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Table of Contents   
ORIGINAL RESEARCH  
Year : 2020  |  Volume : 31  |  Issue : 2  |  Page : 197-202
The location of the inferior alveolar nerve in the malaysian population: Implications for dental implant planning


1 School of Dentistry, International Medical University, Kuala Lumpur, Malaysia
2 Perdana University School of Foundation Studies, Perdana University, Serdang, Malaysia
3 Medical Genetics Laboratory, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang; Department of Biological Sciences, School of Science and Technology, Sunway University, Sunway, Malaysia

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Date of Submission01-Oct-2017
Date of Decision17-Jul-2018
Date of Acceptance09-Jan-2019
Date of Web Publication19-May-2020
 

   Abstract 


Background: The location of the inferior alveolar nerve (IAN) is generally constant in fully grown mandibles. If we know its average distance from the lower border of the mandible, available bone length from the crest of the edentulous ridge can be estimated by physical measurement of the whole length of mandible in that area. This study aimed to measure the superio-inferior distance of the inferior alveolar nerve (SIDIAN) from the base of the mandible in posterior regions on the right and left side based on cone-beam-computed tomography (CBCT) scans and to evaluate gender and ethnicity-related variations in the Malaysian population. Materials and Methods: A total of 100 CBCT-Digital Imaging and Communications in Medicine files of the patients of 3 ethnic populations (Malay, Chinese and Indian) between the ages of 18 and 80 years were selected for the study. The files were imported onto the iCAT software. The measurements of the SIDIAN to the lower border of the mandible in molar regions were done on both sides. The data was analysed using t-test, one-way analysis of variance test, and correlation coefficient test via the SPSS software. Results: Statistically significant positive correlations were identified between the SIDIAN from the lower border of the mandible in the first and second molar regions within the same side as well as between both sides of the mandible (r ≈ 0.8). There were no statistically significant differences between genders. However, there were statistically significant differences on both molar regions and on both sides in all three ethnic groups (P < 0.05). In general, the SIDIAN from the lower border of the mandible was greatest amongst Chinese and smallest amongst Indians. Conclusions: The strong positive correlations on both sides of the mandible indicate the presence of symmetry. Ethnicity-related variations exist in terms of the location of the IAN in the mandible.

Keywords: Dental implants, implant osteotomy, inferior alveolar nerve, mandibular landmarks, nerve injury

How to cite this article:
Kumar SR, Patil PG, Choy CS, Veerakumarasivam A. The location of the inferior alveolar nerve in the malaysian population: Implications for dental implant planning. Indian J Dent Res 2020;31:197-202

How to cite this URL:
Kumar SR, Patil PG, Choy CS, Veerakumarasivam A. The location of the inferior alveolar nerve in the malaysian population: Implications for dental implant planning. Indian J Dent Res [serial online] 2020 [cited 2020 Jul 9];31:197-202. Available from: http://www.ijdr.in/text.asp?2020/31/2/197/284577



   Introduction Top


The inferior alveolar nerve (IAN) enters the mandible from the lingula (medial side of the ramus of the mandible) and passes through the mandibular canal before exiting the mental foramen. These IAN branches form the network of nerve fibers known as the inferior dental plexus that supplies the teeth with sensory innervation. With the help of 3D scans, clinicians can precisely diagnose and formulate a treatment plan involving dental implants. A cone-beam-computed tomography (CBCT) evaluation is the most common diagnostic tool in implantology practice.[1] The IAN is susceptible to iatrogenic injury during implant osteotomy.[2] This nerve is also susceptible to injury during various other dental procedures such as the administration of local anesthetic, endodontics, third molar surgery and other surgical interventions. Damage to the IAN can result in anesthesia, paresthesia, pain, or a combination of these symptoms. Therefore, determining the precise position of the IAN is important.[3] In a study of 29 adults with natural dentition, it was found that the IAN is positioned about 1 cm above the inferior border of the mandible.[3] On average, the distance from the apex of the mandibular first and second molars to the IAN ranges between 3.5 and 5.4 mm. Even a single millimeter could be the difference between injury and a successful implant placement.[4] The current recommendation is to allow a safety zone of 1–2 mm upon review of radiographs prior to implant osteotomy.[5],[6]

Knowing the superio-inferior distance of the inferior alveolar nerve (SIDIAN) from the base of the mandible in the molar regions is potentially helpful in estimating the available bone height in the targeted region above the IAN (safe zone). Apart from routine diagnostic evaluation, CBCT helps in measuring various anatomical structures in the jawbone and the data obtained can be used to determine baseline data for specific populations. Although CBCT can accurately determine the safe zone, this technology is not always available in many dental clinics. In addition, CBCT analysis requires trained radiographers who are not necessarily available in all dental clinics. CBCT also poses a health hazard in certain high-risk individuals due to the radiation exposure.

