Bite Marks: Collection, Examination and Analysis in Forensic Investigations

Teeth leave behind more than dental records. When a person bites into skin, fruit, or a block of cheese, the arrangement of their teeth gets stamped onto that surface like a signature. Forensic odontologists use this signature to link a bite to its source, and this branch of forensic science has helped solve assault cases, identify perpetrators of abuse, and occasionally overturn wrongful convictions when the science was misapplied. Understanding how bite marks are collected, examined, and analysed tells us a lot about how identification science actually works in the field, not just in textbooks.

What makes a bite mark forensically useful 🔗

A bite mark is essentially an impression left by the upper and lower teeth acting together. It records the placement, spacing, and shape of the biter’s dentition. No two people have identical teeth. Even within a single tooth, the wear patterns, chips, rotations, and spacing relative to neighbouring teeth vary enough to make a set of teeth reasonably distinctive, which is exactly why bite marks are treated as significant physical evidence in an investigation.

Bite marks show up most often in cases of physical assault, child abuse, and sexual assault, typically on soft tissue areas like the breasts, arms, legs, neck, back, and shoulders. They aren’t always inflicted by an attacker either. Self-inflicted bite marks appear in cases involving self-harm or as part of staged crime scenes. Outside of the human body, bite marks turn up on food items at a scene, most commonly fruit and hard cheese, both of which hold an impression well because of their texture.

Human bite marks are usually oval or circular in overall shape, formed by the two opposing dental arches. Beyond the visual pattern, a bite mark carries a second, often more decisive form of evidence: saliva. Whenever teeth touch skin, saliva transfers onto the site, and that saliva can carry enough biological material to extract a DNA profile of the person who left the bite, independent of whatever the tooth pattern itself suggests.

Standardising the language: the Bite Mark Severity Index 🔗

For years, forensic odontologists lacked a common vocabulary to describe how serious or how forensically useful a given bite mark was. One examiner’s “moderate” bite could be another’s “severe” one, which made comparing cases and testimony difficult. Iain Pretty addressed this gap in 2006 and 2007 by developing the Bite Mark Severity Index, a standardised scale that rates bite injuries from 1 to 6 based on both physical severity and forensic significance.

At one end, category 1 covers very mild bruising that might not even have been caused by teeth, offering little identifying value. At the other extreme, category 6 involves complete avulsion of tissue, an injury so severe that the underlying tooth pattern may be destroyed entirely. The most useful bite marks for identification sit in the middle of this scale, where the injury is clear enough to show distinct tooth pattern detail without being so extensive that it obscures the very features examiners need to compare. Pretty tested the index with odontologists, forensic pathologists, and police officers, and found it produced consistent ratings across all three groups, which is what made it practical for casework rather than just an academic proposal.

Collecting bite mark evidence from the scene 🔗

Why the first 24 hours are critical 🔗

Bite marks change fast. Bruising develops, swelling shifts the skin’s surface, and the body begins healing almost immediately after the injury occurs. Most of the morphological change in a bite mark’s appearance happens within the first day, so investigators and forensic odontologists are trained to document a suspected bite mark as early as possible. Waiting even a few hours can mean the difference between a clear, comparable pattern and a blurred, aged one that’s much harder to work with.

Following the ABFO protocol 🔗

The American Board of Forensic Odontology (ABFO) lays out a specific sequence for collecting bite mark evidence, and it’s followed closely by trained examiners. Photography comes first, and it has to be done both with and without a scale placed next to the mark, so that the true size of the bite can be measured later without distortion. Photographs are typically taken from multiple angles and under different lighting conditions, including ultraviolet light for older injuries where visible bruising has already started to fade.

After photography, examiners swab the bite site for saliva, which preserves any DNA evidence before it degrades or gets contaminated. If the bite has caused a puncture wound or a deep enough indentation, an impression of the mark itself is taken using dental impression material. On the suspect’s side, the process includes a test bite, where the accused’s dentition is used to create a bite pattern in controlled conditions for direct comparison, along with a review of any existing dental records that might already document their tooth alignment, restorations, or missing teeth.

