Mandible is the strongest, largest, hardest & most durable bone of the skull which retains its shape better than other bones in forensic study and exhibiting high degree of sexual dimorphism. To study the nonmetric characteristics of mandible such as the variations of shape of chin, lower border of mandible and shape of coronoid process and to distinguish between males and females.
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MATERIALS AND METHODS: The material for this study comprised of 90 dry adult human mandibles of known sex which was obtained from Department of Anatomy. The characteristic feature that allowed the sexes to be distinguished was the contour of the lower border of mandible, shape of the chin and shape of coronoid process bilaterally.
RESULTS: Rocker-shaped mandibles predominated in males (58.9%), whereas most females (41.1%) exhibited a straight mandible. The shape of the chin in most males was generally Bilobate (45.5%), Square (43.6%), whereas the chin in females was Pointed (71.4%).Shapes of coronoid process observed were Triangular (41.1%), Rounded (31.1%), and Hook in (27.8%) with p value< 0.05 which indicated statistical significance.
CONCLUSION: The nonmetric analysis of mandible used in this study could be used for sex determination.
Key words: Forensic anthropological, Mandible, Non metric characteristics sex determination.
In forensic investigation identifying the human remains is thought to be a first step & is crucial for futher analysis.1 The sex determination in human skeleton is usually the initial step in the identification process as subsequent methods for age and stature estimation are sex dependent. The accuracy of sex determination depends on the completeness of the remains and the degree of sexual dimorphism inherent in the population.2 When the complete adult skeleton is available for analysis sex can be determined up to hundred percent (100%) accuracy, but in cases of fragmented bones which are usually found in mass disasters, obtaining cent percent (100%) accuracy in sex determination is difficult and it largely depends on the available fragmented bones of skeleton.1, 2
As evident from the earlier studies, the most dimorphic and easily distinguish portion of skeleton among sexes after pelvis is skull, providing accuracy up to 92%.1 But in cases where intact skull is not found, in sex determination mandible may play a vital role, as it is the most durable, largest, strongest , and dimorphic bone of skull.1-4 Mandible is very durable part of skull bone due to the presence of a dense layer of compact bone, and hence remains well preserved than many other bones. The shape and size of mandible reflects the dimorphism characteristics.1 Female bones are generally smaller and less robust than male bones.2
This characteristic feature of mandible helps in sex and age determination in medico legal cases. In anthropological excavations, the morphometric features of the mandible aid to determine the sex, age, food habits and race of the population and also helps to understand the cave dweller / human evolution.5 The relative development such as size, strength, and angulation of the muscles of mastication is known to influence the expression of mandibular dimorphism as masticatory forces exerted are different for males and females.6
The shape of the mandible can vary according to the different lifestyles and chewing habits .7Therefore, the morphological characteristics of the mandible vary among different ethnic groups. There are several causes of differences in the shape of the mandible between the sexes8. The shape and size of the mandible appear to differ between the sexes from the development of the deciduous tooth. Also, the size of the masticatory muscles and mandible appear to differ between males and females before birth9. The size of the ramus differs between males and females according to the stage of mandibular development and muscle growth.10,11 Furthermore, the mandible have different rate of growth in males and females.12,13 Because puberty occurs earlier in females than in males, sexual differences may manifest themselves in the skull and jaws of females earlier than in the later and longer maturing males.14 For the determination of the of males and females mandible many attempts have been made with help of metric standards.15-17 However, metric methods have their disadvantages by their requirement of a complete mandible. Using nonmetric methods, Bass18 found that the shape of the chin could be used to distinguish between males and females. In addition, Loth and Henneberg 19 in his reported cases showed that there is a large difference in the ï¬‚exure of the ramal posterior border during male and female Africans that can be used to differentiate the sexes with 99% reliability. In addition, it was reported that there are discrete differences in the gonial ï¬‚aring of the mandible between the sexes20.
In this study we investigated the criteria that can be used to differentiate between males and females by using the non-metric characteristics of mandible such as variation of contour of lower border of mandible, shape of the chin and variation in shape of coronoid process in mandibles.
MATERIALS AND METHOD
The present study was undertaken on 90 dry adult, complete, undamaged human mandibles of known sex from the collection of Anatomy department. Out of 90 mandibles 53 were of males and 37 of females and were examined for the variations shape of lower border, shape of the chin and shape of coronoid process of both the left and right side of the mandible. The shape of the chin was classified according to the thickness of the mandible in front of and beneath the chin, the proï¬le of the chin according to amount of protrusion of the chin observed from the side, the contour of the lower border of the mandible was classified according to the depth of the antegonial notch, variations in the shape of the coronoid process in right and left sides of adult bones of both sexes were noted and tabulated.
