Journal of Indian Academy of Oral Medicine and Radiology

: 2020  |  Volume : 32  |  Issue : 4  |  Page : 396--398

Unilateral agenesis of the mental foramen

Ajay Pratap Singh Parihar1, Sheetal Singar1, Sonam Gehi2, Ashish Saxena3, Arvind Jain4,  
1 Department of Oral Medicine and Radiology, Government College of Dentistry, Indore, Madhya Pradesh, India
2 Department of Prosthodontics, Government College of Dentistry, Indore, Madhya Pradesh, India
3 Department of Pedodontics, Government College of Dentistry, Indore, Madhya Pradesh, India
4 Department of Conservative Dentistry and Endodontics, Government College of Dentistry, Indore, Madhya Pradesh, India

Correspondence Address:
Dr. Ajay Pratap Singh Parihar
Oral Medicine and Radiology, Government College of Dentistry, Indore, Madhya Pradesh


The inferior alveolar nerve canal opening in the anterior labial aspect called mental foramen (MF) is a vital anatomic landmark of the mandible, through which the mental nerve and blood vessels emerge. The importance of MF is particularly associated with dental implant placement and various surgical procedures within this region. It is elementary to use caution in and around the MF region during surgical procedures and implant placement to avoid nerves and vessel injury. Anatomic variations of the MF are often found, like the prevalence of multiple foramina and unusual locations in the mandible. On rare occasions, the absence of MF is often detected. The modern imaging-resource cone-beam computed tomography (CBCT) permits correct three-dimensional assessment of MF and identification of its variations. This article aims to report the unilateral absence of MF detected in CBCT images of a 70 years-old male patient.

How to cite this article:
Singh Parihar AP, Singar S, Gehi S, Saxena A, Jain A. Unilateral agenesis of the mental foramen.J Indian Acad Oral Med Radiol 2020;32:396-398

How to cite this URL:
Singh Parihar AP, Singar S, Gehi S, Saxena A, Jain A. Unilateral agenesis of the mental foramen. J Indian Acad Oral Med Radiol [serial online] 2020 [cited 2021 Feb 27 ];32:396-398
Available from:

Full Text


The mental foramen (MF) also called mental hiatus is opening on the outer surface on the anterolateral part of the body of the mandible. It transmits the mental nerve branches and blood vessels innervating various parts of the face. The most common position of the MF is in line with a longitudinal axis of the second premolar followed closely by the location between the first and second premolars.[1]

The MF is a vital structure for local anesthesia, implant placement, periapical and orthognathic surgery, and forensic odontology.[2] MF may not be always visible on the radiographs because of superimpositions of anatomic landmarks, trabecular pattern, and distortion of the radiographic image because of common positional errors.[3] Absent MF is an extremely rare anatomic variation. Man is the only primate known to have agenesis of the MF. Other than agenesis, atrophy, post-traumatic fibrosis, hyperplasia, age-related bony changes are the frequent reasons for its absence.[4] Medical literature is scant when it comes to reports of absent MF. Unilateral absence of the MF is very rare ranging from 0.02% to 0.47%, while the bilateral absence is statistically negligible. Since the MF is the exit for the mental nerve and vessels which supply the chin and lower lip. The absence of MF would mean there is no exit for the nerve and vessels which may cause an altered sensation in that area. Clinical implications would include the ineffective mental block in anesthesia and neuromuscular disturbances on the chin and around the lip.[5] This article reports the unilateral absence of MF on the right side of the mandible of a 70-year-old male patient detected in CBCT images.