A study in the Mexican population observed that the average length of the anterior loop ranged between 0 and 6.68 mm, with a mean of 2.19 mm with no significant differences between the left and right sides or between men and women.[7] In another study in California, the mean anterior loop length was 1.46 ± 1.25 mm with no statistically significant differences between the right and left sides or different gender groups as well.[2] Thus, while these parameters may not significantly differ within a specific population, they may vary from one population to another. However, studies measuring the SIDIAN from the lower border of the mandible are limited to date. Since no baseline data for the various stratified parameters in the Malaysian population exist in the literature, this study aimed to measure the SIDIAN from the lower border of the mandible in CBCT scans and to evaluate if gender and ethnicity-related variations exist in the Malaysian population.

By determining the SIDIAN from the lower border of the mandible, the safe zone can be calculated by simply subtracting this value from the total width of the mandible (measured clinically) in the proposed site of implant osteotomy. By identifying correlations between gender and/or ethnicity with the SIDIAN from the lower border of the mandible, clinicians may simply calculate the safe zone for implant osteotomy in the posterior mandible without the need for multiple radiographs and CBCT scans.


   Materials and Methods Top


Institutional ethics committee approval for the study was obtained to allow the use of the CBCT-Digital Imaging and Communications in Medicine (DICOM) files for the measurements. A total of 100 CBCT-DICOM files of patients were obtained from the clinic. The sample size (n = 100) was calculated with a 5% margin of error and 95% confidence level from the pool of total 134 CBCTs (equal number of Malay, Chinese, and Indian patients available in the clinic) using the online “Raosoft” sample-size calculator. The patients were selected based on the following inclusion and exclusion criteria. Healthy dentate or edentulous Malay, Chinese, and Indian patients between the ages of 18 and 80 with a median age of 30 years were selected. Patients with a history of trauma or pathology of the mandible, syndrome conditions, congenital or developmental disorders, and surgical intervention of the mandible were excluded. Reformatted CBCT images are those that appear distorted or blurred due to patients' movements were also excluded from this study. Patients with mixed racial origins were also excluded from the study.

The DICOM data were imported into the iCAT software for image processing and analysis. All the measurements were performed by a single researcher to maintain consistency. The anatomy of the whole mandible was evaluated from the axial, coronal cross-sectional, and panoramic views. The visible IAN, mental foramina, and anterior loop of the mental nerve image were drawn onto the scan using the “draw nerve” tool [Figure 1]. The upper border of the IAN canal was identified. The mesiodistal center of the first (T1) and second premolars (T2) and the first (T3) and second molars (T4) were identified as shown in [Figure 2]. If edentulous space exists in some or all the four teeth mentioned, the center of the edentulous space was identified at the crest of the ridge. The cross-section view of all these four centers (T1, T2, T3, and T4) was used to locate the upper edge of the IAN canal (I1, I2, I3, and I4) and the lower border of the mandible (M1, M2, M3, and M4) as shown in [Figure 2]. Slight modifications were made in the location of the mesiodistal center to compensate for the natural angulation of the tooth, especially in the premolar region. The vertical distances between the IAN and the lower border of the mandible at all given cross-sections (IM1, IM2, IM3, and IM4) were measured. The distances between I and M (IM1, IM2, IM3, and IM4) at four different cross-sections T1, T2, T3, and T4 on the left side were measured [Figure 2] and [Figure 3]. Similar measurements were repeated on the right side of the mandible.
Figure 1: Estimation of IAN nerve canal

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Figure 2: Highlighted area showing how measurements were made in the determination of the SIDIAN from the lower border of the mandible in premolar and molar regions on the left side

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Figure 3: Actual measurement of the SIDIAN from the lower border of the mandible in the premolar and molar regions

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All statistical data analysis was performed using SPSS software version 24.0 (IBM Corporation, USA). Student's t-test was used (a = 0.05) to compare the differences in the mean values of the SIDIAN from the base of the mandible in the premolar and molar regions across different genders and ethnicities as well as between both sides. One-way analysis of variance test was performed to compare the differences in the mean values of the SIDIAN from the base of the mandible in the premolar and molar regions across different ethnicities (Chinese, Malay, and Indian). A post-hoc test using Tukey's Honestly Significant Difference (HSD) statistics was performed to identify subgroups with significant mean differences. The correlation coefficients of the molars between and within the right and left sides were also measured.


