European Journal of Cardiovascular Medicine

The human mandible, known for its complex structure and notable diversity, has been a captivating topic of study and considerable research in the field of human anatomy. The mental foramen is a significant anatomical structure in the mandible that has clinical importance. The mental foramen serves as a crucial pathway for neurovascular structures that provide innervation to the lower front part of the face. This makes it a significant topic of focus for dental professionals, maxillofacial surgeons, and anthropologists. The mental nerve, a branch of the inferior alveolar nerve, carries the sensation from the skin of the chin, lower lip, and labial mucosa Precise identification of the anatomical position of the mental foramen is critical in surgeries such as lower tooth flap operations, periodontal procedures, retrograde amalgam fillings, apicocurretage of mandibular premolars, surgical orthodontics, and other lower lip surgical procedures. To prevent harm to the mental nerve during treatments such as apicocurettage of the mandibular premolars, dental surgeons must have a thorough understanding of the connections between the mental foramen, the lower premolar teeth, and the body of the ramus. Damage to this nerve can result in either a transient or permanent alteration in the sensitivity, temperature and tactile perception within the affected region [2-4]. The objective of this study is to examine the dimensions and morphology of the mental foramen in the mandibles of adult humans. The literature has documented anatomical differences in the size, shape, and position of the mental foramen. These variations have significant consequences for local anesthesia, implantology, orthognathic surgery, and forensic identification. Comprehending the numerical elements of the mental foramen is not only essential in clinical practice but also greatly enhances our understanding of human craniofacial architecture and its evolutionary significance. Therefore, we studied the anatomical location, size, shape, and directions of the mental foramen of the mandible and the incidence of any accessory mental foramina in the population of Bihar and compared it with previous research.

The current research is a cross-sectional study that analyzed 50 fully ossified dentulous adult human mandibles (100 sides) of unknown gender and age. These mandibles were preserved well and were complete in all aspects, making them suitable for accurate morphological observations. They belonged to adult individuals and were obtained from the Department of Anatomy Indira Gandhi Institute of Medical Sciences, Patna, Bihar (India). Any bones that were extensively damaged, fragmented, showed healed fractures, or had significant deformities affecting the ramus of the mandible were excluded from the study. Linear measurements were taken with the help of a digital vernier caliper, which had a sensitivity of 0.01 mm, and the least count observed was 0.01 mm. Measurements were taken twice, and the average was included in the analysis. The following parameters were studied. Before measurement, the mandibles were placed on a horizontal plane surface to which the lower border of the mandible was in direct contact. Different parameters were measured using a digital vernier caliper, metallic wire, and scale on both the right and left sides.

The following parameters were studied:-

(A) Nonmetric Parameters:-

1. Shapes of the mental foramen.
2. Direction of exit of the mental foramen.
3. Locations in relation to the lower teeth.

(B) Metric Parameters:-

1. Transverse and vertical diameter of the mental foramen.
2. The distance from the symphysis menti.
3. The distance from the posterior border of the ramus.
4. The distance from the alveolar ridge.
5. The distance from the inferior border of the mandible.

The measurements were obtained using a metallic wire and a standard scale. The data was collected, tabulated, and statistically analyzed using Graph Pad Prism version 4.03. Mean and standard deviation were used to express continuous variables, while categorical variables were expressed as percentages. Representative photographs were taken with a digital mobile camera.

