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| FORENSIC ODONTOLOGY: ORIGINAL ARTICLE |
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| Year : 2018 | Volume
: 30
| Issue : 1 | Page : 52-57 |
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Craniometric assessment of gender using mastoid process
Harsha Bhayya, ML Avinash Tejasvi, B Jayalakshmi, M Mounika Reddy
Department of Oral Medicine and Radiology, Kamineni Institute of Dental Sciences, Sreepuram, Nalgonda District, Telangana, India
| Date of Submission | 27-Nov-2017 |
| Date of Acceptance | 17-Feb-2018 |
| Date of Web Publication | 23-Apr-2018 |
Correspondence Address:
Dr. M L Avinash Tejasvi
Department of Oral Medicine and Radiology, Kamineni Institute of Dental Sciences, Sreepuram, Nalgonda District - 508 254, Telangana
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/jiaomr.jiaomr_127_17
 Abstract | | |
Background: The mastoid process characteristics are of great utility in the determination of sex. Studies on human skeletal remains for sex determination have been a topic of interest among researchers. Osteometric studies using individual bones exhibiting sexual dimorphism have been reported among different populations. Skull is important in this regard as it resists adverse environmental conditions over time. The mastoid process can be used as a marker of sex determination in unidentified human skull remains. Objective: The objective of this study is to evaluate the use of mastoid process as a tool for sex determination in unidentified skeleton. Aim: The aim of this study was to evaluate the accuracy of different craniometric parameters of mastoid process in sex determination. Materials and Methods: In the present study, 50 adult human skulls of Telangana population were studied to determine the accuracy of mastoid process in sex determination. Parameters studied were length, breadth, antero-posterior diameter, size, and area of mastoid process. Results: Statistics revealed high significance (P < 0.0001) for mastoid length and size for sex determination. Conclusion: To our knowledge, this is the only study including various craniometric parameters of mastoid process.
Keywords: Craniometric, mastoid, sex, skull
How to cite this article:
Bhayya H, Avinash Tejasvi M L, Jayalakshmi B, Reddy M M. Craniometric assessment of gender using mastoid process. J Indian Acad Oral Med Radiol 2018;30:52-7 |
How to cite this URL:
Bhayya H, Avinash Tejasvi M L, Jayalakshmi B, Reddy M M. Craniometric assessment of gender using mastoid process. J Indian Acad Oral Med Radiol [serial online] 2018 [cited 2022 Jul 4];30:52-7. Available from: https://www.jiaomr.in/text.asp?2018/30/1/52/230883 |
| Introduction | |  |
Identify means “determination of the individuality.” In a number of civil and criminal matters, identification of the individual, either living or dead, is required. Anatomical and medical features are the two major aspects to establish identity. The establishment of identity is required from fresh intact corpses, decomposed corpses, mutilated and dismembered corpses, or skeletalized material.
Sex determination of humans or human skeletal remains is considered a vital step in identification and is crucial for further analysis.[1]
Studies on human skeletal remains for sex determination have been a topic of interest among researchers. Osteometric studies using individual bones exhibiting sexual dimorphism have been reported among different populations.[2] In the present forensic scenario, dismemberment or body mutilations has become a frequent method to conceal the identity of the victim. In such instances, the pelvis is considered the best bone to determine the sex of an individual. When the pelvis is unavailable, the skull is also widely considered the best indicator of sex. Skull is the most dimorphic and easily sexed portion of the skeleton after pelvis, providing up to 92% reliability.
In the skull, the mastoid bone is robust and tough making it resistant to physical damage. The mastoid region is favorable for sex determination for two reasons – the compact structure of the petrous portion and its protected position at the base of the skull. Hence, it is commonly found intact in skeletons of very old age. Even though the skull is fragmented, the mastoid stays intact.
The objective of the present study was to determine the accuracy of mastoid process in sex determination based on mastoid process parameters such as length, breadth, antero-posterior diameter, size of mastoid process, and measurement of the area mastoid triangle formed by projection of 3 craniometric points.
| Materials and Methods | | |
This was a retrospective study comprising 50 participants (25 males and 25 females) above the age of 18 years. Study sample was drawn from the Department of Anatomy, Government Dental College (Hyderabad) and Kamineni institute of dental and medical sciences (Narketpally). Skulls of known sex in which the spheno-occipital junction was synostosed and the mastoid part of the temporal bone was intact were included in the study. Damaged skulls of mastoid process, deformed skulls, diseases or where spheno-occipital junction was not synostosed. (juvenile skulls), and those that did not exhibit distinct sexually dimorphic features morphologically were excluded from the study.
