|Year : 2020 | Volume
| Issue : 2 | Page : 23-29
Evaluation of mandibular incisive canal and its relationship to adjacent anatomical landmarks using cone-beam computed tomography
P Ramaswamy, Ch Sai Kiran, B Mrudula Raju, Myla Swathi, Goteti Elizabeth Sharanya
Department of Oral Medicine and Radiology, St. Joseph Dental College, Eluru, Andhra Pradesh, India
|Date of Submission||24-Jul-2020|
|Date of Decision||21-Aug-2020|
|Date of Acceptance||09-Sep-2020|
|Date of Web Publication||5-Oct-2020|
Goteti Elizabeth Sharanya
Department of Oral Medicine and Radiology, St. Joseph Dental College, Eluru, Andhra Pradesh
Source of Support: None, Conflict of Interest: None
Introduction: One of the most common accidental complications that occur during surgical procedures in the mandibular interforaminal region is the numbness of the chin and lower lip. This happens when vital structures such as the mental foramen, the mandibular incisive canal (MIC) and the anterior loop of the inferior alveolar nerve are not properly identified and protected. orthopantomogram has the least accuracy in identifying this structure. Hence, a better image such as computed tomography or cone-beam computed tomography (CBCT) should be used in the inter-mental foramen area. Aim: The aim is to assess the presence, position, and dimensions of MIC and its relationship to adjacent anatomical landmarks using CBCT. Materials and Methods: A total of 50 patients with 100 MICs of age 20–70 years are studied, and the collected data were subjected to statistical analysis. Results: Statistically significant result was obtained with the MIC to root tip of canine, MIC to lower cortex, MIC to buccal cortical plate, and diameter of MIC with regard to gender, which is more in males. MIC is more toward the buccal plate, and there is no statistically significant difference between the right and left sides. The diameter of MIC is larger in males compared to females and larger on left side compared to right side. Conclusion: Analyzing MIC using CBCT scans can be a useful tool in avoiding implant surgical complications in the anterior mandible.
Keywords: Cone-beam computed tomography, dental implants, diagnosis, mandible, prospective study
|How to cite this article:|
Ramaswamy P, Kiran CS, Raju B M, Swathi M, Sharanya GE. Evaluation of mandibular incisive canal and its relationship to adjacent anatomical landmarks using cone-beam computed tomography. J Oral Maxillofac Radiol 2020;8:23-9
|How to cite this URL:|
Ramaswamy P, Kiran CS, Raju B M, Swathi M, Sharanya GE. Evaluation of mandibular incisive canal and its relationship to adjacent anatomical landmarks using cone-beam computed tomography. J Oral Maxillofac Radiol [serial online] 2020 [cited 2020 Nov 25];8:23-9. Available from: https://www.joomr.org/text.asp?2020/8/2/23/297219
| Introduction|| |
Surgical procedures in the lower anterior region of the mandible, including dental implant placement, orthognathic surgeries, lowering genial spines procedures of edentulous patients, and bone grafting, have become more frequent. This area has usually been considered as “surgical safe zone” because of the absence of vital superficial nerves or vessels. There are recent reports of sublingual hematoma after genioplasty, unexplained bleeding, pain, discomfort, and sensory disturbances, failure of osseointegration of implants during or after surgical procedures in the interforaminal region of the mandible. Therefore, detailed knowledge of the anatomy of nerves is crucial for proper surgical procedures performed on the mandibular anterior region.
Prolongation of the mandibular canal anterior to the mental foramen is a mandibular incisive canal (MIC), and it contains the neurovascular bundle. The MIC continues its intraosseous pathway into the mandibular anterior region and provides innervations to the mandibular anterior teeth and canines. Several authors believe that the incisive nerve runs through the intramedullary spaces and not within a bony canal; therefore, it is uncommonly detected by conventional radiography.
Furthermore, anatomical studies using advanced imaging have shown strong evidence supporting the existence of the MIC, located mesially to the mental foramen, smaller in diameter, and less corticalized than the mandibular canal containing the neurovascular bundle.