The average transverse diameter of the foramen was 3.09 mm on the right side and 3.42 mm on the left side, with a statistically significant difference between the two (p-value 0.03). The average vertical diameters were 3.69 mm on the right side and 3.54 mm on the left side [Table 1]. Based on our research, we found that the mental foramen is most often round in shape, occurring in 62% of cases [Table 2]. Additionally, in 90% of cases, the foramen exits in a postero-superior direction on both sides [Table 3]. Table 4 and figure 1 show the position of the mental foramen in relation to the mandibular teeth on both sides. We found that the foramen was most commonly located below the apex of the second premolar in 36% of cases on the right side and 37% on the left side. The second most common position was between the first and second premolars, occurring in 7% of cases on the right side and 6% on the left. A position between the first molar and second premolar was noted in 7% of cases on both sides. We measured the distances between the mental foramen and various anatomical landmarks: the symphysis menti, the alveolar crest, the posterior border of the ramus, and the inferior border of the mandibular body. The distance from the mental foramen to the symphysis menti was 28.87±1.45 mm on the right side and 28.38±1.44 mm on the left. The distance to the posterior border of the ramus was 72.09±1.17 mm on the right and 72.79±1.65 mm on the left, with a statistically significant difference between the sides. The distance from the mental foramen to the alveolar crest was 17.82±1.87 mm on the right and 17.91±1.16 mm on the left. Finally, the distance to the inferior border of the mandible was 16.63±1.26 mm on the right side and 17.23±1.34 mm on the left, with a statistically significant difference [Table 5]. The accessory mental foramina was found in 7% of cases on the right side, 5% on the left side, and 10% bilaterally [Table 6 and Figure 2].

Table 1:  Diameters of the mental foramen

[All measurements were in mm; * Statistically significant]

Table 2:  Shape of the mental foramen

[# Statistically not significant]

Table 3:  Direction of exit of the mental foramen

[# Statistically not significant]

Table 4:  Location of the mental foramen in the mandible

[# Statistically not significant]

Table 5:  Morphometric parameter of the mental foramen

[All measurements were in mm; * Statistically significant; # Statistically not significant]

Table 6: Showing the incidence of different types of accessory foramina of the mandible

Figure 1: Showing different positions of the mental foramen (A) Between 1^st and 2^nd premolar (B) Below the apex of the 2^nd premolar, and (C) Between 2^nd premolar and 1^st molar