 Case Description

A 70-year-old male patient had undergone a cone-beam computed tomography (CBCT) examination for implant planning. A CBCT examination was done by KS stream CS 9300, with a field of view of 5.5 cm, voxel size of 19 mm, and KS stream 3D imaging software. The patient's chief complaint was missing teeth concerning 44 with no history of trauma. His medical history was non contributory. Dental history of patient included root canal treated teeth regarding 31,32,33,37,41,42,43,45, extraction regarding 44, fixed partial denture regarding 45,46,47 with 46 as pontic, implant-retained fixed partial denture with respect to 34,35,36 with implant at site 34 and 36. An experienced maxillofacial radiologist carefully assessed cross-sections of the mandible, axial, and coronal slices. The left MF was detected on the expected location-on the buccal surface in the region of both premolars. MF was not found on the opposite side, which is the right side [Figure 1]. The right mandibular inferior alveolar canal mesially continues up to below the edentulous region of 44. Small incisive canal branches with the vertical course were seen lingually in the regions of 41 and 31 regions [Figure 2] and [Figure 3]. The patient had a negative history of sensory loss in that region. Oblique section of right mandible and Axial view also showed the absence of right mental foramen [Figure 4] and [Figure 5].{Figure 1}{Figure 2}{Figure 3}{Figure 4}{Figure 5}


It is well documented in the literature that the formation of MF starts first as ossification of the expanding flat layer of bone near future MF in the embryo between 13 and 22 mm crown-rump length. Thereafter, an extra bony lamella arises lateral to Meckel's cartilage.[6] According to Kjear and Sperber,[7] formal development and positional changes of MF into a more distal direction resulted from the dragging action of the nerve. Formation of MF is affected by different tissues, such as nerves, blood vessels, connective tissue and bone surrounding it which is a prerequisite for its formation in sense of induction of osteogenesis and production of neurotrophic factors. Further, these adjacent structures are the source of local epigenetic factors with morphogenetic influence.[8]

Silva et al. reported an interesting case of her mother with the absence of MF on one side along with hyperplasia of MF on the other side. Variations of the MF may partly arise because of some genetic factors.[9] There are several reasons MF does not appear clear on all radiographs, according to Yosue and Brooks.[6] Inability to visualize MF can be because of difficulty to differentiate trabecular pattern, thin mandibular bone which gives no radiographic contrast, thick lingual cortical plate or can be because of dark radiographs. Image distortion can also be because of head positioning on panoramic films, angulation of periapical films. MF can also be missed on periapical films if located below the edge of films. Thus, the radiographic assessment of MF is not always possible, because of limitations of periapical and panoramic techniques. Jacobs et al. reported that the MF was detected in 94% of their assessed panoramic radiographs, but only 49% were visible. Fishel et al. reported in their study that MF was detected in 46.8% of periapical films.[10]

We can conclude that the lack of observation of MF in conventional radiographs does not correspond to its absence in reality. Therefore, knowledge of the position of this anatomical landmark facilitates giving local anesthesia, making incisions, performing periapical surgeries, osteotomies like genioplasty, placing implants as the recent trend has increased the use of implant-supported prosthesis for replacing missing teeth. In our reported case, the diagnosis of this anatomic variation was possible because of the previously performed CBCT examination.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient (s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


1Moiseiwitsch JR. Position of the mental foramen in a North American, white population. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1998;85:457-60.
2Angel JS, Mincer HH, Chaudhry J, Scarbecz M. Cone-beam computed tomography for analyzing variations in inferior alveolar canal location in adults in relation to age and sex. J Forensic Sci 2011;56:216-9.
3Lauhr G, Coutant JC, Normand E, Laurenjoye M, Ella B. Bilateral absence of mental foramen in a living human subject. SurgRadiol Anatomy 2015;37:403-5.
4Hasan T, Fauzi M, Hasan D. Bilateral absence of the mental foramen: A rare variation. Int J Anat Var 2010;3:167-9.
5Hu 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.
6O'Rahilly R, Meyer DB. Roentgenographic investigation of the human skeleton during early fetal life. Am J Roentgenol 1956;76:455-68.
7Kjaer I. Formation and early prenatal location of the human mental foramen. Scand J Dent Res 1989;97:1-7.
8Van Limborgh J. A new view on the control of the morphogenesis of the skull. Acta Morphol Neerl Scand 1970;8:143-60.
9da Silva Ramos FernandesLMP, Capelozza ALA, Rubira-Bullen IRF. Absence and hypoplasia of the mental foramen detected in CBCT images: A case report. Surg Radiol Anatomy 2011;33:731-4.
10Fishel D, Buchner A, Hershkowith A, Kaffe I. Roentgenologic study of the mental foramen. Oral Surg Oral Med Oral Pathol 1976;41:682-6.