Assessment of Anatomical Variations of Mandibular Canal Depicted in Panoramic Radiography.

BACKGROUND: Anatomical variations of the mandibular canal play a vital role while performing surgical procedures affecting an area with mandibular canal course in the mandible. The neurovascular bundle may be severed during surgical procedures carried out mandible. AIMS AND
OBJECTIVES: The present retrospective study was aimed to assess and evaluate the mandibular canal and its variations on the panoramic radiography.
MATERIALS AND METHODS: The study included 88 randomly selected panoramic radiographs with complete mandible and associated bone. On a panoramic radiograph, the following parameters were assessed including bifid mandibular canal and location of bifurcation, the diameter of the mandibular canal as recorded in the first molar region, trabeculation in submandibular gland fossa, anterior loop measurement, direction and diameter of the bifid mandibular canal were all evaluated. Statistical analysis was done.
RESULTS: In 51 hemimandibles, the mandibular canal was found to be corticalized, whereas in 21.59% (n = 19), the mandibular canal was visible. In the remaining 20.45% (n = 18) of the study participants, the mandibular canal was not visualized. In the submandibular gland fossa region, diminished trabeculation was seen in 55.68% of the evaluated radiographs, whereas trabeculation was not seen at all in the remaining 23.86% of the subjects. A significant correlation was seen in decreased trabeculation of submandibular gland fossa and absence of the mandibular canal (P value < 0.001). The bifid mandibular canal was seen in 19.31% of the study participants (n = 17) with a mean width of 3.12 ± 1.1 mm. Extension of the anterior loop of the mental nerve was seen as up to 2 mm in majority participants in 67.04% individuals (n = 59).
CONCLUSION: The present study suggests that panoramic radiographs are a reliable tool for assessment of the mandibular canal and associated anatomical variations associated with it. Copyright:

INTRODUCTION

Mandibular canals are the anatomical structures present in the mandible as the name suggests. Mandibular canals are present bilaterally and are have their anatomical course from the mandibular foramen to the mental foramen. These canals carry the inferior alveolar nerves, veins, and arteries.[1] Although these canals have a specific anatomical position and content, various anatomical variations in the structure and course of mandibular canals are not rare. These variations commonly include bifid mandibular canals and anterior loops of the mental nerve. These anatomical variations play a vital role while performing surgical procedures affecting the area with mandibular canal course in the mandible. The neurovascular bundle may be severed during surgical procedures carried out mandible.[2]

Usually, the mandibular canals are a single structure.[3] However, in various individuals, these canals can show various variations in their anatomy including bifid canal, variation in shape (oval, round, or pear-shaped), anterior loop, bifurcation in the retro molar canal, etc. These variations if not identified in the preoperative assessment of mandibular areas, can lead to various complications in the operative and postoperative periods.[4]

The commonly affected dental procedures by the anatomical variations of the mandibular canals are the extractions (most common mandibular third molar), failure/poor implant-planning, and the procedures requiring bone manipulation.[5] Unawareness of various dentists regarding anatomic variations of the mandibular canal radiographically remains the most common reason for such failures. Hence, identification and awareness about various anatomical variations of the mandibular canal can help in the prevention of various complications that can arise during and after procedures of the mandibular region.[6]

In the recent past, studies in the literature have depicted that the presence of the bifid mandibular canals is not a rare finding, hence, their identification radiographically is important, and when in doubt, their presence should be confirmed using advanced three-dimensional radiographic techniques such as computed tomography (CT) and cone-beam tomography. Concerning the presence of the anterior loop in the mandibular canal, the data in the literature show a great variation with anterior extension from 0 mm to 9 mm and a prevalence range of 28%–71%.[7]

These anatomical variations of the mandibular canals require further understanding owing to the huge variation in the data published previously in the literature and to avoid severe complications including surgical procedures of the mandible including ineffective anesthesia, haemorrhage, and sensory disturbances, paraesthesia, and/or traumatic neuromas.[8] The present prospective study was aimed to assess and evaluate the mandibular canal and its variations on the panoramic radiography. Evaluation of the bifurcation and presence of loop anteriorly, if seen in mental nerve were also assessed. Trabeculation of the bone in the submandibular gland fossa and corticalization of the mandibular canals were also evaluated in the present trial.