Figure 2: Showing the mandible having the accessory mental foramen

Researchers from throughout the world have undertaken numerous studies on different races and ethnic groups to examine the morphometry of the mental foramen. We compared our results and observations with the findings of these investigations. Upon comparing and assessing the results of the current study with those acquired by previous researchers, many distinctions and resemblances were observed. Typically, there is just one opening of the mental foramen located on each side of the jaw. Nevertheless, there are instances where the mental foramen is entirely absent or several foramina are present, as documented in some reports [5]. Research has indicated that the occurrence of double mental foramina varies between 3.3% and 11.48%, depending on the specific population under investigation. In their study, Sankar D K et al. [6] discovered the presence of twin mental foramina in 5.6% of patients on the right side and 3.3% on the left side. Meanwhile, a study conducted by Singh S K et al. [7] found that 11.48% of individuals from North India while another study by Zografos and Mutzuri [8] indicated that 6.68% of the Greek population have double mental foramina. Rajkohila J et al. [9] discovered that the accessory mental foramen was present in 8.85% of cases in the South Indian population, with a higher prevalence on the left side than on the right side. Singh and Srivastav [10] revealed that 8% of accessory mental foramina were located on the left side and 5% on the right side. Udhaya et al. [11] observed that 3.33% of accessory mental foramina were identified on the left side and 2.22% on the right side. In contrast, Voljevica et al. [12] identified four more mental foramina, all of which were located exclusively on the right side of the jaw. In our current research, we found that supplementary mental foramina was present in 22% of instances. However, Singh S K et al. [7] reported the presence of triple mental foramen in 2.17% of mandibles from North India. The occurrence of mental foramen absence is a rare finding, as documented by de Frietas et al. [13]. Our observation revealed that the transverse diameter of the mental foramen was 3.09±1.28 mm on the right side and 3.42±1.68 mm on the left side. In addition, the vertical diameter of the mental foramen was measured to be 3.69±1.44 mm on the right side and 3.54±1.59 mm on the left side. According to a study conducted by M Janardhan Rao and S Saritha [14], the horizontal diameter of the mental foramen was found to be 3.12±0.43 mm and 2.99±0.26 mm on the right and left sides respectively. The vertical diameter of the mental foramen measured 2.32±0.31mm and 2.21±0.23 mm on the right and left sides, respectively. A separate investigation conducted by Nimje D A et al. [15] revealed that the mean horizontal measurement of the mental foramen was 3.11mm on the right side and 3.18mm on the left side. In contrast, Udhaya et al. [11] documented a distinct measurement of 2.28 mm on the right side and 2.95 mm on the left side. Based on our observation, the mental foramen was predominantly circular (62%) on both the right and left sides. According to M Janardhan Rao and S Saritha [14], the form that was most frequently observed was oval, with a prevalence rate of 69.28%. Our observations revealed that the mental foramen exited in a postero superior direction in 90% of instances, and in an antero superior direction in the remaining 10% of cases. However, M Janardhan Rao and S Saritha [14] discovered that 87.85% (123 sides) of the mental foramina exited in a postero superior direction, 7.14% (10 sides) exited in a superior direction, and 5% (7 sides) exited in an antero superior direction. Our research discovered that the mental foramen was most frequently located below the apex of the second premolar teeth, occurring in 73% of cases. Although additional research have yielded comparable findings, the occurrence of the phenomenon differed among other populations. The prevalence of the condition was 73.2% in the South Indian population [6], 68.58% in the North Indian population [7], 58.9% in the Chinese population [16], 47.2% in the Iranian population [17], 52.9% in the British population [18], 45.3% in the Saudi population [19], 55.6% in Nigerians [20], and 56.1% in Kenyan African mandibles [21]. The results of our study indicate that the distance between the mental foramen and the symphysis menti was measured to be 28.87±1.45 mm on the right side and 28.38±1.44 mm on the left side. Similarly, the distance from the mental foramen to the posterior border of the ramus was measured to be 72.09±1.17 mm on the right side and 72.79±1.65 mm on the left side. Sankar DK et al. [6] found that the distance between the mental foramen and the symphysis menti was 27.2±2.4 mm on the right side and 27.7±2.4 mm on the left side. Additionally, the distance between the mental foramen and the posterior border of the ramus was 70.7±4.2 mm on both sides. Our findings indicated that the distance between the mental foramen and the alveolar ridge was 17.82±1.87 mm on the right side and 17.91±1.16 mm on the left side. In addition, the distance from the mental foramen to the lower edge of the mandible body was measured to be 16.63±1.26 mm on the right side and 17.23±1.34 mm on the left side. On the contrary, Sankar DK et al. [6] discovered that the gap between the mental foramen and the alveolar crest measured 13.7±2.8 mm on the right side and 16.4±2.9 mm on the left side. Additionally, the distance between the mental foramen and the lower border of the mandible body was 16.5±2.1 mm on the right side and 14.3±2.1 mm on the left side.

The mental foramen is a small opening in the jawbone that is difficult to locate during a clinical exam or by touching the outside of the jaw. Accurate knowledge of its precise location and various distances is important for anesthesia and surgical procedures. However, its location and other related parameters have not been described previously in the population of Bihar. Therefore, this study was undertaken to determine the different dimensions and shapes of the mental foramen. The study provides valuable data regarding the mental foramen's location and shape, which can be useful for dental surgeons, neurosurgeons, and anesthetists in performing various surgical procedures and nerve blocks.

