INTRODUCTION
Identification of sex in forensic odontology, especially using human skeletal remains is still evolving. Sex determination from human skeletal remains is still a challenging task for the forensic anthropologists, especially in mass disasters and with putrefied and mutilated remains. Certain skeletal remains can guide forensic experts toward accurate identification. The human skull is the second most sexually dimorphic region of human skeleton apart from the pelvis.[1] Human mandible is the strongest bone and persists in a well-preserved state longer than any human bone.[2] This study evaluates mental foramen (MF), which is a stable landmark on the mandible. The MF located on either side of buccal cortex of the mandible, lies near the apices of the premolars, and transmits the mental nerves and vessels. Previously, many studies have used radiographs as an indispensable tool in forensic anthropology. However, it has few drawbacks among which inability to view structures three dimensionally is important and it is required for a near accurate predictions in forensic sciences. Now with technological advancement, cone-beam computed tomography (CBCT) aids in identifying the anatomical landmarks by three-dimensional (3D) viewing and reconstruction, which leads to near perfect measurements of landmarks and it can be well documented, preserved, reviewed, and shared with another anthropologist. With this background, the present study was designed to evaluate the sex-based variations in MF using cone-beam computed tomography (CBCT). These data will aid in the future advances of forensic odontology for sex assessments.
MATERIALS AND METHODS
The present study was a retrospective study evaluated 60 CBCT scans which were involved retrieved from the radiological archives of the Department of Oral Medicine and Radiology, Tamil Nadu Government Dental College and Hospital, Chennai. All CBCT scans were taken using CS 9300 select CBCT machine and were analyzed using CS 3D imaging software; all scans were taken with a field of view of 10 mm × 10 mm; and the adjusted scan parameters were 90Kvp, 4 mA, and the exposure time of 8 s with an isotropic voxel size of 180 m [Figures 1 and 2]. 60 CBCT scans, 120 MF were evaluated by a single observer. The scans were divided into two groups: Group A (n = 30) consisting of CBCT scans of male patients and Group B (n = 30) consisting of CBCT scans of female patients. The inclusion criteria were CBCT scans of patients more than 18 years whose skeletal growth has been completed, CBCT scans with no pathological lesions or conditions adjacent to the area of interest, and CBCT scans with no metal artifacts or motion artifacts. The CBCT scans with pathological lesions or conditions adjacent to the area of interest and with metal artifacts or motion artifacts were excluded. The parameters analyzed in this study were the width of MF (W) in the right and left sides, the height of MF (H) in the right and left sides, the distance from superior border of MF to the lower border of the mandible (SMF-LM) in the right and left sides, the distance from inferior border of mental foramen to the lower border of the mandible (IMF-LM) in the right and left sides, and the interforamen distance (IFD). The width (W) and height (H) of the MF were measured on both sides in the sagittal and axial sections, respectively [Figure 3a and b]. MF was identified in the sagittal section of both the right and left sides. Tangents were drawn along the superior and inferior border of the MF, following which a perpendicular line to both tangents was drawn to measure the distance of the superior and inferior border of the MF to the lower border of the mandible [Figure 3c]. The interforamen distance was measured from the axial section from the distal cortical surface of the right to the left MF [Figure 3d]. The data so obtained were noted, tabulated, and subjected to statistical analysis.
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Figure 1: CS 9300 – Cone-beam computed tomography
Figure 2: CS 3D imaging software used in identifying the mental foramen
Figure 3: Measurement of width of mental foramen in axial section (a), measurement of height of mental foramen in sagittal section (b), measurement of SMF-LB and IMF-LB distances in sagittal section (c), measurement of interforamen distance in axial section (d)
Statistical analysis
Data obtained were analysed using the IBM Corp. Released 2020, IBM SPSS Statistics for Windows, Version 27.0 Armonk, New York. Inferential statistics were used to analyse the obtained data, paired t test was done for intragroup analysis and unpaired t test was done for intergroup analysis. Statistical significance was set at P < 0.05
RESULTS
The study analyzed 60 CBCT images, divided into two groups: Group A consisting of 30 CBCT scans of male patients and Group B consisting of 30 CBCT scans of female patients. The mean age in Group A (male) and Group B (female) was 28.3 years and 27 years, respectively [Table 1]. The mean width of MF in the right and left sides in males was 3.54 mm and 3.52, respectively [Figure 4 and Table 2], and in females was 3.11 mm and 2.96 mm, respectively [Figure 5 and Table 3]. The mean height of MF in the right and left sides in males was 3.12 mm and 3.03, respectively [Figure 4 and Table 2], and in females was 2.72 mm and 3.34 mm, respectively [Figure 5 and Table 3], showing no statistical significance in the width and height of MF between the right and left sides and between males and females [Tables 1-3]. The mean distance from SMF-LM in the right and left sides in males were 16.2 mm and 16.63 mm, respectively [Figure 4 and Table 2], and in females was 14.43 mm and 14.76 mm, respectively [Figure 5 and Table 3]. The mean distance from inferior border of MF to the lower border of the mandible (IMF-LM) in the right and left sides in males was 13.13 mm and 13.58 mm, respectively [Figure 4 and Table 2], and in females was 11.65 mm and 12.11 mm, respectively [Figure 5 and Table 3], showing statistically significant difference in SMF-LB between the right and left sides in males and significant difference in the distance from superior border of mental foramen to the lower border of mandible (SMF-LB) between right and left side in males and significant difference in the distance from inferior border of mental foramen to the lower border of mandible (IMF-LB) between the right and left sides in males and females [Tables 2 and 3]. SMF-LB and IMF-LB distances showed a statistically significant difference between males and females (P = 0.001) and were greater in males than in females [Table 1]. The mean IFD in males and females was 49.6 mm and 47.8 mm, respectively, showing statistically significant difference between the sexes (P = 0.22) and was greater in males than in females [Table 1].