MATERIALS AND METHODS

The present retrospective study was aimed to assess and evaluate the mandibular canal and its variations on the panoramic radiography. Evaluation of the bifurcation and presence of loop anteriorly, if seen in mental nerve were also assessed. Furthermore, trabeculation of bone in the submandibular gland fossa and corticalization of the mandibular canals were evaluated in the present trial.

The study included 88 randomly selected panoramic radiographs with complete mandible and associated bone. The included participants were within the age range of 20 years to 58 years with the age range of 36.4 years. The participants were advised panoramic radiographs by the treating dentists for various reasons. All the radiographs were visualized by two oral and maxillofacial radiologists. Any disagreement between the two radiologists was discussed ad a common conclusion was reached.

The study included participants with permanent dentition, both males 41% and females 59%. The exclusion criteria included participants with diseases affecting alveolar one (such as Paget's disease), with malformation in mandible, participants with deciduous dentition, and/or subjects having any tumor or cyst in the mandibular region. The panoramic radiograph was taken on tagged image file format using a flat LCD screen having the resolution value of 1280 × 800 pixels. The software was used to alter the contrast and brightness of the digital panoramic radiographs to allow better examination and interpretation of the mandibular canal of the radiographs. For better evaluation and assessment, the images were evaluated against a black background and in the absence of any other light to avoid any interference. Each hemimandible was evaluated by both the maxillofacial radiologists separately to better appreciate the mandibular canals and the associated parameters.

On a panoramic radiograph, the following parameters were assessed including bifid mandibular canal and location of bifurcation, the diameter of the mandibular canal as recorded in the first molar region, trabeculation in submandibular gland fossa, anterior loop measurement, direction and diameter of the bifid mandibular canal were all evaluated. Statistical analysis was done to evaluate the correlation between trabeculation of submandibular gland fossa and mandibular canal corticalisation. The collected data were evaluated and subjected to the statistical analysis.

RESULTS

The present retrospective study was aimed to assess and evaluate the mandibular canal and its variations on the panoramic radiography. Evaluation of the bifurcation and presence of loop anteriorly, if seen in the mental nerve were also assessed. Trabeculation of the bone in the submandibular gland fossa and corticalization of the mandibular canals were also evaluated in the present trial.

The study included 88 randomly selected panoramic radiographs with complete mandible and associated bone. The included participants were within the age range of 20 years to 58 years with the age range of 36.4 years. The study included participants with permanent dentition, both males 41% and females 59%. The demographic characteristics of the study subjects are listed in Table 1.

Table 1

Demographic characteristics of study participants

Characteristic	Value
Total participants (n)	88
Mean age (years)	36.4±2.6
Age range (years)	20-58
Males (n=36)	41%
Females (n=52)	59%

As observed in the region of the first mandibular molar, in most of the examined, 58% in total (n = 51) hemimandibles, the mandibular canal was found to be corticalized, whereas in 21.59% (n = 19), the mandibular canal was visible but no corticalization was noticed. In the remaining 20.45% (n = 18) of the study participants, the mandibular canal was not visualized. This detection of the mandibular canal in the study participants is summarized in Table 2.

Table 2

Diameters of mandibular canal in study participants as detected in the 1st molar region on panoramic radiograph

The diameter of the mandibular canal on panoramic radiograph	n (%)
Not detected radiographically	18 (20.45)
0-2 mm	19 (21.59)
2.1 mm-4 mm	51 (58)
4.1 mm-6 mm	0
>6 mm	0

Diminished trabeculation was seen in 55.68% of the evaluated radiographs, whereas trabeculation was not seen at all in the remaining 23.86% of the participants. Increased density of the alveolar bone in the mandibular region was seen in 5.68% of the included study participants. A normal pattern in the trabeculation was observed in 14.77% of the panoramic radiographs studied [Table 3].

