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Original Study of anatomical variations of mental foramen in dry adult human mandible

Background: Mandible also known as the largest and inferior, primary facial bone of the face giving a curved shape to it. It changes its shape and gives variations to the bony structure of the face from birth till older age. Mental foramen is known as the ventage of the mandible and is an important mark of the face for carrying out many diagnostics and surgical processes along with anesthetic procedures of the face. Thus, the present study is designed with an aim to get insight knowledge of position and shape of mental foramen in dry adult human mandible. Methods: Totally, 60 bones were studied in 2 years duration. The study was carried out in the Department of Anatomy of Geetanjali Medical College and Hospital and Rabindranath Medical College. The position of mental foramen was studied using an instrument known as digital Vernier Calliper (in mm) while shape was analyzed visually. Position of mental foramen was calculated using Statistical package for social sciences (SPSS) software. Results: The present study showed that the position of mental foramen from symphysis menti and posterior border of ramus of mandible was more from right side than left side and found to be insignificant while position of mental foramen from inferior border of body of mandible was more from left side than right side and found to be insignificant for right side while significant for left side. The shape of mental foramen from right side was found to be (Oval shape- 68.33% and round shape – 31.66%) while for left side was found to be (Oval shape- 71.66% and round shape – 28.33%). Conclusions: Hence, mental foramen plays a pivotal role in performing major facial surgeries and is an important landmark for several facial procedures performed.


INTRODUCTION
Mandible is the largest, strongest and lower bone of the face having a curved body that is convex forwards with two broad ramus ascending posteriorly. Rami of the mandible carries coronoid & condylar processes. 1 Mental foramen of mandible is situated in anterolateral aspect of the body. It lies below either the interval between the premolar tooth, midway between the upper and lower borders of the body of the mandible. 2 On the inner surface of the body of mandible lies mandibular foramen that leads into the mandibular canal and opens on the outer surface of the mandible as mental foramen. 3 Mental foramen transmits mental nerve, artery and vein through its canal. Mental nerve is a branch of inferior alveolar nerve supplying sensations to lower lip, labial mucosa, lower canines and premolars. 2 the relative position/location of the mental foramen changes; thus, providing a clue to the age of an individual. In infancy, the mental foramen is located relatively far posteriorly, below the first molar bud and with the eruption of permanent teeth, the mental foramen moves anteriorly, reaching its final destination that corresponds to the level of the second premolar tooth; Thus, accounting for its relative anteroposterior movement. With regard to its relative vertical movement, the mental foramen appears closer to the alveolar margin in neonates, and with eruption of teeth it descends between the alveolar and inferior border while in adult the mental foramen is nearer to the inferior border and moves upwards. As mental foramen moves upwards, it gets closer to the alveolar border representing an old age. Along with an increase in age it shows the loss of teeth and bone resorption in elderly people. 4,5 Mental foramen is an anatomical landmark for mandible facilitating diagnostic, surgical, local anesthetic and other invasive procedure for dental surgeons performing periapical surgery in the mental region of mandible. 6 Also, it is an important region for performing anesthetic block prior to clinical procedures in lower anterior teeth and to preserve integrity of mental nerve trunk in surgical interventions. 7,8 Precise knowledge of position, shape, and number of mental foramen can be of much use for dental surgeons for performing surgical procedures of mandible such as curettage of the premolars, filling procedures, dental implants for root canal treatments etc.
Many studies have been reported by various authors, performing studies on different ethnic groups and on population of different races. To put more emphasis on an important foramen, present study is designed to deal with measurements of position and shape of mental foramen in dry adult human mandibles (Right side as well as left side).

METHODS
The present study was designed as a comparative and descriptive study, which was started after obtaining ethical clearance from institutional ethical committee. Total 60 bones were included in the study for consideration. Unknown mandibles with intact alveolar sockets removed from cadavers and unknown mandibles from storage room of dry adult mandibles were obtained in 2 years (i.e. August 2016 to August 2018). Thus, a total of 60 mandibles were obtained from Geetanjali Medical College (Udaipur) and R.N.T. Medical College (Udaipur) from the Department of Anatomy after getting permission.

Inclusion criteria
Normal adult human mandibles with intact alveolar processes and without any apparent damage or congenital anomaly was included in the study.

Exclusion criteria
Abnormal human mandible with incomplete alveolar processes, with congenital or Pathological anomalies, damaged specimen, pediatric mandibles were excluded from the study.

Methodology followed during study
For measurement of various parameters of our study, mandible was placed on the horizontal plane and the lower border of mandible interact with greatest force as vertical pressure is applied to the second molar teeth.
The shape of mental foramen in dry human adults was analysed by visual examination of the both sides of the mandible.   Position was measured using Digital Vernier Calliper (in mm). 9 ( Figure 4)

Statistical analysis
Mean and standard deviation of the position of mental foramen was calculated using Statistical package for social sciences (SPSS) software for comparison.

