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 Table of Contents  
CASE REPORT
Year : 2017  |  Volume : 8  |  Issue : 2  |  Page : 85-87

Anatomical variant of the mental nerve and its foramen


Department of Oral and Maxillofacial Surgery, SRM Dental College, Ramapuram, Chennai, Tamil Nadu, India

Date of Web Publication8-Jun-2017

Correspondence Address:
Poornima Ravi
16/57, Balaji Nagar, 1st Main Road, Ekkaduthangal, Chennai - 600 032, Tamil Nadu
India
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DOI: 10.4103/srmjrds.srmjrds_5_17

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  Abstract 

The mental nerve is a sensory nerve that supplies the lower lip, chin, and mandibular labial gingiva. Very few variants of this nerve have been described in the literature. We describe a case in which a patient who was operated for fracture of the mandible, was found to have two mental foramina with three mental nerves. This case report highlights the need for proper radiological evaluation of mental foramina for ideal treatment planning. Clinical implications are discussed.

Keywords: Anatomical variant, mental foramen, mental nerve


How to cite this article:
Ravi P, Elavenil P, Sarkar S, Raja KV. Anatomical variant of the mental nerve and its foramen. SRM J Res Dent Sci 2017;8:85-7

How to cite this URL:
Ravi P, Elavenil P, Sarkar S, Raja KV. Anatomical variant of the mental nerve and its foramen. SRM J Res Dent Sci [serial online] 2017 [cited 2019 Oct 21];8:85-7. Available from: http://www.srmjrds.in/text.asp?2017/8/2/85/207650


  Introduction Top


The mental nerve is a sensory nerve that innervates the lower lip, chin, and mandibular labial gingiva. Any surgical procedure involving the symphysis and parasymphysis of the mandible may potentially result in paresthesia of these regions. The nerve should, therefore, be isolated and protected during all such procedures. This requires knowledge of the anatomy of the mental nerve and foramen, including all its variations. There are very few case reports describing the presence of accessory mental foramina in literature.

The purpose of this article is to describe an unusual anatomical variant of the mental nerve and foramen encountered during surgery.


  Case Report Top


A 20-year-old male patient reported to our institution with pain and bleeding from the left mandibular region following an assault. Clinical and radiographic examination confirmed the presence of a fracture in the left parasymphysis of the mandible. It was noted that the patient had numbness of the left lower lip and chin following the injury. The patient was taken up for open reduction and fixation under general anesthesia. An intraoral vestibular incision was made, and careful subperiosteal dissection was done. During dissection, two foramina were identified, with three nerves emerging [Figure 1]. It was surmised that the anteroinferior foramen containing two nerves was the mental foramen, whereas the postero superior foramen with one nerve emerging was the accessory mental foramen. The nerves were carefully separated from the underlying bone and tissue, protected using a retractor and the plate was passed beneath the nerves for fixation [Figure 2].
Figure 1: Mental foramina with nerves emerging

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Figure 2: Plate fixed beneath the nerve

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Postoperative recovery was uneventful. The patient gradually recovered sensation in the left lower lip region.


  Discussion Top


The mental nerve is the branch of the inferior alveolar nerve, which in turn originates from the mandibular division of the trigeminal nerve. It arises from the inferior alveolar nerve within the inferior alveolar canal of the mandible. At its exit from the mental foramen, it divides into three branches – the mental branch, labial branch, and gingival branch, which supply the chin, lower lip and gingiva, respectively.[1] There are, however, several anatomic variations in the number of foramina and the branching patterns of the nerve.

Several studies have documented the presence of accessory mental foramina. Sawyer et al. studied the frequency of accessory mental foramina in four ethnic groups.[2] The frequency of accessory foramina was found to be higher in Nazca Indians (9%) and African-Americans (5.7%) than American Caucasians (1.4%) and Asian Indians (1.5%). However, in another study on Asian Indian mandibles,[3] the incidence was found to be much higher (6.6%). The location of the mental foramen has also shown variation in some studies. Fishel et al. showed that, while in 70.4% of the population, the mental foramen is located between the apices of two premolars, others showed vertical variations. In 18.9% of the population, it was located below the apex of the second premolar; in 3.3% apical to the first premolar; in 1.5% mesial to the first premolar; in 6.6% between the premolar and the molar, and in 1% beside the molars.[4] Variations in shape have also been reported, with the round shape predominating in certain studies [5] and the oval shape predominating in others.[6]

