Forensic odontology (or forensic dentistry as it is more commonly called) mainly involves the identification of an assailant by comparing a record of their dentition (set of teeth) with a record of a bite mark left on a victim. Other uses in law for dentists include the identification of human remains, medico-legal assessment of trauma to oral tissues, and testimony about dental malpractice. The forensic dentist, however, is to an ordinary dentist what the forensic pathologist is to an ordinary physician. They are board-certified specialists who deal primarily with bite mark evidence. Although one doesn't have to be a board-certified specialist to become an expert witness in this area, it does help to lend validity to any scientific opinions rendered. Courts have been remarkably generous in granting qualification to experts, regardless if they are a forensic dentist or a non-specialist dentist.
It must be remembered that it was bite mark evidence back in 1975 that gave us the Marx standard of admissibility, and it's probably worth quoting that standard at length (People v. Marx 1975):
|In making their painstaking comparisons and reaching their conclusions, the experts did not rely on untested methods, unproven hypotheses, intuition or revelation. Rather, they applied scientifically and professionally established techniques -- x-rays, models, microscopy, photography -- to the solution of a particular problem which, though novel, was well within the capability of those techniques. In short, in admitting the evidence, the court did not have to sacrifice its independence and common sense in evaluating it.|
Identification by teeth is not new. It goes back as far back as 66 A.D. at the time of Nero. As the story goes, Nero's mother Agrippina had her soldiers kill Lollia Paulina, with instructions to bring back her head as proof that she was dead. Agrippina, unable to positively identify the head, examined the front teeth and on finding the discolored front tooth confirmed the identity of the victim. During the U.S. Revolutionary War, none other than Paul Revere (a young dentist) helped identify war casualties by their bridgework. Teeth are highly resistant to destruction and decomposition, so dental identification can be made under extreme circumstances. It was used on Adolf Hitler and Eva Braun at the end of World War II, the New York City World Trade Center bombing, the Waco Branch Davidien siege, and numerous airplane crashes and natural disasters. The U.S. has a fairly well-developed system of dental records system (the Universal System), so it's not surprising to find it used for the identity of remains or "Jane Doe" victims. You can also tell age solely by analysis of teeth -- the Gustafson method (looking for six signs of wear) or the Lamendin method (looking at transparency of roots). With the Universal System, each tooth is assigned its own number from 1- 32 and the five surfaces of each tooth are also classified.
| All dental records are based
on a universal numbering system, and contain an amazing amount of
information. For example, they note:
3. surface structure/root configuration
4. adjacent teeth
5. twisted/tilted teeth
Antemortem/Postmortem match determines identity.
Bite mark comparison is fairly new, however, going back to the mid-1970s. Police investigators have always noticed that at some crime scenes, criminals seem to leave their bite impressions on food products, chewing gum, or more commonly on the skin of their victims, especially in cases of battery, rape, child abuse, and homicide. There are seven (7) types of bite marks which can be classified by four (4) degrees of impression:
|1. hemorrhage -- small
2. abrasion -- undamaging mark on skin
3. contusion -- ruptured blood vessel, bruise
4. laceration -- punctured or torn skin
5. incision -- neat puncture of skin
6. avulsion -- removal of skin
7. artifact -- bitten-off piece of body
|1. clearly defined --
2. obviously defined -- first-degree pressure
3. quite noticeable -- violent pressure
4. lacerated -- skin violently torn from body
Contusions are the most common type of bite mark, and incisions offer the best three-dimensional image of the teeth. When avulsions and artifacts can be combined, you've also got three-dimensional imaging. The Marx case involved very clear three-dimensional bites. The forensic science of analyzing degree of impression involves (at least with #3 and #4), the specification of "violence", and this kind of testimony can be taken as evidence of the defendant's state of mind, aggravating circumstances, or especially heinous behavior. Bite marks on a live body also have different characteristics from those on a dead body, so a forensic dentist might be able to assist with things like time of attack and/or time of death. Generally, the better the bite mark, the better an expert can make a comparison. The Illinois appellate case of People v. Milone (1976) establishes this principle in that, to be admitted, dental evidence must be agreed upon by the scientific community as "good quality". This means that bite mark evidence usually meets the Frye standard, at least in this regard.
