Bite mark analysis – A valid science?

In recent years, scientific research into bite mark analysis has highlighted its unreliability.

An important assumption underlying this analysis is that the human dentition, particularly the anterior teeth involved in the biting incident are unique. This claim has not been scientifically established and came under scathing criticism in the report of the US National Academy of Sciences in 2009. The report noted that no thorough study had been conducted of large populations to establish the uniqueness of bite marks. As per the report, there was no scientific evidence to assess the percentage of the population that could also have produced the specific bite. For decades, the work by RD Rawson, et al in 1984 was used to support the claim of uniqueness of human dentition. The study assumed that the position of one tooth did not affect the position of another and tooth locations do not gather into common patterns. However, studies by Mary Bush, et al, challenged this claim and noted correlation and nonuniform distributions of dental features significantly contribute to the frequency of match. It further noted that “it is also rational to anticipate that the number of matches will increase as the database size is enlarged”.

Research has also demonstrated that in analysing such injuries, odontologists cannot even agree on whether a patterned injury is a bite mark or not. In one such study, bite mark analysts certified by the American Board of Forensic Odontology were asked to examine 100 patterned injuries. Out of the 38 examiners who completed the study, there was unanimous agreement in only 4 out of 100 cases that the injury was a human bite mark. Another study by Mark Page, et al, titled ‘Expert Interpretation of Bitemark Injuries—A Contemporary Qualitative Study’ (2013) conducted among 15 forensic odontologists also notes that there is disagreement among experts on the basic question of whether an injury is a bite mark. There were different ways of expressing the likelihood of whether an injury was a bite mark. These ranged from absolutely positive comments such as “Well, this is definitely a bite mark, that’s for sure” to “I’m not sure if it is even a bite mark” and “I don’t think it is a bite mark.” The study notes that the variations and lack of consistency in methods of analysis and terminology leads to inconsistencies in opinion. It concluded that “this is a failing of bite mark analysis practices that needs to be addressed”.

In 2016, a group of eminent scientists known as the US President’s Council of Advisors on Science and Technology (PCAST) reviewed literature relating to seven forensic disciplines. It noted that few empirical studies had been conducted to analyse the ability of examiners to identify the source of bite marks. Among the studies that were conducted, the observed false positive rates were high. In light of this, the Report found bitemark analysis to be scientifically invalid.

While bite mark analysis is still relied on by courts, institutions such as the American Board of Forensic Odontology have recognised the limitations of the discipline. Accordingly, they have amended their guidelines on bite mark analysis to disallow opinions which provide a conclusive match. Presently, the 2018 Guidelines does not provide for a conclusion which identifies an individual to the exclusion of all others. The conclusions can only be stated as ‘excluded as having made a bite mark’; ‘not excluded as having made the bitemark’ and ‘inconclusive’.