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References

Sawyer DR, Kiely ML, Pyle MA. The frequency of accessory mental foramina in four ethnic groups. Arch Oral Biol. 1998; 43:417-420 https://doi.org/10.1016/s0003-9969(98)00012-0
Katakami K, Mishima A, Shiozaki K Characteristics of accessory mental foramina observed on limited cone-beam computed tomography images. J Endod. 2008; 34:1441-1445 https://doi.org/10.1016/j.joen.2008.08.033
Borghesi A, Bondioni MP. Unilateral triple mandibular canal with double mandibular foramen: cone-beam computed tomography findings of an unexpected anatomical variant. Folia Morphol (Warsz). 2021; 80:471-475 https://doi.org/10.5603/FM.a2020.0057
Torres MG, Valverde Lde F, Vidal MT, Crusoé-Rebello IM. Accessory mental foramen: a rare anatomical variation detected by cone-beam computed tomography. Imaging Sci Dent. 2015; 45:61-65 https://doi.org/10.5624/isd.2015.45.1.61
Naitoh M, Hiraiwa Y, Aimiya H Accessory mental foramen assessment using cone-beam computed tomography. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2009; 107:289-294 https://doi.org/10.1016/j.tripleo.2008.09.010
European Commission. Cone beam CT for dental and maxillofacial radiology: evidence-based guidelines. Radiation protection No 1722012. 2012. https://ec.europa.eu/energy/sites/ener/files/documents/172.pdf
Renton T. Medico-legal issues: a focus on preventable nerve injuries. Dent Nurs. 2013; 9:398-406

Letters to the editor

From Volume 49, Issue 7, July 2022 | Pages 601-602

Authors

Elizabeth Morphet

Trust Doctor Maxillofacial Surgery

Articles by Elizabeth Morphet

Emma Elliott

Academic Longitudinal Foundation Dental Trainee

Articles by Emma Elliott

Jiten Parmar

Consultant in Oral and Maxillofacial Surgery, Leeds Teaching Hospitals NHS Trust

Articles by Jiten Parmar

Ed Walker

Consultant in Dental and Maxillofacial Radiology, Leeds General Infirmary

Articles by Ed Walker

Article

Unilateral trifid mental nerve and foramen: a case report

A 29-year-old African male patient presented with a fractured right parasymphysis and left condylar base following an altercation while under the influence (Figure 1). On examination the patient had a deranged occlusion with mobility of the anterior mandibular segment. He had an apparent skeletal base Class 3 and an anterior open-bite, yet incisal edge wear facets indicated an edge-to-edge occlusion prior to the incident. Plain film imaging demonstrated significantly reduced height of the left condyle and displacement of the right parasymphyseal fracture (Figure 1). The patient was admitted and consented for open reduction and fixation of both fracture sites.

Figure 1. Pre-operative OPG evidencing fractured right parasymphysis and left condylar base.

Interestingly, during access to the right parasymphyseal fracture, three separate mental nerves and foramina were discovered unilaterally. It was initially thought that there was only a second foramen and associated nerve; however, further exploration of the surgical field revealed a third foramen and nerve. All three foramina and mental nerves were anatomically distinct from each other and had comparative diameters (Figure 2). It was unclear which was anatomically dominant, and which were accessory foramen. All three nerves were preserved during reduction and plating with some post-operative paraesthesia to the lower lip observed clinically. A CBCT was acquired post operatively due to possible fracture displacement. A consultant radiologist reviewed the CBCT independently, confirming the finding of a unilateral triplicate nerve with a single mental foramen contralaterally (Figure 3).

Figure 2. Three anatomically independent and distinct mental foramen and nerves unilaterally in line with right parasymphysis fracture.
Figure 3. CBCT showing three apparent distinct mental nerve foramina on the right-hand side.

Variation in mental nerve anatomy is widely reported, ranging from multiple mental nerves and foramen to complete absence.1 Detection of such variations is increasing alongside imaging availability, with retrospective studies based on analysis of CBCT/CT records2–5 reflecting the potential limitations of pre-operative plain film radiographs.

Although some clinicians recommend pre-operative CBCT for surgical procedures,3 this must be justified depending on the planned procedure, in line with national and local radiography guidelines.6 As such, an awareness of significantly variable anatomy promotes increased caution for the practitioner and, perhaps, the additional need to inform and consent a patient of the innate operative risk accompanying individual anatomy.

We hope to illustrate the potential for significant anatomical variation among patients with key points from this letter applying to all dental professionals:

  • Preventable nerve injuries impact patient quality of life and can precipitate complaints or litigation;7
  • Patients should be appropriately consented for their risk of nerve damage;
  • Pre-opertive imaging may not indicate unusual anatomy and the potential for such nerve anatomy cannot be dismissed;
  • As CBCT use increases, the reported prevalence of unusual nerve anatomy may become more significant.

    • Ultimately, a cautious, considered surgical approach to prevent avoidable morbidities should always be employed.