Study on the position and symmetry of the mental foramen on panoramic radiographs in Indian population

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1 Original article DOI: JOURNAL OF INTERNATIONAL MEDICINE AND DENTISTRY To search..to know...to share p-issn: e-issn: X Study on the position and symmetry of the mental foramen on panoramic radiographs in Indian population Saritha Maloth 1, Shrinivas TR 2, Padmashree S 3, Pramod Krishna B 4, Priya M 5 Abstract: The position of mental foramen varies in different ethnic groups. Precise identification of the mental foramen is important in diagnostic and clinical procedures to prevent repeated local anesthesia failures and damage to neurovascular bundles passing through it. The aim of the study was to evaluate the most common radiographic position and symmetry of the mental foramen on panoramic radiographs in relation to the adjacent teeth. Four hundred and eighty panoramic radiographs of dentate Indian patients were interpreted. Radiographically in 48.96% of cases, the mental foramen was located in line with the second premolar and was common in age group of years and in 40.83% was in between the first and second premolars. The position of mental foramen was symmetrical in 74.6% of cases and asymmetrical in 25.4% of the radiographs analyzed. In the present study, the most frequent position of the mental foramen was in line with the second premolars and was symmetrically placed. Knowledge of the most common location of the mental foramen among Indian population may enable effective regional anesthesia during dental procedures. Key words: Indian, mental foramen, Orthopantomogram Introduction: The mental foramen is a funnel-like single opening bilaterally situated on the anterolateral aspect of the mandible apical to mandibular premolars through which the mental neurovascular bundle passes. The mental nerve and vessels pass through the mental foramen and supply sensory innervations and vascularity to soft tissues of the mental region, lower lip and gingiva ipsilaterally on the anterolateral part of the mandible. 1 Generally, the mental foramen cannot be visualized or palpated by clinical examination. In radiographs, the mental foramen appears as a radiolucent area in the lower premolar region and it can be found in various locations ranging from the root of the first premolars to the roots of the first molars. 2 Some of these are considered possibly the mental incisive foramen complex. 3 On rare occasions, the mental foramen may be absent and the existence of multiple mental foramen has also been described in the literature. 3,4,5 Moreover, the location of the mental foramen has been investigated radiographically in several populations and it varied according to gender, race and ethnic origin. Knowledge of the variation in the position of the mental foramen is necessary for differential diagnosis of small radiolucencies in premolar and molar region of the mandible. The accurate identification and actual location of the mental foramen is very important while performing periapical surgery, dental implant surgery, mandibular osteotomy, dental regional anesthesia and other surgical procedures involving premolar and molar areas of the mandible to prevent anesthesia failures and the relative risks associated with these procedures. 1 This necessitates thorough knowledge on the anatomical variations in location and number of the mental foramen to reduce damage of the corresponding

2 neurovascular structures. 6 Despite the development of advanced radiographic imaging modalities, conventional radiographs are the commonly used diagnostic imaging technique for localization of mental foramen in dentistry. 7 The present study was undertaken to evaluate the position of the mental foramen in horizontal and vertical relation of teeth using panoramic radiographs in a selected Indian population. Materials & Methods: A total of 480 dental panoramic radiographs from the patients referred to the department of Oral Medicine and Radiology, Vydehi Institute of Dental Sciences, Bangalore were evaluated. The patients were divided into different age groups as years, years, years, years and 58years and older. All panoramic radiographs were taken by using Planmeca Proline XC having following specifications; tube potential: KV, tube current: 4-12ma and total filtration: >2.5mm AL, focal spot: 0.5mm and time: 18s. The magnification factor was 1.2 (from posterior border of the ramus to canine), as reported by the manufacturer. The panoramic radiographs were of dentate Indian patients with completely erupted premolars and molars. Radiolucent and radiopaque lesions in the lower jaw were excluded. Patients with severe periodontal lesions, those with orthodontic treatment and with crowding and spacing in lower arch were also excluded from the study. The panoramic radiographs used were free from exposure/ artifacts. The method of evaluation of panoramic radiographs was adopted from Green. 8 Position of mental foramen to the teeth was determined by placing a transparent plastic sheet which was marked with a T over the radiograph. The occlusal plane of the lower teeth was aligned to the horizontal portion of T and the vertical bar was used to locate the mental foramen (Figure I). The longitudinal axis of the nearest tooth and the position of mental foramen were recorded on each side on the basis of age and gender. The horizontal position of the foramen was recorded as either in line with the long axis of a tooth or as lying between the two teeth. 9 Position of the mental foramen is represented in Figure II. The horizontal position of the mental foramen relative to the adjacent mandibular teeth on both sides were recorded according to the categories by Jasser and Nwoku 3 as: (1) Position 1: Situated anterior to the first premolar, (2) Position 2: Situated in line with the first premolar, (3) Position 3: Situated between first and second premolars, (4) Position 4: Situated in line with the second premolar, (5) Position 5: Situated between the second premolar and molar. The vertical position of the mental foramen in relation to the premolar apex was classified according to Fishel et al 10 as Position A = mental foramen situated coronal to the apex, Position B = mental foramen at the apex, Position C= mental foramen apical to the apex. Statistical analysis: The subjects age, sex and the position of the foramen on each side (to assess symmetry) of the mental foramen were recorded in the recording form and their percentage was calculated and the data was analyzed using Statistical Package for Social Sciences software (SPSS software package version 16). A Chi-square test was applied to explore the relation between two categorical variables. The level of significance was set at P < Results: The appearance and location of the mental foramen of 480 subjects was determined on panoramic radiographs; of these, 257 were males and 223 females (Table I-III, Figure III - IV). Categorization according to age group is shown in Figure V. 148

