Case report

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For citation purposes: Verma M, Soni S, Saxena A, Das AR. Unilateral variation of the mental foramen. OA Case Reports 2013 Sep 10;2(11):102. Co

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*Corresponding authorEmail: alok.sxna@gmail.com

Department of Anatomy, Veer Chandra Singh Garhwali Government Medical Science and Research Institute, Srinagar, Uttarakhand, India

AbstractIntroductionMental foramen is present on the anterolateral aspect of the body of the mandible. Mental nerve and ves­sels pass through it and supply the area from canine to first molar. The mental nerve is the neurosensory nerve. Foramen present on the body of the mandible other than the men­tal foramen is considered as acces­sory foramen. This study reports a case of unilateral variation of the mental foramen. Case report During the anatomical teaching cur­riculum, we observed an accessory mental foramen on the right side of dried mandible. Morphometric ana­lysis of mental foramen and acces­sory mental foramen from various anatomical landmarks was done and results were tabulated.Discussion Variations in the number of mental foramen are important when the premolar region is targeted for sur­gical intervention like osteotomy, root canal treatment and maxillo facial surgeries. Determination of implantation site and achievement of complete nerve block in that region depends upon the anatomical posi­tion and possible variation of mental foramen.Conclusion Variations in number of mental foramen is not uncommon. The knowledge of accurate position of MF is important to avoid damage

to neurovascular bundles passing through it and also to achieve abso­lute anaesthetic effect at the antero­lateral mandibular region.

IntroductionMental foramen (MF) is present bilaterally on the anterolateral aspect of the mandible. It is present below the alveolar margin. The MF is an important anatomical landmark for dental surgeons planning for peri epical surgery in the mental region as well as for the local anaesthesia in the anterolateral mandibular region. The neurovascular bundle (men­tal nerve and vessels) emerges out through the MF. The mental nerve is the sensory nerve supplying the chin, lower lip and gingiva. The men­tal nerve is coming out from the MF and divides in to four branches named as angular, medial and lateral inferior labial and mental branch1.

Up to the 12th gestation week, the MF remains incomplete. When the mental nerves ramify in to various fascicules before the formation of MF, an accessory foramen is formed to provide an exit to these fascicules2. Accessory MF (AMF) carries the

mental branch and the medial infe­rior labial branch. It is also important to differentiate the AMF from nutri­tious foramen. Nutritious foramen is not related with the mandibular canal but AMF always takes origin from the mandibular canal1. Incidence of AMF varies between ethnic groups3. A pre­vious study reported by Balcipoglu and Kocaelli 4 revealed no gender dif­ferences in the variations of number of MF. This study reports a case of unilateral variation of the MF.

Case report During osteology demonstration cur­riculum for undergraduate medical students in the department of ana­tomy, we came across of dried man­dible of unknown sex having double foramina on the right side of the mandible (Figure 1). No accessory foramen was observed on the left side of mandible (Figure 2). Digital calliper was used to measure the dimensions and position of MF and AMF. The relation of MF with lower teeth and its position in relation to symphysis menti, the posterior bor­der of the ramus of the mandible and lower border of the body of the

Unilateral variation of the mental foramenM Verma, S Soni, A Saxena*, AR DasA

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Figure 1: Showing MF and AMF on right side of mandible.

Case report

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Licensee OA Publishing London 2013. Creative Commons Attribution License (CC-BY)

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For citation purposes: Verma M, Soni S, Saxena A, Das AR. Unilateral variation of the mental foramen. OA Case Reports 2013 Sep 10;2(11):102.

mandible was observed. The dis­tance between AMF and MF was also measured (Table 1).

DiscussionPrevalence of AMF is variable among ethnic groups and is reported as follows: 2.6% in French, 1.4% in American white, 5.6% in American black, 3.3% in Greek, 1.5% in Russians and 9.7% in Melanesians. Among Japanese it was slightly higher; 6.7–12.5%5.

Three AMF were observed in a study conducted on 100 dried mandi­bles of the South Gujarat population6.

Triple MF was also reported by Ramadhan et al.7 in 2010 during surgical treatment of mandibular fracture. Gershenson et al.8 observed 0.67% incidence of triple foramina in 525 dried mandibles. Katakami et al.9 examined 150 patients retro­spectively using limited cone beam computed tomography and found 16 dual foramina, one triple MF uni­laterally. V De Freitas et al.10 exa­mined 1435 mandibles i.e. 2470 sides and found three sides of Mandible devoid of MF.

Thus, the variations in the num­ber of openings in the mental

region also varied. Most of the time a single foramen is present on both sides of the body of the mandible but it may double or triple or rarely be absent.