   Results Top


Of the 100 patients recruited in this study, 48 were males and 52 were females. In the context of ethnicity, 34 of them were Malays, 35 Chinese, and 31 Indians [Table 1]. The descriptive findings of the measurements of the SIDIAN are summarized in [Table 2]. The results showed that there was a statistically significant correlation in the SIDIAN between the first and second molar regions on both sides [Figure 4]a and [Figure 4]b. In addition, there were also statistically significant correlations between the SIDIAN from the lower border of the mandible of the first and second molar regions between the left and right sides, indicating symmetry [Figure 4]c and [Figure 4]d. There was no statistically significant difference in the SIDIAN from the lower border of the mandible in the molar regions on both the left and right sides between males and females [Figure 5]. However, the SIDIAN from the lower border of the mandible in the molar regions was statistically significantly different between the Chinese and Indian ethnic groups [Table 3], [Figure 6]. There were statistically significant differences between the Malays and Indians in the first molar region on the left side and between the Malays and Chinese in the second molar region on the right side.
Table 1: Demographic statistics of the patients included in the study

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Table 2: Description of the measurements between the inferior alveolar nerve and the lower border of the mandible

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Figure 4: (a) There is correlation between the SIDIAN from the lower border of the mandible in the first and second molar regions on the left side (L1 vs. L2) with a correlation coefficient, r = 0.784 (P < 0.05). (b) There is correlation between the SIDIAN from the lower border of the mandible in the first and second molar regions on the right side (R1 vs. R2) with a correlation coefficient, r = 0.837 (P < 0.05). (c) There is correlation between the left and right side measurements of the SIDIAN from the lower border of the mandible in the first molar regions (L1 vs. R1) with a correlation coefficient, r = 0.840 (P < 0.05). (d) There is correlation between the left and right side measurements of the SIDIAN from the lower border of the mandible in the second molar regions (L2 vs. R2) with a correlation coefficient, r = 0.828 (P < 0.05)

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Figure 5: (a) Mean difference in the SIDIAN from the lower border of the mandible in the first molar region on the left side. (b) Mean difference in the SIDIAN from the lower border of the mandible in the first molar region on the right side. (c) Mean difference in the SIDIAN from the lower border of the mandible in the second molar region on the left side. (d) Mean difference in the SIDIAN from the lower border of the mandible in the second molar region on the right side

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Table 3: Ethnicity.stratified mean differences in the SIDIAN from the lower border of the mandible in the molar region

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Figure 6: (a) Mean difference in the SIDIAN from the lower border of the mandible in the first molar region on the left side was statistically significantly different between Malay and Indian (P < 0.05) as well as between Chinese and Indian (P < 0.05) ethnic groups. (b) Mean difference in the SIDIAN from the lower border of the mandible in the first molar region on the right side was statistically significantly different between Chinese and Indian (P < 0.05) ethnic groups. (c) Mean difference in the SIDIAN from the lower border of the mandible in the second molar region on the left side was statistically significantly different between Chinese and Indian (P < 0.05) ethnic groups. (d) Mean difference in the SIDIAN from the lower border of the mandible in the second molar region on the right side was statistically significantly different between Malay and Chinese (P < 0.05) as well as between Chinese and Indian (P < 0.05) ethnic groups. (*indicates a statistically significant difference between two ethnic groups, P < 0.05)

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   Discussion Top


There was no statistically significant difference between males and females in the context of mean difference in the SIDIAN in the molar region on the left and right sides. There was also a strong correlation between the left and right measurements of SIDIAN. This is the first report on these findings. In all three ethnic groups, namely, Malays, Chinese and Indians, the SIDIAN measurements between left and right sides showed statistically significant differences. However, there was also a statistically significant difference between the Malay and Indian ethnic groups in the first molar region on the left side as well as between the Chinese and Malay ethnic groups in the second molar region on the right side. The variables, namely, gender, ethnicity, and symmetry are essential precursors that may be used to develop methods to address the problem statements stated earlier and provide an easier and cheaper alternative to CBCT; especially when CBCT is unavailable. However, because some of the variables such as gender and sides (both right and left) did not show statistically significant differences, we may need to find additional anthropometric variables such as height, body mass index and mandible dimensions.