3 Saritha M et al: Position and symmetry of the mental foramen Figure I: Position of mental foramen (arrow) to the teeth determined with a T- shaped marking over the panoramic radiograph Figure II: Position of mental foramen (arrow mark) on panoramic radiograph The youngest patient included in the study was 14 years old. In 48.96% of cases, the mental foramen was in position 4 and was common in age group of years and in 40.83% in position 3. Only in 9.97% of cases, mental foramen was in position 5. The position of the mental foramen was symmetric in 74.6% and asymmetric in 25.4% of cases. For symmetrically placed mental foramen, the most common position was position 4 (38.13%) followed by position 3 (30.41%). In the asymmetric cases, on the right side of the mandible, 54.55% of mental foramen was located in position 4 in males and % in females. While on the left side, 39.44% mental foramen was located in position 3 in males and 46.29% in females. Position 4 was most common in male (49.2%) than in females (48.65%). On the right side, the most common position was position 4 (50.63%) and 47.29% on the left side. There was no case found in position 1 and only one case in position 6. No statistically significant differences were seen between males and females in symmetric and asymmetric location of mental foramen on both sides. The most frequent vertical position of mental foramen was apical to premolar apex (69.58% cases), 19.79% of cases at premolar apex and 10.63% cases coronal to premolar apex. Discussion: Variations in the position of the mental foramen by race, age, loss of teeth and resorption of alveolar bone has been recorded in the literature. Due to lack of consistent anatomic landmarks and inability to clinically palpate the mental foramen, conventional radiographs are more commonly used for localization of the mental foramen. According to the present study, in 48.96% of the cases, the foramen was located in line with the second premolar and 40.83% in between 1st premolar and 2nd premolar; thus these two positions accounted for 89.79% of the cases. Studies done in different populations such as Kenyan Africans, Asian Indians, Egyptians, British, Nigerians and Saudis showed that the usual location of the mental foramen was along the long axis of second premolar. Their findings are consistent with our results.11 The radiographs are the only available non-invasive method that is used routinely for diagnosis and treatment planning of major 149

4 Table I: Distribution of position of the mental foramen in 480 panoramic radiographs in relation to right and left sides of mandible by gender Position of mental foramen Male Side frequency Female Side frequency Right (%) Left (%) Right (%) Left (%) Total side frequency Right frequency ( %) Left frequency (%) Position 1 0 (0) 0 (0) 0(0) 0(0) 0(0) 0(0) Position 2 1(0.39) 1(0.39) 0(0) 1(0.45) 1(0.21) 2(0.42) Position 3 101(39.30) 102(39.69) 91(40.81) 98(43.95) 192(40.0) 200(41.67) Position 4 134(52.14) 119(46.30) 109(48.88) 108(48.43) 243(50.63) 227(47.29) Position 5. 21(8.17) 35(13.62) 23(10.31) 15(6.73) 44(9.17) 50(10.42) Position 6 0(0) 0(0) 0(0) 1(0.45) 0(0) 1(0.21) Total 257(100) 257(100) 223(100) 223(100) 480(100) 480(100) NOTE: Position 1: Situated anterior to the first premolar, Position 2: Situated in line with the first premolar, Position 3: Situated between first and second premolars, Position 4: Situated in line with the second premolar, Position 5: Situated between the second premolar and molar Table II: Frequency of position of the mental foramen in 480 radiographs by gender and symmetry Position of mental foramen Male Female Total (%) S (%) S (%) S (%) Position 1 0(0) 0(0) 0(0) Position 2 1(0.28) 0(0) 1(0.28) Position 3 74(38.95) 72(42.86) 146(30.41) Position 4 97(51.05) 86(51.19) 183(38.13) Position 5 18(9.47) 10(5.95) 28(5.73) Position 6 0(0) 0(0) 0(0) Total 190(100) 168(100) 358(74.58) S= Symmetry, Position 1: Situated anterior to the first premolar, Position 2: Situated in line with the first premolar, Position 3: Situated between first and second premolars, Position 4: Situated in line with the second premolar, Position 5: Situated between the second premolar and molar 150

