The Forensic Odontologist as Expert Witness

Courts in most jurisdictions distinguish sharply between a witness of fact, who reports only what they perceived, and an expert witness, who is permitted to draw inferences and give opinions within a defined area of expertise. The expert's overriding duty runs to the court, not to the lawyer or agency who commissioned the work. In England and Wales this is codified in the Criminal Procedure Rules. In the United States federal system it arises under Federal Rule of Evidence 702 and the case law around it. The principle is the same everywhere: the expert must give an honest, independent assessment even when it is unhelpful to the retaining party.

In practice this means the forensic odontologist must not advocate, must acknowledge the limits of their conclusions, and must tell the court about contrary views in the literature if they are substantial. A report that presents only the evidence supporting one conclusion, while ignoring the contrary findings, fails that duty. Courts have excluded experts and in serious cases referred the matter for professional sanction when partisan advocacy was found.

The forensic odontology report is the primary document through which the court receives the expert's findings. It must stand on its own: a judge reading it without the expert present should be able to understand what was examined, what methods were used, and what the conclusions mean. The ABFO and most national forensic bodies recommend a standard structure, and deviating from it without good reason invites challenge.

1. Case details and materials examined
   List every item received: radiographs, charts, models, photographs, swabs, casts of the injury. State condition and provenance. This chain-of-custody section forms the basis for admissibility arguments about continuity of evidence.
2. Methods and standards
   Identify the comparison protocol used (ABFO guidelines, INTERPOL DVI, national standard). State who conducted the work and when. If a second examiner reviewed the findings independently, say so explicitly.
3. Findings
   Describe the antemortem dental features, the postmortem findings, or the injury characteristics, and then the points of concordance and discordance. Do not mix findings with interpretation: keep them in separate sections.
4. Opinion and conclusion
   State the conclusion in the standardised scale language. Explain the basis. If expressing an identification opinion, state how many concordant features were found and whether any unexplained discordances remain.
5. Limitations and caveats
   State what could not be assessed (poor image quality, missing records, postmortem dental change). A clean statement of limitations is more persuasive than its absence: it shows the expert has considered the boundaries of their knowledge.

Dental identification and bite-mark analysis are often grouped because the same specialist performs both, but their evidentiary foundations are very different and courts increasingly treat them that way.

The US President's Council of Advisors on Science and Technology (PCAST) report of 2016 was particularly direct. It concluded that bite-mark analysis had not been shown to be foundationally valid and that courts should require a demonstration of validity before admitting it. That finding has been cited in subsequent Daubert hearings, and several US states have moved to restrict or exclude bite-mark evidence.

In 1993 the US Supreme Court replaced the older Frye 'general acceptance' test with a more demanding framework in Daubert v Merrell Dow Pharmaceuticals. Under Daubert the trial judge acts as gatekeeper, assessing not just whether a method is accepted but whether it is actually reliable. The court looks at four main factors, though these are guides rather than a checklist.

• Testability: has the methodology been or can it be tested? For bite marks this means controlled studies in which analysts compare marks to dentitions without knowing the ground truth.
• Peer review and publication: has the methodology been scrutinised in peer-reviewed literature? Some bite-mark techniques have been published; validity studies have returned mixed results.
• Known or potential error rate: this is the hardest question for bite-mark analysis. Proficiency studies at ABFO meetings in the 1990s and controlled research since have documented error rates that, depending on the study design, run from moderate to high.
• General acceptance: the original Frye question. For dental identification: yes. For bite-mark comparison: the forensic odontology community remains divided, and broader scientific bodies such as the National Academy of Sciences (2009) and PCAST (2016) have expressed serious reservations.

Frye-standard states (California remains the most significant example, continuing to apply the Kelly-Frye standard) asked a simpler question: is the method generally accepted in the relevant scientific community? For years this protected bite-mark evidence because the forensic odontology community accepted it. The problem is that 'the relevant community' became increasingly circular: methods were accepted by the community that used them, regardless of outside scientific opinion.

A competent defence lawyer facing bite-mark testimony will arrive with the PCAST report, the relevant NAS chapter, studies on inter-examiner agreement, and the case files from DNA exonerations. The expert must be able to engage with all of this accurately and calmly. Dismissing contrary literature, claiming to have a personal method that produces perfect results, or overstating the certainty of the conclusion are the most damaging things an expert can do.

• Acknowledge the literature honestly. If a study found that examiners disagreed on 40% of test marks, say so. Then explain what controls your own methodology applies to reduce that risk.
• Stick to your scale level. If your report says 'consistent with', do not upgrade to 'I believe this is a match' when pressed by the prosecution. The scale language exists precisely to prevent overstating.
• Separate identification from bite-mark testimony. If you are giving identification evidence, make clear that dental identification has a different and better-validated basis than bite-mark comparison.
• Distinguish class from individual characteristics. Most features seen in a bite-mark comparison are class-level (arch width, number of teeth). True individual features such as a rotated tooth or a fracture chip are rarer and carry more weight.

The Daubert/Frye debate is American, but the underlying question about reliability of expert testimony is universal. In England and Wales the Criminal Procedure Rules Part 19 require the expert to state the range of opinions on the matter, identify where they stand, and explain the basis. The Forensic Science Regulator's Codes of Practice set validation requirements for methods used in criminal proceedings, and bite-mark comparison is flagged as a method with limited validation.

Australia and Canada have case law frameworks (HG v The Queen in Australia; R v Mohan in Canada) that ask whether the expert's opinion is helpful, whether the expert is qualified, and whether the methodology is reliable. Courts in both countries have admitted dental identification evidence routinely while treating bite-mark evidence with greater caution, especially following American exoneration cases.

In mass-disaster identification contexts governed by INTERPOL DVI guidelines, the expert produces a Dental Identification Form (Pink Form) and submits findings to a central reconciliation process. The admissibility framework is less prominent here because the purpose is administrative identification, not criminal attribution, but the standard of documentation and the requirement for an independent check remain the same.