present study were 3.36 and 2.54 mm, respectively, which were similar to the values reported by Von Arx et al. using CBCT (3.0 mm and 3.2 mm, respectively) and the values reported by Oliveira et al. (3.11 mm and 3.20 mm, respectively). In addition, both Von Arx et al. and Oliveira et al. found that the MF was larger in men than in women. This difference between the genders was also found in this study for the MF in sagittal CBCT images, and men presented higher average values of MF (height 3.48 mm, length 2.68 mm) than women (height 3.23 mm and length 2.54 mm).
The location of MF was greater between the first and second premolar region with 62% of total CBCT images. The more prevalent shape of MF was oval (69.2%). The AL was detected only in 20% of total scans.
Al-Mahalawy et al. assessed 302 CBCT scans of Saudi population and concluded that MF was commonly found below the apex of the second premolar and the AL was regarded as the least common pattern in Saudi population (15.2%) which is agreement with this study.
Lu et al. assessed 366 CBCT scans and identified AL in 85.2% of cases which is in disagreement with this study. Sheikhi et al. assessed 180 CBCT scans in Iranian population and observed that the most common shape of the MF was oval which is in agreement with this study. According to Rios et al., the quality of image is more important than the clinician's diagnostic ability and thoroughness.
Wang et al. assessed 100 Chinese cadaver mandibles and reported that the most common location of MF among Chinese population was apical to the second premolar (59%). Olasoji et al. (2004) assessed 157 panoramic radiographs of North Nigerian adults and repored the most common position of MF was between the first and second premolars. Rupesh et al. assessed 500 digital panoramic radiographs of Asian Indian population and found that the most common position of MF was between first and second premolars. The results of the above studies were concurrent with those of this study.
However, there were few panoramic studies in other populations such as Kenyan African by Mwaniki and Hassanali (1992), Malay population by Ngeow and Yuzawati (2003), Krudish population by Al-Talabani et al. (2008), and Bareilly population by Alok et al. (2016) indicating that MF was in line with the second premolar.,,, Al-Shyayab et al. (2015) assessed 518 panoramic radiographs. They found the most common shape of MF was round. These results were not in accordance with the present study because of the difference in the race and group of population selected and also because of the two-dimensional imaging technique used in the above studies.
This study recommends the clinician to use CBCT for better evaluation of the anatomical and morphological variations in MF in the interforaminal region during surgical interventions. The CBCT is a good diagnostic technique for assessing the presence of AL of inferior alveolar nerve.
| Conclusion|| |
Considering these variations in MF and AL, the use of CBCT seems necessary for better evaluation and treatment planning. The possible presence of MF and AL should be borne in mind to avoid the occurrence of a neurosensory disturbance/hemorrhage following surgical procedures. It can be concluded that the most prevalent location for MF is between the first and second mandibular premolars. The most common shape of MF was oval, and its mean dimensions were 2.54 mm in length and 3.36 mm in height. The presence of AL was detected in only 20% of scans.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]