Both of these assumptions have been challenged in recent years, rooted in a robust scientific skepticism surrounding bite mark analysis, highlighted by an October 2004, Chicago Tribune investigation. The Tribune examined some 150 murder and rape cases in which bite marks played a key role, finding in a quarter of those cases the prosecution and defense offered forensic dentists who gave diametrically opposed opinions.
The whole tooth
David Faigman, a professor at the University of California's Hastings College of Law, who has called bite mark analysis the poster child for bad forensic science, says it's not a question of whether or not bite mark identification is reliable, it's a question of whether it's been demonstrated to be reliable.
Faigman says when someone has a hypothesis — like the ability of forensic examiners to identify bite mark imprints — the burden of proof lies with the proponent.
"Since Daubert (Daubert v. Merrell Dow Pharmaceuticals Inc., 113 S.Ct. 2786 (1993), [forensic examiners] have not met the rules of evidence standards for admitting expert testimony," he says. Just as with lip prints, bite mark identification has a long way to go before claims are substantiated.
Courts require experts must identify published papers that form the basis of scientific conclusions. Such works do not exist in the field of bite mark analysis.
Skeptics like Faigman aren't necessarily doubting the technical proficiency of odontologists and lip print proponents. Rather, they want to see bite mark and lip print analysis, like DNA profiling before them, subjected to rigorous scientific testing.
"Only through testing can the courts develop confidence in new technologies," Faigman says.
So far, no research has been conducted to confirm that human bite marks are unique to each individual, to what degree tooth alignment changes over time, or how much the elasticity of human skin may distort bite patterns.
Not love at first bite
Meanwhile, some of the most staunch criticism of bite mark analysis comes from the fraternity of odontologists — the very group of forensic experts who practice the craft.
One of the problems is that bite mark analysis is subjective evidence. Unlike DNA or fingerprinting, it does not yield positive identification, says Brian Chrz, DDS, a private forensic odontologist in Perry, Oklahoma, and a diplomat of the American Board of Forensic Odontologists (DABFO). Rather, the appropriate application of bite mark evidence is to exclude individuals.
Chrz says forensic odontologists first look for class characteristics, such as whether the wound was caused by teeth or a bottle cap, if it has a human arch, and is the right size. To be forensically useful, however, individual characteristics are needed — rotations, chips or missing teeth.
"The problems come when a poor bite mark is used to render a legal decision, when forensic experts go beyond what that bite mark can tell them," Chrz says.
According to Cincinnati odontologist Franklin Wright, DMD, DABFO, the problem is lack of standardization of bite mark evidence.
"This results in subjectivity in the way the odontologist reads the evidence," Wright says.
Odontologist Michael Bowers, DDS, DABFO, an assistant professor of dentistry at the University of Southern California, believes it's time to reconsider the admissibility of bite mark identification being reliable evidence for positive identification.
"Our small group of forensic dentists has some members who are reluctant to diminish the forensic identification roles they have enjoyed in the criminal courts," Bowers says.
Bowers says this subset of the forensic dental community still clings to the belief that bite mark identification is as forensically reliable as DNA identification, that court acceptance of bite mark evidence implies affirmation of accuracy and reliability.
On the bite track
That reliability, however, is often compromised by shoddy evidence collection, Bowers says.
Many bite mark cases cannot be adequately analyzed due to poor evidence collection, highlighting the fact that police officers, forensic pathologists and dental practitioners aren't adequately trained to collect, record, duplicate, store and transport relevant bite evidence correctly.
"A big issue is lack of education of law enforcement, in recognizing what a bite mark is, how to take impressions, DNA samples, and properly photograph it with measurements in place for reference," says Edward Woolridge, DDS, DABFO, a North Carolina forensic odontologist.