Methodology for Analyzing Human Bite Marks in Skin

An evidence-based methodology for the analysis and comparison of human bite marks in skin with teeth

Douglas R. Shasby, BDS, MFML

Honorary Clinical Senior Lecturer in Forensic Odontology, University of Glasgow, Glasgow G12 8QQ, UK

OPEN ACCESS

PUBLISHED 31 January 2025

CITATION Shasby, D. R. 2025. An evidence-based methodology for the analysis and comparison of human bite marks in skin with teeth. Medical Research Archives, Volume 13 Issue 1.

Keywords

Bite marks; human skin; forensic odontology; distortion; bias.

Introduction

Bite marks are a cornerstone of forensic medico-legal evidence. In the interests of science and justice, the controversy around bite mark analysis and comparison needs to be resolved. Due to the nature of skin and the action of biting, human bite marks in skin are distorted, partial representations of the biter’s anterior dentition. The interpretation of ambiguous dental features in a bite mark involves subjective judgments that are susceptible to cognitive bias. The unquantified degree of distortion in bite marks in skin and the unquenchable influence of bias in the analysing odontologist necessitate a new methodology.

The manuscript examines the scientific evidence that underpins the validity comparison of bite marks in skin with the dental casts of the biter’s dentition. The results indicate that statements of dental uniqueness related to bite marks in an open population were unsystematic and confirmed that the use of the product rule was inappropriate.

Unique Aspects of Human Dentition

Importantly, the study reported correlations and non-uniform distributions of the six anterior mandibular tooth positions in two sets of scanned dental models, found seven and 16 matches in the respective data sets, n = 172 and n = 344. The results indicated that statements of dental uniqueness related to bite marks in an open population were unsystematic and confirmed that the use of the product rule was inappropriate.

Forensic Significance of Bite Marks in Skin

Experimental research of bite marks in human skin, by its nature, is difficult to conduct and consequently, studies have mainly used artificial media or animal skin. The dentition that produced test bites in skin was recognised with a high degree of reliability by examiners; however, bite marks in non-vital skin, which can be ambiguous, are more difficult to interpret. The forensic significance of bite marks is determined by the background of the individual, including their dental history, and the context in which the bite mark is found.

Cognitive Bias in Bite Mark Analysis

Research on expert performance and decision making has been conducted in many branches of forensic science. Studies demonstrated that contextual information undermined the reliability of fingerprint experts making identification. A meta-analysis of the two studies implied that the fingerprint experts’ judgments involved significant bias and were subject to the reference material. Human bite marks in skin invariably demonstrate ambiguous features and are more susceptible to cognitive bias. This is particularly evident when the crime scene is ambiguous.

Rationale for Bite Mark Analysis and Comparison Methodology

The nature of skin and the action of biting create a potentially unique, three-dimensional episode of contact that prevents the accurate and complete recording of the features of the anterior dentition in skin. Consequently, research indicated that statements of dental uniqueness related to bite marks were unsupportable in an open population. Research also found that it was impossible to reliably differentiate between two individuals based on the unique characteristics of their dentition.

Feature Based Analysis and Comparison Methodology

The examination of the suspect biter’s dental casts commences after the attested completion of the unbiased predictor of the causal dentition. On receipt of the dental casts the analysing odontologist confirms that the casts conform to the accredited standards of dental tone and surface integrity.

Interpretation of Bite Mark, Preparation of Predictor of Causal Dentition – Predictive Stage

The human dentition demonstrates anatomical features that are classified as class characteristics and individual characteristics that may be evident in a bite mark. The representations of the class and individual characteristics of the anterior dentition form the basis for assessing the forensic significance of a bite mark.

Examination of Suspect Biter’s Dental Casts

The sizes and shapes of the maxillary and mandibular anterior teeth, arches and inter-canine distances, are noted. The presence or absence, position, rotation and facial detail of the incisors, canines and premolars are recorded. The teeth may be classified as normal, irregular or abnormal.

Confirmation Bias in the Analysing Odontologist

The scientific evidence demonstrates that distortion in human bite marks in skin and cognitive bias in the analysing odontologist are significant factors in the forensic techniques of bite mark analysis and comparison with teeth. A feature based analysis and comparison methodology is proposed that retains the effects of secondary distortion and cognitive bias; the terms, predictive stage and comparative stage are introduced.

Conflict of Interest

None declared.

Funding Statement