It's Evident


Bites, Bytes and the Unidentified
Jeff Chesen, Research Attorney

The National Academy of Sciences report, Strengthening Forensic Science in the United States: A Path Forward reached the conclusion that courts are incapable of "curing the documented ills of the forensic science disciplines."
1 It offered recommendations for addressing the concerns identified in several forensic science disciplines, including forensic odontology. These published recommendations have not changed how bitemark analysis receives contentious and questioning interpretation.

Subsequent to the NAS report was a Congressional hearing into the future of forensic science, emphasizing the NAS report findings. Among the forensic disciplines that the NAS report identified, bitemark analysis received critical analysis. During the hearing, Innocence Project co-founder Peter Neufeld introduced Roy Brown who was wrongfully convicted from bitemark evidence.

"The forensic dentist [at Roy Brown's trial] used what was then the prevailing method of comparing bitemarks found on a body with the dentures of a suspect," said Neufeld. "He examined them and decided that he had a match with Roy's bite. He so testified in court and Roy was convicted."2

The prosecution relied on a forensic dentist's testimony that the seven bite marks on the victim were "entirely consistent" with Brown's dentition. A defense expert testified that six of the bite marks were insufficient for analysis and the seventh excluded Brown because it had two more upper teeth than he had. Despite this defense testimony Brown was convicted.3

DNA evidence exonerated Brown after he spent 15 years in prison and identified the real killer.4

Neufeld said at the Congressional hearing that bitemark analysis is just one of several forensic techniques that remain untested.

"And they need more research, basic research, applied research. They need standards like DNA has," Neufeld said.5

Neufeld's contention is that many forensic specialists introduce forensic evidence in criminal trials without any identifiable scientific guidelines or limits. Certain forensic disciplines, including bitemark analysis, lack scientific validation, determination of error rates, or reliability testing to explain limitations.

The NAS report listed a number of basic problems inherent in bitemark analysis and interpretation:
  1. The uniqueness of the human dentition has not been scientifically established.
  2. The ability of the dentition, if unique, to transfer a unique pattern to human skin and the ability of the skin to maintain that uniqueness has not been scientifically established.
    • The ability to analyze and interpret the scope or extent of distortion of bite mark patterns on human skin has not been demonstrated.
    • The effect of distortion on different comparison techniques is not fully understood and therefore has not been quantified.
  3. A standard for the type, quality, and number of individual characteristics required to indicate that a bite mark has reached a threshold of evidentiary value has not been established.6
These three criteria lay the groundwork for the deficiencies prevalent in bitemark analysis testimony. The first point is that there exists no scientific research showing the uniqueness of human teeth marks. This contrasts with the unique identifying qualities found in fingerprints and DNA examination. Additionally, even if bitemark uniqueness could be proven, it is still unclear that the uniqueness could be transferred into an impression on the human body. The study found that the due to human skin's elasticity, swelling and healing and unevenness of the skin's surface, bitemarks on skin can change or be altered over time.7

The report also states that there is no scientific research showing that the various methods used by bitemark experts can be reproduced, both "between experts and with the same expert over time."8 This restates one of the Daubert rules of expert admissibility, that a scientist's results can be reproduced by other scientists. Several scientific studies have been conducted where bitemark experts in controlled laboratory tests showed "widely differing results and a high percentage of false positive matches."9

The NAS report concluded, "Although the majority of forensic odontologists are satisfied that bite marks can demonstrate sufficient detail for positive identification, no scientific studies support this assessment, and no large population studies have been conducted. In numerous instances, experts diverge widely in their evaluations of the same bite mark evidence."10

Perhaps the most publicized recent example of the NAS report's identified bitemark analysis flaws could be found in Eric Frimpong's 2007 conviction in California. Frimpong came from his native Ghana to play soccer at the University of California, Santa Barbara and helped the team win its first NCAA championship in 2006. In 2007, Frimpong was arrested for allegedly sexually assaulting a 19-year-old white female on a beach. The victim claimed that after drinking together Frimpong threw her down to the ground, removed her jeans, pried her legs apart with his hands and raped her.11 Bitemarks were on the victim's face and semen samples were taken from her. Frimpong did not testify at his trial.

