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How Forensic Experts Analyze Bite Mark Evidence



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Weapons are tools, and tools leave marks. A weapon in a violent crime can be anything from a gun to a knife, to a fist, to a mouthful of teeth. Each of these tools leaves a signature mark that can be analyzed and matched to the specific tool used. Odontology is the study of teeth, in a non-dentistry way. The odontologist is concerned with the physical characteristics of teeth more than the functional characteristics as your personal dentist is concerned. Forensic odontology is the field where the physical characteristics of teeth meet law.

Teeth can be used to identify bodies when other sources of identifying information may be unavailable, such as with victims of fires. A one-to-one comparison with dental records looks at the structure of teeth and act like a finger print in identification of an individual. Because of the uniqueness of the teeth size and shape, the marks left behind from a bite can also be used for identification purposes. If you have ever watched a cartoon individual eat a sandwich or cookie you are familiar with the exaggerated bite marks left behind. While real life doesn’t work quite the same way, a distinct mark is left behind when someone bites a pliable surface.

Whatever the situation of the bite mark, a set of teeth needs to be available to compare to the mark left behind. Just as forensic fire arms experts can’t match a bullet to a gun they don’t have, a forensic odontologist cannot match a bite mark to a set of teeth they don’t have. When a suspect is available, photographs, x-rays, and molds can be taken of the mouth for the purpose of matching or excluding the suspect’s teeth as the tool used to inflict the damage.

In the case of a bite on human skin, there is an initial impression made that can be visible to the eye, but the damage runs deeper into the tissue. Bruising on the surface may fade while remnants of an impression may last much longer deep beneath the skin. With surface impressions, regular photographs can be taken to capture the setting, size and shape of the teeth. Photographs are not perfect, however, as the type of camera used, lighting at the scene, and time relevant to the bite occurring are all factors that affect the accuracy of the picture.

UV light photographs are used to see beneath the surface. Deep tissue damage lasts longer than surface impressions in the skin and can be seen using UV light. Images generated in this way can still capture the spacing, size, and shape of the teeth.

Plaster molds can be made directly from the bite mark and can be an accurate representation of spacing, size, and shape of the teeth used, but this process also degrades as time increases from the time of bite to the time the body heals.

Fingerprints are unique to every individual, and so are sets of teeth. A fingerprint can be lifted and compared to the fingerprint obtained from a suspect to determine a match. In the same way, a bite mark can be compared to a set of teeth to determine if they left the mark. Although bite marks are not left as frequently as fingerprints they can be just as useful to an expert in identifying a suspect.

Source

Genge, N.E. (2002). The Forensic Casebook. New York, NY. The Random House Publishing Group

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