For this study, the premolar region was not considered for measurements because in all cases analyzed, the IAN did not reach the first premolar, thus making this measurement impossible. Similarly, the second premolar region was also not included because the SIDIAN from the lower border of the mandible in the second premolar region on the right and left sides could not be measured in the majority of cases. This was because the vertical measurements from the mesiodistal center could not be extrapolated to locate the upper border of the IAN. This is due to the natural angulation of the tooth as well as tooth drifting. However, measurements could be made for the second premolar region in cases where the IAN extended beyond the 2nd premolar right before looping anteriorly, but these measurements were not included in the statistical analysis. However, we intend to record the angulated measurements following the natural angulation of the tooth of the superior–inferior distance of the upper border of the anterior loop to the lower border of the mandible as an additional measurement in the future. This measurement may be useful for implant placements in the second premolar region as IAN loops anteriorly at this region in the majority of the cases.

There were few limitations faced while recording the measurements in this study. The drifting of the teeth (E.g. First molar drifts to the second premolar region) as well as a wide variation in the angulation of the teeth may result in the wrong estimation of the vertical line drawn from the mesiodistal center to locate the upper body of the IAN. As a result, the SIDIAN will be wrongly predicted. Modification of the mesiodistal center was done in cases of moderate angulation, whereas severely angulated cases were not used. Even cases with significant drifting were not taken into account.

Even though the CBCT is a gold standard, it is not always available in some places and clinicians depend upon conventional diagnostic measures such as the combination of intraoral radiographs and bone-sounding procedures. The findings from this study may help in providing adjunct information in such situations to enhance the accuracy of implant planning. Although the SIDIAN is symmetrical on both sides and ethnicity-related variations were identified, this preliminary information should not be extrapolated to make clinical decisions until the findings from this study are validated in a larger cohort.


   Conclusions Top


Within the limitations of this study, the following conclusions can be drawn:

  1. Strong positive correlations on both sides of the mandible indicate the presence of symmetry.
  2. Ethnicity-related variations exist in terms of the location of the IAN in the mandible.


Acknowledgments

Authors thank Ms Choi Wan for her assistance in operating the iCAT software.

Financial support and sponsorship

This study was supported completely by SSM Research Grant from the International Medical University, Kuala Lumpur, Malaysia, grant number BDS I-01-13 (05) 2016.

Conflicts of interest

There are no conflicts of interest.



 
   References Top

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2.
Lu CI, Won J, Al-Ardah A, Santana R, Rice D, Lozada J. Assessment of the anterior loop of the mental nerve using cone beam computerized tomography scan. J Oral Implantol 2015;41:632-9.  Back to cited text no. 2
    
3.
Alhassani AA, Al-Ghamdi AST. Inferior alveolar nerve injury in implant dentistry: Diagnosis, causes, prevention, and management. J Oral Implantol 2010;36:401-7.  Back to cited text no. 3
    
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Gowgiel JM. The position and course of the mandibular canal. J Oral Implantol 1991;18:383-5.  Back to cited text no. 4
    
5.
Kushnerev E, Yates JM. Evidence-based outcomes following inferior alveolar and lingual nerve injury and repair: A systematic review. J Oral Rehab 2015;42:786-802.  Back to cited text no. 5
    
6.
Worthington P. Injury to the inferior alveolar nerve during implant placement: A formula for protection of the patient and clinician. Int J Oral Maxillofac Implants 2004;19:731-4.  Back to cited text no. 6
    
7.
Juan DV, Grageda E, Crespo SG. Anterior loop of the inferior alveolar nerve: Averages and prevalence based on CT scans. J Prosthet Dent 2016;115:156-60.  Back to cited text no. 7
    

Top
Correspondence Address:
Dr. Pravinkumar G Patil
Division of Clinical Dentistry, School of Dentistry, International Medical University, Jalan Jalil Perkasa- 19, Bukit Jalil, Kuala Lumpur - 57000
Malaysia
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijdr.IJDR_553_17

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    Figures

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