The prosecution called Norman Sperber, a dental expert, to testify as to the bitemarks photographed on the victim's face the morning after the incident. Sperber testified he could not exclude Frimpong as having made the bite mark.12

The defense objected at trial that the prosecution first contacted a different dental expert than Sperber. This witness testified, outside the hearing of the jury, that he told the detectives the "best he could do would be to not exclude Mr. Frimpong since the bitemark was vague."13 The defense's odontology expert, C. Michael Bowers, was unavailable to testify because he became ill. After the trial, Bowers evaluated the materials and concluded that Frimpong could not have made the bitemark found on the victim. In a post-conviction motion Bowers claimed that the teeth transparencies "showed the opposite of what [was] testified to at trial."14

Noteworthy in the opposing odontology testimony is the experts' impressive backgrounds within their field. Sperber twice served as the vice-president of the American Board of Forensic Odontology15 and he is the Chief Forensic Dentist for the California Department of Justice's Dental Identification System and Missing/Unidentified Persons Unit.16 Bowers is the Deputy Medical Examiner for Ventura County (Cal.) and was appointed to the American Society of Forensic Odontologists' Board of Governors.17 The two are considered among California's leading odontology experts yet reached polar opposite conclusions from the same evidence.

The NAS report states "the majority of forensic odontologists are satisfied that bite marks can demonstrate sufficient detail for positive identification."18 However, the conclusion in the report, like the experts' opinions in the Frimpong case, could not be more different: "[N]o scientific studies support this assessment, and no large population studies have been conducted. In numerous instances, experts diverge widely in their evaluations of the same bite mark evidence."19

Courts that attempt to interpret the NAS report when considering forensic odontology evidence may be faced with the question of whether a state that utilizes the Frye standard for scientific testimony admissibility should shift to the Daubert standard. There were 18 states that utilized the Frye standard as of 2008, 28 states fully applied the Daubert standard or used a Daubert-like standard and four states developed their own standards.20 The NAS report criticizes many of the same procedures that are accepted in Frye jurisdictions. Courts could use the NAS report's conclusions as an argument for shifting to the Daubert standard. Though this is empirically possible it has yet to happen in any of the 18 Frye states since the NAS report's release.

In order to satisfy the Frye standard scientific evidence must be "generally accepted" by a significant proportion of the related scientific community.21 It is possible that an influential publication such as the NAS report could lead to further debate and potential acceptability shifting from the Frye to the Daubert standard.22

It is likely premature to conclude that the lack of courtroom challenges since the NAS report means it will have no such impact related to forensic odontology testimony. Examples such as the Frimpong case illustrate how odontology "expertise" fails to be a universal or measurable standard. It may be the responsibility of a reputable organization such as the American Board of Forensic Odontology (ABFO) or the American Society of Forensic Odontology (ASFO) to recognize the NAS report's findings and to set standards that allow experts to reach the same conclusions.

Visit for more information about forensic odontology.


1  Strengthening Forensic Science in the United States: A Path Forward, National Academy of Sciences, National Research Council report (2009), page 85.
2  Ari Shapiro, Congress Weighs in on Forensics Study, NPR, Sept. 9, 2009, found at (last checked on Oct. 4, 2010).
3  Innocence Project, "Roy Brown," found at (last checked on Oct. 4, 2010).
4  Innocence Project, found at (last checked on Oct. 4, 2010).
5  Id.
6  Supra, n.1, at 175-6.
7  Id., 174.
8  Id.
10  Id.
11  Id., 176.
12  Chris Meagher, Updated: No Retrial for Frimpong, Santa Barbara Independent, Mar. 7, 2008, found at (last checked on Oct. 4, 2010).
13  Kathleen Stinson, Motion Filed for New Trial on Frimpong Conviction, Citing Juror's Testimony, Santa Barbara News-Press, Feb. 6, 2008, found at (last checked on Oct. 4, 2010).
14  Id.
15  Id.
16  American Board of Forensic Odontology, 2009 Diplomates Reference Manual, p. 54, found at (last checked on Oct. 4, 2010).
17  Id., 292.
18  Id., 353.
19  Supra, n.1 at 176.
20  Id.
21  viaForensics, found at (last checked on Oct. 4, 2010).
22  Fluoroquinolone Toxicity Research Foundation, "Frye Standard" found at (last checked on Oct. 4, 2010).
23  Edward J. Imwinkelried, Forensic Science: The Role of the Hearsay Rule in Litigating Frye Challenges to the Admissibility of Scientific Evidence, 29 CRIM. L. BULL. 158, 162-63 (Mar.-Apr. 1993).