Methods
The mastoid measurements were obtained with the help of a sliding Vernier caliper to the nearest millimeter (mm) as per the standard anthropological conventions, and then the size of the mastoid process was calculated along with the area and perimeter. Mastoid measurements were taken from both sides, i.e., right and left side, and then an average of both sides was considered for statistical analysis. All measurements were done by a single observer to avoid any interobserver errors.
Following landmarks were considered for the measurements of various mastoid process variables.
Frankfort Horizontal plane (FH): Frankfort plane is the horizontal plane passing through the upper acoustic meatus and the lower margin of the orbital opening [Figure 1].
Porion (Po): Highest point on the surface of the external auditory meatus.
Mastoidale (Ma): Lowest craniometric point at the mastoid process.
Asterion (As): Meeting point of lambdoid, occipitomastoid, and parietomastoid sutures. Straight lines joining these three points (Po, Ma, and As) formed the mastoid triangle.
The following measurements were taken with the help of sliding calipers [Table 1]: | Table 1: Description of the delineated distances for the craniometric measurements
Click here to view |
Po-As (Porion to Asterion): The straight distance between Porion and Asterion.
As-Ma (Asterion to Mastoidale): The straight distance between Asterion and Mastoidale.
Po-Ma (Porion to Mastoidale): The straight distance between Porion and Mastoidale.
Perimeter and area of the mastoid triangle were calculated.
Heron's formula was used for calculating the area of the mastoid triangle in mm. It needs to be highlighted here that the mastoid triangle does not constitute of a flat surface but a slightly curved one, and hence, the area calculated in the study cannot be considered as a true area but area for a two-dimensional planar view.[3]
Statistical analysis was performed using the IBM SPSS software version 22 (IBM Corp., Armonk, NY). Data were represented as mean ± standard deviations (SD) or frequency and percentage, wherever appropriate. Discriminant equation was derived separately for individual parameters, combination of several parameters, and when all parameters were considered.
| Results | | |
In the present study, mean values of all the parameters were calculated and showed a statistically significant variation between males and females [Table 2].
The relationship was further explored by binary logistical analysis for sex determination. Discriminant function equation derived for sex determination was
Y (Sex) = 29.84 − 0.022 × ML + 0.421 × MB + 0.226 × APM − 0.027 × SM – 0.265 × MP − 0.084 × Po-As − 0.371 × As-Ma – 0.011 × Po-Ma + 0.00 × AM
By substituting the respective values into the equation, we get the y value; samples were categorized as males if Y < 1.5 and as females if Y > 1.5
Discriminant function analysis was performed for all the variables of mastoid, which correctly classified 82% of the cases [Table 3].
When all the individual parameters were evaluated for sex determination, length showed higher predictable score of 74% followed by Po-Ma with a predictable score of 69% [Table 4].
When combination of various parameters was evaluated, combination of perimeter, size, area, Po-As, As-Ma, and Po-Ma showed 83% predictable score followed by combination of perimeter and As-Ma (77%) and length, breadth, and antero-posterior combination (72%) [Table 5].
The individual discriminant function equation for sex determination is presented in [Table 6]. If the calculated discriminant score using the equation(s) was less than 1.5, the case was classified as male, and if the score was greater than or equal to 1.5 the case was classified as female. | Table 6: Individual discriminant function equation for the determination of sex
Click here to view |
Hence, it can be concluded that, when all the parameters in the study are considered, the mastoid process is a good indicator for sex determination with an accuracy of 82%. When the best significant parameters are considered (perimeter, size, area, Po-As, As-Ma, Po-Ms), the accuracy was 83% followed by (perimeter, As-Ma) the accuracy is 77%. When length was considered, accuracy was 74%. It can be concluded that, overall, perimeter and As-Ma and length are the best predictors of sex with their respective formulas. Individual parameters are the least indicators of sex except the length.
| Discussion | | |
Anthropometry is the study of measurements or proportions of human body such as bone, muscle, adipose (fat) tissue according to sex and age for identification purposes. Forensic anthropology is the application of the science of physical anthropology and human osteology, i.e. the study of the human skeleton.[4] The objective of the present study was to evaluate the use of mastoid process as a tool for sex determination in unidentified skeleton.
In previously conducted studies, many authors have shown more accurate results similar to that of the present study.
