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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) in Rockville, Maryland where
the sequencing is undertaken.
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OdontoSearch Overview
Dental comparison of antemortem (before death ) and postmortem (after death)
records provides one of the best avenues for establishing personal
identification in the forensic sciences. Ideally, dentists work with antemortem
dental x-rays since these provide a sort of "photographic" image of a known
person at a specific point in time. These x-rays can be compared with dental
x-rays taken from an unidentified set of remains in order to determine a match
or exclusion. Commonly, the sizes and shapes of fillings present in the teeth
can be matched to establish a "positive identification." Unfortunately, in many
of the CIL cases these antemortem x-rays are not available and dental
comparisons must be completed based only on written notes and charts obtained
from a missing individual's medical records. A new computer program developed at
the Central Identification Lab (CIL), called OdontoSearch, creates a means of
using these charts and notes (in the absence of x-rays) for identification
purposes.
The problem with dental treatment charts and notes is that, unlike x-rays,
the information cannot be shown to be exclusively correlated to a specific
individual. For example, several people may have the same teeth filled or
extracted and their treatment notes would be the same. In the past, the strength
of a match between a missing person's dental treatment records and the treatment
observed on an unidentified set of remains has been based on the clinical
experience of the dentist (different dentists may come to very different
conclusions). The OdontoSearch computer program developed at the CIL provides an
objective means of assessing the frequency of occurrence for dental treatment.
The program works by comparing an individual's pattern of missing, filled, and
unrestored teeth to a large, representative sample of the U.S. population. The
methodology and rationale behind the OdontoSearch program is very similar to the
procedures that have been established for mitochondrial DNA comparisons.
Two important points need to be recognized about the OdontoSearch program:
1) The OdontoSearch program is not a means to select a specific person from
a database of missing individuals. In actuality, a large portion of the
OdontoSearch database is composed of individuals who simply participated in
dental health studies. The goal of the OdontoSearch database is only to
provide a representative sample of the dental treatment of the adult U.S.
population.
2) A possible dental association must be established between a specific
individual and an unidentified set of remains for the results of OdontoSearch
to be meaningful. In other words, determining that an unidentified set of
remains exhibits an extremely rare dental pattern is worthless unless there is
some correlation to a missing individual.
With the OdontoSearch program, uncommon dental patterns can be recognized as
such, and a frequency value can be associated with the pattern. In many
instances these results may be counterintuitive since the presence of only a few
"common" fillings may create a very rare dental pattern when all of the teeth
are considered. For example, with OdontoSearch it would be possible to determine
that out of a comparison with 40,108 individuals, a specific dental pattern was
observed only 48 times, or about 1 out of 833 people would be expected to have
this specific pattern. The fact that a match of this dental pattern was found
between a missing individual's records and an unidentified set of remains is
convincing evidence for an association. The OdontoSearch results are used along
with other analytical information (e.g., skeletal analysis) in order to build a
convincing identification to a specific individual.
This program allows for any number of teeth from 1 to 28 (excludes third
molars) to be entered, which allows for cases involving postmortem loss. All
questions and comments would be appreciated and can be submitted via email to
the Webmaster.
If you have access to large samples of dental data (modern or historic), or
if you know someone who does, please contact the
Webmaster. The information could
potentially be integrated into a future edition of the program. Input is greatly
appreciated!
Read articles from the Journal of Forensic Sciences, Vol. 48, No. 3.
"Establishing Personal Identification Based on Specific Patterns Of Missing,
Filled, And Unrestored Teeth"
"The Diversity of Adult Dental Patterns in the United States and the
Implicationsfor Personal Identification"
These articles are made available with permission from the Journal of
Forensic Sciences, Vol. 48, No. 3, copyright ASTM International, 100 Barr Harbor
Drive, West Conshohcken, PA 19428.
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