Prevalence and anatomical characteristics of bifid and trifid mandibular canals: a computed tomography analysis

doi:10.21203/rs.3.rs-1561216/v1

PDF

Research Article

Prevalence and anatomical characteristics of bifid and trifid mandibular canals: a computed tomography analysis

https://doi.org/10.21203/rs.3.rs-1561216/v1

This work is licensed under a CC BY 4.0 License

You are reading this latest preprint version

Purpose: To assess the prevalence and configuration of bifid (BMC) and trifid (TMC) mandibular canals using computed tomography, describing the anatomical characteristics of the accessory canals, especially of the retromolar type.

Methods: Computed tomographic scans of 123 patients were analyzed. BMCs were identified and the patterns of bifurcation were classified, including trifid canals. The width of accessory canals was measured. Retromolar canals were further classified according to their course and morphology, while their position and width were evaluated using linear measurements on CT/CBCT images.

Results: The majority part of patients (53.6%) presented at least one BMC or TMC. A percentage of 36.2% of mandibular canals were bifid, while 4.5% trifid. The forward canals (12.6%) and retromolar canals (10.2%) were the most common among BMCs. In relation to the retromolar canals, 60% were vertical and 40% curved, with a mean width of 1.03 ± 0.28mm.

Conclusion: BMCs and TMCs are common 3D radiographic findings, so that they should be considered as anatomical variants, not anomalies. Preoperative CT or CBCT evaluation should aid to identify these variations, analyzing the position and course.

Mandibular nerve

Third molar

Cone-beam computed tomography

Computed tomography

Oral surgery

The mandibular canal (MC) is an anatomical structure with a great clinical importance since it is an intraosseous canal containing different structures which contribute to form the inferior alveolar bundle [14].

Determining the position and morphology of the mandibular canal could avoid damaging its neurovascular plexus during oral surgery. It is also advisable to identify its anatomical variations, such as Bifid Mandibular Canals (BMCs) and Trifid Mandibular Canals (TMCs).

Indeed, the mandibular canal could present several ramifications, dividing it into a main branch, which keep its path to the mental foramen, and one or more accessory branches, which have a different course in the mandible [1].

Several studies showed that accessory canals may contain neurovascular tissue [2, 5, 8]. A lesion of these structures during oral surgery could determine the onset of complications such as paresthesia, bleeding or traumatic neuroma [3].

One of the most frequent accessory canals is the retromolar canal, a type of BMCs which is often associated with surgical complications; this anatomical structure arises from the mandibular canal behind the third molar and travels antero-superiorly to the retromolar foramen, located in the retromolar fossa [20].

Different classification systems have been proposed for BMCs, based on the anatomical position and configuration of the accessory canals. The earliest classification systems, such as that of Nortje et al. and that of Langlais et al., were based on panoramic radiographs [19], while Naitoh et al. proposed a system based on computed tomographic scans (CT) [10].

Localization of accessory canals on panoramic radiographs is often difficult or not possible, due to the overlapping of buccal and oral bone structures and to the dimensional distortion given by the irregular magnification [10]. Instead, computed tomography provides three-dimensional images and allow an easier identification of position and width of accessory canals [4].

However, there are not classifications including the trifid canal type (TMCs), although many cases were reported in the past publications [15].

Hence, the aim of this study was to determine the prevalence and configuration of BMCs and TMCs using Computed Tomography (CT) and Cone-Beam Computed Tomography (CBCT). In addition, the anatomical characteristics of the accessory canals (i.e., retromolar type) were also reported.

A selection of CT and CBCT scans of patients treated at Department of Oral Surgery - University of Naples Federico II from May 2018 to January 2020 were retrospectively collected and evaluated. The inclusion criteria were the following:

Male and female;
Age ≥ 18 years;
Computed tomographies performed for odontostomatological evaluations (i.e., tooth extraction, dental implant planning);
Scans with a field of view (FOV) showing full lower arch.

The exclusion criteria were:

Scans that did not clearly show the entire path of the mandibular canal (from mandibular foramen to mental foramen);
Presence of osteolytic and/or osteosclerotic lesions in the posterior area of the mandible.

