Evaluation of Mandibular Canal Anatomy, Variations, and its Classification in Panoramic Radiographs: A Retrospective Study

INTRODUCTION

Oral surgical procedures such as exodontia of mandibular third molars, osteotomy, bone remodeling, and implant placement involve the risk of injuring the mandibular alveolar nerve, buccal nerve, and lingual nerve, with consequent transient or permanent paresthesia.¹ Knowledge about the mandibular canal is essential to decrease the rate of surgical complications.²

The mandibular canal contains its nerve, artery, and vein.³ It runs downward and forward in the ramus of the mandible, and then horizontally forward in the body of the mandible, where it is placed under the small openings.

An orthopantomogram (also commonly known as panoramic radiography) is a 2D representation of a 3D structure and plays a specific role in dentistry.⁴

The mandibular canal is best viewed in CBCT than in OPG. Advantages of OPG over CBCT include patient exposure being low, valuable aid in patient education, cost-effectiveness, and easily available in all dental hospitals.⁴ Taking into consideration of advantages of OPG and easy availability, the study was conducted using the OPGs of the patients who visited Karpaga Vinayaga Institute of Dental Sciences for the past 5 years from the population age of 14 years and above.

Radiographically, the mandibular canal appears as a tube-like passage, a radiolucent area surrounded by two radiopaque lines below mylohyoid lines.⁴ The presence of an accessory canal is called bifid. Since bifid is not common among all individuals, dentists should be aware of its presence to avoid further complications after and during surgical procedures and implants.⁴ Some of the complications are unexpected bleeding, nerve damage, and inadequate anesthesia. Some of the complications that occur after surgery include paresthesia and uncontrolled bleeding.

The objective of our study was to find the variations in the inferior alveolar canal (i.e., mandibular canal) anatomy by making the use of OPGs. The motive of the study was to evaluate the mandibular canal anatomy, variations, and classification based on OPG images.

MATERIALS AND METHODS

The retrospective study sample consisted of OPGs of the patients who visited the Karpaga Vinayaga Institute of Dental Sciences for the past 5 years with a count of 500. The submitted project was approved by the Institutional Ethics Committee. The study included OPGs of patients of both genders over 14 years and above and the radiographs that were properly recorded. The OPGs have misrepresentations of tissue structures produced by imaging techniques, the radiographs that were improperly recorded, and the radiographs of the patients who have undergone procedures such as extractions, implants, osteotomy, etc., the radiographs of patients who have undergone orthognathic surgeries, orthodontic treatment, and reconstructive surgeries, and the radiographs that have pathologies such as cysts and fractures were excluded.

The OPG images were collected from the Sirona Orthophos XG machine with exposure for 14.1 seconds at 64 kvp and 8 mA. The images were selected and normal anatomy of the mandibular canal and its variations were observed.

A Microsoft Excel spreadsheet was created and the data collected were tabulated according to Freitas et al.’s classification, patient age, and sex, the number of normal canals, and the number of variations present according to the classification given by Freitas et al. (A: lower, B: mesial, C: alveolar, D: retromolar), and the side in which the variation of mandibular canal present.

The variation of mandibular canal classification was given by Freitas et al. They classified the BMCs into four classes (Table 1 and Figs 1 to 4).

The classification given by Freitas et al. was according to the direction of the divided mandibular canal.

The mandibular canal observed in OPGs, age, sex, and side in which the BMC was present (right/left) was carefully examined and analyzed by percentage frequency. Absolute and relative frequencies were described by sex, the site in which BMC present [(right/left)/(unilateral/bilateral)], Freitas et al., classification, and sex and classification. The association between the existence of a bifurcated canal and sex is analyzed by Fisher’s exact test. The association between bifurcated canal locations was analyzed by Chi-square tests.

The analysis was carried out by applying the SPSS version 22.

RESULTS

There are 500 OPGs that were examined, of which 447 (89.4%) had normal mandibular canals, while 53 (10.6%) had variations in mandibular canals. The ubiquity rate of variations in the mandibular canal of this study is 10.6%. The bifurcated mandibular canal is more predominant in men (56.6%) than in women (43.4%) with a p-value of 0.003 (Table 2).

The Chi-square test indicated that the presence of bifurcated mandibular canals was mostly unilateral and mostly present on the left side than the right side. (Table 3).