Clinical significanceMental injection or mental nerve block is given to achieve complete anaesthesia in the region of the ante­rior teeth including premolars and canines. It is important to consider the position of the MF and its mor­phological variations for the effec­tiveness of anaesthesia11.

While performing surgical pro­cedures below the second premolar tooth it has to be kept in mind that there could be two mental nerves as observed by Sahin et al.12 during maxillofacial surgery in a trauma patient.

Before coming out of the MF, the nerve loops in to the body of the mandible so the extent of the loop can affect the position of the implant, therefore, panoramic radiograph should be taken to assess the proper location for the implant placement2. Wang et al.13 observed the average distance between the upper bor­der of the MF and the bottom of the lower second premolar is about 2.50 mm. While performing root canal treatment in this region, the mental nerve could be injured due to close proximity to the lower part of the premolars .

ConclusionAfter reviewing the literatures, it can be concluded that variations in number of MF is not uncommon. If any surgery is planned in the area of canine to first molar tooth, one should always keep in mind these variations. Precise identification of these variations could be done by using advanced diagnostic tech­niques like Q­speed prospiral com­puted tomography (CT) scanner, 3D-CT and spiral CT. The knowl­edge of accurate position of MF is

Table 1 Positions and dimensions of MF and AMF

Parameters MF (Right side)

mm.

MF (Left side)

mm.

AMFmm.

Distance from symphysis menti 30 28 31Distance from posterior border of ramus of mandible

57 60 53

Distance from lower border of mandible

17 14 13

Size: Vertical diameter 1.5 1.8 1.2Horizontal diameter 1.5 1.8 1.0

Shape Round Round OvalDistance of AMF from MF - - 4Position of foramina with respect to lower teeth

Between 1st and 2nd premolar

Below 2nd premolar

Between 1st and 2nd premolar

Figure 2: Front view of mandible showing AMF unilaterally and MF bilaterally.

Case report

Page 3 of 3

Licensee OA Publishing London 2013. Creative Commons Attribution License (CC-BY)

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For citation purposes: Verma M, Soni S, Saxena A, Das AR. Unilateral variation of the mental foramen. OA Case Reports 2013 Sep 10;2(11):102.

important to avoid damage to neuro­vascular bundles passing through it and also to achieve absolute anaes­thetic effect at the anterolateral mandibular region.

References1. Neves FS, Soares L, Freitas DEA, Guanaes M, Torres G, Oliveira C. Acces­sory mental foramen: case report. RPG Rev. pos­grad. 2010 Jul;17(3):173–6.2. Aher V, Pillai P, Ali FM, Mustafa M, Ahire M, Kadri M, et al. Anatomical posi­tion of mental foramen: a review. GJMPH. 2012 Jan–Feb;1(1):61–4. 3. Singh R, Srivastav AK. Study of posi­tion, shape, size and incidence of mental foramen and accessory mental foramen in Indian adult human skulls. Int J Mor­phol. 2010 Dec;28(4):1141–6.

4. Balcioglu HA, Kocaelli H. Accessory mental foramen. N AM J Med Sci. 2009 Nov;1(6):314–15.5. Sawyer DR, Kiely ML, Pyle MA. The frequency of accessory mental foramina in four ethnic groups. Arch Oral Biol. 1998 May;43(5):417–20.6. Agarwal DR, Gupta SB. Morphome-tric analysis of mental foramen in human mandibles of South Gujarat. People’s J Sci Res. 2011 Jan;4(1):15–8.7. Ramadhan A, Messo E, Hirsch JM. Anatomical variation of mental fora­men. A case report. Stomatologija. 2010; 12(3):93–6.8. Gershenson A, Nathan H, Luchansky E. Mental foramen and mental nerve: changes with age. Aeta Anatomica (Basel). 1986;126(1):21–8.9. Katakami K, Mishima A, Shiozaki K, Shimoda S, Hamada Y, Kobayashi K.

Characteristics of accessory mental foramina observed on limited cone­beam computed tomography images. J Endod. 2008 Dec;34(12):1441–5.10. V De Friestas, Madeira MC, Tolledofillo IL, Chagas FV. Absence of the mental foramen in dry human mandibles. Acta Anat (Basel). 1979;104(3):353–5.11. Prabodha LBL, Nanayakkara BG. The position, dimensions and morphological variations of mental foramen in mandi­bles. Galle Med J. 2006;2(1):65–7. 12. Sahin B, Selman H, Gorgu M. An ana­tomical variation of mental nerve and foramen in a traumatic patient. IJAV. 2010 Jan;3:165–6.13. Wang TM, Shin C, Lin JC, Kuo KJ. A clinical and anatomical study of the location of the mental foramen in adult Chinese mandibles. Acta Anat (Basel). 1986;126(1):29–33.