A morphological study of retromolar foramen and canal in Indian dried mandibles.
Neurovascular structures passes through this canal gives additional supply to mandibular molars and buccal area. Extraction of lower 3rd molar, which is commonly known as Wisdom teeth, is a common dental procedure. A complete knowledge of the region around 3rd molar is necessary to minimize complications like unexpected bleeding, hematoma formation etc. The neurovascular bundles may get damage during placement of osteointegrated implant, endodontic treatment, sagittal split osteotomy & bone harvesting as a donor site for bone graft surgery. 
Since most of the anatomical textbooks and dental literatures do not mention about this foramen or canal and very few studies have been conducted on Indian populations. Hence, we study the possible variations in position of retromolar foranen (or canal) i.e. distance of RMF (or RMC) from the posterior border of 3rd molar socket, anterior border of the ramus & lingula and document its incidence in Indian population.
MATERIALS AND METHODS: The present study has been carried out on 224 dried fully ossified adult human mandibles, which are obtained from Department of Anatomy of Indira Gandhi Institute of Medical Sciences (Patna, Bihar, India), Maitri College of Dentistry & Research Centre (Durg, Chattishgarh, India), Lord Buddha Koshi Medical College (Saharsa, Bihar, India), F. I. Maulana Ali Mian Medical College (Unnao, Uttar Pradesh, India) & Patna Medical College (Patna, Bihar, India) by the consents and permission from heads of the institutes and anatomy department. These 224 mandibles are segregated into male and female mandibles on the basis of following criteria:
1. In males: The angle of mandible is everted.
2. In females: The angle of mandible is inverted.
Finally, these are segregated as 134 male and 90 female mandibles. Mandibles having marked deformities and fractured mandibles are excluded from the study. Each mandible are observed carefully for presence of retromolar foramen and retromolar canal. Wherever foramina are noticed, the distance of foramina from posterior border of 3rdmolar socket, anterior border of the ramus and lingula are measured, using a vernier caliper. The mean, range and standard deviation of all the measurement are statistically analyzed.
RESULT: The retromolar foramen and canal (Fig. 2 & 3) are found in 33 among 224 mandibles (14.7%) of which 11 on the right side (4.9%), 7 on the left side (3.1%) and 15 bilaterally (6.7%) (Table 1 & Figure 1). It is seen that the distance of RMF from posterior border of 3rd molar socket, anterior border of the ramus, and lingula (Fig. 4, 5 & 6) varies between 3 to 10 mm, 4 to 11 mm & 3 to 9 mm respectively in right side and 5 to 12 mm, 3 to 11 mm, & 2 to 8 mm respectively in left side (Table-2 & 3).
From the above observations, it is found that the occurrence of RMF is more common in females as compared to males. It is more common in right side of mandible. The bilateral occurrence of RMF is found to be also higher in females. The position of RMF is nearer to third molar in right side in comparison to left side.
DISCUSSION: The incidence of RMF, located in the retromolar triangle, in our study is 14.7%, which is lesser than incidence of Park MK et al  (93.5%), followed by incidence of Schejtman et al  (72%), Kawai et al  (52%), Rossi et al  (26.6%), Von Arx et al  (25.6%), Bilecenoglu and Tuncer  (25%), Kodera and Hashimoto  (20%) followed by Lagrana et al  (18%). The highest incidence of retromolar foramen is found in Korean population.  An our incidence (14.7%) is greater than incidence of Sawyer and Kiely  (7.7%), Pyle et al  (7.8%), Ossenberg  (8.2%) followed by Suazo et al  (12.9%).
The incidence of the RMF in our study is also compared with the studies of different authors on different races of world (Table-4). Percentage presence of RMF in our study falls somewhere within the range reported from study of Athavale et al  (14.1%) and Gupta et al  (18%), which were done on Indian population. The incidences reported from Indian population [16-19] are varying from 7.8 to 21.9%. The differences in the incidence of the RMF in these studies may be due to differential origins in Indian population.
Our findings show that the distance between the third molar and RMF is within the short range of 3 to 10 mm in right side and 5 to 12 mm in left side which is comparable with the recent study published in the literature. [16,18,19] This close relation of RMF with 3rd molar may damage the structures passing through RMF during 3rd molar extraction and causes postoperative hematomas due to rupturing of the blood vessels.
Pinsolle et al  found in his study that the RMF contain blood vessels, so this may be a cause of the spread of infection and metastasis from oral cavity to the blood circulation. Ossenberg NS  did not found any difference in incidence of RMF in male and female. But in our study, incidence is more common in female. He also found a positive intertrait relationship between presence of RMF and presence of accessory mandibular foramen & mental foramen.