Analysis of the tomographic scans and data collection was performed by two clinicians (V.P. and L.G.). The inter examiner agreement was analyzed by kappa coefficient. A k-score of 0.90 was accepted for agreement. Any discrepancy between the two clinicians was resolved by discussion.

Evaluation and classification of accessory canals using CT/CBCT images

RadiAnt DICOM Viewer software (version 4.6.9; Medixant, Poznan, Poland) was used to process the projection data. For each evaluation site, the entire path of the mandibular canal was evaluated under free angulation of three-dimensional slices on multiplanar reconstruction (MPR) images.

When necessary, brightness and contrast of the images were adjusted to optimize the recognition and determination of the mandibular canal and any accessory canals.

For each evaluation site, the mandibular canal was classified as normal, bifid (BMC) or trifid (TMC), according to the number of accessory canals branching from it (none, one or two).

The BMCs were classified according to the classification of Naitoh et al.[10] (Table 1).

Table 1

Classification of Bifid Mandibular Canals (BMCs)
Canal type	Description
Retromolar canal (Type I)	Branches off the mandibular canal in ramus region, runs anterosuperiorly and opens at the retromolar foramen, in the retromolar region
Dental canal (Type II)	Bifurcates from the mandibular canal and reaches the root apex of the second or third molar
Forward canal (Type III)	Arises from the superior wall of the mandibular canal and runs forward parallel to the main canal, with or without confluence
Buccolingual canal (Type IV)	Arises from the buccal or lingual wall of the mandibular canal

The width of the accessory canals was measured immediately after bifurcation on the coronal CT-derived images.

Retromolar canals were further classified into three categories based on their course and morphology, according to the classification of von Arx et al.[20] (Table 2).

Table 2

Classification of retromolar canals
Retromolar canal type	Description
Vertical (Type A)	Arises from the mandibular canal and runs vertically upwards, with a more or less straight and direct course, up to the retromolar foramen
Curved (Type B)	Arises from the mandibular canal, runs in an anterior direction and then curves supero-posteriorly towards the retromolar fossa
Horizontal (Type C)	Arises from the mandibular foramen and runs anteriorly in a horizontal direction to open on the anterior face of the mandibular branch or into the retromolar fossa

Furthermore, sagittal CT- or CBCT-derived images were used to determine position and width of retromolar canals [20]:

Horizontal distance from midpoint of retromolar foramen to second molar (on the distal cementum-enamel junction or CEJ; Fig. 1A);
Height of retromolar canal: vertical distance from the midpoint of the retromolar foramen to the upper border of the mandibular canal (Fig. 1B);
Width of retromolar canal: measured at a level of 3 mm below the mesial aspect of the retromolar foramen (Fig. 1C).

In addition, two other distances were measured on the sagittal CT- or CBCT-derived images:

Distance from the mandibular foramen to the branch point of the retromolar canal;
Width of mandibular canal from which a retromolar canal branch off: measured immediately before bifurcation.

Scans were subjected to a second analysis using Simplant pro 18 software (version 18.0.0; Dentsply Implants NV, Hasselt, Belgium). This software was used to process the volumetric reconstructions and to visualize the mandibular canal and any accessory canals in three-dimensional space after having reconstructed them starting from axial, trans-axial and panoramic-like images.

The 3D rendering of the mandible allows to rotate the reconstruction without constraints, for a more accurate evaluation of the position and direction of the accessory canal and for a correct identification of any retromolar foramen.

Statistical analysis

Descriptive and comparative statistical analysis were performed by means of computer software (Microsoft Excel; Microsoft Corporation, Washington, DC, USA and IBM SPSS; SPSS Inc., Chicago, IL, USA).

The data were presented as like frequencies, means and standard deviations.

Differences in the prevalence rate of accessory canals according to gender, side and type were evaluated using the Chi squared test and Fisher’s exact test.

The analysis of variance (ANOVA) test was used to evaluate differences in width among accessory canal types. A value of p < 0.05 was considered statistically significant.

