Bite Marks as Evidence to Convict
The Dentist's Role in Forensics
Some people think that the role of a dental expert in the investigative process of crime solving is to identify victims—especially burn victims—by their dental records. In fact, the dental expert, or forensic odontologist, has numerous roles, one of which is to match the bite-mark impressions on a victim to the tooth structure of suspects. Teeth are tools and a tooth mark is like a tool mark. Generally the teeth that leave the strongest impressions are in the front, both top and bottom.
One of the important things to remember about teeth is that they can chip, get worn down, or be reshaped in various ways. The teeth that we're born with do not necessarily remain the teeth we live with. Often, that factor helps to distinguish one set of bite-marks from another. There are also restorations, fillings, rotations, tooth loss, breakage, and injury that can make one person's teeth unlike anyone else's. Sometimes a bite-mark has to be charted and examined from many angles; sometimes it can be identified from one tooth. A landmark case in California involved the bite mark on a victim's nose that left a three-dimensional impression.
The American approach to charting teeth, which is one among over two hundred methods around the world, is called the universal system. A number is assigned to each of the thirty-two adult teeth, beginning at #1 with the upper right third molar and ending with the lower right third molar. Each tooth has five visible surfaces, and the composite information about each surface makes it possible to make grids, which are known as odontograms. Each individual's grid is unique to that person, and if they have dental disorders, gum problems, or poorly formed teeth, it makes them even easier to identify.
Forensic odontologists develop the skill of comparing dental impressions taken from a person's mouth to bite-mark impressions on the skin (or possibly the bones) of a victim. There are from thirty to seventy-six comparison factors to consider, including matching for striations, whorls, indentations, pitting, and abrasions, and often this is done through computer-enhanced photography. They can also analyze bite marks on food in cases where a perpetrator (even just a burglar) might have taken a bite out of something in the victim's home and left it behind. What experts seek are a sufficient number of points of similarity between the evidence and a suspect to be able to say with a reasonable degree of certainty that this is the perpetrator.
In one case, a wad of chewing gum caught the guy. Two men were arrested in connection with a murder. Dental impressions were taken and remade into silicone because a piece of used chewing gum at the premises of the victim indicated clear teeth marks. The silicone was placed into the gum to make an identification. Impressions were also made of the victim's teeth in order for that person to be eliminated as the person who had chewed the gum. One of the suspects was also eliminated but the other proved to be a match. From there, it made sense to do saliva tests, which matched the suspect for blood type, and faced with this evidence, he entered a guilty plea.
However, bite marks left on foodstuff, such as cheese or gum, offer a three-dimensional impression, which is superior to the two-dimensional impression often left on skin. A bite might penetrate the skin, but often only leaves bruising—and sometimes the blood marks of a bruise are mistaken for the impression of a tooth. It also seems to be the case that skin gets distorted when bitten, or the teeth slide during the act of biting. Some bites are forceful enough to leave a good impression, others are not.
The physical characteristics of both the bite mark wound and the suspect's teeth include:
- the distance from cuspid to cuspid
- the shape of the mouth arch
- the evidence of a tooth out of alignment
- teeth width and thickness, spacing between teeth
- missing teeth
- the curves of biting edges
- unique dentistry
- wear patterns such as chips or grinding.
All of these are examined in detail and than compared, preferably in a blind test in which the odontologist is not aware of which teeth impressions belong to the suspect. At the very least, the injury pattern itself should be completely analyzed first before looking at the data from the suspect.
"Most bite marks," says Vernon Geberth in Practical Homicide Investigation, "are found in the following type of homicides: (1) the homicide victim involved in sexual activity around the time of death; and (2) the battered-child homicide victim." He goes on to point out that homosexual homicides, when they have bite-marks involved, tend to have them on the back, arms, shoulders, face, and scrotum of the victim. Breast and thigh bite marks indicate heterosexual aggression and tend to be done slowly and sadistically, which leaves an excellent impression. Battered children have randomly placed bite marks that are generally diffuse and of poor detail.
Forensic odontologist, Dr. Lowell Levine, says that the markings on the skin indicate such things as jaw musculature, mental state, and tongue-lip coordination of the offender. He lists two types of bite-mark patterns:
The bite marks that appear to have been inflicted slowly show a "suck mark" area with an abrasion pattern that resembles a sunburst.
A tooth-mark pattern, which is an attack or defensive bite. It does not leave as clear a pattern as the first type and is difficult to identify.
It can also be determined from the type of bleeding beneath the skin whether the victim was alive or dead at the time the bite mark was delivered.
In addition to bite marks left in an attack, there may also be defensive bite marks left on an offender when the victim fights back. It may be a good idea to get dental impressions of victims just in case that is the only link to be found in a case. And where there's a bite mark, there may also be DNA evidence from saliva left behind.
Although bite-mark testimony dates back to Paul Revere, only a few cases have been notable in making legal history.