Case report
A rare anatomic variation: Triple mental foramina

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Summary

Multiple mental foramina (MF) are rarely found in the human mandible. We report on the case, as documented using cone beam computed tomography (CBCT), of the triple MF that were identified on the right hemimandible of a 28-year-old female patient. The distal foramen was located on the mandible between the apices of the second premolar root and the first molar mesiovestibular root, being reached by a thin canal that left the mandibular canal. A pair of mesial foramina were identified between the apices of the premolar teeth. Thus, the three foramina corresponded to a surface area of 23.49 mm2 of the mandible. On the opposite side, a single mental foramen had a surface area of just 13.25 mm2. On each side, retromolar canals that opened into the retromolar fossae were also found. The anatomic possibility of multiple MF increases the surface area at risk during surgical procedures, increases the risk of neurovascular damage and obscures the common tooth-related location of the mental foramen. Practitioners should, therefore, consider a personalised and imaging-documented approach so as to avoid treatment failure.

Résumé

Les foramina mentonniers multiples (MF) sont rarement rencontrées dans la mandibule humaine. Nous rapportons un cas documenté par cone beam CT (CBCT) d’un triple MF situé dans l’hémimandibule droite d’une patiente d’origine européenne âgée de 28 ans. Le foramen distal était situé entre l’apex de la deuxième prémolaire et la racine mésiovestibulaire de la première molaire et était rejoint par un canal fin qui sortait du canal mandibulaire. Une paire de foramina mésiaux ont été identifiés entre les apex des deux prémolaires. Ainsi, les trois foramina cumulaient ensemble une surface de 23,49 mm2. Du côté opposé, l’unique foramen mentonnier présentait une surface de seulement 13,25 mm2. De chaque côté ont également été découverts des canaux rétromolaires s’ouvrant dans les fosses du même nom. L’existence de MF multiples augmente globalement la surface exposée au risque lors d’interventions chirurgicales, majore le risque de lésions neurovasculaires et contredit l’idée commune que l’on se fait de l’emplacement du foramen mentonnier. L’imagerie s’impose donc avant toute intervention dans cette région.

Introduction

The mandibular canal runs from the mandibular foramen through the ramus and body of the mandible and it contains the inferior alveolar nerve and vessels. The mandibular canal splits into the mental and incisive canals. The mental canal runs in a postero-supero-lateral direction towards the mental foramen (MF) in the buccal aspect of the mandible body, and contains the mental nerve and vessels [1]. The topography of the MF is variable within and between various adult ethnic groups [2], [3].

The mental foramen is located on the external surface of the body of the dentate mandible, most often at the level of the 2nd mandibular premolar tooth, and at an approximately equal distance from the superior and inferior borders of the mandible body [2], [3], [4], [5], [6]. The extremely rare absence of the MF was reported [7]. Generally, three trunks emerge from the mental nerve after it has traversed the mental foramen [8], namely the inferior labial, mental and anguli oris (angular) branches [9]. Four nerve trunks result when the mental nerve gives off medial and lateral inferior labial branches [2]. The bifurcated variant of the mental nerve into inferior labial and mental branches was also documented [10].

Multiple mental foramina (MF) have been reported [11], with the additional ones being described as ‘accessory’ mental foramina (AMF) [8], [12].

We report a rare case of unilateral multiple MF that could be regarded as either triple MF or double AMF. Two of the three MF were adjacent in the site of a normal MF, while the third one was distally placed.

Section snippets

Material and method

A retrospective CBCT study involving the archived files of 50 patients who were scanned for dental-medical purposes was performed. The anatomic variation we report in the present study was encountered in a 28-year-old female native European subject. The subject has been scanned using an iCat CBCT machine (Imaging Sciences International) with the following settings: a resolution of 0.250, a field of view of 130˚, an image matrix size of 640 × 640, sensor dimensions of 20 × 25 cm, a 14-bit grayscale

Results

Mandibular canals were identified on both sides by means of the MPRs. The right canal was located on the lingual cortical of the body of the mandible in its course beneath the right molar teeth, while the left canal was positioned between the lingual and buccal cortical plates of the mandibular body.

On the right side, three MF were found on the outer surface of the mandibular body (Figure 1, Figure 2). The distal, posterosuperior AMF was located between the apices of the second premolar root

Discussion

In summary, depending on the terminology used, we identified unilateral triple MF or double AMF added to the main foramen. However, use of the latter terminology may lead to a misunderstanding.

The accessory MF (AMF) is defined as the smaller foramen located in the vicinity of the main MF, which also is continuous with the mandibular canal [13]. Such AMF should be differentiated from other orifices on the outer surface of the mandibular body. A nutrient foramen does not originate in the

Conclusion

The triple MF is a rare anatomic variation that increases the mandibular surface exposed at risk during specific medical or surgical procedures.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Acknowledgements

None.

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