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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 30  |  Issue : 1  |  Page : 32-37

Efficacy and evaluation of cone beam computed tomography in determining the prevalence and length of anterior loop of inferior alveolar nerve in North Indian population


1 Department of Dental Surgery, Muzaffarnagar Medical College, Muzaffarnagar, Uttar Pradesh, India
2 Department of Oral Medicine and Radiology, Institute of Dental Studies and Technologies, Modinagar, Uttar Pradesh, India
3 Department of Oral Medicine and Radiology, D J College of Dental Sciences and Research, Modinagar, Uttar Pradesh, India

Date of Submission14-Nov-2017
Date of Acceptance07-Mar-2018
Date of Web Publication23-Apr-2018

Correspondence Address:
Dr. Zeba Siddiqui
Department of Dental Surgery, Muzaffarnagar Medical College, Muzaffarnagar - 251 203, Uttar Pradesh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jiaomr.jiaomr_121_17

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   Abstract 


Introduction: The section of the inferior alveolar nerve (IAN) in front of the mental foramen and just before its ramification to the incisive nerve is known as anterior loop (AL) of IAN. Surgeries in the area of the anterior mandible may violate the AL resulting in neurosensory disturbances. Cone beam computed tomography (CBCT) is a new imaging modality that provides a multidimensional view of the facial skeleton. Aim: To evaluate the efficacy of CBCT in measuring the anterior looping of IAN. Objectives: To determine the prevalence of AL of IAN using CBCT, and to determine AL length using CBCT. Materials and Methods: Out of the total 1075 reported patients, 193 study participants fulfilling the inclusion criteria constituted the sample size were assessed for estimating the prevalence and determining the length of AL of IAN. They were scanned with a suitable digital imaging system for a variety of clinical indications using appropriate Dental Imaging Software. Results: The prevalence of anterior looping was found to be 37.3% and was highest (43.5%) in the age group of 36–56 years and was found to be statistically significant. The mean length of anterior looping was found to be 3.661 mm (SD ± 1.9933) with a maximum loop length of 8.8 mm. Conclusion: CBCT provides an accurate means to determine the anterior looping of IAN, measures its length, and thereby, helps in preoperative surgical planning.

Keywords: Anterior loop length, anterior looping, cone beam computed tomography, inferior alveolar nerve


How to cite this article:
Siddiqui Z, Rai S, Ranjan V. Efficacy and evaluation of cone beam computed tomography in determining the prevalence and length of anterior loop of inferior alveolar nerve in North Indian population. J Indian Acad Oral Med Radiol 2018;30:32-7

How to cite this URL:
Siddiqui Z, Rai S, Ranjan V. Efficacy and evaluation of cone beam computed tomography in determining the prevalence and length of anterior loop of inferior alveolar nerve in North Indian population. J Indian Acad Oral Med Radiol [serial online] 2018 [cited 2020 Jan 24];30:32-7. Available from: http://www.jiaomr.in/text.asp?2018/30/1/32/230882




   Introduction Top


We all know that mandibular nerve is the third division of the trigeminal nerve and it enters the mandible through the mandibular foramen on the medial surface of the ascending mandibular ramus. After passing through the mandibular foramen, it is called the inferior alveolar nerve (IAN). The IAN and the mental foramen (MF) are important anatomical structures that should be taken into account during preoperative planning in the anterior mandible.[1] The final part of the IAN sometimes passes below the lower border and the anterior wall of the MF. After giving off the smaller mandibular incisive branch, the main branch curves back to enter the foramen and emerge to the soft tissues as the mental nerve. The section of the nerve in front of the MF and just before its ramification to the incisive nerve is called as the anterior loop (AL) of IAN.[2] A more precise description of anterior looping was reported by Bavitz et al. (1993)[3] and Misch (1999),[4] who described AL as the structure where the mental neurovascular bundle crosses inferior and anterior to the MF, then doubles or loops back to exit the MF. Jalbout et al. (2004)[5] described the AL as an extension of the IAN, anterior to the MF, prior to exiting the canal [Figure 1]. It is essential for dental practitioners to understand the detailed anatomy of the IAN so as to avoid potential injuries to the nerve during surgical procedures or endodontic treatment.[6] The AL of IAN cannot be seen clinically but can be detected in radiographs which include dental panoramic radiographs, magnetic resonance imaging, computed tomography (CT scans), and cone beam computed tomography (CBCT).[7] The panoramic radiograph may result in distortion, and the magnification of the anatomical structures is often present and results in either over or underestimation of the real size. It is said that CBCT gives more accuracy with low radiation exposure and allows to generate multiplanar slices of a region of interest and is capable to reconstruct a 3D imaging via a series of mathematical algorithms.[8],[9] The present study aimed to evaluate the efficacy of CBCT in measuring the length and prevalence of anterior looping of IAN, and thereby confirm whether it help dentists to avoid injuries during selective surgeries in anterior mandible or not.
Figure 1: Schematic diagram showing key image of anterior loop of IAN