The most part of computed tomography scans were requested for planning surgical extraction of one or both lower third molars, when the panoramic radiographs showed an intimate relationship between dental roots and mandibular canal. The process of collecting CT and CBCT scans resulted in the selection of 123 patients and 246 mandibular canals: 64 women and 59 men, with a mean age of 31.4 ± 11.62 years. A total of 53.6% patients (n = 66/123) had at least one bifid (Fig. 2) or trifid mandibular canal, with a prevalence in female patients of 46.8% (n = 30/64) and of 61% (n = 36/59) in male patients (Table 3).

Table 3

Frequencies of accessory canals (gender)
Gender	Accessory canals		Total	p-value ^a
	Present	Absent
Male	36 (61%)	23 (39%)	59 (48%)
Female	30 (47%)	34 (53%)	64 (52%)	0.148
Total	66 (53.6%)	57 (46.4%)	123 (100%)
^a p-value refers to the Fisher’s exact test

No significant differences in the prevalence of accessory canals for gender (p ≤ 0.05).

In 66 patients with at least one bifid or trifid mandibular canal, 51.5% (n = 34/66) showed accessory canals bilaterally.

In 27 patients both mandibular canals were bifid, in 4 patients one canal bifid and the contralateral one trifid, and in only 3 patients both canals were trifid. The remaining 48.5% (n = 32/66) had one or two accessory canals only on right or left side.

The prevalence of BMCs and TMCs was, respectively, 50.4% (n = 62/123) and 6.5% (n = 8/123).

The prevalence on single sites (hemimandibles) was 36.2% (n = 89/246) for BMCs and 4.5% (n = 11/246) for TMCs (Table 4).

Table 4

Prevalence of bifid and trifid mandibular canals
Canal type	n	Percentage
Non-bifid canal	146	59.3%
Bifid mandibular canal (BMC) Retromolar canal (Type I) Dental canal (Type II) Forward canal (Type III) Buccolingual canal (Type IV) Not classifiable BMC	89 25 15 31 9 9	36.2% 10.2% 6% 12.6% 3.7% 3.7%
Trifid mandibular canal (TMC)	11	4.5%
Total	246	100%

The most common variant among BMCs was the forward canal (type III;12.6%), followed by retromolar canal (type I; 10.2%), dental canal (type II; 6.2%) and buccolingual canal (type IV; 3.7%). Figure 3 shows the different types of accessory canals.

The remaining 9 mandibular canals (3.7%; n = 9/246) were not classified, because of a path not included in the adopted classification: in eight evaluation sites an accessory branch departing from the inferior wall of mandibular canal and running antero-inferiorly, while in one hemimandible a Temporal Crest Canal (TCC) has been observed (Figs. 4, 5).

No significant differences in the prevalence of different types of accessory canals for gender (p = 0.145) and right or left side (p = 0.742) were found.

The mean width and standard deviation of different types of accessory canals was reported in Table 5. The mean width of retromolar canals (1.44 ± 0.65 mm) was significantly greater than anterior canals (1.08 ± 0.26 mm; p = 0.043). Furthermore, no significant differences were observed in the width of the other types of accessory canal.

Table 5

Mean width and standard deviation of accessory canals
Canal type	Mean width	SD	Range
Bifid Mandibular Canal (BMC) Retromolar canal (Type I) Dental canal (Type II) Forward canal (Type III) Buccolingual canal (Type IV) Not classifiable BMC (excluding TCC)	1.22 mm 1.44 mm ^a 1.27 mm 1.08 mm ^a 1.19 mm 1.00 mm	± 0.45 mm ± 0.65 mm ± 0.38 mm ± 0.26 mm ± 0.40 mm ± 0.28 mm	0.56–3.01 mm 0.66–3.01 mm 0.63–2.01 mm 0.57–1.49 mm 0.65–1.82 mm 0.56–1.48 mm
Trifid Mandibular Canal (TMC)	1.18 mm	± 0.35 mm	0.62–1.80 mm
Total	1.21 mm	± 0.44 mm	0.56 – 3.01 mm
^a Statistically significant (p < 0.05)

A percentage of 15.5% of patients (n = 19/123) showed at least one retromolar canal and, of these, six patients present it on both sides. Therefore, a total of 25 retromolar canals (10.2%) were detected with CT and CBCT images in 246 sites (Fig. 6).

