Work will help establish protocol for using bite marks as forensic evidence
MILWAUKEE – A team of researchers at Marquette University and the Medical College of Wisconsin has completed a three-year, $715,000 study funded by the National Institute of Justice (NIJ) to determine whether bite-mark patterns have evidentiary value in criminal investigations. The group’s findings have demonstrated that bite patterns can sometimes be recovered from skin and correlated with a high degree of probability to a member of the population – a significant step forward for forensic odontologists who have long been challenged on the scientific legitimacy of bite-mark analysis.
The NIJ has published the research paper on its website. It will also provide a template that enables imaging specialists to evaluate and rank bite patterns against a benchmark to determine their evidentiary value.
The team was led by veteran forensic odontologist Dr. L. Thomas Johnson and Dr. Thomas W. Radmer, both of the Marquette University School of Dentistry, and included Tom Wirtz, the dental school’s dental informatics director; Dr. Dean Jeutter, a professor of biomedical engineering at Marquette; and Dr. Joseph Thulin, director of the Biomedical Resources Center at the Medical College of Wisconsin.
The researchers randomly selected 50 hard resin dental models from a pool of 550 volunteer samples. To actually make the marks, they mounted the models to a device that would standardize the replication of the patterns in porcine skin, the closest substitute for human skin. The injury patterns were photographed and digitally documented according to strictly prescribed forensic protocols.
The injury patterns were then analyzed using Johnson and Radmer’s earlier research, which demonstrated that characteristics of human dentition could be quantified and expressed statistically based on seven dental criteria, including tooth width, rotation and displacement.
But Johnson cautions that such patterns cannot be used as an identification to the exclusion of all others.
“It’s not an identification where you’re individualizing,” Johnson explained. “It’s showing that certain characteristics of teeth are outliers, and when you see one of these, you can eliminate a great percentage of the population. And if you see a second one, or a third one, then it’s not likely that very many people in the world are going to have teeth like that.”
Johnson emphasizes that the study’s real value is in establishing protocols rooted in hard science that can be replicated by crime laboratories – standards that have been absent in bite-mark analysis. And he hopes that, with this scientific foundation, crime laboratories can expand on this work.
“With continued expansion of a population database of quantified dental characteristics, calculating the level of probability a bite-mark pattern has with a member of the population should be possible,” Johnson said.
Like with other types of forensic evidence, case selection is an important part of keeping the process scientific, Johnson noted.
“A lot of the patterns we studied are not useable. If it is indistinct or distorted, it has no evidentiary value,” he said. “With bite-mark analysis, we can’t say for certain, ‘That’s Charlie.’ But if he has some very unusual teeth that few people in the population are likely to have, then the attorneys can take this into account along with the proximity, the opportunity, the motive to argue their case. Done correctly, it’s one more piece of evidence that attorneys can present.”
The project team also included consultants, including: Dr. George Corliss, professor emeritus of electrical and computer engineering at Marquette; Dr. Gary Stafford, assistant professor of general dentistry at Marquette; Dr. Kwang Woo Ahn, assistant professor of biostatistics at MCW; Alexis Visotky, biostatistical and database support at MCW; and Ronald Groffy, retired forensic scientist and forensic imaging specialist with the Wisconsin State Crime Laboratory system.
To interview Johnson and Radmer, contact Christopher Stolarski, senior communication specialist, at (414) 288-1988 or firstname.lastname@example.org.