The National Institute of Standards and Technology (NIST) has reviewed the scientific foundations of bitemark analysis, a forensic technique in which marks on the skin of a biting victim are compared with the teeth of a suspected biter. NIST has published its findings in a draft report, Bitemark Analysis: A NIST Scientific Foundation Review, which will be open for public comment for 60 days. The authors will consider all comments submitted before publishing a final version of the report.
NIST scientific foundation reviews fill a need identified in the 2009 study by the National Academies of Sciences, Engineering, and Medicine, which called for research to address issues of accuracy, reliability and validity in many forensic science disciplines, including bitemark analysis.
The draft review finds that “forensic bitemark analysis lacks a sufficient scientific foundation because the three key premises of the field are not supported by the data. First, human anterior dental patterns have not been shown to be unique at the individual level. Second, those patterns are not accurately transferred to human skin consistently. Third, it has not been shown that defining characteristics of those patterns can be accurately analyzed to exclude or not exclude individuals as the source of a bitemark.”
In bitemark analysis, a finding of “exclude” means that a bitemark contains features that could not have been caused by a particular person’s teeth, and that person is therefore excluded as the source of the bitemark. A finding of “not exclude” means that the bitemark could have been caused by a particular person’s teeth. Current guidelines from the American Board of Forensic Odontology (ABFO) — the main professional organization representing bitemark examiners in the United States — only allow for findings of “exclude,” “not exclude” and “inconclusive.”
The first unsupported key premise is that the dental patterns formed by a person’s teeth — particularly the front-most teeth involved in biting — are unique. The draft review finds no studies that establish the uniqueness of this aspect of human dentition. In addition, no population studies have been conducted to identify the distinguishing features of the biting surfaces of human teeth and estimate how common or rare they are.
The second unsupported key premise is that those patterns can be accurately transferred to human skin. The draft review notes that bitemarks can be distorted by the elasticity of skin and the movement of the victim while they are being bitten. Swelling and healing can also alter bitemarks after the fact. Due to these distortions, the patterns in a bitemark injury may not accurately reflect the dental characteristics of the biter.
The third unsupported key premise is that bitemark examiners can accurately analyze the pattern of injury on a person’s skin. The draft review notes several studies that do not provide validation for this assumption, including a 2016 study in which practitioners were presented with images of pattern injuries and asked to determine whether they were bitemarks, and if so, whether they were produced by adults, children or animals. In many cases, practitioners differed as to whether the injuries were even bitemarks, let alone who might have produced them.
The draft review involved a thorough review of the literature, according to Kelly Sauerwein, a biological anthropologist at NIST and lead author of the study. “We examined every publicly available, English language scientific article we could find on this topic,” Sauerwein said. The authors also examined book chapters, conference presentations, professional standards and guidelines, and other material totaling more than 400 publications.
In addition, NIST funded a 2019 meeting of forensic dentists, researchers, statisticians, lawyers and other experts to identify key challenges and knowledge gaps in this field. The report from that meeting also provided information for the NIST review and has been published as a supplement to it.
The scope of the NIST review did not extend to the practice of identifying human remains using dental records.
NIST has no regulatory role in forensic science. NIST scientific foundation reviews, conducted as part of the agency’s Forensic Science Program, are meant to help laboratories identify appropriate use of forensic methods and identify priorities for future research.
Comments on the draft report may be submitted through Dec. 12, 2022. NIST will host a webinar about the draft report on Oct. 27, 2022. Instructions for submitting comments and registration information for the webinar are available on the NIST website.
