|Year : 2022 | Volume
| Issue : 1 | Page : 41-46
Assessment of Anterior Loop of Inferior Alveolar Nerve – A Cone Beam Computed Tomography Study
Juluri Sairamya Suneetha, Yalamanchili Samatha, Alaparthi Ravi Kiran, Nunsavathu Purnachandra Rao Naik, Boddu Naveen Kumar, Garikapati Anoop
Department of Oral Medicine and Radiology, SIBAR Institute of Dental Sciences, Guntur, Andhra Pradesh, India
|Date of Submission||02-Jul-2021|
|Date of Decision||10-Mar-2022|
|Date of Acceptance||01-Apr-2022|
|Date of Web Publication||05-Aug-2022|
Juluri Sairamya Suneetha
Dno-12-7-100, Ganeshwar Rao Street, Kothapet, Guntur-1, Andhra Pradesh, 522001
Source of Support: None, Conflict of Interest: None
Introduction: The anterior loop (AL) of the inferior alveolar nerve (IAN) and the mental foramen (MF) are important anatomical structures that should be taken into consideration during preoperative planning in the anterior mandibular region. This study aims to assess the prevalence, length, and type of the AL of the IAN in males and females in a South Indian population. Additionally, the distance from the MF to the lower border of the mandible is assessed. Materials and Methods: A total of 115 cone-beam computed tomography (CBCT) scans of 230 sides of mandibles were taken using a Carestream Select CS9300 CBCT machine (Carestream Dental LLC, Atlanta, USA). The scans were selected from archives and divided into three different age groups (<40, 41–60, >61 years). The scans were analyzed to detect the canal of the AL of the inferior alveolar nerve canal (IANC). The IANC, along with the AL canal and part of the incisive nerve canal, was traced using the CS 9300 software. The length of the mandibular nerve was measured for each patient in cross-sectional and panoramic views. Results: The AL was present in 92.6% of the 115 participants. Overall anterior loop length ranged between 0.9 and 15.2 mm. The mean length of AL in panoramic view on the right side was 3.284 ± 2.314 mm and it was 3.015 ± 2151 mm on the left side. Y-shaped AL was more predominant when compared to T-shaped AL in the sample. Conclusion: The prevalence of AL was relatively higher in subjects ranging from 41 to 60 years with a slight increase in female predominance.
Keywords: Anterior loop, cone-beam computed tomography, mental foramen, inferior border of the mandible
|How to cite this article:|
Suneetha JS, Samatha Y, Kiran AR, Naik NP, Kumar BN, Anoop G. Assessment of Anterior Loop of Inferior Alveolar Nerve – A Cone Beam Computed Tomography Study. J Orofac Sci 2022;14:41-6
|How to cite this URL:|
Suneetha JS, Samatha Y, Kiran AR, Naik NP, Kumar BN, Anoop G. Assessment of Anterior Loop of Inferior Alveolar Nerve – A Cone Beam Computed Tomography Study. J Orofac Sci [serial online] 2022 [cited 2022 Aug 16];14:41-6. Available from: https://www.jofs.in/text.asp?2022/14/1/41/353468
| Introduction|| |
The mandibular nerve is the third division of the trigeminal nerve. After passing through the mandibular foramen, it is called the inferior alveolar nerve (IAN). The section of the nerve anterior to the mental foramen (MF) and just before its ramification to the incisive nerve is called the anterior loop (AL) of IAN. Surgeries in that region may result in neurosensory disturbances such as paresthesia of the lip and chin.
The AL of IAN cannot be detected clinically, but the inferior alveolar nerve canal (IANC) can be seen in diagnostic imaging, which includes dental panoramic radiography, multi detector computed tomography (MDCT scans), and cone-beam computed tomography (CBCT). CBCT superiorly visualizes the anatomical variations of IANC, which infers the path of the IAN. Visualization of the path of the nerve can prevent nerve damage and resultant complications during surgery. While similar studies have been carried out on other populations, this study aims to determine whether the differences found in a South Indian population are significant enough to warrant separate surgical recommendations.
| Materials and Methods|| |
The present study was carried out using CBCT images of patients taken for various clinical indications during the period from December 2018 to May 2020. All images were obtained using a single Carestream select 9300 CBCT machine (Carestream Dental LLC, Atlanta, USA). Analysis of the AL of the IANC was carried out for both sides of each scan by tracing the inferior alveolar canal and its anterior branches. Ethical approval for this study (Pr.149/IEC/SIBAR/2018) was provided by the ethical committee of Sibar Institute of Dental Sciences, Guntur, on 29/10/2018.
