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Setting Standards

In his more than 40 years of work in the field of forensic dentistry, Thomas Johnson has served as president of the American Board of Forensic Odontology, as an Associate Medical Examiner for the Milwaukee County Medical Examiner, as a consultant for the Crime Laboratories of the Wisconsin Department of Justice and is a certified senior crime scene analyst. In those roles, he identified victims of serial killer Jeffrey Dahmer and victims of a commercial plane crash. The Marquette University School of Dentistry professor has also testified in some criminal cases where killers bit their victims before killing them.

But Johnson says that the majority of bite marks should not be used as evidence because they are “diffuse and indistinct.” He calls these patterns “smoke rings” and says that some of the recent cases in which bite mark evidence was overturned might be attributed to using unreliable wound patterns or improper techniques.

Johnson’s fellow professor and collaborator, former prosecutor Daniel Blinka, explains that when properly used, such evidence can be powerful and accurate, but points out exceptions. “There have been a number of cases from around the country where techniques weren’t properly done, where there were miscarriages of justice,” Blinka says.

They say that could be remedied if techniques for cataloguing and matching bite marks to a suspect’s teeth are standardized, and have completed the first phase of a project to show how it can be done.

Their first phase of research set out to determine if it was possible to quantify the probability of any two individuals having the same set of six dental characteristics. Johnson’s team included a biostatistician, a computer programmer, forensic imaging specialists from Wisconsin State Crime Laboratory, and Blinka. They started by getting exemplars or tooth impressions of 419 male volunteers in Wisconsin. The researchers made life size digital images and used two computer programs to measure characteristics like tooth width, arch width and tooth rotation. The first program they used was Adobe Photoshop and the second, called Tom’s Toolbox, was developed by team member Thomas Wirtz.

Johnson presented their preliminary results at a meeting of the American Academy of Forensic Sciences. They found that of the 419 samples, no two were identical.

Johnson adds, “Several of our volunteers had several outliers, that is, characteristics which occurred in less than one percent of the sampling. This doesn’t provide an identification to the exclusion of all others, but does demonstrate that there is a scientific basis for opinion testimony.”

Johnson says that means that dental characteristics could be quantified. But he makes it very clear that this is just the beginning.

“It’s a start in the right direction, but this has to be continued for many hundred of thousands or maybe even millions of samples, so that we could get an adequate population database,” Johnson says.

He says that samples from different regions and ethnicity would be needed in order to scientifically determine how frequently a specific set of characteristics occurs in the general population.

Researchers collecting similar data at other forensics programs around the country have offered to share their samples to help build the database.

And Johnson has applied for grants to continue the research using 3D imaging. Once he has reached the goal of eventually standardizing the way bite marks are analyzed, he says the same computer program could be used to then match a suspect’s teeth to the sample. But even if there is a perfect match, Johnson says that only with an exhaustive database, such as the one he envisions, could the probability of someone else having the same set of characteristics. be determined.

While DNA evidence has become the gold standard in terms of courtroom reliability, Johnson says it is not always available.

“If you have DNA from the bite mark, that’s ideal, and that’s what should be used,” he says. “But in cases where DNA has been degraded or lost, bite mark patterns are still valuable evidence that should be collected. If there is a bite mark and you ignore it, that’s not the right thing to do. The defense attorney could ask why you didn’t gather that evidence.”

RESEARCH PRESENTED AT: American Academy of Forensic Sciences Conference, February, 2008

RESEARCH FUNDED BY: U.S. Department of Justice via the Midwest Forensic Resource Center, Iowa State University, Ames Laboratory, American Board of Forensic Odontology, the American Society of Forensic Odontology, the California Forensic Dental Association and Marquette University School of Dentistry.

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