engleski

Quantitative analysis of sexual dimorphism on frontal inclination angles measured from digital 3D models of human dry crania

The development of forensic anthropology in the last decade has evidenced the importance of applying reliable and standardized methods to forensic anthropology cases, in order to provide objective quantitative results with known error rates that can be accepted by a court of law. The assessment of an individual’s biological profile, especially sex, is the primary step in any forensic anthropology analysis. To date, different quantitative sex assessment methods have been developed, but visual inspection and subjective trait-scoring is still preferable to existing quantitative methods. Besides the five sexually dimorphic traits of the skull identified by Buikstra and Ubelaker’s volume of standard methods, there are many more traits that can be used to estimate the sex of skeletal remains. One such trait is the inclination of the frontal bone. Although it is generally accepted that the frontal bone is more inclined in males than the females, no one has so far quantified these characteristics using inclination angles. Here, we present an easy and replicable method for quantifying frontal bone inclination. The method was developed on digital 3D models, but that can be equally well applied to traditional 2D photographs of skulls. A total of 121 Croatian male and female medieval skulls (m=60 ; f=61) were used in the study. The crania were scanned with a CT scanner, and the resulting DICOM 3D data was converted into STL models using the 3D doctor imaging software. The STL models were then oriented along the Frankfurt horizontal plane, and the inclination of the frontal bone was measured from these 2D images of lateral screen shots. The inclination angle was calculated from two lines intersecting at glabella: first, the most prominent point of the glabellar region (assessed as the upper-most external pixel in the region) was identified, then a line parallel to the Frankfurt horizontal plane was drawn through this point, next a tangent from glabella to the frontal bone outline was drawn, and finally the angle between this tangent and the other line was measured. Males were found to have a more inclined frontal bone (m=73, 77°), while females displayed a more vertical forehead (f=79, 73°). A t-test showed the difference between the sexes to be statiscally significant (p<0, 0001). Discriminant function analysis showed that 71% of crania could be correctly classified from the frontal inclination angle, with better results in females (73, 77%) than males (68, 33%). The presented method evidences the possibility to acquire objective data on a sexual dimorphic trait such as the inclination of the frontal bone, which can be used to determine the sex of an individual. The frontal inclination angle calculated this way correlates with and is affected by, the dimensions of the glabellar region (Spearman correlation R=0, 7), which itself is a sexually dimorphic trait. In the future, inclination angles measured from other landmark points in the glabellar region should be investigated, and the method should be evaluated on other populations, as well as on modern samples, to test its validity in practice.

forensic anthropology; legal medicine; virtual anthropology; skull; sexual dimorphism

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