Topography of the location of mental foramen in dried edentulous human mandible and its clinical implication

Introduction

The mandible bone is the strongest and largest bone of the human face that develops from the first pharyngeal arch. Mandible bone is a U- shaped bone consists of horizontal part body and vertical part ramus. Horizontal part has alveolar process that supports mandibular teeth. Mental foramen is present on the outer surface of mandible inferior to second premolar teeth through which mental nerve and mental vessels emerge.1

About 6^th week in utero one center of ossification appear in each half of mandible near mental foramen in the mesenchymal sheath of Meckel’s cartilage near the future mental foramen. In neonate body of mandible is mere a shell, each half enclosing deciduous teeth. At this stage mandibular canal is near lower border of body and mental foramen located below the first deciduous molar and directed forward. With the development of chin and eruption of teeth direction of mental foramen alters and it is directed backwards. Elongation of the body of mandible occurs mainly on the posterior to the mental foramen and increase in the height of mandible is achieved by formation of alveolar bone and deposition of bone on the lower border. So with development the foramen and canal gradually shift upwards. In adults, the mental foramen lie mid way between the upper and lower borders of the body. In edentulous mandible the alveolar border is resorbed so the mental foramen and the mandibular canal are close to the alveolar border or sometimes inferior alveolar nerve lies beneath the oral mucosa.1, 2

The mental foramen transmits mental nerve, artery and vein. Mental nerve is a terminal sensory branch of the inferior alveolar nerve which receives sensation from lower lip, buccal vestibule and gingiva mesial to the first mandibular molar.

Mental foramen is an important anatomical landmark. Knowledge of the orientation and position of it facilitate local anesthetic, surgical and other invasive procedures for oral and maxillofacial surgeries.3

During radiographic examination the foramen may be misdiagnosed as a radiolucent lesion in the apical area of the mandibular premolar teeth. So identification of accurate anatomical position of mental foramen is very important in periodontal surgery especially during flap surgery in lower teeth, retrograde amalgam fillings, apical curettage of mandibular premolars.

Accurate location of mental foramen will facilitate the administration of local anesthesia of the terminal incisive branches of the inferior alveolar and mental nerves. Many studies and textbooks describe the location of the mental foramen as being below the apex of the second premolar or between the apices of the first and second premolar but in edentulous mandible it become difficult to locate the position of mental foramen.

Material and Methods

Present study 60 dried edentulous mandibles of unknown sex were selected for the study. Damaged and broken and congenitally malformed mandible were excluded. Shape of mental foramina were macroscopically observed and noted. Various measurements were taken on both side using digital vernier caliper.

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Results

Out of 60 mandible 18 mental foramina on right and 18 on left side were oval in shape rest were round. Most common shape of mental foramen was round (70%).

Correlation between distance of MF from symphysis menti and length of mandible and its analysis shows significant positive correlation.

Figure 5

The mental foramen usually found on the anterolateral surface of the mandible which is a single circular or oval opening lies 13-15 mm superior to the inferior border of the body of mandible.4 In most cases mental foramen is the interval between the two premolars and the apex of second premolar is the another most common site.5 In our study, the distance from inferior margin of mental foramen and the lower border of mandible is 12.28 mm on right side and 12.49 mm on left side in edentulous human mandibles comparatively less than the study done by Srinivas Moogala et al.6 The study done in Korean population by Chung et al.7 reported that the average distance between the inferior border of the mandible and the center of mental foramen was 15.5 mm in males and 14.0 mm in females.

In edentulous human mandible location of mental foramina will depend upon the degree of bone resorption. The position of mental foramen moves towards the upper border of mandible and in severe cases alveolar nerves and vessels exposed out of the bone and it lies just deep to the oral mucosa that sometimes causes pain to who wears denture.9

Commonly there is single mental foramen on right and left side. In our study, any accessory mental foramen was not found. In most studies accessory mental foramen is a rare anatomical variation.6, 9, 10, 11, 12, 13, 14 Having a knowledge of accessory mental foramen for clinicians is important to prevent neurovascular complications, while doing surgical procedures, during dental implant surgery and any other surgical procedure involving the molar and premolar region.

In our study, the distance from most anterior margin of mental foramen to posterior border of ramus of the mandible (D3) on right side it is 64.44 ± 5.23 mm and left side it is 64.26 ± 4.58 mm which found less than the studies conducted by Srinivas Moogala et al.6 and Shankar et al.14

In study done by Mraiwa et al.15 showed that in dentate mandibles the MF was commonly located at a half way distance from the alveolar crest to the inferior border of mandible. The alveolar bone resorption after teeth loss, transposes the MF closer to the alveolar crest and in extreme situations the foramen might be found on the crest of the alveolar ridge. Study done by Srinivas Moogala et al.6 conclude that in dentate and edentulous human mandibles the distance from symphysis menti to the most anterior margin of mental foramen nearly same. While study by Qiufei Xie et al16 summarizes no significant reduction in the average distance between the lower most point of the mandibular canal and the lower border of mandible in the edentulous human.

In our study, we found significant positive correlation in distance between mental foramen and symphysis menti, and between length of mandible. Obtained data can be use to locate the vertical plane of possible location of mental foramen.

In clinics dental surgeons should be aware of the possibility of variation found in abnormal location of MF in the mental area in order to prevent the injury to the MN and adjacent blood vessels and the resulting postoperative sensory complication of the teeth and surrounding skin and mucosa during various dental surgery like genioplasty, vestibuloplasty and dental implantation. To have a safety zone of 2mm must be there between coronal aspect of nerve and implant to avoid mental nerve injury in surgery nearby mental foramina.

Conclusion

The location of the mental foramen needs to be considered before any surgical procedures in this region to avoid mental nerve injury during surgery. The position of the foramen is altered in edentulous mandibles compared with the dentate ones. The MF location is directly affected by dental status. Evaluation of the status of the alveolar ridge in edentulous mandibles is very important during the process of construction of removable dentures and dental implants placement. The morphology of edentulous mandibles increases the risk of intraoperative complications at the anterior mandible.

Limitation of the Study

Small sample size and gender differences were not studied.

Source of Funding

None.

Conflicts of Interest

None.