Bite Mark Documentation on Skin
A suspected bite mark is photographed, scaled, and measured before it fades.
- Poor: Skin as recording medium (stretches, heals, distorts)
- Hours: Photo timing window (bruise pattern changes fast)
- Yes: ABFO scale used (reference ruler in frame)
- Low: Mark permanence (fades within days)
Photographing the wound
Mark is shot straight-on with a scale ruler.
Measuring the pattern
Arch width and individual tooth marks are measured.
Why timing matters
Bruises swell, shift, and fade within days.
Dental Cast Collection
A suspect's teeth are impressioned and cast in stone for comparison.
- Alginate: Impression material (or silicone putty)
- Dental stone: Cast material (hardens to rigid model)
- 6–8: Teeth typically cast (anterior biting teeth)
- High: Cast accuracy (rigid, unlike skin)
Taking the impression
Suspect bites into a soft impression tray.
Pouring the cast
Stone is poured to create a rigid tooth model.
A rigid reference
Unlike skin, the cast does not distort over time.
Overlay Comparison Technique
The cast's biting edge is overlaid onto the photographed bite mark.
- Transparency: Overlay method (or digital overlay)
- Scale ruler: Alignment reference (matches photo scale)
- High: Subjective judgment (examiner-dependent fit)
- None: Standardized protocol (no single accepted method)
Building the overlay
Cast edge is traced onto clear film.
Aligning to the mark
Overlay is scaled and rotated onto the photo.
Judging the fit
Examiner visually rates how well outlines align.
Individual Feature Comparison
Tooth spacing, width, and arch curve are compared point-by-point.
- 8: Features assessed (individual tooth edges)
- Yes: Rotations checked (tilted or crowded teeth)
- Loose: Spacing tolerance (no fixed numeric standard)
- Low: Inter-examiner agreement (studies show poor consistency)
Spacing comparison
Gaps between tooth marks are measured and compared.
Width and rotation
Individual tooth width and tilt are checked.
Arch curvature
Overall jaw curve shape is compared last.
Reliability Caveat of Bite Mark Evidence
Bite mark comparison has never been scientifically validated as reliable.
- Critical: NAS 2009 report (found no scientific basis)
- Multiple: Wrongful convictions (later overturned by DNA)
- Severe: Skin distortion factor (undermines pattern fidelity)
- Contested: Current legal status (many courts now exclude it)
Skin is not a stable medium
Skin stretches, swells, and heals unevenly.
No validated match standard
No agreed statistical threshold defines a match.
Caution regardless of fit
Even a strong-looking overlay is not proof of identity.