In this study, the assessment of AL and its measurements were done in all three projections (axial, coronal cross-sectional, and panoramic views) using the CBCT scans viewed with the Carestream software. The IANC was traced with the software along with the AL and part of the incisive nerve canal. The entry and exit of the MF were then located from the cross-sectional view. Vertical lines were drawn on the panoramic view from the slice that corresponded to the anterior and posterior walls of the MF and the most anterior point of the anterior nerve loop length (ANLL) as seen from the cross-sectional view. The vertical length of the nerve was estimated from the canal to the opening of the MF from the cross-sectional view and translated to the panoramic view and marked as point 1. Point 2 was marked on the most anterior confinement of the AL, and a measurement was made from point 1 to point 2 [Figure 1]. This provided an actual length for the ANLL compared with the anteroposterior spread of the loop as it followed the diagonal trajectory of the nerve in panoramic view.
|Figure 1 CBCT images with anterior loop length in panoramic view. CBCT, cone-beam computed tomography|
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The visualization of sections in the three spatial dimensions (axial, sagittal, and coronal sections) is known as multiplanar reconstruction. The type of AL in the sagittal view and length of the AL in the axial view was measured by marking three lines. The posterior part of the MF was drawn as the third line, the anterior part of the MF was drawn as the second line, and the anterior most confinement of the AL was drawn as the first line. Measurement was made from the first line to the second line. This provided an actual length for the AL [Figure 2] in axial view.
|Figure 2 CBCT images with anterior loop length in oblique view. CBCT, cone-beam computed tomography|
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Cross sections of 1 mm thickness were obtained in cross-sectional slices. The length of the loop has been measured by counting the number of consecutive contiguous vertical cross sections performed between the anterior border of the MF and the anterior border of the loop. This number is multiplied by the resolution of the slice [Figure 3].
|Figure 3 CBCT images with anterior loop length in cross-sectional slice view. CBCT, cone-beam computed tomography|
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We used the classification described by Solar et al. for evaluating the various types of AL of IAN [Figure 4].
|Figure 4 (a) CBCT images depicting T shape of the anterior loop. (b) CBCT images depicting Y shape of anterior loop. CBCT, cone-beam computed tomography|
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Type 1 – the AL is absent.
Type 2 – the AL is T shaped.
Type 3 – the AL is Y shaped.
The distance from the lower point of the MF to the lower border of the mandible was drawn and measured [Figure 5].
|Figure 5 CBCT images of distance from mental foramen to the lower border of the mandible. CBCT, cone-beam computed tomography|
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| Results|| |
The total number of subjects included in the study group was 115 and the total number of sides observed was 230. The AL was present in 92.6% of the 230-subject sample [Table 1]. The subjects in the study group comprised 33.9% (39) males and 66.1% (76) females, suggesting a female predominance in this sample. The length of the AL was found to be greater in the females on the left side, whereas it was found to be greater in males on the right side in all the three age groups. The AL prevalence and its length were greater in the 41 to 60 years age group than in other age groups. Overall anterior loop length (ALL) ranged from 0.9 to 15.2 mm, with a mean length of AL in panoramic view on the right side and left side being 3.284 ± 2.314 and 3.015 ± 2151 mm, respectively [Table 2]. Measurements were also done in oblique and cross-sectional views, in which the oblique view demonstrated similar measurements to the panoramic view, whereas in cross-sectional view, it showed a variation in the length of AL. The Y shape type of AL was more predominant when compared to the T shape in the sample [Chart 1]. Analyzing the relationship between the length of the AL and distance from the MF to the lower of the mandible on the right side depicts that with a one unit increase in distance from the right MF to the lower border of the mandible, the length of AL increased by 0.136 times and on the left side, with a one unit increase in distance from right MF to the lower border of the mandible, the length of AL increased by 0.163 times. This finding is statistically significant with a P < 0.05.
|Table 2 Length of the anterior loop in panoramic, oblique, and cross-sectional slicing views|
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| Discussion|| |
The AL can be described as the extension of the mandibular canal anterior to the MF. It is formed just before the ramification of the mandibular canal into the incisive canal. It includes the mental and incisive nerves simultaneously; therefore, caution should be taken during surgical procedures in the interforaminal region to avoid nerve damage. Surgery in the area of the anterior mandible may violate the AL, resulting in neurosensory disturbances in the area of the lower lip and chin.
