The Bite Stuff?

Ray Krone, once known erroneously as the "snaggletooth killer," was convicted in 1991 of the murder of a Phoenix cocktail waitress and sentenced to death, based largely on bite mark evidence taken from the victim's breast which the state's forensic odontologist says matched Krone's dentition.

Ten years later, DNA evidence cleared Krone and he was released from the Arizona State Prison in 2002.

Bite mark analysis, however, remains incarcerated in controversy.

The same shadow of doubt has now been cast on lip print identification. An appellate decision in the State of Illinois (People v. Lavelle Davis) was recently reversed in post-conviction proceedings on the grounds that the courts erred in admitting evidence of a lip print "match."

Cut to the face
The use of lip prints for human identification was first suggested in 1950. Sporadic research followed over the next decades. Although lip print identification has been utilized in court in isolated cases, more research is necessary to confirm lip pattern uniqueness. Protocols also must be established to govern collection and interpretation of evidence.

"Because lip print identification is not a generally accepted forensic science, experience with it has been sparse, unorganized and devoid of true scientific inquiries," says well-known forensic consultant Andre Moenssens, Douglas Stripp Professor of Law Emeritus, University of Missouri, Kansas City.

Moenssens says there are no court decisions on the appellate level that support the admissibility of lip print identification, no organized body of lip print examiners, and no accepted methodology for the comparison of known and unknown lip impressions. Neither are there standards for when a potential "match" exists.

There is no training available to become a lip print examiner, no professional bodies organizing conferences for lip print technology and comparison, no certification bodies in the field, and in general no peer-reviewed literature supporting the contention that lips contain individual characteristics that make each person's lips different from all other persons' lips.

"No forensic organization of any size has officially endorsed lip print identification," Moenssens says. "The FBI laboratory will not conduct lip print examinations, and has instructed its examiners not to accept such cases in the future."

Forensic examiners eager to pursue lip print identification evidence in court do so on shaky ground. There is a substantial amount of scientific foundation to be laid before proponents can reasonably demonstrate to be proficient at what they claim.

Bite on target
Bite mark identification, on the other hand, is legally admissible in courts of law, although over the past 30 years this branch of forensics has endured a number of legal challenges, most centered on the scientific efficacy of the field. Several cases whose convictions were based on bite mark evidence have been reversed on later DNA testing.

Bite mark identification is based on the supposed individuality of a dentition, which is used to match a bite mark to a suspected perpetrator. This matching is based on a tooth-by-tooth and arch-to-arch comparison utilizing parameters of size, shape and alignment.

Human bite marks are commonly found in child abuse cases, rape and rape homicide cases, and also in many instances of assault, battery and aggravated battery. Bite marks also are left by victims of violent crimes on perpetrators.

Bite marks can be found at crime scenes on inanimate objects such as pencils, Styrofoam cups, gum, candy bars, apples, cheese, and other soft foods.

The central tenet of bite mark analysis is based on two assumptions: that human teeth are unique, and that sufficient detail of this uniqueness is rendered during the biting process to enable identification.

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.

Woolridge says it's not the fault of law enforcement. They just aren't educated to recognize bite marks.

"We see a lot of this in child abuse cases," Woolridge says. "We know bite marks are being overlooked."

Bowers, who has reviewed 73 cases in the last five years, says things on the street are not as they are portrayed on popular "CSI" television programs.

"I wish every bite mark I get had been properly processed at the crime scene, autopsy suite or police station, but they aren't," he says. "Incredibly, most cases of suspected bite mark injuries on living or dead persons are not swabbed for possible DNA collection of the biter's trace saliva."

When the proper protocol is followed, bite mark evidence can be of surprising value. David Sweet, DMD, a Canadian odontologist, once reported (J Forensic Sci. 1999 Sep;44(5):1069–72) collecting salivary DNA from a bite mark on a body submerged over five hours in a river, concluding it is advisable that investigators routinely swab for salivary DNA in bite mark cases, even when the amount is thought to be minimal.

There are standards for collecting fingerprints and DNA, and while the American Board of Forensic Odontology has published standards pertaining to collecting bite mark evidence, crime scene investigators are not trained in it, Wright says.

"That's a huge reform that would be beneficial to the field," he says

Faigman advises getting the academic scientific community involved, particularly the National Academies of Science and American Association for the Advancement of Science.

Faigman says currently there are two problems. Most bite mark examiners lack the technical wherewithal to collect research data and do the kinds of statistical analysis necessary, and most academic scientists are not interested in forensic issues.

"The real challenge for people like me who try to bridge the gap between science and the law is to try to come up with ways to get the mainstream scientific community interested in forensic issues," he says.

3D or not 3D
Occasionally, rogue research results in a step forward. Some photographic science, for instance, has emerged that could enhance bite mark analysis, whose future may now lie in the realm of the third dimension.

Traditionally, bite mark photo analysis is carried out in 2D space — 3D information preserved two dimensionally with corresponding distortions. A 2003 paper (Forensic Sci Int. 2003 Aug 12;135(2):115–21) introduced a new 3D documentation, analysis and visualization approach based on a technique called forensic 3D/CAD supported photogrammetry (FPHG) and a 3D surface scanner, which the researchers say is the first 3D approach to bite mark analysis in an actual case.

According to lead author M.J. Thali, Institute of Forensic Medicine, University of Berne, Switzerland, 3D documentation has none of the distortion artifacts that are commonly found with standard 2D photography. All data is documented with a metric 3D measurement, orientation and subsequent analysis in 3D space, providing unprecedented clarity.

The Thali research is an example of the types of results that might be expected when academia embraces law enforcement.

The quality of information and the quality of law enforcement can be enhanced by enlisting mainstream academic scientists, Faigman says.

"Bite mark evidence a decade or two from now might be partly validated and partly invalidated but we might have 50 or 100 percent more information because the research pointed us in directions that we didn't anticipate," he says.

Douglas Page ( writes about science, technology, and medicine from Pine Mountain, California.