Radiographic position of mental foramen in selected urban population of Bangladesh

a. Assistant Professor and Head, Dept. of Paediatric Dentistry, Update Dental College and Hospital b. Lecturer, Dept. of Dental Public Health, Update Dental College and Hospital c. MPH(On course),Department of Health promotion & Health Education, Bangladesh University of Health Science. d. Associate Professor & Head Department Of Oral Anatomy, Update Dental College & Hospital e. Assistant Professor & Head, Department of Science of Dental Material, Update Dental College & Hospital f. Assistant Professor, Department of Oral Pathology & Periodontology, Update Dental College & Hospital, Dhaka g. Lecturer, Dept. of Dental Public Health, Sapporo Dental College and Hospital


Introduction
Mental foramen is an important anatomical landmark.It is located on the anterolateral aspect of the body of mandible,lateral to and above the mental tubercle.It is felt as a slight depression .It gives passage to the mental nerve and vessels. 1,2,3Mental foramen is located about 2.8-4 cm from the median fusion of the two halves of the mandible (Symphysis menti) and lies in lower half of the mandible in vertical axis.Mean diameter of mental foramen is reported to be 3.8 mm. 4,5,6 natomically there is one mental foramen each on each side of mandible.Variation in number of mental foramina also been reported.More than one mental foramina in one side ranges from 2%to 10% 9,10 , whereas up to 0.06% incidence of absence of mental foramina is also reported. 13THOPANTOGRAM (OPG) gives a panoramic view of the mandible and teeth.On an OPG, mental foramen is visible as a round or oval radiolucency.Generally it is situated in the lower half of the body of mandible in Updat Dent.Coll .j2015;5 (1):03-09 vertical axis, 1-2 mm below the apices of the adjacent teeth.The aim of this study is identification of the accurate anatomical location of the MF helps in several clinical procedure and nerve block anesthesia.Identification of the accurate anatomical location of MF helps in endodontics surgery, periapical surgery, surgical orthodontics exodontia, perprosthetic surgery, implant surgery, management of trauma and fracture in mandiblular body and nerve block anesthesia. 1

Methodology
This study was based on one hundred and one (OPGs)of adult patients .This was a nonprobability convenient sampling,cross sectional study design.The study was conducted during a period of six months from 15 th September 2011 to 14 th march 2012 at Out Patient Department, Update Dental College, Dhaka, Bangladesh.All OPG were examined two times in a dark room on an X-ray viewer.Here the mental foramen was located as radiolucency, traced by following the inferior alveolar canal.The data was analyzed by (SPSS Version 16),Following some inclusion &Exclusion Criteria was used . 15,19,23clusion criteria are (1)Age 15

Radiographaicmeasurement:
The accurate position of mental foreman is observed by many researchers using data from different ethnic and racial groups.There both horizontal and vertical positions are described.
The horizontal position in relation to the apices of adjacent teeth is more emphasized in different clinical procedures.Commonest position of mental foramen is described to be apical to the second premolar tooth 13,14,15,17 and betweenthe rootsof two mandibular premolar teeth. 18,19 [16][17][18][19] position 1: MF situated anterior to the first premolar tooth.position2: MF situated in the line with the long axis of first premolar tooth.position3: MF Situated between the apex apices of the first and second premolar teeth.position4: MF situated in the line with the long axis of second premolar tooth.position5: MF Situated between the apex apices of the second premolar and first molar teeth.position6: MF situated in the line with the long of first molar tooth.
The vertical position mental foreman was viewed by two angles .One was vertical axis and another was Vertical distance.
Invertical axis position 1: The location of MF in lower half of body of mandible .position2: The location of MF in upper half of body of mandible [14][15][16][17][18] .
In vertical distance, the distance between the mental foramen to the lower border of mandible was measured on both side of OPGs.Here distance was measured from lower border of mental foreman to the lower border of mandible and upper border of mental foreman to the lower border of mandible on both sides of OPGs. 24Position A : Distance between 0.4 mm to 0.9 mm .Position B :Distance between 1.0 mm to 1.5 mm .Position C :Distance between 1.6 mm to above.In Vertical distance, Position A was found to be in 26 OPGs on the right sideand24 OPGs on the left side from lower border of mental foreman to the lower border of mandible.Its frequency was 25.7% on the right side and 23.8% on the left side and 7 OPGs on the right side and 5 OPGs on the left side from upper border of mental foreman to the lower border of mandible.Its frequency was 6.9% on the right side and 5.0 % on the left side.Position B was found to be in 58 OPGs on the right side from lower border of mental foreman to the lower border of mandible and 67 OPGs on the left side from lower border of mental foreman to the lower border of mandible.Its frequency 57.4% on the right side and 66.3% on the left side and 53 OPGs on the right side from upper border of mental foreman to the lower border of mandible and 61OPGs on the left side from upper border of mental foreman to the lower border of mandible.Its frequency was 52.5% on the right side and 60.4% on the left side.Position C was found to be in 17 OPGs on the right side and 10 OPGs on the left side from lower border of mental foreman to the lower border of mandible.Its frequency was 16.8% on the right side and 9.9% on the left side and 41 OPGs on the right side and 35 OPGs on the left side from upper border of Mental foreman to the lower border of mandible.Its frequency was 40.6% on the right side and 34.7% on the left side.Hence; Position B is the most common position of MF in all aspect as viewed in OPGs shown in Table 4& Table 5.

Discussion
Determination of position of mental foramen has been a topic of great interest for the investigators emphasizing on important anatomical land marks of the maxillofacial region. 19Radiography is the only available non-invasive method for diagnosis and treatment planning of major surgical procedures of the mandible. 25,26 utilized panoramic radiographs because they have certain advantages over intra-oral radiography.It includes a greater area of hard and soft tissues and also the visualized area in continuity, thus allowing for a more accurate location of the mental foramen in both and the horizontal and vertical dimensions.On the other hand, periapical radiographs may not show several positions of the mental foramen if it is below the edge of the film 28 In the research literature the mental foramen is frequently described as situated in the region of the second premolar in the fully developed mandible. 28,29,30.Sample size of the studies above varied between 40 to 2000. 31In our study our sample size was 101 people.The weighted frequency of the location of the mental foramen in the above studies was in position 3.But in our study most common position in horizontal axis is position 4. Position 3 is the second most common position.Our study design and results weresimilar with Gungor 's and Jasser's study design 26,34 shown (Table 6).
In vertical axis, position 1 was found in all OPGs (100%) is similar to another Pakistani study 19 .
In vertical distance, Position B is the most common position of MF in all aspect as viewed in OPGs.
Although our study is limited with a group of people; according to the analyze of the Table 10, our results are almost similar with the other countries.But also advanced studies are necessary to achieve clearer results.

Conclusion
In conclusion, according to our results the location of the mental foramen on the panoramic radiographs of selected Bangladeshi population was most commonly in the line with the long axis of second premolar tooth.In majority of cases there was bilateral symmetry in the position.Location of mental foramen is studied in cadavers, interaoperativelyand radiographicaly.Ethical issues,limitation of sample size and procedural difficulties have limited the cadeveric and interaoperative studies a lot.Whereas, radiographic studies have made a large account of studies of position of mental foramen, as these are easily accessible, large sample sizes available and non-invasive. 25,26linicians and anthropologist should expect to find the positions of the mental foramen to be symmetrical and in the line with the long axis of second premolar tooth.

Table 6 ,
Summary data on the Horizontal position of the mental foreman (K.