Cone-beam computed tomography (CBCT) is an excellent imaging system for oral and maxillofacial applications. The advantages of CBCT-based systems include uniform magnification, a high-contrast image with a well-defined image layer free of blurring, easier identification of bone grafts or hydroxyapatite materials used to augment maxillary bone in the sinus region, multiplanar views, three-dimensional (3D) reconstruction, the simultaneous study of multiple implant sites, and the availability of software for image analysis, low radiation dose as compared to computed tomography (CT). Several authors have reported that measurements and dimensional accuracy are more precise when using CBCT scans over any other radiographic techniques.
To locate the MIC, measuring its length and width and describing its course and its relationship to other anatomical structures should become mandatory for surgeons who mostly rely on the clinical and radiographic sign for preoperative information concerning the vital structures in the area of the symphysis. The topographic anatomy may show anatomical variations that can go unnoticed on the 2D images. With the help of CBCT, the prevalence and incidence, location, course, and type of the incisive canal in the anterior mandible can be easily mapped and thus helps the surgeon to its presence during surgery.
Assess the dimensions of MIC and its relationship to adjacent anatomical landmarks using CBCT.
The objective is to explore the ability of the CBCT to provide information regarding the dimensions of the MIC with adjacent anatomical landmarks.
| Materials and Methods|| |
This prospective study was conducted in the department of oral medicine and radiology after obtaining ethical committee clearance (CEC/01/1/2020-21). The importance of the study was explained to each patient, and the study sample was selected only upon their acceptance. Inclusion criteria include A total of 50 patients of both the genders of age between 20 and 70 years CBCT images of the entire mandible from the anterior two-thirds of the ramus on the right side to the anterior two-third of the ramus on the left side, with the presence of canines and 1st premolars bilaterally. Exclusion criteria include patients below and above 20–70 years of age, pregnant and lactating mother, congenitally disorders, patients with a history of trauma, pathology or surgical intervention in the interforaminal region, distorted or blurred images due to patients' movements, patient with a history of systemic illness.
Patients were subjected to CBCT scans, which were acquired from Care stream 9300 unit 4 mA current, 90 kV, exposure time 8 s, 180 μmvoxel size, 10 × 5 field of view (FOV) [Figure 1]. An obtain scan was evaluated for the MIC and its spatial relationship with adjacent vital structures. First, the incidence of MIC was noted on the panoramic image of the CBCT scan; then, it is marked with a nerve tracking tool. Next, it is confirmed in the transaxial sections of the CBCT scan [Figure 2]. The length of the MIC can be done in two methods. First, the visible length of the canal was measured from the mesial aspect of the mental foramen to the most mesial location that was visible on the panoramic reconstruction view of CBCT scans [Figure 3]. Second, in the transaxial section of the CBCT, five sections were taken with the starting point noted at the mental foramen region. The section was multiplied with slice thickness, and the resultant value was the precise length of MIC [Figure 4].
|Figure 2: Mandibular incisive canal noted on the panoramic image cone-beam computed tomography scan. Next, it is confirmed in the transaxial sections|
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|Figure 3: Visible length of the canal measured from the mesial aspect of the mental foramen to the most mesial location that was visible on the panoramic reconstruction view of cone-beam computed tomography scans|
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|Figure 4: Transaxial section of the cone-beam computed tomography, five Sections were taken with the starting point noted at the mental foramen region. The section was multiplied with slice thickness, and the resultant value was the precise length of mandibular incisive canal|
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For measuring the spatial relationship of MIC with adjacent anatomic structures, five measurements were done on the sagittal section of 1st premolar and canine bilaterally.