Many researchers have made attempts to detect the prevalence and location of the AL, as well as the anterior loop length (ALL). To avoid injury to the IAN, a 5 mm “safe” distance to the most distal fixture from the AL and a 5 mm distance from the MF for harvesting chin bone for grafts have been proposed.
CBCT is a highly efficient imaging modality for the assessment of vital anatomical structures. Moreover, CBCT provides acceptable three-dimensional (3D) views and accessibility to the craniofacial structures in comparison with the conventional radiographic techniques. Because of this, CBCT is preferred to MDCT and most often used in dental practice due to its advantages, including a lower cost and a lower radiation dose, in combination with the fact that CBCT image quality is comparable or even superior to that of MDCT for evaluating dento-maxillofacial structures.
In the present study, 230 CBCT scans of the right and left sides were evaluated, in which the AL of the IAN canal was identified in 213 scans (92.6%). Similar studies done in the literature using 3D CBCT scans had proven to exhibit high precision and reliability in the diagnosis of the AL and other bony anatomical landmarks of the mandible with great reliability to identify the presence and measurement of length. In a study done by Wong and Patil, it was noted that the AL was present in 94% of the 100 CBCT scans in three different ethnic groups (33 Malaya, 33 India, 34 Chinese). Lu et al had done a study on 366 CBCT images in the USA population in which the prevalence of AL was seen in 85.2% of scans. Parnia et al. had done a study on 96 CBCT scans in the Irani population, of which the AL was visualized in 84% of the CBCT scans.
In the present study, 115 CBCT scans were evaluated, out of which 33.9% were of males and 66.1% were of females. On comparing the prevalence of AL in both genders, AL was found to be more in females than in males, but this was not statistically significant. In a previous study done by Lu et al. on 68 CT scans of the mandible for the presence of AL on each side, 113 sides, that is, 68 patients out of 136 mandible sides, exhibited no difference in the prevalence of AL between males and females. Here some scans are single sided Siddiqui et al. conducted a similar study on 193 CBCT scans. The prevalence of AL was 40.4% among males and 33.7% among females. Nakib et al. had done a study on 400 CBCT images in which AL was noted in 56% males and 44% females, but this variable was statistically significant.
In the present study, the prevalence of AL was categorized based on age into three groups: less than 40 years, 41 to 60 years, and greater than 60 years. The prevalence of AL was found to be slightly greater in the age group of 41 to 60 years. Kajan and Salari had done a study on 84 mandibular CBCT scans, and they found a significant difference in determining the visibility of AL in different age groups. Their results showed that the prevalence of the AL: was lower in patients over 40 years of age. do Nascimento et al. conducted a study on CBCT scans of 250 patients among different age groups, and they reported the highest prevalence of AL in subjects in the second to fifth decades of life. Apostolakis and Brown had done a study on 93 CBCT images in the Greek population in which the prevalence of AL was 48%. No significant correlation with the age ranges of individuals was found.
In the present study, the mean length of AL in the panoramic view was 3.284 ± 2.314 mm on the right side and 3.015 ± 2.151 mm on the left side (P = 0.001), whereas in the oblique view, it was 3.211 ± 1.8317 mm on the right side and 3.313 ± 2.2083 mm on the left side (P = 0.001). In cross-sectional slicing, it was 2.61 ± 1.19 mm on the right side and 2.43 ± 1.35 mm on the left side (P = 0.001). The greatest length of AL was 15.1 mm and the lowest length was about 0.9 mm. Panoramic and oblique view measurements of the length of AL did not demonstrate any statistical variation, but in cross-sectional slicing, there was a marked difference. This finding might be attributed to the thickness of the slicing in this view. Rosa et al. conducted a study on 352 CBCT scans of the mandible and reported that in 21 of the images, the length of the AL exceeded 4.5 mm, with the greatest length being 7 mm. Apostolaksis and Brown had done a study on 93 CBCT scans with a prevalence of Al in 62% of patients, and they found the mean and range of ALL as 0.89 and 0.0 to 5.7 mm, respectively. The longest loop measured was 5.7 mm. In a study done by Kaya et al. on 73 panoramic radiographs and spiral CT, they reported that the mean length of AL was 0.71 ± 0.21 mm greater in panoramic radiographs than in MDCT.