The nonmetric items observed in this study is as follows:
1. The contour of the lower border of the mandible (fig 1)
2. The shape of the chin (fig 1)
3 Coronoid process of mandible (fig 1)
Hooked, rounded and triangular
INCULSION CRITERIA: well-formed mandible
EXCULSION CRITERIA: Fractured, deformed, bony growths of Coronoid process [osteochondroma] were excluded from the study.
Data were analyzed using a chi-square test & p value of 0.05 was obtained which showed that this study was statistically significant.
Rocker-shaped mandibles predominated in males (58.9%), whereas most females (41.1%) exhibited a straight mandible. The shape of the chin in most males was generally Bilobate (45.5%), Square (43.6%), and Pointed (10.9%), whereas the chin in females was either Square (8.6%) or Bilobated (20.0%) Pointed (71.4%).Shapes of coronoid process observed were Triangular (41.1%), Rounded (31.1%), and Hook in (27.8%) with p value< 0.05 which indicated statistical significance.
Differentiating features of males from females and the differences in ethnic groups by analyzing the morphological characteristics of bone is important in the ï¬eld of physical and forensic anthropology. Sound bone is difï¬cult to obtain because the quality of bone deteriorates over time due to factors such as environment-induced erosion. In sex determination examination of the pelvic bone is the most accurate means, but this bone is rarely found intact. Skull is most easily distinguishing portion of the skeleton as a part of the skull mandible shares its own characteristics. The mandible is the strongest and largest bone in the human body and persists in a well-preserved state longer than any other bone. Hence mandibular characteristics are significantly useful for determining sex and race. The shape of the chin and the lower border of the mandible had a different shape between males and females in the present study.
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The shape of the chin is used widely to distinguish between the sexes, because the male chin is usually bilobate /square whereas the female chin is more pointed. Similar observations were made in the present study; specifically, 90.7% of males had either a bilobate or square chin, whereas 72.2% of females had a pointed chin. However, while the shape of the chin is more distinctive in males than in females, sex determination based only on the shape of the chin is not sufï¬ciently reliable.
The characteristic that was the most distinguishable between the sexes in this study was the shape of the lower border of the mandible. The lower borders of mandibles from males tended to be rocker shaped (58.9%), whereas lower borders of mandibles from females tended to be straight (41.1%) (Table1). Therefore, the shape of the lower border of the mandible may be used as a reliable index for sex determination. However, we believe that using only this characteristic is not sufï¬ciently reliable for sex determination; instead, evaluating both the shape of the chin and the shape of the lower border of the mandible improve the precision of sex determination. When these two items were combined, 90.7% of males exhibited the characteristics of male mandibles (a bilobate or square chin and a rocker-shaped lower border of the mandible), whereas 77.2% of females exhibited the characteristics of female mandibles (a pointed chin and a straight lower border of the mandible, (Table3). Few males (9.3%) had a pointed chin and a straight lower border, which are characteristics of females, while 27.7% of the females exhibited mandibular characteristics that were characteristic of males (Table 3). Therefore, the probability of assigning the incorrect sex to a mandible when examining both the shape of the chin and the shape of the lower border of the mandible is very low. Moreover, the shape of the chin is the most distinctive characteristic in males (90.7%), whereas the lower border of the mandible is the most distinctive characteristic in females (77.2%). Therefore, we can determine the sex using the following two-step approach. During the ï¬rst step in determining sex based on the characteristics of the mandible, if the lower border of the mandible is rocker shaped, it is likely to be the mandible of a male, but if the lower border is straight, it is likely to be the mandible of a female; during the second step, if the chin of the mandible that has a straight lower border is bilobate/square, it is likely to be the mandible of a male whereas pointed and straight is likely to be of female.
Shapes of coronoid process observed were Triangular (41.1%),Rounded (31.1%), and Hook in (27.8%) where Triangular and hook shape had slight male predilection and triangular and rounded had slight more of female predilection(Table 4).Issac B21reported in a study of 157 mandibles incidence of hook shaped was 27.4%, triangular 49% and rounded type 23.6%.He found the incidence of the rounded type almost equal in male and female mandibles, triangular type slightly more in the females, while hook type more in the male mandibles. Comparing with Issac B the incidence of hook type was closely similar to the present study, but triangular and rounded shape incidence observed was more in males and so the findings did not coincide with the author.
The differences between the sexes and among ethnic groups the morphological characteristics of the mandible are determined by the environment and different growth patterns. Therefore, males and females can be distinguished based on the shapes of various parts of the mandible. We found that the simultaneous use of the shape of the lower border of the mandible and the shape of the chin is the best method of predicting sex with a rate of accuracy that is higher than 90% and the morphological variation of shapes of coronoid .Triangular shape of coronoid process is the most common presentation .Incidence of Triangular, Rounded and Hook shape were found more in the in male bones compared to female bones. The above findings could be of substantial significance for the anatomist, anthropologist and forensic researchers.
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