Bite Mark Analysis: Anatomy, Mechanism and Patterns

Adults carry up to 32 permanent teeth in two opposing arches. The incisors at the front are the primary biting teeth: the four upper and four lower central and lateral incisors do most of the work in a typical bite mark case. Canines sit at the corners of the arches and often leave the deepest individual impressions. Premolars and molars matter mainly in unusual biting angles or when a bite involves the posterior region of the jaw.

The arch itself has a characteristic shape. The maxillary (upper) arch is broader and more parabolic. The mandibular (lower) arch is narrower and more U-shaped. In a straight-on bite, the upper arch leaves a wider arc above and the lower arch a narrower arc below, with the two arcs facing each other across a central zone. This paired-arch footprint is the first thing an analyst looks for when deciding whether a rounded injury is a bite at all.

Individual teeth add their own signatures. A rotated central incisor leaves a mark offset from the arc. A chipped lateral incisor leaves an incomplete impression. A gap from an extracted tooth leaves a missing segment in the arch pattern. These individual characteristics are what analysts hope to match back to a suspect, though the quality of their registration in skin is highly variable.

A bite involves more than just teeth pressing into skin. The jaw muscles generate force; the tongue and lips create suction and lateral movement; the victim may twist or pull away during the bite, smearing the pattern. Understanding what happened mechanically during the bite is essential for interpreting what the mark shows.

1. Initial contact and compression
   The incisors and canines contact the skin surface and compress the tissue as bite force increases. At this stage the skin deforms both at the tooth contact points and between them. The compressed tissue blanches or bruises depending on bite force and vascular status of the victim.
2. Suction and central zone
   Lips seal around the bite site and suction draws the central skin upward between the arches. This creates the petechial haemorrhage or central ecchymosis sometimes visible inside the ring, and it also stretches the surrounding tissue in ways that distort the arch perimeter.
3. Release and recoil
   When the teeth release, the compressed tissue partially rebounds. The mark left is not a direct cast of the teeth: it is the residue of compression plus recoil, and the geometry has shifted. How much it shifts depends on the tissue thickness, elasticity, and the force and duration of the bite.
4. Post-bite evolution
   Bruising often develops and spreads over the following 24 to 72 hours as blood tracks through tissue planes. In living victims the mark seen at first examination may look less defined than the mark seen the next day; documentation must be repeated.

Unlike impression materials, skin does not passively record tooth geometry. It is layered (epidermis, dermis, subcutaneous fat), regionally variable in thickness and mobility, and actively maintained by a living vascular system in the antemortem case. Every one of these properties degrades the fidelity of the registration.

The regional location of the bite matters enormously. Bites on the breast and buttocks, the most common sites in sexual homicide, land on fatty, mobile tissue that stretches in multiple directions under load. Bites on the arm or shoulder land on more fixed tissue over muscle, and register somewhat better. No location registers with the accuracy of a dental impression material, and analysts who treat a bite mark photograph as equivalent to a dental cast are misrepresenting the evidential value.

Bite marks are classified by the type of tissue injury they create, and these types map roughly onto the force applied and the way the teeth engaged the skin. The ABFO (American Board of Forensic Odontology) recognises a spectrum from clear patterns with individual tooth marks down to patterns where it is unclear a bite occurred at all.

• Contusion: bruising without skin break. The most common pattern in living victims. Individual tooth marks may or may not be distinguishable within the arch arc.
• Abrasion: superficial scraping of the skin surface, often at the leading edge of an arch where incisors dragged across the skin. Can show individual tooth widths.
• Laceration: tearing through the skin with enough force. Occurs more often on thin skin or with high bite force. May produce individual tooth-shaped cuts.
• Avulsion: tissue removed by the bite. Preserves a tissue specimen for DNA but destroys the surface pattern.
• Artefact: the mark in a detached piece of skin or in food or another substrate.

The same person biting the same victim in slightly different locations or with slightly different orientation can produce patterns that look visually quite different. A rotated head, a shifted jaw angle, or a bite taken at an oblique angle to the skin surface all change the apparent arch width and the relative positions of tooth impressions. This variability within a single biter is one of the core validity problems that the later NAS and PCAST critiques would formalise.

The American Board of Forensic Odontology published guidelines for bite mark terminology and methodology that have become the de facto standard across many jurisdictions, including reference laboratories in the UK, Australia, and parts of South Asia. The guidelines define what counts as a bite mark, how analysts should describe patterns, and the language they may use when reaching conclusions.

The ABFO's conclusion scale (revised in 2018 after the PCAST report) runs from 'Inconclusive' through 'Consistent with,' 'Probably made by,' and 'Made by,' with a parallel exclusion scale. The 2018 revision removed the most definitive identification language from single-examiner use and recommended that positive identification conclusions only be reached through a formal consensus panel process. This shift acknowledged the validity concerns without entirely abandoning the discipline.

• Patterned injury: a wound whose shape reflects the shape of the object that caused it. A bite mark is one subtype.
• Definitive bite mark: a patterned injury consistent with human dentition that shows individual tooth marks arranged in a recognisable arch pattern.
• Possible bite mark: a patterned injury that may be a bite but lacks enough features to rule out other causes.
• Not a bite mark: a patterned injury that, after analysis, is inconsistent with human or animal biting.

The gap between the teeth that made a bite and the mark that can actually be documented is not a single distortion. It is an accumulation of distortions at every stage: the mechanics of the bite itself, the response of the tissue, the postmortem or post-incident changes, and the photography and analysis methods applied. Naming each source of variability is essential for honest court testimony.

• Victim movement during bite: twisting, pulling, or pushing shifts the mark relative to the teeth's actual position.
• Multiple bites in the same area: overlapping marks create a composite pattern that can look like a single bite with anomalous features.
• Healing in living victims: the bruising process can sharpen, blur, or spread the pattern over hours to days.
• Decomposition: postmortem changes after death can create or destroy apparent tooth marks.
• Photo documentation angle: even a small tilt in the camera axis introduces apparent geometric distortion in the pattern.

These sources compound. A bite on mobile skin, followed by victim movement, documented twelve hours later with a slightly tilted camera, and compared to a dental cast taken six months after the event, has passed through enough distortion stages that the remaining signal may be insufficient to support a confident identification. Naming each distortion stage is a prerequisite for honest court testimony.