Sawyer DR & Kiely ML  also did not found any difference in incidence of RMF between right and left side & between sexes. In our study, it is more common in female and right side of mandible. Park MK et al  classified the retromolar triangle according to its shape into three types: triangular, drop and tapering shape, in which triangular was most common. On Japanese cadavers, Kodera & Hashimoto  studied during dissection that a branch from the inferior alveolar artery originated and passed through RMC.
When this branch ran forward get joined with branches of buccal and facial artery. They also found that the nerve in RMC originated from inferior alveolar nerve. Anderson et al  studied the components of RMF & RMC and found that these contained nerve fibres, which supplied the 3rd molar pulp, retromolar area, temporalis and buccinator. So, damage of nerve fibres in RMC leads to alteration in function of temporalis and buccinator. Carter et al  also found in his study that nerve fibres which supplied the lower molar, arises from the inferior alveolar nerve or from the retromolar branch that passes through the RMC.
The course of neurovascular structures originating from the retromolar foramen was also studied by Schejtman et al  during dissection. He found that after leaving the foramen, these fibres were distributed mostly to temporalis tendon, buccinator, most posterior part of alveolar process and lower 3rd molar. They also studied under microscope & observed that the most constant element in RMC was a myelinated nerve. The branches of mandibular division of inferior alveolar nerve may arise high in the infratemporal fossa as explained by Ikeda et al  in his study.
These fibres extend to the base of coronoid process & enter the mandible in retromolar fossa and innervates the lower molar. Sutton  first of all explained additional sensory nerve fibres in RMF. He explained the relationship between the presence of this foramen and the failure of obtaining analgesia using classical anesthetic techniques. The bone surrounding the retromolar triangle is heavier as compared to cortical plate over triangle & cortical plate is more cancellous.  During routine anesthetic, surgical and implantation procedure of mandible, its cancellous nature always kept in mind to prevent damage of neurovascular bundles in RMF.
CONCLUSION: In this study, we report the incidence of retromolar foramen and its distance from the posterior border of 3rd molar socket, anterior border of the ramus, and lingula in Indian population, it is helpful in better understanding of clinical and surgical practice in this region. There is still possibility to study of this canal in living subjects by introducing the dye into the inferior alveolar artery. This may provide more information about this canal. It remains unknown, how the retromolar canal develops in the mandible, so there is need of further studies on large population across the world to understand its origin and evolutionary importance.
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(1.) Md. Jawed Akhtar
(2.) Sufia Parveen
(3.) Premjeet Kumar Madhukar
(4.) Nafees Fatima
(5.) Avanish Kumar
(6.) Binod Kumar
(7.) Rajiv Ranjan Sinha
(8.) Vinod Kumar
PARTICULARS OF CONTRIBUTORS:
(1.) Senior Resident, Department of Anatomy, Indira Gandhi Institute of Medical Sciences, Sheikhpura, Patna, Bihar, India.
(2.) Lecturer, Department of Prosthodontics, Maitri College of Dentistry and Research Centre, Anjora, Durg, Chattishgarh, India.
(3.) Assistant Professor, Department of Anatomy, Lord Buddha Koshi Medical College & Hospital, Saharsa, Bihar, India.
(4.) Assistant Professor, Department of Anatomy, F. I. Maulana Ali Mian Institute of Medical Sciences, Unnao, U.P. India.
(5.) Associate Professor, Department of Anatomy, Indira Gandhi Institute of Medical Sciences, Sheikhpura, Patna, Bihar, India.
(6.) Assistant Professor, Department of Anatomy, Indira Gandhi Institute of Medical Sciences, Sheikhpura, Patna, Bihar, India.
(7.) Assistant Professor, Department of Anatomy, Indira Gandhi Institute of Medical Sciences, Sheikhpura, Patna, Bihar, India.
(8.) Professor & HOD, Department of Anatomy, Indira Gandhi Institute of Medical Sciences, Sheikhpura, Patna, Bihar, India.
NAME ADDRESS EMAIL ID OF THE CORRESPONDING AUTHOR:
Dr. Md. Jawed Akhtar, Senior Resident, Department of Anatomy, Indira Gandhi Institute of Medical Sciences, Sheikhpura, Patna-800014, Bihar, India.
Date of Submission: 15/10/2014.
Date of Peer Review: 16/10/2014.
Date of Acceptance: 30/10/2014.
Date of Publishing: 01/11/2014.