1. Standring, Susan, et al. "Mandible: Infratemporal and Pterygopalatine Fossae and Temporomandibular Joint." Gray’s Anatomy: The Anatomical Basis of Clinical Practice, 40th ed., Churchill Livingstone, Elsevier, 2008, pp. 530-532.
2. Nkenke, Emeka, et al. "Morbidity of Harvesting of Chin Grafts: A Prospective Study." Clinical Oral Implants Research, vol. 12, no. 5, 2001, pp. 495-502. DOI: 10.1034/j.1600-0501.2001.120512.x.
3. Raghoebar, Gerry M., et al. "Morbidity of Chin Bone Harvesting." Clinical Oral Implants Research, vol. 12, no. 5, 2001, pp. 503-507. DOI: 10.1034/j.1600-0501.2001.120516.x.
4. Sbordone, Luigi, et al. "Clinical Survey of Neurosensory Side-effects of Mandibular Parasymphyseal Bone Harvesting." International Journal of Oral and Maxillofacial Surgery, vol. 38, no. 2, 2009, pp. 139-145. DOI: 10.1016/j.ijom.2008.12.007.
5. Sankar, D. K., et al. "Morphometrical and Morphological Study of Mental Foramen in Dry Dentulous Mandibles of South Andhra Population of India." Indian Journal of Dental Research, vol. 22, no. 4, 2011, pp. 542-546. DOI: 10.4103/0970-9290.87058.
6. Singh, S. K., et al. "Variations in the Position and Number of Mental Foramen in Mandibles of North Indian Population." Journal of Anatomical Society of India, vol. 41, 1992, pp. 47-51.
7. Zografos, J., and A. Mutzuri. "Incidence of Double Mental Foramen in a Sample of Greek Population." Odontostomatology, vol. 43, 1989, pp. 521-523.
8. Rajkohila, J., et al. "Morphological and Morphometric Analysis of Accessory Mental Foramen in Dry Human Mandibles of South Indian Population." Indian Journal of Dental Research, vol. 29, no. 1, 2018, pp. 56-60. DOI: 10.4103/ijdr.IJDR_381_17.
9. Singh, R., and A. K. Srivastav. "Study of Position, Shape, Size, and Incidence of Mental Foramen and Accessory Mental Foramen in Indian Adult Human Skulls." International Journal of Morphology, vol. 28, no. 4, 2010, pp. 1141-1146.
10. Udhaya, K., et al. "The Morphometric Analysis of the Mental Foramen in Adult Dry Human Mandibles: A Study on the South Indian Population." Journal of Clinical and Diagnostic Research, vol. 7, no. 8, 2013, pp. 1547-1551. DOI: 10.7860/JCDR/2013/5990.3230.
11. Voljevica, Almir, et al. "Morphological and Morphometric Analysis of the Shape, Position, Number, and Size of Mental Foramen on Human Mandibles." Acta Medica Academica, vol. 44, no. 1, 2015, pp. 31-38. DOI: 10.5644/ama2006-124.122.
12. De Freitas, V., et al. "Absence of the Mental Foramen in Dry Human Mandibles." Acta Anatomica, vol. 104, 1979, pp. 353-355. DOI: 10.1159/000145118.
13. Janardhan Rao, M., and S. Saritha. "A Study on the Morphometric Analysis of the Mental Foramen in South Indian Dry Adult Human Mandibles." International Journal of Anatomy Research, vol. 5, no. 4.2, 2017, pp. 4590-4594. DOI: 10.16965/ijar.2017.438.
14. Nimje, D. A., et al. "Morphometric Study of the Mental Foramen in Dry Adult Human Mandibles." International Journal of Recent Trends in Science and Technology, vol. 12, 2014, pp. 47-49.
15. Wang, T. M., et al. "A Clinical and Anatomical Study of the Location of the Mental Foramen in Adult Chinese Mandible." Acta Anatomica, vol. 126, no. 1, 1986, pp. 29-33. DOI: 10.1159/000146229.
16. Haghanifar, S., and M. Rokouei. "Radiographic Evaluation of the Mental Foramen in a Selected Iranian Population." Indian Journal of Dental Research, vol. 20, no. 2, 2009, pp. 150-152. DOI: 10.4103/0970-9290.52900.
17. Santini, A., and M. Land. "A Comparison of the Position of the Mental Foramen in Chinese and British Mandibles." Acta Anatomica, vol. 137, no. 3, 1990, pp. 208-212. DOI: 10.1159/000146814.
18. Al Jasser, N. M., and A. L. Nwoku. "Radiographic Study of the Mental Foramen in a Selected Saudi Population." Dentomaxillofacial Radiology, vol. 27, no. 6, 1998, pp. 341-343. DOI: 10.1038/sj.dmfr.4600378.
19. Kekere Ekun, T. A. "Antero-posterior Location of the Mental Foramen in Nigerians." African Dental Journal, vol. 3, 1989, pp. 2-8.
20. Mwaniki, D. L., and J. Hassanali. "The Position of Mandibular and Mental Foramina in Kenyan African Mandibles." East African Medical Journal, vol. 69, no. 4, 1992, pp. 210-213.