RESULTS
In the present study, the statistical analysis was evaluated as mean and standard deviation. The mean and standard deviation of mental foramen (left and right side) were calculated. It was done using SPSS software and p>0.05 was considered insignificant while p<0.05 was considered significant.
In our study, the mean and standard deviation of the mean and standard deviation of position of mental foramen from symphysis menti was found to be (25.729±1.927) on right side and (25.277±1.977) on left side. The distance from right side was more than the left side and was found insignificant (p>0.10 for both sides) ( Table 1).
The mean and standard deviation of position of mental foramen from posterior border of ramus of mandible was found to be (62.333±5.045) on right side and (62.248±5.423) on left side. The distance from right side was more than the left side and was found insignificant (p value >0.10 for left side and p>0.0900 for right side) ( Table 2).
The mean and standard deviation of position of mental foramen from inferior border of body of mandible was found to be, (12.531±1.994) on right side and (12.684±2.273) on left side. The distance from right side was less than the left side and was found insignificant for right side while significant for left side (p>0.10 for right side and p value 0.024 for left side) ( Table 3).
The shape round and oval of mental foramen was also compared for both the sides and the results for right side (Oval shape -68.33% and round shape -31.66%) while for left side (Oval shape -71.66% and round shape -28.33%) ( Table 4).

DISCUSSION
Mental foramen is situated in anterolateral aspect of the body of the mandible. It lies below either the interval between the premolar tooth, midway between the upper and lower borders of the body of the mandible. 2 It is an anatomical landmark for facilitating diagnostic, surgical, local anesthetic and other invasive procedure for dental surgeons performing periapical surgery in the mental region of mandible. 6 Knowledge of position, shape and size of mental foramen is important for performing anesthetists block prior to clinical procedure in lower anterior teeth and to preserve integrity of mental nerve trunk in surgical interventions. 7,8 Prabodha et al. reported in 24 dry adult mandibles the mean distance of mental foramen from symphysis menti, lower border of the body of mandible and posterior border of the ramus of the mandible were 26.25 mm, 12.25 mm and 65.38 mm respectively. The shape of mental foramen was oval in 66.67% and rounded in 33.33% of mandibles. 10 In contrast to our study the mean distance of mental foramen from symphysis menti were 25.72 mm (right side) and 25. 27 mm (left side), inferior border of body of mandible were 12.53 mm (right side) and 12.68 mm (left side) and from posterior border of ramus were 62.33 mm (right side) and 62.24 mm (left side) while the shape of mental foramen was oval in 70% and rounded in 30% of mandibles.
Ilayperuma et al. reported that in 51 adult dry mandibles the mean distance of mental foramen from symphysis menti was 24.86 mm. The most common position for the mental foramen was in line with longitudinal axis of the lower second premolar 52.94% followed by a position between first and second premolar 26.47%. In most of the mandibles the shape of the mental foramen was oval i.e. almost 59%. 11 In contrast to our study the position of mental foramen from symphysis menti was 25.72 mm (right side) and 25.72 mm (left side). The most common position for the mental foramen was in line with apex of the lower second premolar 68.33% and the second most common position was in line with apex of second premolar and first molar is 15.83%. The shape of mental foramen was oval in 70% and rounded in 30% of mandibles.
Udhaya et al. reported that out of 87 dry mandibles, in 75 mandibles (83.33%) the mental foramen was bilaterally showing an oval shape and in the remaining 15 mandible (16.67%) the mental foramen was bilaterally showing a round shape. 12 In contrast to our study out of 120 mandibles, in 70% mandible the mental foramen was bilaterally showing an oval shape and in 30% mandible the mental foramen was bilaterally showing a round shape.
Sukla et al reported that the oval shape of mental foramen was 87.1% on right side and 88.6% on left side. Round shape mental foramen was observed to be 12.9% on the right side and 11.4% on the left side13 while in contrast to our study oval shape of mental foramen is more prominent in both sides. Suman et al observed that the most common position of mental foramen in relation to lower (mandibular) teeth was below the apex of second premolar teeth in 56.86% of mandibles followed by space between second premolar and first molar teeth. 14 While in present study the most frequent position of the mental foramen was in line with apex of the lower second premolar 68.33%on both left and right side, respectively.
Hence, its deep awareness is necessary while performing various surgical procedures and in applying anaesthesia to the patients to avoid any complications. Mainly dentists must take proper care and precautions of that important bone to avoid any type of injuries.

CONCLUSION
In conclusion, we observed the mean value of position of mental foramen from the symphysis menti is 25.72±1.927 on the right side and 25.27±1.977 on left side, and from the posterior border of the ramus of mandible was 62.33±5.045 on the right side and it was 62.24±5.423 on the left side, and position from the lower border of the body of mandible was 12.53±1.994 on the right side and 12.68±2.273 on the left side respectively. When it comes to the shape of mental foramen it was observed that oval shape is more markable in right side with 68.33% while rounded shape is less marked with 31.66%. On contrary, oval shape is again more dominant on left side with 71.33% while rounded shape is less dominant with 28.33%. No variations were found in the number of mental foramen.
In hypothesis, knowledge of position, shape and size of mental foramen is important for performing anesthetic block prior to clinical procedure in lower anterior teeth and to preserve integrity of mental nerve trunk in surgical interventions while knowledge of the morphology of the mental foramen is important when administering regional anaesthesia, performing periapical surgery, dental implant surgery and endodontic treatments in the mandible. Its understanding is also useful in preserving and avoiding injury to the mental nerve and vessels during surgical procedures and in interpreting anatomical landmarks in oral pathology and forensics. In the present study we also discovered already non-common insignificant variations associated with position of mental foramen from symphysis menti, lower border of the body of mandible and from posterior border of ramus of the mandible. The future scope of the study can be to properly identify all the variations by extensive review of published articles.