Examining and analysing the bite pattern 🔗

Building the odontogram 🔗

Once evidence is collected, the real comparative work begins. Forensic odontologists start by mapping out the suspect’s dentition in detail, a record called an odontogram. This documents the total number of teeth present, any missing teeth, abnormal positioning, gaps between teeth, broken or chipped teeth, and any teeth that sit unusually prominent compared to the rest of the arch. The overall shape and size of the dental arch itself, whether it’s rounded, narrow, or asymmetric, adds another layer of individual detail to compare against the bite mark.

Casting and comparison techniques 🔗

To compare the suspect’s teeth against the bite mark itself, examiners create a cast using the same type of material the original bite mark was found on when possible, which helps account for how different surfaces record an impression differently. Silicon-based materials and fast-setting rubber compounds are the standard choice here because they capture fine detail accurately and set quickly enough to prevent distortion. The resulting dental casts are then compared to life-sized photographs of the bite mark, sometimes with the use of overlays that trace the suspect’s biting edges directly onto an image of the wound. Examiners look at biting patterns, spacing between individual teeth, and how closely the arrangement in the cast lines up with what’s visible in the mark, always accounting for the incisal height of the teeth involved.

What saliva adds to the picture 🔗

Saliva recovered from a bite mark does more than just carry DNA. It can also reveal whether the person is a secretor or non-secretor, referring to whether ABO blood group antigens are present in their bodily fluids, including saliva. Around three-quarters of people are secretors, meaning their blood type markers show up in saliva and can narrow down a pool of suspects even before full DNA profiling is complete. Combined with DNA extraction, this makes saliva swabbing one of the most valuable steps in the entire collection process, often more decisive in court than the tooth pattern comparison itself.

How reliable is bite mark identification, really 🔗

It’s worth being upfront about a genuine controversy in this field. Bite mark comparison rests on two assumptions: that human dentition is unique enough to be individually identifiable, and that this uniqueness transfers reliably onto skin. Neither assumption has held up perfectly under scientific scrutiny. A 2009 report by the U.S. National Academy of Sciences found that no forensic method besides nuclear DNA analysis has been rigorously shown to reliably connect evidence to a specific individual, and bite mark analysis was singled out as one of the weaker disciplines in this regard.

Since then, several wrongful convictions built on bite mark testimony have been overturned using DNA evidence, prompting organisations like the Innocence Project to argue that bite mark comparisons should carry far less weight in criminal trials than they historically have. A more recent scientific review by the National Institute of Standards and Technology also raised doubts about whether dental uniqueness has ever been convincingly demonstrated in the first place. This doesn’t mean bite mark evidence is useless. Saliva-based DNA testing remains scientifically solid, and the ABFO’s tightened guidelines, the Bite Mark Severity Index, and more conservative reporting standards have all been direct responses to these criticisms. But the pattern-matching side of bite mark analysis is now treated by many courts as corroborating evidence rather than standalone proof, and understanding this history is part of understanding the discipline itself.

What do you think? 🔗

What do you think? Given how much bite mark reliability depends on timing, does it surprise you that most identifying detail can be lost within the first 24 hours? And where do you think the line should be drawn between using bite marks as supporting evidence versus treating them as conclusive proof in a criminal case?

References

1. https://abfo.org/wp-content/uploads/2016/03/ABFO-Bitemark-Standards-03162016.pdf
2. https://pubmed.ncbi.nlm.nih.gov/17456096/
3. https://www.dentalcare.com/en-us/ce-courses/ce401/bite-marks
4. https://abfo.org/wp-content/uploads/2012/08/ABFO-Standards-Guidelines-for-Evaluating-Bitemarks-Feb-2018.pdf
5. https://deathpenaltyinfo.org/policy-issues/policy/junk-science/bite-mark-comparison
6. https://innocenceproject.org/news/why-bite-mark-evidence-should-never-be-used-in-criminal-trials/