- MIC to root tip of canine and premolar: From the inner side of the upper cortical border of the MIC to the root tip of 1st premolar and canine [Figure 5]
- MIC to lower cortex: From the inner side of the inferior cortical border of the MIC to the outer portion of the inferior cortical border of the mandible [Figure 6]
- MIC to buccal plate: From the inner side of the buccal side of the cortical border of the MIC to the outer side of the buccal plate [Figure 7]
- MIC to lingual plate: From the inner side of the lingual cortical border of the MIC to the outer portion of the lingual border [Figure 8]
- The diameter of the canal: The longest distance between the inner cortical borders of the canal [Figure 9].
|Figure 5: From the inner side of the upper cortical border of the mandibular incisive canal to the root tip of 1st premolar and canine|
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|Figure 6: The inner side of the inferior cortical border of the mandibular incisive canal to the outer portion of the inferior cortical border of the mandible|
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|Figure 7: From the inner side of the buccal side of the cortical border of the mandibular incisive canal to the outer side of the buccal plate|
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|Figure 8: From the inner side of the lingual cortical border of the mandibular incisive canal to the outer portion of the lingual border|
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|Figure 9: The longest distance between the inner cortical borders of the canal|
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Obtained values were entered in the excel sheet and subjected to statistical analysis using SPSS software.
| Results|| |
Out of 100 MICs, 54 canals were seen in female patients, and 46 canals were seen in male patients. Group statistics were done between male and female patients, which shows the statically significant difference for MIC to root tip of canine, MIC to lower cortex, MIC to buccal cortical plate, and the diameter of the MIC, i.e., P value 0.037, 0.001, 0.037, and 0.046, respectively [Table 1].
[Graph 1] shows the length of MIC to the root tip of canine and its frequency in males and females. More female patients show a length of 6–8 mm, and more number of male patients show a length of 4–6 mm, and the maximum length in female patients was 10–12 mm, and the maximum length in the male patients was 8–10 mm [Graph 1].
[Graph 2] shows the length of MIC to lower cortical border and its frequency in males and females. More number of female patients show a length of 8–9 mm, which is the maximum length, and more number of male patients shows the length of 6–8 mm maximum length in the male patients was 10–12 mm [Graph 2].
A graph was drawn between the length of MIC to buccal cortical plate and frequency in males and females. More number of male and female patients shows a length of 3–4 mm maximum length in the male and female patients was 6–7 mm [Graph 3].
[Graph 4] shows the diameter of MIC and frequency in males and females. More number of patients shows the diameter of 1.5–2 mm with a maximum diameter of 3.5–4 mm in male and 3–3.5 mm in female patients [Graph 4].
Group statistics were done between right and left side, which shows the statistically significant difference with respect to the diameter of MIC for which the mean value was more on the left side compared to the right side, and its P = 0.044 [Table 2].
A graph was drawn between the diameter of the MIC and the frequency between the right and left sides. More number of cases show a diameter of 1.5–2.0 mm, and the maximum diameter noted on the left side was 3.5–4.0 mm, and the maximum diameter noted on the right side was 2.0–2.5 mm [Graph 5].
Paired sample statistics were done to check the difference between the two methodologies used to measure the length of MIC (visible length of MIC and MIC measured in the transaxial section). No statistically significant difference was evident between both the methods used to measure the length of MIC. Hence, both methods can be used to measure the length of MIC [Table 3].
|Table 3: Paired sample statistics were done to check the difference between the two methodologies used to measure the length of mandibular incisive canal|
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| Discussion|| |
Some authors found the MIC, which is a continuation of the mandibular canal. In some instances, neurovascular bundles may run through intertrabecular spaces of the cancellous bone of the chin. Obradovic et al. examined mandibles of 105 cadavers and confirmed the presence of a clearly defined MIC mesially from the mental foramen in 92% of the 70 dentate mandibles, but they found only 31% MIC in 30 edentulous mandibles. The canal diameter ranged from 0.48 mm to 2.9 mm, whereas in our study diameter of the canal ranged from 1 mm to 4 mm. Mraiwa et al. examined 50 cadavers' mandibles and concluded that MIC was observed in 96% of mandibles, and the mean inner diameter of the canal was 1.8. The MIC was located on average 9.7 mm from the lower cortical border; in our study, canal to lower cortical border has a distance of 8–9 mm. Jacobs et al. examined 230 spiral CT scans and identifies MIC in 93% of the cases, with excellent visibility in 22% of the cases. Mean vertical diameter, buccolingual diameter, and an inner diameter of the MIC were 4.7, 3.7, and 1.1 mm, respectively.