The branching patterns of the mental nerve have also been studied extensively. Hu et al.[7] described various branching patterns of the mental nerve which were observed by the dissection of 31 cadavers. They categorized various branches as angular (A), medial inferior labial (ILm), lateral inferior labial (ILl) and mental (M) branches based on the area of distribution. They found four branching patterns. In Type 1, the mental nerve divided into A, M, and IL branches and IL further divided into medial and lateral branches. In type II, the nerve divided into A, M, and ILm, while ILl emerged from A. In type III, the nerve divided into A, M, and ILl, while ILm emerged from M. In Type IV, only A and M emerged from the nerve while ILm and ILl emerged from M and A, respectively. Type V is the same as Type IV, except that the IL separates from the A and then divides into ILm and ILl branches. Of these, Type II appears to be the most common variant.

Alantar et al.,[8] in an earlier paper, had discussed these branches and, by dissection of sixteen cadavers, aimed to determine the causes of injury to the mental nerve. Based on the course of the nerve that they observed, the authors recommended a U-shaped incision for surgery to the mandible, which would be parallel to the inferior labial nerve branch.

There are, however, currently no studies that document branching variations with regard to accessory mental foramina. Most studies report the exit of one nerve from each foramen.[9],[10] This case, however, had a total of three nerves – two from the main foramen that supplied the lower lip and chin, and one from the accessory foramen, which appeared to supply the gingiva. Future cadaveric studies should focus on branching patterns in correlation with the number of mental foramina present.


  Conclusion Top


This case report highlights the need for careful preoperative radiographic assessment of the mandibular canal and foramina. The accessory mental foramen may be visible on panoramic radiographs and computed tomography scans. This would aid in correct preoperative selection of plates for fixation, and avoid modification of plates, which was required in this case. However, careful subperiosteal dissection during surgery is advisable.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
  References Top

1.
Standring S, editor. Gray's Anatomy: The Anatomical Basis of Clinical Practice. 39th ed. London: Elsevier Churchill Livingstone; 2005. p. 601-2.  Back to cited text no. 1
    
2.
Sawyer DR, Kiely ML, Pyle MA. The frequency of accessory mental foramina in four ethnic groups. Arch Oral Biol 1998;43:417-20.  Back to cited text no. 2
    
3.
Gupta S, Soni JS. Study of anatomical variations and incidence of mental foramen and accessory mental foramen in dry human mandibles. Nat J Med Res 2012;2:28-30.  Back to cited text no. 3
    
4.
Fishel D, Buchner A, Hershkowith A, Kaffe I. Roentgenologic study of the mental foramen. Oral Surg Oral Med Oral Pathol 1976;41:682-6.  Back to cited text no. 4
    
5.
Al-Khateeb T, Al-Hadi Hamasha A, Ababneh KT. Position of the mental foramen in a northern regional Jordanian population. Surg Radiol Anat 2007;29:231-7.  Back to cited text no. 5
    
6.
Oliveira Junior EM, Araiyo AL, Da Silva CM, Sousa-Rodrigues CF, Lima FJ. Morphological and morphometric study of mental foramen on the M-CP-18 Jiachenjiang point. Int J Morphol (Temuco) 2009;27:231-8.  Back to cited text no. 6
    
7.
Hu KS, Yun HS, Hur MS, Kwon HJ, Abe S, Kim HJ. Branching patterns and intraosseous course of the mental nerve. J Oral Maxillofac Surg 2007;65:2288-94.  Back to cited text no. 7
    
8.
Alantar A, Roche Y, Maman L, Carpentier P. The lower labial branches of the mental nerve: Anatomic variations and surgical relevance. J Oral Maxillofac Surg 2000;58:415-8.  Back to cited text no. 8
    
9.
Sahin B, Ozkan HS, Gorgu M. An anatomical variation of mental nerve and foramen in a trauma patient. Int J Anat Var 2010;3:165-6.  Back to cited text no. 9
    
10.
Ramadhan A, Messo E, Hirsch JM. Anatomical variation of mental foramen: A case report. Stomatologija Balt Dent Maxillofac J 2010;12:93-6.  Back to cited text no. 10
    


    Figures

  [Figure 1], [Figure 2]



 

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