5 Table III: Frequency of position of the mental foramen in 480 radiographs by gender and asymmetry at 960 sides (right & left sides) Position of mental foramen AS-R (%) Males AS-L (%) Females AS-R (%) AS-L (%) Total 960 sides (%) AS (%) Position 1 0(0) 0(0) 0(0) 0(0) 0(0) Position 2 0(0) 0(0) 0(0) 1(1.85) 1(0.1) Position 3 27(40.90) 28(39.44) 18(33.96) 25(46.29) 98(10.2) Position 4 36(54.55) 22(30.99) 23 (43.39) 22(40.74) 103(10.7) Position 5 3(4.55) 21(29.57) 12(22.64) 5(9.26) 41(4.2) Position 6 0(0) 0(0) 0(0) 1(1.85) 1(0.1) Total 66(100) 71(100) 53(100) 54(100) 244(25.42) AS= Asymmetry; AS-R= Asymmetry-Right; AS-L=Asymmetry-Left; Position1: Situated anterior to the first premolar, Position 2: Situated in line with the first premolar, Position 3: Situated between first and second premolars, Position 4: Situated in line with the second premolar, Position 5: Situated between the second premolar and molar Figure III: Frequency of position of the mental foramen in 480 radiographs by gender 151

6 Figure IV: Distribution of position of mental foramen on the panoramic radiographs of 480 patients Figure V: Age distribution of mental foramen 152

7 surgical procedures involving the mandible. 12 Orthopantomographs are the most commonly used extra-oral radiographs for screening, diagnosis and pre-operative assessment. We utilized panoramic radiographs as it has the ability to display the entire area of the body of the mandible for more accurate visualization of the mental foramen in horizontal and vertical dimensions than on peri-apical radiographs. We evaluated the patients with completely developed permanent teeth as the location of the mental foramen could change with development of the jaws. 13 Most studies, conducted in different ethnic and racial groups reported that the most common position was in line with the longitudinal axis of the lower second premolar. 14 The second most common place was between the longitudinal axis of the first and second premolars. The studies include analysis of radiographs or direct measurements on human specimen. 15 Few studies showed that the most common position of the mental foramen was the one between the areas of the first and second premolar closely followed by the one below the longitudinal axis of the second premolar. 15 In our present study, the location of the mental foramen did not show gender variation. This finding agrees with similar studies in other populations. 3,11 In 74.58%, mental foramen was symmetrical and in 25.41% the mental foramen was asymmetrical. This shows that variability exists in the mental foramen position of same subjects. 15 Studies done in other populations such as Kenyan African by Mwaniki and Hassanali (1992), Asian Indian by Shankland (1994), Saudi population by Al Jasser and Nwoku (1998), Malay by Ngeow and Yuzawati (2003), Kurdish population by AL Talabani et al (2008) and in Brazilian population by Amorium et al (2008) reported that the mental foramen is most commonly positioned in line with the second premolar tooth. 5 In some studies done by Moiseiwtsch 16 in a North American white population and by Fishel et al and Olasoji et al in Northern Nigerian adults, 11 studies done in Turkish population by K Gingor et al and Jasser and Nwoku in Saudi population 12 showed that the most common location of the mental foramen was between the two premolars. In our study, the most common location of the mental foramen was found in line with the longitudinal axis of the second premolar tooth. The second most common position was between the longitudinal axis of the first and the second premolars. The most common vertical position of mental foramen was apical to the premolar apex (69.58 % of cases), at the apex in 19.79% cases and coronal to apex in 10.63% cases. In a study by Fishel et al 11, the frequent vertical position of mental foramen was apical to the second premolar. The mental foramen was symmetrically positioned in majority of cases and this was in agreement with results in other ethnic groups Turkish 90.4%, North Jordanian 77%. According to Philips et al 17, the size of the foramen on panoramic radiographs appeared slightly larger than those on peri-apical radiographs. However, the horizontal position of the mental foramen on panoramic radiographs was similar with the position reported on peri-apical radiographs. Our study is limited with a group of people with permanent dentition as the permanent tooth buds in mixed dentition would obscure the visibility of mental foramen. Studies involving advanced imaging modalities are necessary to achieve more precise results. 11 Knowing the normal range of possible location of mental foramen is essential for better treatment planning. In spite of the limitations of the panoramic radiographs, its importance in initial diagnosis before any dental surgical procedures cannot be disregarded. 153