Table 1: Comparison between males and females
Figure 4: Bar chart representing mean values of Group A - Male
Table 2: Paired mean differences of right and left sides among Group A-male
Figure 5: Bar chart representing mean values of Group B - Female
Table 3: Paired mean differences of right and left sides among Group B-female
DISCUSSION
Forensic dentists play an important role in establishing the sex of an unknown individual, especially during mass disasters. They can assist other experts to determine sex using skeletal and teeth remains. Sex determination from skeletal remains is one of the important forensic considerations because from the view of examiner, it eliminates approximately half the population.[3] Garn et al. studied sexual dimorphism by measuring the mesiodistal width of canine teeth in different ethnic groups. They concluded that mandibular canine showed a greater degree of sexual dimorphism than the maxillary canine and canine teeth sexual dimorphism varies among different ethnic groups.[4] Sex can also be determined by the study of X and Y chromosomes in the cells obtained from tooth pulp. The presence or absence of X chromosome can be determined by X chromatin and intranuclear structures are also known as Barr body as they were first discovered by Barr et al. They are present as a mass usually lying against the nuclear membrane in the females. After death, it persists for variable periods depending on the humidity and temperature of the ambient atmosphere.[5] Other soft tissue methods of sex determination includes rugoscopy, the study of the pattern on the palatal rugae to identify a person, and cheiloscopy, the study of lip prints. Sex determination of an unknown individual especially in mass disasters and with putrefied and mutilated remains on the morphology and metrical measurements of the skull and mandible is used.[6,7] The human skull is the second most sexually dimorphic region of human skeleton apart from the pelvis.[1] Mandible, as a component of the skull, is the strongest bone in human body and it is often recovered intact.[2] MF is located on either side of the buccal cortex of the mandible. The opening of MF is directed upward and outward, transmitting the mental vessels and nerves. Mostly, MF on either side is located near the apices of premolars; sometimes, its location varies from the mesial root of mandibular first molar up to canine.[8] The present study evaluated various parameters of MF for its utility in sex determination.
In 1974, Wical and Swoope described that despite alveolar bone resorption above the MF, the distance from the MF to the lower border of the mandible (basal bone) remains relatively constant throughout life.[9] Lindh et al. in 1995 and Güler et al. in 2005 also suggested that the stability of basal bone does not depend on resorption of alveolar bone above the foramen.[10,11] Based on the proven works of above literature, the lower border of the mandible (LB) was selected as a reference point in our study. The present study utilized CBCT (CS 9300) 3D imaging to reduce the errors that commonly occur in a panoramic radiograph. CBCT imaging sections through the MF which leads to near perfect measurements of the landmarks, which is required during accurate predictions in forensic sciences. In the present study, both Group A (male) and Group B (female) had a mean age of 28.3 years and 27 years, respectively, with no statistically significant difference. The difference in height and width (diameter) of MF in males and females showed no statistical significance. The results of paired t-test showed that the mean value of SMF-LB was significantly higher on the left side in males and IMF-LB was significantly higher on the left side in males and females. These results were in agreement with the studies of Agthong et al. who have found differences in several measurements, suggested that both sex and side should be considered when applying the anatomical variation data to an individual subject.[12] On the contrary, Thomas et al.'s study found that the distances SMF-LB and IMF-LB were same on both sides.[13] This difference in findings of the present study may be due to population variations and radiographic techniques. The intergroup analysis using unpaired t-test revealed a statistically significant difference (P = 0.001) in the mean values of both SMF-LB and IMF-LB distances between males and females. The SMF-LB and IMF-LB distances were greater in males than in females. This was in accordance with the results of the study conducted by Mahima et al. in South Indian population,[14] Chandra et al. in North Indian population,[15] and Thomas et al. and Catovie et al. in population belonging to different parts of the world.[13,16] On the contrary, Vodanovic et al. found that the mean value of IMF to LBM does not exhibit sexual dimorphism.[17] The IFD showed a statistically significant difference between sexes. IFD was greater in males than in females. This result was in accordance with the study conducted in the South Indian population by Vinay et al., which evaluated 250 dry human adult mandibles using metrical parameters, including bigonial breadth, which was higher in males compared to females.[7] There is no study available in literature evaluating IFD comparing between males and females; this would be the first study comparing the IFD of the MF between sexes using CBCT. The limitations of this study are the small sample size, lack of data related to ethnicity of the population, and failure to evaluate the impact of ethnicity in sex determination using MF, since it is a short study conducted using the scans retrieved from the archives. Blinding was not done in this study, but a single observer was used to analyze all the scans and to locate landmarks to avoid interobserver error. Future studies analyzing these parameters in a larger population and analyzing both age- and sex-based variations are needed to use MF as a parameter for identification of an individual in forensic odontology.
CONCLUSION
Based on the results of this study, we would like to conclude that the distance from MF to the lower border of the mandible and the IFD shows clear sexual dimorphism. Hence, measurement of SMF-LM, IMF-LM, and IFD in both sexes can be used as an effective tool for sex discrimination. The measurements compared between right and left sides of an individual showed a certain significant difference, suggesting that both sex and side should be considered when applying the anatomical variation data to an individual subject. However, future studies analyzing these parameters with a larger population would be of significant value in generalizing these results and would aid in the determination of sex in forensic odontology.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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