Table 3

Correlation of mandibular canal corticalization and submandibular gland fossa trabeculation

Trabeculation pattern	n (%)
Decreased	49 (55.68)
Corticalization visible	31 (63.26)
Corticalization not visible	18 (36.73)
Not visible	21 (23.86)
Corticalization visible	6 (28.57)
Corticalization not visible	15 (71.42)
Increased	5 (5.68)
Corticalization visible	5 (100)
Corticalization not visible	-
Normal	13 (14.77)
Corticalization visible	9 (69.23)
Corticalization not visible	4 (30.76)

In the present study, a significant correlation was seen in decreased trabeculation of submandibular gland fossa and absence of mandibular canal (P < 0.001). The bifid mandibular canal was seen in 19.31% of the study participants (n = 17), and the majority of the bifid canals were associated with the presence of extramental foramen. The position of bifurcation was also assessed, and it was seen that bifurcations were seen in the posterior mandible near the angle of the mandible. The average mean width of the bifid mandibular canal was found to be 3.12 ± 1.1 with the range of 1.02 to 3.4 mm.

The study also evaluated the presence of mental nerve, its loop anteriorly, and its extension on the assessed panoramic radiographs. The assessed results are listed in Table 4 where the extension of the anterior loop of the mental nerve was seen as up to 2 mm in the majority of participants in 67.04% individuals (n = 59).

Table 4

Anterior loop of the mental nerve seen on panoramic radiographs

Extension of the anterior loop	n (%)
Up to 2 mm/not visible	59 (67.04)
2.1 mm-4mm	17 (19.31)
4.1 mm-6mm	6 (6.81)
>6 mm	1 (1.13)
Not clear	5 (5.68)

DISCUSSION

The present clinical trial was aimed to assess and evaluate the mandibular canal and its variations on the panoramic radiography. Evaluation of the bifurcation and presence of loop anteriorly, if seen in mental nerve were also assessed. Furthermore, trabeculation of bone in the submandibular gland fossa and corticalization of the mandibular canals were evaluated in the present trial.

The bifid mandibular canal was seen in 19.31% of the study participants (n = 17), and the majority of the bifid canals were associated with the presence of extramental foramen. The results found here were in contrast against the studies by Sanchis et al.[9] in 2003 where authors reported <1% detection of the bifid canals on the panoramic radiography, whereas the results of the present trial were also in disagreement with the study by Naitoh et al.[10] in 2009 and Kuribayashi et al.[11] in 2010 where authors on their cone beam CT (CBCT) study reported the presence of bifid canal in up to 65% of assessed cases. This shows greater accuracy of the 3D imaging over conventional radiography in the detection of bifid canals. The average mean width of the bifid mandibular canal was found to be 3.12 ± 1.1 with the range of 1.02 mm to 3.4 mm. Similar findings were reported by Kuribayashi et al.[11] in 2010 where the diameter of the bifid canal ranged from 0.9 to 3.4 mm.

The results showed that trabeculation in the region of submandibular gland region was significantly less as compared to other regions. In 20.455% of study participants, the mandibular canal was not visible. In 58% of study participants, 2.1–4 mm diameter was seen in the first molar region. Similar results were shown by the study of Oliveira-Santos et al.[12] in 2011 where 66% of the canals were visible.

CONCLUSION

The present study suggests that panoramic radiographs are a reliable tool for the assessment of the mandibular canal ad associated anatomical variations associated with it. Furthermore, panoramic radiographs are suggested for detailed evaluation and identification of bifid mandibular canals before any surgical procedures to avoid postoperative complications. However, the present study had few limitations as conventional radiography to properly show these anatomical variations as compared to CT and CBCT. Furthermore, the study had a smaller sample size about a particular geographical area.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.