8 Conclusions: In panoramic radiographs of Indian population, the most frequent position of the mental foramen is in line with the second premolars. The most common vertical position of mental foramen was apical to premolars. Although the mental foramen was symmetrically positioned in majority of cases, existence of asymmetric location demonstrates the variable position in same subjects. Our results are in agreement with the results of similar studies on other ethnic groups reported in the literature. The data is of clinical importance for accurate delivering of local anesthesia for dental procedures and avoidance of damage to neurovascular bundle during surgical procedures. References: 1. Ilayperuma I, Nanayakkara G, Palahepitiya N. Morphometric Analysis of the Mental Foramen in Adult Sri Lankan Mandibles. Int J Morphol 2009; 27(4): ; 2. Al-Khateeb TL, Odukoya O, El-Hadidy MA. Panoramic radiographic study of the mental foramen locations in Saudi Arabians. Afr Dent J 1994; 8: Al Jasser NM, Nwoku AL. Radiographic study of the mental foramen in a selected Saudi population. Dentomaxillofac Radiol 1998; 27(6): ; 4. Talabani NA, Gataa IS, Jaff K. Precise computer-based localization of the mental foramen on panoramic radiographs in a Kurdish population. Oral Radiology 2008; 24(2):59-63; Rupesh S, Winnier JJ, John SA, Joy T, Rao AP, Reddy V. Radiographic study of the location of mental foramen in a randomly selected Asian Indian population on Digital Panoramic Radiographs. J Med Sci 2011; 11(2):90-95; 6. Kqiku L, Weiglein A, Kamberi B, Hoxha V, Meqa K, Städtler P. Position of the mental foramen in Kosovarian population. Coll Antropol 2013; 37(2): Ahmed B, Rasheed T, Khan MAU, Rashid A and Ahmad S. Rib suppression in chest radiographs using ICA algorithm. Inform Technol J 2007; 6: ; Green RM. The position of the mental foramen: A comparison between the southern (Hong Kong) Chinese and other ethnic and racial groups. Oral Surg Oral Med Oral Pathol 1987; 63(3): ; 9. Juodzbalys G, Wang HL, Sabalys G. Anatomy of Mandibular Vital Structures. Part II: Mandibular Incisive Canal, Mental Foramen and Associated Neurovascular Bundles in Relation with Dental Implantology. J Oral Maxillofac Res 2010; 1(1):e3; Fishel D, Buchner A, Hershkowith A, Kaffe I. Roentgenologic study of the mental foramen. Oral Surg Oral Med Oral Pathol 1976; 41(5):682-86; Haghanifar S, Rokouei M. Radiographic evaluation of the mental foramen in a selected Iranian population. Indian J Dent Res 2009; 20(2): ; Gungor K, Ozturk M, Semiz M and Brooks SL. The radiographic study of location of mental foramen in a selected Turkish population on panoramic radiograph. Coll Antropol 2006; 30(4): Kjaer I. Formation and early prenatal location of the human mental foramen. Scan J Dent Res 1989; 97(1):

9 14. Liverdos F, Delantoni A, Delantoni- Papadimitriou P. A radiological study concerning the anterior loop of the mandibular canal and the location of the mental foramen in a Greek population. Balk J Stom 2007; 11(2): Gangotri S, Patni VM, Sathwane RS. Radiographic determination of position and symmetry of mental foramen in central Indian population. Journal of Indian Academy of Oral Medicine and Radiology 2011; 23(2):101-03; Moiseiwitsch JR. Position of the mental foramen in a north American, white population. Oral Surg, Oral Med Oral Pathol Oral Radiol Endod 1998; 85:457-60; Prabodha LBL, Nanayakkara BG. The Position, Dimensions and Morphological variations of mental foramen in mandible. Galle Medical Journal 2006; 11(1):13-15; *************************************************************************** Conflict of interests- Nil Date of submission: Source of funding- Nil Date of acceptance: Authors details: 1- Corresponding author: Assistant Professor, Department of Dentistry, Koppal Institute of Medical Sciences, Koppal , Karnataka, India; saritha.maloth@gmail.com 2- Assistant Professor, Department of Anaesthesiology, Koppal Institute of Medical Sciences, Koppal 3- Professor and Head, Department of Oral Medicine and Radiology, Vydehi Institute of Dental Sciences, Bangalore 4- Reader, Department of Oral and Maxillofacial Surgery, Farooqia Dental College and Hospital, Mysore 5- Reader, Department of Oral Medicine and Radiology, Teerthankar Mahaveer Dental College and Research Centre, Moradabad 155