Why Bite Mark Matching Evidence Should be Limited

Despite some high profile cases in which people were wrongly convicted of serious criminal offenses based upon the testimony of forensic odontologists, bite mark experts, courts continue to allow bite mark evidence in court.

While some courts may be cautious about how the evidence is presented to a jury, the risks that a jury will be led astray by bite mark evidence remain significant.

What is Bite Mark Evidence

In its early days, forensic odontology focused on the identification of people by comparing their teeth to dental records. Using dental records to identify human remains has proved to be highly reliable, and is not controversial.

Starting in the 1970’s forensic odontologists started to examine bite marks with the goal of identifying the person who was responsible for the bite. They would first examine markings on a person’s skin to try to evaluate whether or not the marks came from a human bite mark. If they concluded that it was a human bite, they would make a comparison between the marks and a suspect’s teeth to try to determine if the suspect was responsible for the bite mark.

Sometimes comparison is made through a photograph of the bite mark, while other times a cast is made of the bite mark for later comparison. Some odontologists make comparisons by using plaster casts of the suspect’s teeth, while others use an overlay to compare two-dimensional images of the bite mark with the suspect’s teeth.

Although forensic odontology and bite mark matching grew more common, the methodology of bite mark matching remained much more an art than a science. Forensic odontologists do not follow a consistent standard for identification, and there can thus be significant difference in opinion between experts as to whether or not a bite mark could have been made by the teeth of a specific suspect.

Starting in the 1990’s, through DNA evidence, a considerable number of bite mark identification cases were found to have resulted in wrongful conviction. Although subsequent examinations of bite mark evidence and the methodology used in bite mark matching have consistently cast a shadow over the quality and reliability of bite mark evidence, courts continue to allow bite mark evidence in criminal cases.

What is the Problem With Bite Mark Evidence

The primary problem with bite mark evidence is that it is non-scientific.

  • There is no evidence that bite mark patterns as might be observed on a crime victim are so unique that they can be reasonably attributed to a specific individual.
  • There are no established criteria for matching bite marks that are consistently applied by experts, and individual experts may change their approach from one case to another.
  • The elasticity of skin makes it a poor material for recording a bite mark, and post-bite bruising may distort the image left by the biter’s actual teeth.
  • When a crime victim is bitten by an attacker, their skin is often stretched or distorted, and as a result the tooth pattern on the victim’s skin may be very different from the arrangement of the attacker’s teeth.
  • Many bite marks may show marks from four to eight teeth, leaving few points of comparison for matching purposes. Also, even the teeth involved in a bite may have little contact with the skin, resulting in an impression that is partial and potentially misleading.
  • In studies of the accuracy of bite mark identification, forensic odontologists often disagree as to whether bite marks are even human in origin, even before trying to identify a suspect.
  • Studies of dental impressions have illustrated how bite marks that are visually very similar can be left by different sets of teeth.
  • Bite marks are rarely three dimensional, so that an expert might more accurately assess how a suspect's upper and lower teeth align with each other.

When a forensic odontologist claims that there is a “match” between the suspect’s teeth and a bite mark left on a victim, that assertion may be highly convincing to a jury but may in fact be highly misleading.

In forensic work the term “match” may mean nothing more than that there are significant similarities between the bite mark and marks that might have been left by a suspect’s teeth, but without any further assertion or showing that the match reliably identifies the suspect as the person who left the bite mark. Juries hearing the term “match” are nonetheless likely to infer that the suspect was responsible for the bite.

What to Do if Bite Mark Evidence is Being Used Against Your Client

If you are representing a client based upon bite mark evidence, be aware that in the past defendants have been convicted on the strength of bite mark comparisons even when other, more reliable forensic evidence, such as DNA evidence from the crime scene, excluded them as suspects. Juries who have watched shows like CSI may be inclined to believe the accuracy of forensic evidence, with little understanding of its shortcomings.

When responding to an effort to introduce bite mark evidence,

  • Try to challenge the admissibility of the evidence, or the weight that can be attributed to the evidence by the jury.
  • Examine the bite mark expert’s history, as it may include cases of misidentification and even having contributed to wrongful conviction.
  • Find out what the expert means by a “match” and, if it’s an exceptionally broad definition, consider a motion in limine to try to have the court require a different description for the expert’s findings that reflect their lack of actual certainty.

Contact critics of bite mark evidence for the latest developments, including studies on bite mark identification. Not all forensic odontologists believe that bite mark matching is appropriate for use in criminal prosecutions. Innocence projects have represented people wrongly convicted based on bite mark evidence, and may be able to share information that will be helpful to challenge the qualification of an expert or the claim of a match.

Further Reading

In a 2016 article, researchers examined thirteen studies on the uniqueness of human dentition, and none were able to conclusively demonstrate that bite mark patterns are unique to an individual. The four studies that claimed to show uniqueness were found to be methodologically flawed. Forensic bitemark identification: weak foundations, exaggerated claims. Journal of Law and the Biosciences, November 2016.

The American Board of Forensic Odontology has conducted a study to try to demonstrate the validity of bite mark identification, but the study instead highlighted many of the weaknesses of bite mark matching.

Bite mark evidence has also been called into question by the National Academy of Sciences (NAS), by the Texas Forensic Science Commission and, under President Obama, by the President’s Council of Advisors on Science and Technology (PCAST). Forensic Science in Criminal Courts: Ensuring Scientific Validity of Feature-Comparison Methods, President's Council of Advisors on Science and Technology, September 2016.

Copyright © 2017 Aaron Larson, All rights reserved. No portion of this article may be reproduced without the express written permission of the copyright holder. If you use a quotation, excerpt or paraphrase of this article, except as otherwise authorized in writing by the author of the article you must cite this article as a source for your work and include a link back to the original article from any online materials that incorporate or are derived from the content of this article.

This article was last reviewed or amended on May 8, 2018.