This article constitutes a review of the literature and an evaluation of the anatomical relationships between skull and face including the soft tissue thickness at various anthropometrical points of the skull, along with a comparison of the methodologies involved in the three techniques, that is, photographic, video and computer-assisted superimposition techniques used in forensic science. In addition, an evaluation of cosistency between skull and face is discussed from the aspect of personal identification.
Forensic examiner must be well versed in the anatomy of skull and face for effective utilization of the superimposition technique. When evaluating anatomical consistency between these parts, special attention should be paid their outline, the facial tissue thickness at the anthropometrical points, and positional relationships between skull and face. Data on the thickness of facial soft tissue has been accumulated for each race, Caucasoid, Negroid and Mongoloid. The positional relation of the eyebrow and eye to the orbit, the ala to the nasal aperture, and the lips to the teeth has been investigated by many researchers.
Over the last two decades, video superimposition technique has widely been used for identifying unknown skull. The video superimposition presents enormous advantage over the conventional photographic superimposition. This technique allows the fade-out of either the skull or facial image on the monitor for overall assessment of how well the two images match. This also allows the various sectioning images of the skull and facial images for evaluating the positional relationships between the skull and face. In this technique, however, the anthropometrical examination including soft tissue thickness could not directly be performed on the TV monitor.
On the other hand, in the last ten years, the computer-assisted cranio-facial superimposition has been developed. The use of a video-computer with appropriate software allows to take the images of the skull and facial photograph with only one camera and to directly compare the digitized both images on the monitor. The computer technology has also been used to determine the size of natural head and optimum objective length. The software such as the polynomial functions and Fourier harmonic analysis has been applied to evaluate the fit between the outline of skull and facial photograph.
It is suggested that the outline from the forehead to the gnathion in the lateral or oblique view is the preferable portion for personal identification, and the cranio-facial superimposition method is reliable for personal identification when two or more facial photographs taken from different angles are used in the examination. The computer-assisted skull identification system using video superimposition is useful to demonstrate the cosistency between skull and facial photograph because the quantitative data including anthropometrical measurements obtained from this system provide objective and reliable results in skull identification.