In relation to their morphology, 60% had a vertical pattern (n = 15/25, type A), while 40% had a curved course (n = 10/25, type B); horizontal pattern (type C) was not identified.

The data related to the main position and width of the retromolar canals were summarized in Table 6.

Table 6

Linear measurements of the retromolar canals
Distance	Mean	SD	Range
Horizontal distance from midpoint of retromolar foramen to second molar	15.7 mm	3.5 mm	11–29.3 mm
Height of retromolar canal	12.9 mm	2.7 mm	9.6–21.5 mm
Width of retromolar canal	1.03 mm	0.28 mm	0.45–1.47 mm
Distance from the mandibular foramen to the branch point of the retromolar canal	12.18 mm	5.32 mm	2.7–23.3 mm
Width of mandibular canal from which the retromolar canal branch off	3.12 mm	0.67 mm	1.96–4.44 mm

The distance from the midpoint of the retromolar foramen to the second molar was 15.7 ± 3.5 mm (range 11-29.3 mm). The height of the retromolar canal was 12.9 ± 2.7 mm (range 9.6–21.5 mm). The width was 1.03 ± 0.28 mm (range 0.45–1.47 mm). The distance from the mandibular foramen to the bifurcation point was 12.18 ± 5.32 mm (range 2.7 23.3 mm). The width of the mandibular canal from which the retromolar canals branch off was 3.12 ± 0.67 mm (range 1.96–4.44 mm).

The present retrospective observational study analyzed the prevalence and morphological characteristics of bifid and trifid mandibular canals using CT and CBCT. A high prevalence of these anatomical variants was reported. Previous studies[11, 12, 17] analyzed the accessory canals of the mandibular canal, considering CT or CBCT a suitable modality for a detailed evaluation. In other words, tomographic scans, provide high-resolution three-dimensional images and they can detect accessory canals with narrow width and those that bifurcate in buccal or lingual direction [21].

In order to correctly evaluate the canals that branch out in a more posterior position of the mandibular canal, near the mandibular foramen, only tomographic scans which allowed an analysis of the whole mandible were included. Mandibles with osteolytic or osteosclerotic lesions in the posterior region were excluded because the pathology could have modified the original anatomy.

Finally, the retromolar canal (type I) has been subjected to a more accurate analysis since it represents one of the most frequent types of bifurcation and more often associated with surgical complications [18].

In agreement to previous studies [7, 9, 16] (i.e., prevalence rate of BMCs ranging from 15.6–66.5%), the prevalence of BMCs was 50.4%. However, this outcome is in contrast respect to those reported by Naitoh et al.[10] and Orhan et al.[12].

In the present investigation the prevalence of trifid mandibular canals (TMCs) was 6.5%. These results are in agreement to those reported in a previous study, in which a prevalence of 5.8% [15] was reported.

The classification proposed by Naitoh et al.[10] was adopted to analyze the anatomical variant of BMCs. Forward (type III) and retromolar (type I) canals were the most frequent types recorded, with a percentage of 34.83% and 28.09%, respectively. These data are confirmed by Naitoh et al.[10] and Orhan et al.[12], which found a higher frequency of type III and I canals with a prevalence of 59.6% and 29.8% for forward canals, respectively, and of 29.8% and 28.1% for retromolar canals, respectively.

The prevalence of dental (type II; 16.85%) and buccolingual (type IV; 10.11%) canals was in present study lower than type I and III, according to Naitoh et al. which reported a rate of 8.8% for type II and 1.8% for type IV.

In addition, we also found some anatomical variants (3.7%; n = 9/246) not described by the adopted classification [10]. In eight hemimandibles, the accessory canal originates from the inferior wall of mandibular canal and running antero inferiorly.

Moreover, a very rare anatomical variation (Temporal Crest Canal, TCC) was recorded in one patient. This anatomical variation was described in 1986 by Ossenberg et al. [13] It originates from an accessory mandibular foramen, positioned anteriorly and cranially to the mandibular foramen, runs first antero-inferiorly and then antero-superiorly and opens at a bony foramen located in the anterior region of the temporal crest.