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   Materials and Methods Top


It was a cross-sectional study in which a total of 1075 patients reported for CBCT scan at randomly selected Diagnostic and Research Centre (Delhi-NCR), India, during the period of study (January 1, 2014 to December 31, 2014) were selected first as part of the data pool. Inclusion criteria were patients between 15 and 90 years of age of both sexes with dentulous and partially edentulous arch, patients having images of anterior mandible and at least 2 cm distal to MF up to the lower cortical border unilaterally and bilaterally. Patients with pathological lesions that could affect the position of the mandibular canal and the MF such as periapical abscess, cyst tumor, fracture line, implant in MF, osteoradionecrosis, giant cell lesion, dense bone island were excluded from the study. Prior informed consent was taken from the concerned and patients' confidentiality has been maintained. This thesis research work has got ethical clearance from the Institutional Ethical Committee well before the start of the study. Presence of AL was considered in the cases/subjects where the mental neurovascular bundle crosses inferior and anterior to the MF. Out of 1075 reported patients, 193 patients who were fulfilling the prescribed inclusion criteria were ultimately included in the current study as study subjects. The CBCT examinations were made using a Kodak 9000 C digital imaging system (Carestream Dental LLC, Atlanta, GA, USA). The scanning of all the patients were accomplished using one of the following imaging protocols available with this CBCT unit: 74 kVp, 32.4 s, 10 mA. The milliamp setting was computed by the device based on the anatomy of the patient, voxel size of 0.2 mm, and field of view of 8 × 8 cm. The Kodak Dental CS 3D Imaging Software V3.5.7.0 (Carestream Health Inc., St. Rochester, NY, USA) was used. The data of the CBCT images were sliced in three dimensions, i.e., axial, coronal, and sagittal.

Measurement of anterior loop length

For the measurement of anterior loop length (ALL), all the patients were instructed to remain seated/standing in the device, with their head placed so that the Frankfurt horizontal plane remained parallel to the floor and the mid-sagittal plane remained perpendicular to the floor. The area of interest was centered in the beam. During a CBCT examination, gantry rotates around the head in a complete 360° rotation, while capturing multiple images from different angles that gets reconstructed to create a single 3D image. The images obtained from CBCT are generated in Digital Imaging and Communication in Medicine (DICOM) format. After copying the exam file to a conventional computer using CS 3D software, image placement was standardized prior to selecting the sections to be used for measurement. The visualization of sections in the three spatial dimensions (axial, sagittal, and coronal sections) is known as multiplane reconstruction [Figure 2] and [Figure 3]. Cross-section of different thickness has been obtained like that of 1, 1.1 mm, etc. in different slices.
Figure 2: Reconstructive panoramic image of CBCT showing anterior looping of IAN

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Figure 3: Axial reconstructive image of CBCT showing anterior looping of IAN

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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 has been multiplied by the resolution of the slice. For example, in a case shown in where the number of cross-sections in which the anterior looping noted were 8, and thickness of the slice in this case was 1.1; so the length of the loop would be 8 × 1.1 = 8.8 mm [Figure 4]. The initial slice for measurement is considered to be the first slice just after the anterior margin of the MF disappears as done by Apostolakis et al. (2011).[10] The images were studied and evaluated by all the authors independently.
Figure 4: Longest anterior loop length of 8.8 mm in male

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Statistical analysis

For suitable and appropriate statistical analysis, Statistical Package for the Social Sciences (SPSS) version 22.0.0.0 has been used. A 5% level of significance has been chosen and the P value of <0.05 has been considered as statistically significant and <0.001 has been considered as highly significant.


   Results Top


A total of 1075 patients reported during the period of study (Jan 1, 2014 to Dec 31, 2014) were first selected as data pool. In the present study, 193 patients who were fulfilling the prescribed inclusion criteria were included as study subjects. Out of which, 104 were males and 89 were females with age range from 15 to 90 years. Based on the age, patients were divided into three groups to find out prevalence of looping in respective age groups, viz., (i) 15–35 years, number of subjects in this group were 40 (20.7%); (ii) 36–56 years, number of subjects in this group were 92 (47.7%); and (iii) >56 years, numbers of subjects in this group were 61 (31.6%). All the authors measured the same variations independently in the current study.

