Forensic odontology is the sub-discipline of dentistry that applies the principles of dental science to matters of legal interest. The majority of a Forensic Odontologist's casework at the JPAC CIL involves the identification of unknown individuals who died as a result of conflict. Forensic Odontologists from the CIL have also been called upon to assist in recent mass fatality cases, examine bitemark evidence, assess injuries in child abuse cases, and to serve as expert witnesses in civil litigation proceedings.
Scientifically valid means of positively identifying unknown individuals, as in many branches of forensic science, centers around the comparison of an unknown item, sample, or character against a known exemplar, sample, or record. In the case of identifying human remains these methods include the comparison of fingerprints, nuclear DNA sequences, medical/anthropological comparison, and dental comparison.
There are several reasons why the dentition is especially valuable for human identification. Tooth enamel is the hardest substance in the human body, which makes teeth very robust and capable of surviving in conditions that are extremely detrimental to other human tissues. Dental restorations, such as: fillings, crowns, bridges, and root canal therapy, are individually customized for each patient. It is this uniqueness that enables Forensic Odontologists to use dental restorations and other treatments in the identification of unknown remains. Further, not only are restorations in individual teeth unique, but the number of teeth in an adult mouth (the full compliment in a normal adult dentition is thirty two) means that there is the potential to identify, or exclude, possible missing individuals with a very high level of probability. Dental treatments have varied through time (even in the latter half of the twentieth century, which is where most of the CIL's casework dates to) and can be of assistance as circumstantial evidence for identifications too.
Most of the remains accessioned into the CIL are from individuals who have been missing for decades and hence they are usually skeletonized. For remains in this state of preservation forensic dental comparison is usually the most viable means of positive identification. The likelihood of making an identification is largely dependent on two issues - the relative preservation of the dentition and the existence of dental records, especially radiographs (or X-rays). Identifications can be made from dental charts alone, but sometimes these lack sufficient detail. Despite being relatively low-tech, the effectiveness of dental comparison and the wide availability of records for military personnel means that forensic odontology is still the most commonly used methodology for identifying missing people at the CIL.
When a Forensic Odontologist is assigned a case they start by studying any existing dentition. They will record the presence, or absence, of individual teeth, their condition, anomalies and antemortem (before death) dental treatments and conditions. The Forensic Odontologist will then make a radiograph of the dentition in a manner that is analogous to the individual having a dental x-ray in life. Once the dentition of the unknown individual has been analyzed it is compared with the records and X-rays (where available) of any potential individuals that might be associated with a particular loss incident, date of loss, or geographic search area. The aim of this comparison is to assess the strength of any correlation between a known individual's records and the unknown dentition as analyzed by the Forensic Odontologist. Points of concordance are looked for, as are any discrepancies.
Discrepancies between the records and the analysis of an unknown's teeth sometimes occur when an individual's last set of dental records were made a long time prior to their death. This allows the possibility of an unrecorded treatment, or other event that affected the teeth or jaws, to have taken place. These "explainable differences" are sometimes problematic in cases with multiple individuals all of whom have older, or poor quality dental records. Once a comparison has been made, the Forensic Odontologist has a choice of possible recommendations: positive identification, probable identification, possible identification, insufficient evidence to reach a conclusion, and exclusion. This recommendation is then submitted to the Scientific Director of the CIL as part of an illustrated, and intensively peer-reviewed written report, in order to assist the Director in making an identification.
Forensic Odontologists also assist in the identification process through other avenues. If an individual's teeth have not completed development, their relative stage of maturity can be compared with standards developed from chronological growth studies. This provides an estimate of age for an unknown individual. The chronological age (e.g. 21 years old) that is calculated from age estimation techniques of this type is called a point estimate. It represents the average age of individuals in the growth study that had attained a particular stage in dental development. Around the point estimate is a range, or confidence interval, which reflects the variation around the point estimate of the age of individuals in the growth study that had attained a particular stage of development in the dentition. An advantage of age estimates from the dentition is that they tend to have a narrow associated range around the point estimate. This is because dental development is tightly controlled and protected against disturbances (a process known as canalization). A disadvantage of age estimates based on development is that most adults have completed their dental development by 25. For individuals who have attained full dental maturity, dental development is useless as an age estimator. Fortunately for the CIL, the majority of our casework is of individuals who are between the ages of 18 and 25. Age estimates can be used as useful corroborative circumstantial information in the identification process. They are also helpful in segregating individuals from large cases with multiple, commingled decedents.
Forensic Odontologists are also responsible for sampling the dentin of teeth for the analysis of mtDNA. These samples are sent away to the Armed Forces DNA Identification Laboratory (AFDIL) where the sequencing is undertaken.