DNA & Bite Mark Analysis
Forensic science has numerous specialties that sometimes overlap. Tool mark analysis has been casually considered an analog of bite mark analysis by some dental commentators. The connection is weak, but that's another story.
Footprint analysis uses dental materials. Fingerprint analysis uses areas of similarity or concurrent "points" to quantify the degree of "match" between Known and Unknown evidence samples.
Odontology has tried this approach as well. Analysis of fibers and ballistics use the comparison microscope. Some dentists use wax, others use computers. The modes of analysis for the physical comparison 'sciences" are boundless. In the area of biological evidence, bitemarks has an underdeveloped relationship with DNA identification from saliva. This article discusses this particular overlap.
What is the optimum protocol available when an odontologist compares a suspect to a possible bite mark when the DNA results are still pending? The purists would say the two fields -physical matching and DNA analysis - are independent. The literature suggests that the investigation of a bitemark mark be made independently of extraneous information to prevent either intentional or expectational bias. Knowing the suspect was caught crawling through the window doesn't add weight to an otherwise nonprobative bitemark in skin or inanimate object. The legal consumer of expert testimony and opinion expects odontological testing to be independent and blind to other expert conclusions. This is despite the fact that physical matching of bite marks is a non-science which was developed with little testing and no published error rate. Its is supported by anecdotalism and a minuscule number of inadequate population studies. The number of rotated left maxillary central incisors present in adult males of a certain racial group is left for future investigation. Alternatively, DNA has arrived on the criminalistics scene with well-established guidelines and laboratory safeguards. The statistical justification for DNA has been scrutinized and approved through rigorous testing and technique standardization. The frequencies in the population of polymorphic loci are known.
What the, should a prudent odontologist do in this situation? The temptation to create an opinion early in an investigation is normal. Who wants to say that odontology cannot conclusively establish a bite mark as unique? We are trained to expect to accomplish this if the evidence is "good." It is left to the individual dentist to determine what is sufficient evidence for this determination. This is the foundation where a fragmentary or unclear bite mark develops into a "positive or probable match" between common dental characteristics.
The greater experience of one expert over another has been argued as a guarantee of a "better" result. This is unproven conjecture and serves as the single support for proponents of the non-science approach. The interpretation of a bite mark case must be determined by methods that are reproducible and obvious. The "I can see it, you can't" school of expertise will not lead us into the 21st century. Instead, it will spell the doom of this particular aspect of crime investigation.
An opinion is worth nothing unless the supportive data is clearly describable and can be demonstrated in court. How does one weigh the importance of a single rotated tooth in a bite mark when the suspect has a similar tooth? The value judgements range widely on the value of this feature. This is not science. Instead, statistical levels of confidence must be included in this process. Until then, the DNA results are far superior to the odontologist's position. There is no honest way to deny this.
You may form an opinion before the DNA results are in, but the majority of cases will be proven conclusively by the biological tests. If they are performed. If the two independent tests do not correlate, I hope odontologists will not rely on the theory that there were two assailants involved in the same case-one biting and the other spitting.
About the Author: C.Michael Bowers provides expert and criminal litigation support in matters pertaining to forensic dentistry, pathology, and DNA profiling. Originally published in the American Society of Forensic Odontology Newsletter, Winter 1996.
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