Bite Mark on a Victim: Odontology and the Limits of Comparison
A 24-year-old woman is found dead with a crescentic area of bruising and abrasion on her left forearm, 3 cm across, with what appear to be small paired marks. A suspect is identified. The forensic odontologist is asked to compare the injury with the suspect's dental casts. The suspect has noticeable dental crowding and one chipped incisor. The photographs of the injury were taken at autopsy without a scale in some frames and with oblique lighting. The victim's skin was not excised. The prosecutor asks whether the odontologist can 'match' the bite mark to the suspect.
1. What are the limitations of bite mark comparison, and how should the odontologist respond to the request for a 'match'?
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Bite mark analysis has well-documented limitations and has been heavily criticized (e.g., the 2009 National Academy of Sciences report and subsequent reviews). Key points:
- Skin is a poor medium: it is elastic, curved, and changes with swelling, positioning, and postmortem change. Bite marks distort.
- Uniqueness is not established: the claim that human dentition is individually unique to the exclusion of all others is not scientifically validated.
- Photographic quality: missing scale and oblique lighting prevent accurate measurement and comparison; without a scale, dimensions cannot be reliably assessed.
- No excised tissue: the injury was not excised and fixed, losing the best possible specimen.
A responsible response is to not offer a 'match' or individualization. The odontologist may describe the injury (location, size, pattern), state whether it is consistent with a human bite in general terms, and note that the available records are inadequate for meaningful comparison. If comparison is attempted, it should be framed as 'cannot exclude' or 'not consistent,' never as a positive identification. The odontologist should also note that DNA from salivary residue would be a far more probative test if available.
2. What should the odontologist recommend to strengthen or replace the analysis?
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- Swab the injury for DNA (saliva) if not already done; this is the most probative avenue.
- Re-photograph with a scale and appropriate lighting, and consider excising the injury with a margin, fixing it, and preserving it for examination.
- Document the injury's location, size, shape, and relationship to underlying anatomy.
- Avoid overinterpretation of the chipped incisor or crowding as 'matching' features; these are common and not unique.
- If a comparison opinion is still requested, use a conservative scale (e.g., 'excluded,' 'inconclusive,' 'cannot exclude') and disclose the limitations in the report.
The pathologist/odontologist should be prepared to explain in court why a definitive match is not scientifically supportable.