Parnia et al. conducted a study on 96 CBCT scans in the Irani population and noticed the mean length of AL to be 3.54 mm in the study group. do Nascimento et al. performed a study on 250 CBCT scans and noticed that the mean length of the AL was 1.1 mm, and the largest ALL was 4 mm. The AL length had shown a mean of 0.2 to 7.61 mm presentation in various studies, but most of these studies had shown a mean length concentrating around 2 to 3 mm. Therefore, the proposed 5 mm safe distance appears to be ideal for surgical intervention in that region.
In the present study, comparing the length of AL in both genders, the mean length of AL was greater on the right side in males and on the left side in females, with a statistically significant variation. According to the study conducted by Rosa et al., the AL was significantly longer in men than in women. do Nascimento et al. performed a study on 250 CBCT scans, and their results showed the mean length of the AL was 1.1 mm, and AL was more prevalent in male patients compared to the females.
In the present study, the mean length of the AL was found to be greater in the 41 to 60 age group. do Nascimento et al. had done a study on 250 CBCT scans where they found that AL was more prevalent in young patients compared to the older individuals.
In the present study, Y-shaped AL was noticed in 90.4% of cases on the right side and 82.6% of cases on the left side. On comparing the type of AL, Y shape was more predominant when compared to the T shape in the sample, with no significant difference between the right and left sides of the mandible. Shaban et al. conducted a study on 71 CBCT images, of which 36 were males and 35 were females, and they found that type-III AL was a more prevalent variant and type-I (Y type) was the least prevalent type. Demir et al. performed a study on 279 CBCT scans in the Turkish population. It was found that type-III AL (not appreciated) was a more prevalent variant and type-I AL (Y shape) was the least prevalent type.
In the present study, the mean distance from the MF to the lower border of the mandible was greater on the right side (8.454 mm) than on the left side (7.939) and greater in males than in females. It was also greater in the age groups between 41 and 60 years on both sides. Similar studies in the literature also showed a varying presentation. Shalash et al. conducted a study on 120 CBCT scans and found that the MF was present, on average, 10.27 mm above the inferior border of the mandible, with no significant gender difference. In a study done by Kalender et al. examining 386 CBCT scans, MF was found to be 12.4 mm above the lower border, which is more compared to our study.
In the present study, linear regression was also evaluated. With one unit increase in distance from the right side of the MF to the lower border of the mandible, the length of AL increased by 0.136 times, whereas with one unit increase in distance from the left side of the MF to the lower border of the mandible, the length of AL increased by 0.163 times.
| Conclusion|| |
The prevalence of AL in this study was relatively higher and the AL prevalence was greater in subjects ranging from 41 to 60 years, with a slight increase in female predominance. The mean length of AL in panoramic and oblique views did not show any statistical variation, but measurement in cross-sectional slices showed a marked difference, which could be attributed to the thickness of the slicing in this method. Length of AL was greater on the right side in males, and on the left side, it was greater in females, with a significant variation in Y-shaped AL noticed more predominantly than in T shape. The distance from the MF to the inferior border of the mandible was greater on the right side than on the left side. In comparison, it was greater in females than in males.
After analyzing the data, it has been concluded that CBCT has emerged as a superior diagnostic modality for the evaluation of AL and thereby is useful in preoperative surgical planning. There are similar studies reported in the literature, but they have been carried out in different geographical areas. The present study depicts the ANL presentation in a South Indian population. The findings of this study support the present recommended surgical considerations. Further studies with a greater sample size would be required in order to make a strong recommendation with regard to safety margins required in the anterior region of the mandible.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2]