Table 1: Distribution of Retromolar foramen Sex Right side Left side Bilateral Total (%) (%) (%) (%) Male 5(2.2%) 3(1.3%) 6(2.7%) 14(6.2%) Female 6(2.7%) 4(1.8%) 9(4%) 19(8.5%) Total 11(4.9%) 7(3.1%) 15(6.7%) 33(14.7%) Table 2: Distance of retromolar foramen from posterior border of socket for third molar, anterior border of the ramus, and lingual respectively of Right side Distance between the retromolar foramen and Mandible Side Number in 3rd molar Ant. Border Lingula which socket of ramus (mm) RMF (mm) (mm) found 7 Right 3 11 7 11 Right 4 4 8 21 Right 6 8 7 25 Right 3 9 6 32 Right 4 4 4 37 Right 7 8 7 39 Right 3 9 6 43 Right 9 4 4 57 Right 8 5 8 63 Right 3 7 6 71 Right 7 6 9 75 Right 5 7 7 79 Right 3 5 5 81 Right 8 6 5 84 Right 4 10 6 109 Right 5 8 4 135 Right 8 5 7 147 Right 3 9 8 150 Right 9 4 4 172 Right 7 4 8 189 Right 10 9 4 192 Right 8 10 6 203 Right 5 9 8 217 Right 7 8 6 221 Right 8 4 3 224 Right 6 6 5 Mean[+ or -]SD 5.88 6.88 6.08 [+ or -] [+ or -] [+ or -] 2.25 2.25 1.62 Min-Max 3-10 4-11 3-9 Table 3: Distance of retromolar foramen from posterior border of socket for third molar, anterior border of the ramus, and lingual respectively of Left side Distance between the retromolar foramen and Mandible Side Number in 3rd Ant. Lingula which molar Border (mm) RMF socket of ramus found (mm) (mm) 11 Left 6 7 5 17 Left 8 5 4 21 Left 7 7 6 32 Left 9 6 8 39 Left 5 10 6 41 left 11 5 2 43 Left 9 3 4 63 Left 11 9 5 75 Left 5 4 3 81 Left 5 9 2 95 Left 7 7 6 109 Left 9 9 3 143 Left 8 7 2 147 Left 9 11 5 167 Left 11 9 7 172 Left 6 11 6 192 Left 12 6 8 197 Left 8 4 4 203 Left 11 7 8 213 Left 9 6 6 217 Left 7 5 2 224 Left 10 8 8 Mean[+ or -]SD 8.32 7.04 5 [+ or -] [+ or -] [+ or -] 2.15 2.26 2.09 Min-Max 5-12 3-11 2-8 Table 4: Incidence of retromolar foramen and canal in different population studied by different authors Sr. Population Author No. of Incidence No. (year of study) mandible (%) studied 1. Argentine Schejtman et 18 13 (72%) aborigines al. (1967) 2. Eskimos Ossenberg 485 40(8.2%) (1987) 3. American Sawyer and 234 18(7.7%) Kiely (1991) 4. Japanese Kodera and 41 8 (20%) Hashimoto (1991) 5. Caucasian (n=226) Pyle et al. 475 37 (7.8%) Afro-American (1999) (n=249) 6. Argentinean Lagrana et 50 9 (18%) al.(2006) 7. Turkish Bilecenoglu and 40 10 (25%) Tuncer(2006) 8. Brazilian Suazo et 294 38 (12.9%) al.(2008) 9. Swiss Von Arx et al. 121 31 (25.6%) (2011) 10. Japanese Kawai et 46 24 (52%) al.(2012) 11. Brazilian Rossi et 222 59 (26.6%) al.(2012) 12. Turkish Orphan et al. 126 14 (11.1%) (2013) 13. Korean Park MK et al. 154 144 (93.5%) (2014) 14. Indian Narayana et 242 53 (21.9%) al. (2002) Priya et al. 475 37 (7.8%) (1999) Athavale et 71 10 (14.1%) al. (2013) Gupta et al. 50 9 (18%) (2013) 15. Indian OUR STUDY (2014) 224 33(14.7%) Fig. 1: Distribution of Retromolar foramen in male and female Right Left Bilateral Males(6.2%) 2.20% 1.30% 2.70% Female(8.5%) 2.70% 1.80% 4% Note: Table made from bar graph.
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|Title Annotation:||ORIGINAL ARTICLE|
|Author:||Akhtar, Md. Jawed; Parveen, Sufia; Madhukar, Premjeet Kumar; Fatima, Nafees; Kumar, Avanish; Kumar,|
|Publication:||Journal of Evolution of Medical and Dental Sciences|
|Date:||Nov 3, 2014|
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