HOW FORENSIC DENTISTRY WORKS
Forensic dentists are either called by medical examiners or police investigators. There's a movement underway to set up emergency call-out procedures in many jurisdictions. What has happened is that someone has discovered a bite mark while conducting an autopsy or viewing the body at a crime scene. While the bite mark can be photographed or even excised from the decedent, it's better to let the forensic dentist get there as soon as possible. One of the first things they'll do is obtain a saliva sample from the bite. This, of course, can be done by others, but a forensic dentist can make sure sample extraction doesn't affect quality of the bitemark. Next, the forensic dentist will take photographs. This is a technique shared by all experts, and it's fairly important to get the lighting, color, and camera angle right. A linear (ABFO) scale should be placed somewhere in the photograph. A camera angle of 90 degrees is best for a flat surface, while a 40 degree angle causes 25% distortion of a bite mark. Next, the forensic dentist makes multiple impressions, casts, or molds of the bitemark, and has access to a variety of materials in which to choose the right gum, rubber, plastic, or powder to make a cast. Some forensic dentists used the Dorion method, which advocates the removal of bitten tissue for microscopic examination. Others use advanced techniques such as scanning electron microscopy, computer-enhanced digitization, and xeroradiology. Computerized bite analysis software also exists. Once a suspect is apprehended, the forensic dentist makes one or more impressions of the suspect's teeth, comparing them to the recorded bite marks, and if called to testify, renders an opinion of the probability of a match. Courts have upheld the constitutionality of involuntarily taking a dental impression from a suspect, as they have for most biological specimens from suspects (Schmerber v. California).
The THEORY behind forensic dentistry is that no two mouths are alike (even identical twins are different), and that teeth, like tools, leave recognizable marks. A bitemark, however, is not an accurate representation of the teeth. A lot depends on the mechanics of jaw movement and use of the tongue. Inside the mouth, the lower jaw (mandible) is movable and usually delivers the most biting force. The upper jaw (maxilla) is stationary, holding and stretching the skin, but when skin is ripped or torn, the upper teeth are involved more deeply. Most bitemarks usually show a curvature where the upper teeth, at least, made an impression.
The skin is elastic, tending to slip along the upper teeth until it catches hold. Depending upon the type of victim, some bitemarks last for hours and others for days, but almost all bitemarks alter themselves as time elapses. Photographing bitemarks at intervals over a set period of hours or days is part of the standard protocol recommended by the ABFO. Bitemarks also change or become distorted when the posture of the victim changes, so the forensic dentist might be able to assist with determination of how the perpetrator moved the body.
PROBLEMS AND ISSUES
It's unlikely that the qualifications of a forensic dentist will be successfully challenged on the stand since so much judicial notice has been given to this expertise. It's also doubtful that you will find a forensic dentist associated with a law enforcement agency on more than a part-time basis. Board certification requires such association, having observed autopsies, having worked 25 cases, and having accumulated 350 qualification points, which are earned by attending meetings, conferences, etc. Final certification is granted after successful passing of an examination, and is good for five years.
One issue is the problem of standard protocol. This appears to be a field in which several experts go their own way, creating their own methods. There's also a digital divide in that some dentists have access to sophisticated lab equipment and others don't. Blind reviews also tend to be either not done or reflect poorly on the profession. In a blind review, a sample of experts would be unknowingly given the same material to analyze and compare, but might come to different conclusions. Experts have not followed a points of comparison approach, but instead have relied upon a probabilistic assessment of the confidence in their opinion approach. A moderate amount of literature can be found in peer-reviewed journals, but this field has a long way to go before many of its claims can be scientifically substantiated.
ABFO and ASFO (under construction)
Bureau of Legal Dentistry and Strange but True Stories
Dr. Robert Dorion's Forensic Dentistry Homepage
Forensic Odontology: An Overview
Human and Animal Bitemark Management
Inter. Org. for Forensic Odonto-Stomatology
Univ. of Pitt's Dentistry Resources
Univ. of Queensland Odontology Links
U.S. Armed Forces Forensic Dentistry Detachment
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De La Cruz, R. (1987). "Forensic Dentistry and the Law: Is Bite Mark Evidence Here to Stay?" Criminal Law Review 24:983-1005.
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Gold M., Roenigk H., Smith E., Pierce L. (1989). "Evaluation and treatment of patients with human bite marks: a Review" Am. J. of Foren. Med & Path 10:140-143>
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Moenssens, A., J. Starrs, C. Henderson & F. Inbau. (1995). Scientific Evidence in Civil and Criminal Cases. Westbury, NY: Foundation Press.
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Sperber N. (1986). "Identification of children and adults through federal and state dental identification systems: Recognition of human bite marks" Foren. Sci. Int. 30:187-193.
Vale G., Rawson R., Sperber N., Herschaft E. (1988). "Discussion of "Reliability of the scoring system of the American Board of Forensic Odontology for Human Bite Marks" J. Forens Sci. 33:20-25.
Last updated: 01/06/04
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