The present study distinguishes itself from previous studies by focusing on sex determination using the various variables of mastoid processes such as length, breadth, anterio-posterior diameter, size, perimeter, Po-As, As-Ma, Po-Ma, and area of mastoid triangle.
The results of the present study are interesting and revealed the marked sexual dimorphism in the dimensions of the mastoid region, establishing its value as a sex indicator for Telangana population. Using discriminant function analysis, as high as 82% correct classification was achieved with all variables. It is similar to, and in some cases considerably better, than those of conventional cranial measurements used previously.[5],[6] Moreover, separate discriminatory equation has been calculated based on each variable so that, even by measuring one variable from a fragment of skull, sex can be effectively determined.
Mastoid region is considered as one of the slowest and later growing regions of the cranium,[7] showing a higher degree of sexual dimorphism in adulthood.[8],[9] Difference between the size of mastoid process in males and females could be due to the variation in the growth of mastoid process in both males and females along with response of stronger muscle action of sternocleidomastoideus, splenius capitis (the posterior belly of the digastric muscle); and longissimus capitis could enhance the greater development of mastoid process in males.[8]
Based on the direction of mastoid process in relation to a vertical plane, Hoshi classified mastoid process into male, female, and neutral types. He observed that when skulls are placed on a flat surface, male skulls rest on the mastoid processes whereas female skulls on occipital condyles or other portions of the skull.[10]
The results of the present study highlighted the significant difference between males and females in all the measurements of mastoid process. These results were similar with the findings reported by Keen in 1950,[11] Giles and Elliot in 1963,[12] and Sumati et al. in 2010;[13] who observed that mean mastoid length was more in male skulls compared to female skulls, irrespective of race or region; all studies concluded that females have smaller mastoids than males.
Mastoid triangle was introduced by Paive and Segre [14] on dry skulls in a population of Sao Paulo, Brazil using xerographic method by calculating the area of the left and right mastoid triangle, and then adding the two areas to calculate the total area. Since then, to the best of our knowledge and literature search, only 8 studies have published on mastoid triangle and its ability in sex determination.[15],[16],[17],[18],[19],[20] The results of the present study indicate significant sex difference in the mastoid; however, for the classification, the overall accuracy rate achieved with the triangular area technique was unimpressive and similar to that reported by previous researchers.[14],[15],[16],[17],[18],[19]
Kemkes and Gobel [14] observed that, by using discriminant function analysis, only 65% of all skulls could correctly identify exact gender. Singh et al.,[17] observed an accuracy of gender determination by mastoid area as 61% and also observed that the accuracy of the area of mastoid triangle varies in different age groups, an observation not explored in any of the previous studies. Present study showed an accuracy of only 51%, which was very low compared to that of previous study. Whereas Madadin et al.[20] concluded that the area of the mastoid triangle showed sexual dimorphism in Saudi population, which was not consistent with the results of the present study.
Discriminant function statistics and correct prediction accuracies for all variables are given in [Table 6]. All our measurements of the nine mastoid-related parameters in our study sample analyzed with the highly objective discriminant function; the equation derived from all the parameter showed sex determination accuracy of 82%. When individual parameters were considered, length showed the highest accuracy of 74%, which was consistent with previous study;[11],[12] the least accuracy was noted for area and anterio-posterior diameter at 51%. When various combinations were taken in to consideration, perimeter, size, area, Po-As, As-Ma, and Ma-Po showed an accuracy of 83%. When area of mastoid triangle and length of three sides of mastoid triangle were considered, they showed an accuracy of 79%; perimeter and As-Ma and perimeter showed accuracy of 77%, which is the highest when compared to other studies.
Discriminant function analysis was used by various authors for gender determination in north Indian population,[13] Japanese population,[21] Thai population,[22] Central India population,[23] Wichita-Kansa, USA population,[24] and South India populations.[25] All these studies showed that the sex within a given population is best described by a specific discriminant equation given by the respective authors. In the present study, discriminant equation is derived separately for individual parameters, combination of several parameters, and when all the parameters are considered. Finally, the discriminant function equation derived in this study is unique to our sample of adult and middle-age Telangana population.
| Conclusion | | |
We conclude based on the results of the present study and a comparative analysis of previous studies that mastoid process is a good indicator of sex when all the parameters are considered; length is the best parameter when individual parameters are considered. Combination of various parameters can be used for gender determination with a good accuracy. However, area of mastoid triangle is considered a poor indicator of sex and has limited significance.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]
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