Forensic dentist Mary Bush and others publish commentary outlining problems with bite mark analysis
BUFFALO, N.Y. – During trials for murder and other violent crimes in which victims were bitten, prosecutors may display photographs of bite marks next to the suspect’s tooth marks. And the two may seem like a perfect match. Is the case resolved?
Not always, according to Mary Bush, DDS, a forensic dentist and associate professor of restorative dentistry at the University of Buffalo School of Dentistry. Bush has long argued that human dentition is not unique when it comes to bite mark analysis, and that seemingly perfect bite marks could be from a series of suspects.
Mr. Bush said bite marks were not only inadequate, but were also abused in court. In a commentary published in the May 2023 issue of the California Dental Association Journal, President Bush noted that 26 people were wrongfully convicted, largely due to bite marks found on the victims. At least three of the suspects were sentenced to death.
Bush co-authored an article, “Bite Analysis: Law vs. Science Battles for Justice,” with Raymond Miller, a clinical associate professor at UB and a forensic dental consultant with the Erie County Office of Medical Examiners, and Peter Bush, director of UB’s South Campus Instrument Center and co-founder of the Forensic Dental Research Institute.
Bytemark analysis is based on two assumptions
“The premise of the Bytemark analysis is based on two main assumptions,” explained Mary Bush. “First, the placement of human teeth in the mouth is unique, and second, that unique feature is transferred to the skin.”
She noted that problems usually arise when jurors are shown photographs of a suspect’s dentition marks and scars that fit fairly well.
“They always do,” Bush said. “And once a jury finds that ‘proper,’ it’s hard to overrule. The question is, how many other people might fit that bite? The jury doesn’t even know this. “
In assaults and murders, the victim usually wrestles with the attacker, causing the skin to move and bruise.
“For real bite marks, it’s usually the bruise, not the dent, that’s examined,” Bush argued. “The bruise is diffuse and may not accurately reflect the placement of the teeth that created the scar, which can create additional uncertainty.”
People think the human dentition is unique because dental records are often used to identify the deceased. But in such cases, he noted, a combination of 32 teeth (existing, missing, or repaired) are analyzed, compared to only the incisal edges of the six teeth, which usually bear bite marks.
“The court has admitted the evidence and is content to debunk the ‘science’ through rigorous cross-examination,” Bush said. “This leaves the appropriate cross-examination to lawyers who may not have a scientific background.”
Interestingly, Bush found that the best-matching tooth profile is usually not that of the actual perpetrator.
History of bite marks as evidence
Bite marks have been used in criminal cases as far back as the 1800s, but it wasn’t until the 1970s that they actually gained credibility. One of his most famous cases is that of notorious serial killer Ted Bundy in 1979.
Prosecutors had a large amount of circumstantial evidence linking him to at least one of the many murders Bundy allegedly committed. But it was a tooth mark found on one of the victims that ultimately confirmed Bundy’s guilt. He was convicted of first-degree murder, attempted first-degree murder and robbery. Bundy then confessed that between 1974 and 1978 he murdered 30 women. Bush noted that the highly publicized incident increased the value of the bite mark evidence.
But Richard Soubiron, a forensic dentist who testified at Bundy’s trial, recently said his bite testimony would have been different had he worked in the field for another 30 years.
Bush said the introduction of DNA into criminal trials would be a game changer, with bite mark evidence often lost, but DNA is still in the prosecution’s toolbox.
“It’s not just that prosecutors are using the byte mark inappropriately,” Bush said. “It’s just a lack of awareness of how different the two sets of teeth are.”
Beginning of Bush’s research
Bush never intended to venture into the controversial realm of Bytemark analysis. She only became involved in 2006 when one of her students chose bite marks as her field of study in forensic dentistry. As part of a student study, they took impressions of Bush’s teeth and marked bite marks on 23 corpses.
“We then photographed the bitten body parts in different positions to see the effects of movement,” she said. “It’s understandable that a body part quarrel could have been bitten in one position, but the examination of the traces is done when the body part is in another position.”
None of the 23 were measurably identical.
They carried out subsequent studies, such as geometric morphometric analysis, which can quantify the variability of shape change between large datasets. Again, they made multiple bites with the same set of teeth to ensure that the bites did not reliably transfer to the skin.
Evidence of bite marks is still allowed
Bush and his team also testified before the 2015 Texas Forensic Commission and the 2016 Presidential Council on Science and Technology Assistance hearings.
A Texas state commission ruled in favor of Bush, recommending the state suspend the use of Bitemark analysis in prosecutions statewide. The Presidential Council also recommended against using Bytemark evidence, concluding that “the development of Bytemark evidence into a scientifically valid method is unlikely.”
Bush also testified before the 2015 Texas Forensic Commission and the 2016 Presidential Council on Science and Technology Assistance hearings.
A Texas state commission ruled in favor of Bush, recommending the state suspend the use of Bitemark analysis in prosecutions statewide. The Presidential Council also recommended against using Bytemark evidence, concluding that “the development of Bytemark evidence into a scientifically valid method is unlikely.”
And in October 2022, the National Institute of Standards and Technology published its findings in a draft report, “Bytemark Analysis: A Review of NIST’s Scientific Basis,” stating that “forensic bytemark analysis lacks a sufficient scientific basis because key assumptions in the field are not supported by the data.”
Despite these official findings, the practice of presenting bite-mark evidence to juries has not ended.
“There are no courts that I know of that don’t accept bite marks as evidence, but ‘some courts don’t,'” Bush said.
By raising awareness and helping lawyers and the public understand the limits of bite marks and how they can be distorted, Bush hopes to ultimately eradicate false accusations that rely on this flawed evidence.