Overall anterior looping was present in 72 (37.3%) subjects [Figure 5]. The prevalence of anterior looping of IAN was 42 (40.4%) among male and 30 (33.7%) among female study subjects [Table 1]. Out of the total 72 scans having anterior looping, 38 scans (52.7%) and 34 scans (47.22%) belong to left and right side, respectively. No significant difference has been noted in the prevalence of anterior looping of IAN among male and female with P value of 0.339. Prevalence of anterior looping was highest in the age group of 36–56 years, i.e., 40 (43.5%), followed by 26 (42.6%) in the age group of >56 years. Lowest prevalence of anterior looping was seen in the age group of 15–35 years, i.e. 6 (15%) [Table 2]. The difference in the prevalence of all the three groups was found to be statistically significant with P value = 0.005. The mean ALL of all the male study subjects was 3.886 (SD ± 2.065) which was found to be more as compared to females, i.e., 3.347 (SD ± 2.877). The maximum loop length was noted in male, i.e., 8.8 mm [Figure 4] and minimum loop length in male was 1 mm. In females, maximum loop length was 8 mm and minimum loop length was noted as 1 mm [Table 3]. The mean ALL of study subjects in the age group 36–56 years was maximum, i.e., 3.95 mm (SD ± 1.99), followed by age group >56, i.e., 3.37 mm (SD ± 2.145). However, maximum loop length has been noted in 36–56 years and >56 years age group as 8.8 mm. Minimum loop length was noted in age group 36–56 years and in >56 years as 1 mm; however, no significant difference was found between the age groups for the same [Table 4].
Figure 5: Prevalence of anterior looping of IAN* among study participants

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Table 1: Distribution of gender-wise prevalence of anterior looping of IAN* among study participants

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Table 2: Distribution of age group-wise prevalence of anterior looping among study participants

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Table 3: Gender-wise distribution of study subjects by anterior loop length

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Table 4: Age group-wise distribution of study subjects by anterior loop length

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   Discussion Top


Selective 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. To avoid such a sequel, a 5 mm safe distance to the most distal fixture from the AL and a 5 mm distance from the MF for chin bone harvesting have been proposed.[10]

In the present study, out of 193 CBCT scans evaluated, anterior looping of IAN was identified in 72 (37.3%) CBCT scans. Prevalence of anterior looping of IAN was 40.4% among male and 33.7% among female study subjects. No significant difference has been noted in the prevalence of anterior looping among male and female subjects. There are several studies in which authors tried to measure the prevalence of AL using CT or CBCT. Jacobs et al. (2002)[11] studied 230 spiral CT scans of the lower jaw bone and found anterior looping of the mandibular canal in 7% of the cases. Kaya et al. (2008)[2] did a study on 73 panoramic radiography and spiral CT. They reported the prevalence of the AL in panoramic radiographs and spiral CT images as 28 and 34%, respectively. Uchida et al. (2009)[12] studied 71 Japanese cadavers (140 hemimandibles) and revealed the prevalence of anterior looping to be 71%. Nakib et al. (2013)[13] noted that the AL was present in 6.25% of all subjects (400 subjects). AL was noted in 56% males and 44% females. Findings of all these studies are not consistent with our study, however, it is mandatory to mention that methodologies are different. Parnia et al. (2012)[14] did a study on 96 CBCT scans from patients with partially edentulous mandibles. Anterior looping could be visualized in 83.3% of the cases in the right side and in 62.5% of the cases in the left side. This finding is also not consistent with our study as their prevalence of AL of IAN is too high as that of 37.3% of the current study. Kajan and Salari (2012)[15] did a study on 84 mandibular CBCT scans and reported the anterior looping as 36.9% (62 of 168 cases). No significant differences between observing the AL associated with either sex or sides were detected. A significant difference between determining the visibility of the AL in the age group was found. This finding is almost consistent with the finding of the current study. They also reported that the AL was seen less frequently in patients aged over 40 years, which is contrary to our finding where prevalence of AL is less in the age group of 15–35 years. Li et al. (2013)[16] conducted a study on 68 CT scan of mandible from Chinese patients and revealed that the anterior looping of IAN was present in 113 of 136 mandible sides from 68 patients and noted the prevalence of the same as 83.1%. There was no difference in the prevalence of the AL between the left and right sides of the mandibles, between genders, or between different age groups. Mardinger et al. (2000)[17] did a study on 46 hemimandibles and reported the AL of the mental canal to be 28% after observing physically in 13 hemimandibles. Apostolakis et al. (2011)[10] evaluated the anterior looping in 93 CBCT scans, and it was identified in 48% of the sides, which is a bit high as that of our finding. Neiva et al. (2004)[18] reported that prevalence of anterior looping was seen in 88% of study subjects. Solar et al. (1994)[19] studied and revealed the prevalence of anterior looping to be 59%. The above two studies reported much higher prevalence as compared to ours.