Among the 53 patients, 30 men and 23 women presented with the BMC. In class B, the direction of the BMC to mesial or anterior was more predominant [33 (62.3%)], followed by class C in which the direction of the BMC to alveolar was 13 (24.5%). Then, in class D, the direction of the BMC to retromolar region was 6 (11.3%), and in class A, the direction of mandibular canal toward the face of inferior alveolar canal was 1 (1.9%) (Table 4).

According to sex and classification, the BMC was prevalent in 30 male patients, and the class B was more predominant (39.6%) (Table 5).

DISCUSSION

This study helps in evaluating the anatomy, variations, and classification of mandibular canals using panoramic radiographs. It represents that the bifurcated mandibular canal is not an infrequent detection.⁵

According to Thakur et al., OPGs are a valid aid for the evaluation of mandibular canal and correlated variations.⁶ According to Yang et al., CBCT should be used as a reliable detection, which provides useful information to help prevent presurgery and post-surgery complications.⁷

According to Nithya et al., CBCT is recommended for distinguishing normal canal and its variations prior to any surgical procedures to keep away from further hurdles.⁸

In the present study, the mandibular canal anatomy was evaluated based on Freitas’s classification, which includes four groups.⁹

Langlais et al. classified mandibular canals based on location and position: Type I (mandibular canal [bifid], which extends up to the third molar or area surrounding it), Type II (mandibular canal [bifid], which extends and rejoins within it), and Type III (combination of the first two types).¹⁰ Naitoh et al. classified the variations in the mandibular canal into four categories: Class I: retromolar, Class II: dental, Class III: forward, and Class IV: buccolingual.¹¹

According to Rashsuren et al., the most common type was retromolar (71.3%) and they also found a prevalence of trifid canal type (5.8%).¹² One of the studies conducted by Freitas et al. using CBCT reported a ubiquity rate of 30% which had more type B canals and provided more accuracy in the identification of canals; no cases were found in class A and class C.¹

According to the study conducted by Manfron et al., there was no change between the right and left sides.¹³ According to Lima et al., the bifurcated canal was identified on the right side and female predilection.¹⁴ According to Kalantar Motamedi et al., the presence of BMC was only 1.2% and not correlated with age/gender.¹⁵ According to Sonneveld et al., a less prevalence rate (1.3%) of BMC was found compared to our study and it has a female predilection.¹⁶

According to Kuczynski et al., a low prevalence of variations of mandibular canal anatomy. All these variations were unilateral.¹⁷ In our study, all the types of variations were observed, that is, unilateral – both right and left and bilateral. Some studies did not consider the criteria of the affected side.^18,19

Elnadoury et al. stated that insufficient knowledge about the canal variations can cause more complications after surgery.²

According to Perin et al., most dentists lack knowledge about the bifurcation of the mandibular canal. Complications include nerve damage, lower efficiency in anesthetic technique, paresthesia, and uncontrolled bleeding.²⁰

According to Eliades et al., the mandibular canal and its contents are very important in minor and major surgeries and also in dental implants because these are more prone to damage while performing surgical procedures. Hurdles that can occur are unsuspected bleeding and nerve injury. Hence, the one who performs surgery should be conscious of the bifurcated canals of the mandible.²¹

According to Sonneveld et al., the BMCs play a crucial role in extractions, surgical removal, and implants. Moreover, 1% of patients can have this kind of canal anatomy and one cannot able to acknowledge this variation can result in poor outcomes.¹⁶

According to Freitas et al., the CBCT is considered a suitable option for the evaluation of anatomy and its variations.¹ However, it can also be best viewed in panoramic radiographs.

A thorough radiological planning and evaluation are very important prior to surgical approaches in the mandible in order to prevent and avoid potential complications during and after the surgical procedures.

CONCLUSION

Based on the results, 10.6% of the BMC was prevalent. It was most predominant in males, unilaterally, on the left side and class B was mostly present. Thus, the present study implies that a panoramic radiograph can also be a valid aid in identifying the inferior alveolar canal and its changes in anatomy, that is, the presence of a BMC since it also provides accuracy as that of CBCTs.

ORCID

Nivethitha Pandithurai https://orcid.org/0000-0002-4426-4687

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