Bite Mark Analysis

Intro & Significance - Tooth Truths 101

• Definition: Pattern or injury caused by teeth (human/animal) on skin or other materials.
• Significance:
  • Limited reliability for individual identification due to scientific concerns about dental uniqueness transfer to skin.
  • May provide class characteristics but individual identification is scientifically questionable.
  • Can corroborate or refute witness accounts with significant limitations.
  • Considered evidence in assault, abuse cases under BSA but with reliability concerns.
• Scientific Challenges:
  • Dental uniqueness assumption not scientifically validated for bitemark analysis.
  • Skin distortion affects accurate pattern transfer.
  • Multiple wrongful convictions linked to bitemark evidence.
  • Limited admissibility due to reliability issues under BSA standards.

⭐ Human bite marks typically display a double arch pattern; incisors and canines are the most prominent marking teeth, though pattern interpretation remains scientifically controversial.

Mark Morphology - Dental ID Clues

• Arch Pattern:
  • Typically double (maxillary & mandibular).
  • Shape: U-shaped, ovoid, V-shaped.
  • Size: Intercanine distance, arch width.
• Tooth Mark Types:
  • Incisors: Rectangular.
  • Canines: Triangular/pointed, often deepest.
  • Premolars: Round/oval, single/double cusps.
  • Molars: Broad, shallow, rarely distinct.
• Class Features:
  • Arch size/shape, tooth count, general alignment.
• Individual Features (Limited Reliability):
  • Rotations, spacing (diastema), fractures.
  • Wear, unique restorations.
• Considerations:
  • Skin elasticity distorts.
  • Healing alters marks; photograph early.
  • Scientific validity for individual identification widely discredited.

⭐ Scientific Limitation: Bite mark analysis lacks scientific foundation for individual identification per NAS/PCAST findings. Focus on injury documentation under BSA provisions rather than perpetrator identification.

⚠️ Legal Update: Under BSA 2023, forensic evidence must meet scientific reliability standards. Bite mark comparison for individual identification no longer considered scientifically valid in most jurisdictions.

Evidence Collection - Capture & Conserve

• Initial Steps:
  • Consent (living victim).
  • Document: location, description (shape, size, colour, severity).
  • Serial observation: note changes over 5-7 days.
• Photography: Essential for 2D analysis with limitations.
  • Overall, orientation, close-ups (perpendicular, with ABFO No. 2 scale).
  • Varied lighting; re-photograph at 24h, 48h, 72h.
  • Note: ABFO 2023 guidelines prohibit unconditional linking of bite marks to specific dentition.
• Saliva Swabbing (DNA):
  • Before cleaning.
  • Double swab technique (wet then dry).
  • Swab bite area; control swab (unbitten skin).
  • Air dry; paper envelope.
• Impressions (3D Analysis):
  • For clear, indented marks.
  • Dental impression materials (e.g., PVS).
• Tissue Samples (Deceased):
  • Excise bite mark with underlying tissue.
  • Preserve: 10% formalin or saline.
• Chain of Custody: Critical for BSA admissibility.
  • Meticulous tracking prevents contamination/degradation.
  • Essential for digital evidence and DNA samples.

⭐ Saliva from bite marks (double swab technique) is crucial for DNA analysis to identify the perpetrator, with proper chain of custody documentation under BSA 2023.

Analysis & Legal - Match, Misgivings, & Law

• Analytical Approaches:
  • Pattern analysis (comparison of mark with suspect's dentition).
  • Methods: Overlays (manual/digital), direct comparison, metric analysis.
  • Identify: Class (group) characteristics only - individual identification lacks scientific basis.
• Interpretation & Conclusions:
  • Limited conclusions: Excluded, Possibly consistent (positive identification no longer accepted).
  • Based on exclusionary analysis rather than individualisation.
• Significant Misgivings (Controversies):
  • Skin unreliability: Distortion, elasticity, healing obscure details.
  • Individual identification: Fundamentally lacks scientific validation for forensic use.
  • Subjectivity, cognitive bias, lack of standard protocols.
  • High error potential; NAS (2009)/PCAST (2016) heavily criticised methodology.
• Legal Standing & Challenges:
  • Admissibility highly restricted under BSA provisions: Scientific reliability consistently questioned.
  • Expert testimony under BNSS procedures must emphasise severe limitations.

  • ⭐ ABFO (American Board of Forensic Odontology) guidelines no longer support positive identification conclusions from bite marks alone.

High-Yield Points - ⚡ Biggest Takeaways

• Human bite marks: Typically elliptical/ovoid, but individual identification is scientifically unreliable.
• Saliva: Essential for DNA analysis - the only reliable method for linking bite marks to individuals.
• Photography: Must include an ABFO No. 2 scale for accurate documentation of injuries.
• Animal bites: Often V-shaped/punctures; narrower and deeper than human.
• DNA evidence: Admissible under BSA when proper chain of custody maintained.
• Distortion/Healing: Significantly alters bite mark appearance over time.
• Scientific consensus: Bite mark comparison for identification is largely discredited in forensic science.