Probably, TCC conveys the long buccal nerve and the associated blood vessels, pierces the temporalis tendon and travels to the cheek and mandibular buccal gingiva [6, 13].

The data on width and position of the retromolar canals of our study are in agreement with the results reported by von Arx et al.[20], who applied the same measurement modalities, detecting a horizontal distance from midpoint of retromolar foramen to second molar of 15.2 ± 2.4 mm, a height of retromolar canal of 11.4 ± 2.7 mm and a width of retromolar canal of 1 ± 0.31 mm.

In the present investigation, a total of 123 CT or CBCT scans was retrospectively collected and analyzed. Unfortunately, the small sample available represents a limit of the study.

Another limitation is the collection of tomographic scans only of patients who had performed it for surgical purposes (possible selection bias) and in different radiological centers, with different radiological exposure settings, positioning and methodology (CT or CBCT).

Within the limits of the present study, bifid and trifid mandibular canals have an important clinical relevance, in relation to their prevalence and their morphological characteristics.

Outcomes of this study suggest performing an accurate radiographic diagnosis using CT or CBCT in order to avoid possible surgical complications.

Ethical approval This study was performed in line with the principles of the Declaration of Helsinki. Approval was granted by the Ethics Committee of the University of Naples “Federico II” (No. 286/20).

Informed consent Informed consent for processing personal data was obtained from all participants included in the study.

Conflict of interest The authors have no relevant financial or non-financial interests to disclose.

Funding No funds, grants, or other support was received.

Author contributions L Ramaglia: research conception and design, project development. A Blasi: data analysis. L Galasso: scans selection and analysis, data collection. V Pezzella: scans selection and analysis, data collection. A Cuozzo: manuscript writing. V Iorio-Siciliano: manuscript writing, review of the original draft.