In 2009, Uchida etal., stated that MIC has a diameter ranged from 1.0 to 6.6 mm, which was confirmed using CBCT in 4 cadavers and anatomy in 71 cadavers' mandibles. Jacobs etal., reported that the MIC was identified only in 15% of the 545 panoramic radiographs, with excellent visibility in only 1% of cases. On the contrary, the canal was observed on 93% of cases using CT scans. Pires et al. showed that all MIC parameters are better determined by CBCT imaging rather than by panoramic radiography. They found MIC in 83% of the CBCT scans (n = 89), but only 11% of the panoramic radiographs showed the presence of MIC. Therefore, it is recommended to use CBCT images for better imaging of the interforaminal area.
A study conducted by Pires et al. conclude that the range of the MIC diameter was from 0.4 mm to 4.6 mm × 3.2 mm, The mean length of the MIC was 7 ± 3.8 mm, the distance from the canal to the lower cortex was 10.2 ± 2.4 mm, and the mean distance to the buccal cortical plate was 2.4 mm. The tooth apex-canal distance (in dentate subjects) was 5.3 mm, whereas in our study canal diameter ranged from 1 mm to 4 mm, the mean length of the canal was 13 mm ± 3 mm, the distance from the canal to the lower cortex was 7 mm ± 1.5 mm, mean distance to the buccal plate was 3.5 ± 1.5 mm, and root tip to canal distance was 6 mm ± 2 mm. In the case of large MIC, a patient can experience discomfort during osteotomy development precluding implant placement or experience postoperative pain requiring implant removal.
In the past decade, CBCT has perhaps been one of the most revolutionary innovations in the field of dentistry, and it provides a novel platform for imaging of the maxillofacial area., In terms of its clinical significance, CBCT provides an outstanding tool for precise diagnosis, more predictable treatment planning, more efficient patient education and management and improved treatment outcome, and patient satisfaction., The radiation dose in CBCT is significantly lower than medical CT but generally higher than conventional dental radiography. The Sedentexct working group projected provisional evidence-based selection criteria with indications in clinical use, as to when CBCT should be performed.
CBCT should be used only when the clinical question cannot be answered by conventional radiography, and the FOV must be limited to the region of interest. Ideally, the CBCT machine should be able to offer a choice of various volume sizes to reduce patients' radiation exposure levels. A risk-benefit analysis must be performed on each patient when CBCT is being considered.
In this study, statistically significant result was obtained with the MIC to root tip of canine, MIC to lower cortex, MIC to buccal cortical plate and diameter of MIC with regard to gender, which is more in males compared to females.
MIC is more toward the buccal plate, and there is no statistically significant difference between right and left side, which is in accordance with Tirumala Ravali et al. except for the diameter of MIC, which is higher in male and on the left side.
Apostolakis and Brown et al. concluded that the MIC is in closer proximity to the buccal plate (4.62 ± 1.41 mm), which is in accordance with the present study.
Yovchev et al. concluded that the diameter of MICs in males is wider than in females. This was in accordance with the present study.
Interestingly, we have done two methods to measure the length of MIC, and we could not find any statistically significant difference in both the methods used to measure the length of MIC, so both methods can be used to measure the length of MIC.
| Conclusion|| |
MIC is a normal but RARE variant in CBCT. The variation in diameter and distance up to the cortical bone suggested that preoperative evaluation of the MIC should be carried out for every case, using CBCT. MIC is more close to the buccal cortical plate so that implants can be placed toward lingual side.
Shorter length of implants should be planned as MIC is near to the lower cortex of the mandible. Paramount care has to take while planning implants in LEFT SIDE, particularly in MALES.
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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], [Figure 6], [Figure 7], [Figure 8], [Figure 9]
[Table 1], [Table 2], [Table 3]