Rosa et al. (2013)[20] studied 352 CBCT scans and reported that in 21 of the CT scan images, the length of loop exceeded 4.5 mm, with the greatest length being 7 mm. No significant differences were found between left and right sides or between edentulous and dentate subjects. However, the loop was significantly longer in men than in women. Chen et al. (2013)[6] performed study on CBCT of two different groups. Group I consisted of 100 Americans (53 males and 47 females). Group II had 100 Taiwanese adults (55 males and 45 females). ALL of Group II (7.61 ± 1.81 mm) was significantly longer than that of Group I (6.22 ± 1.68 mm). There was no significant difference in ALL between males and females within Group I, but there was a significant difference in ALL between males and females within Group II. Apostolakis et al. (2011)[10] found the mean and range of ALL as 0.89 and 0.0–5.7 mm, respectively. In 62% of the cases with an AL, the length was up to 1 mm, while it was up to 2 mm in 85% of the cases and up to 3 mm in 95% of the cases. Two percent of the sides showed an ALL of >4 mm. The longest loop measured was 5.7 mm. According to Kaya et al. (2008),[2] length of the AL showed the measurement to be 0.71 ± 0.21 mm greater in the panoramic radiographs than the spiral CT. Uchida et al. (2009)[12] found the mean value for samples with an AL to be 9 mm. Longest ALL was of 9 mm. Their finding is consistent with the findings of the present study, in which maximum length of ALL was seen in male, i.e., 8.8 mm. Parnia et al. (2012)[14] noticed the mean size of AL to be 3.54 mm, which is almost consistent with our finding. Li et al. (2013)[16] found the ALL of the entire population under study ranged from 0 to 5.31 mm. The longest AL measured in his study was 5.13 mm. There was no significant difference in ALL between sides. The ALL in males was significantly longer than in females, and this finding is consistent with our study also.

Strengths of the study

This is the first effort of its kind in North Indian population using the new imaging modality with relatively lower radiation exposure to patient called CBCT, which is not readily available everywhere. The findings of this study will help and add on to the policymakers and modern researchers to rely upon the efficacy of CBCT scans. The sample is of appreciable size to reinforce the efficacy and evaluation of CBCT in determining the prevalence and length of AL of IAN.

Limitations of the study

As this was a thesis research work and supposed to be completed within stipulated time interval, this study was conducted at one of the randomly selected diagnostic and research center catering mostly the patients from North India and surrounding regions. It would have been much better to include more than one center for the purpose of study. But because of the time constraint, it was not possible on behalf of the authors to do so. Otherwise, justice could have been done to generalize the findings of the current study on the whole North Indian population.


   Conclusion Top


Keeping all these facts in mind and since no such study has been conducted in North Indian population yet, the current study has been designed to evaluate the efficacy of CBCT in measuring the anterior looping of IAN by using CBCT. After analyzing the data, it has been concluded that CBCT has emerged as a better and proven diagnostic modality for evaluation of anterior looping and thereby fruitful in preoperative surgical planning. This study reinforces the use of CBCT to assist dental practitioners and or surgeons to localize the anterior looping and hence avoid injury to the neurovascular bundles and facilitate surgical, local anesthetic as well as other invasive procedures such as implant placement and chin bone harvesting, etc.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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Uchida Y, Noguchi N, Goto M, Yamashita Y, Hanihara T, Takamori H et al. Measurement of anterior loop length for the mandibular canal and diameter of the mandibular incisive canal to avoid nerve damage when installing endosseous implants in the interforaminal region: A second attempt introducing cone beam computed tomography. J Oral Maxillofac Surg 2009;67:744-50.  Back to cited text no. 12
    
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
 
 
    Tables

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



 

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