Forensic Odontology: Bite Marks and Wrongful Convictions

By Bianca Cortez

In the United States, between two and ten percent of convicted criminal defendants have been convicted wrongfully. A major contributor to these wrongful convictions is the misapplication of forensic science. Forensic science widely accepted at the time of conviction but ultimately disproven due to scientific advancements accounts for at least some wrongful convictions. Within this field, exaggerated statistical claims by experts in bite mark, hair, and DNA analysis have historically been used to support unscientific conclusions. The Innocence Project has recorded at least thirty-one wrongful convictions and indictments based on bite mark evidence but estimates there remain many more innocent people incarcerated. Altogether, these wrongfully convicted individuals have spent approximately 374 years wrongfully incarcerated.

In the field of forensic odontology, bite mark analysis is used to compare suspected bite marks typically imprinted on crime victims’ flesh with the suspect’s own dental records. Bite marks are classified within seven categories (hemorrhage, abrasion, contusion, laceration, incision, avulsion, artefact) and can sometimes be found on victims (typically on the stomach, breasts, or buttocks) or suspects (inflicted during victim’s self-defense attempts). When possible, forensic dentists make casts of the bite mark to allow for later comparison. Otherwise, the biting edges of the suspect’s teeth and the suspected bite mark are traced onto transparent sheets of acetate for comparison.

In 1987, Steven Chaney went on trial for the murder of a couple from whom he previously bought drugs. At trial, Dr. Jim Hales testified a mark found on the male victim’s left arm matched the upper and lower arches of Chaney’s mouth. The expert even went so far as to claim that only one in one million people could have made the mark on the victim. As a result of this testimony, Chaney was convicted and sentenced to life in prison.

The Innocence Project and a Dallas County assistant public defender filed for a writ of habeas corpus to vacate Chaney’s conviction. As part of the petition, a sworn affidavit was included wherein Dr. Hales recanted his one in one million claim and stated that “conclusions that a particular individual is a biter and their dentition is a match when you are dealing with an open population are now understood to be scientifically unsound.” Files later turned over to Chaney’s new legal team show that although Dr. Hales’ initial bite mark assessment was around the odds of thousands to one, the prosecution allowed Dr. Hales to up the odds to one hundred thousand to one and finally one million to one.

On October 12, 2015, Judge Dominique Collins ordered Chaney’s conviction vacated and recommended the granting of the writ. After serving more than twenty-five years in prison, Chaney was released. The Texas Court of Criminal Appeals granted the writ in December 2018 after Judge Barbara Parker Hervey released a sixty-eight-page decision declaring Chaney “actually innocent.” In it, she acknowledged the underlying science of bitemark comparisons developed after Chaney’s conviction discredited the testimony that helped convict him.

Because of Chaney’s wrongful conviction, the Texas Forensic Science Commission launched a six-month investigation into the scientific bases underlying bite mark analysis. In its findings, the Commission recommended that this technique no longer be allowed inside Texas courtrooms and launched an audit into all convictions in the state that occurred as a result of bite mark evidence. In 2016, the President’s Council of Advisors on Science and Technology called bite mark analysis a “subjective” science without validity.

Bite mark analysis has been used in cases across the United States although there remains no underlying science to prove that bite marks are as unique to individuals as fingerprints or DNA. One major issue that persists within this contested field is its highly subjective nature in that different experts can draw different conclusions from the same evidence. Bite mark analysis alone should not lead to criminal convictions because of the lack of underlying science.

While there is hope for the wrongfully convicted in the form of post-conviction DNA testing, many cases do not involve any biological evidence. Even in the cases where biological evidence was collected, that evidence is often lost or destroyed after the defendant is convicted, potentially ruling out any possibility of proving one’s innocence. Greater scientific study and research are necessary before the criminal justice system should allow convictions based heavily or solely on bite mark analysis. Until the consistent reliability of testing bite mark evidence against suspects’ own dental records is proven, bite mark analysis should not be treated as a reliable, credible, or conclusive method of proving guilt.

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