Allison JR, Carr A (2017) A prevalence study of bifid mandibular canals using cone beam computed tomography. Oral Surg 10:e55-e61. https://doi.org/10.1111/ors.12267
Bilecenoglu B, Tuncer N (2006) Clinical and Anatomical Study of Retromolar Foramen and Canal. J Oral Maxillofac Surg 64:1493–1497. https://doi.org/10.1016/j.joms.2006.05.043
Claeys V, Wackens G (2005) Bifid mandibular canal: Literature review and case report. Dentomaxillofac Radiol 34:55–58. https://doi.org/10.1259/dmfr/23146121
Elnadoury EA, Gaweesh YSE-D, Abu El Sadat SM, Anwar SK (2022) Prevalence of bifid and trifid mandibular canals with unusual patterns of nerve branching using cone beam computed tomography. Odontology 110:203–211. https://doi.org/10.1007/s10266-021-00638-9
Fukami K, Shiozaki K, Mishima A, Kuribayashi A, Hamada Y, Kobayashi K (2012) Bifid mandibular canal: Confirmation of limited cone beam CT findings by gross anatomical and histological investigations. Dentomaxillofac Radiol 41:460–465. https://doi.org/10.1259/dmfr/60245722
Kawai T, Asaumi R, Kumazawa Y, Sato I, Yosue T (2014) Observation of the temporal crest canal in the mandibular ramus by cone beam computed tomography and macroscopic study. Int J Comput Assist Radiol Surg 9:295–299. https://doi.org/10.1007/s11548-013-0931-6
Kuribayashi A, Watanabe H, Imaizumi A, Tantanapornkul W, Katakami K, Kurabayashi T (2010) Bifid mandibular canals: Cone beam computed tomography evaluation. Dentomaxillofac Radiol 39:235–239. https://doi.org/10.1259/dmfr/66254780
Motamedi MHK, Gharedaghi J, Mehralizadeh S, Navi F, Badkoobeh A, Valaei N, et al. (2016) Anthropomorphic assessment of the retromolar foramen and retromolar nerve: anomaly or variation of normal anatomy? Int J Oral Maxillofac Surg 45:241–244. https://doi.org/10.1016/j.ijom.2015.10.017
Muinelo-Lorenzo J, Suárez-Quintanilla JA, Fernández-Alonso A, Marsillas-Rascado S, Suárez-Cunqueiro MM (2014) Descriptive study of the bifid mandibular canals and retromolar foramina: Cone beam CT vs panoramic radiography. Dentomaxillofac Radiol 43:20140090. https://doi.org/10.1259/dmfr.20140090
Naitoh M, Hiraiwa, Y, Aimiya, H, Ariji E (2009) Observation of Bifid Mandibular Canal Using Cone-Beam Computerized Tomography. Int J Oral Maxillofac Implants 24:155–159.
Nithya J, Aswath N (2020) Assessing the prevalence and morphological characteristics of bifid mandibular canal using cone-beam computed tomography - A retrospective cross-sectional study. J Clin Imaging Sci 10:30. https://doi.org/10.25259/jcis_67_2019
Orhan K, Aksoy S, Bilecenoglu B, Sakul BU, Paksoy CS (2011) Evaluation of bifid mandibular canals with cone-beam computed tomography in a Turkish adult population: A retrospective study. Surg Radiol Anat 33:501–507. https://doi.org/10.1007/s00276-010-0761-y
Ossenberg NS (1986) Temporal crest canal: Case report and statistics on a rare mandibular variant. Oral Surg Oral Med Oral Pathol 62:10–12. https://doi.org/10.1016/0030-4220(86)90062-9
Pogrel MA, Dorfman D, Fallah H (2009) The Anatomic Structure of the Inferior Alveolar Neurovascular Bundle in the Third Molar Region. J Oral Maxillofac Surg 67:2452–2454. https://doi.org/10.1016/j.joms.2009.06.013
Rashsuren O, Choi JW, Han WJ KE (2014) Assessment of bifid and trifid mandibular canals using cone-beam computed tomography. Imaging Sci Dent 44:229–236. https://doi.org/10.5624/isd.2014.44.3.229
Shah NP, Murtadha L, Brown J (2018) Bifurcation of the inferior dental nerve canal: an anatomical study. Br J Oral Maxillofac Surg 56:267–271. https://doi.org/10.1016/j.bjoms.2018.01.016
Sonneveld KA, Mai PT, Hogge M, Choi EY, Portnof JE (2018) Bifid mandibular canal: A case review and retrospective review of CBCTs. Implant Dent 27:682–686. https://doi.org/10.1097/id.0000000000000819
Truong MK, He P, Adeeb N, Oskouian RJ, Tubbs RS, Iwanaga J (2017) Clinical Anatomy and Significance of the Retromolar Foramina and Their Canals: A Literature Review. Cureus 9:e1781. https://doi.org/10.7759/cureus.1781
von Arx T, Bornstein MM (2021) The bifid mandibular canal in three-dimensional radiography: morphologic and quantitative characteristics. Swiss Dent J 131:10–28.
von Arx T, Hänni A, Sendi P, Buser D, Bornstein MM (2011) Radiographic study of the mandibular retromolar canal: An anatomic structure with clinical importance. J Endod 37:1630–1635. https://doi.org/10.1016/j.joen.2011.09.007
Zhang YQ, Zhao YN, Liu DG, Meng Y, Ma XC (2018) Bifid variations of the mandibular canal: cone beam computed tomography evaluation of 1000 Northern Chinese patients. Oral Surg Oral Med Oral Pathol Oral Radiol 126:e271-e278. https://doi.org/10.1016/j.oooo.2018.06.008

No competing interests reported.

PDF

Reviewers invited by journal
20 Apr, 2022
Editor assigned by journal
18 Apr, 2022
Submission checks completed at journal
17 Apr, 2022
First submitted to journal
15 Apr, 2022

You are reading this latest preprint version

Prevalence and anatomical characteristics of bifid and trifid mandibular canals: a computed tomography analysis

Status:

Version 1

Abstract

Figures

Introduction

Materials And Methods

Evaluation and classification of accessory canals using CT/CBCT images

Statistical analysis

Results

Discussion

Conclusion

Declarations

References

Competing Interests

Status:

Version 1