Download Forensic Odontology

Forensic Odontology
Forensic odontology is a branch of forensic medicine and, in the interests of justice, deals with
the proper examination, handling and presentation of dental evidence in a court of law. The work
of a forensic odontologist covers:





identification of bite marks on the victims of attack
comparison of bite marks with the teeth of a suspect and presentation of this evidence in
court as an expert witness
identification of bite marks in other substances such as wood, leather and foodstuffs
identification of unknown bodies through dental records
age estimations of skeletal remains
A forensic odontologist would often work with a forensic pathologist or forensic anthropologist.
Identification of human remains.
Unidentified bodies come to light frequently, having drowned, burned, been murdered, having
committed suicide or dead from natural causes. Usually, sufficient evidence is apparent to be
able to positively identify the body, but from time to time, this identification will rely on dental
evidence. All mouths are different and the trained eye of the forensic odontologist will be able to
offer a considerable amount of useful information. Most obvious will be to provide an accurate
charting of the teeth and fillings present to compare with dental records of missing persons. This
often leads to a positive identification.
Even if only a few teeth are available, one can still offer an age estimation, smoking habit, state of
oral hygiene, and identification of individual features which may match with ante-mortem records.
Where the subject has no teeth, useful information can still be gleaned from the study of any
dentures and by X-raying the mouth and skull.
It is important that the services of a forensic odontologist be sought early in these cases, as much
time consuming police work can be avoided given a dental report early in the investigation.
For example; The mummified remains of a female were discovered in the disused cellar of a
hotel. At post mortem the forensic odontologist, by studying the development of the tooth roots
was able to determine the age at death to within 12 months. This led to a name being suggested
by the Missing Persons Bureau and a positive identification using dental records within 48 hours.
Bite Marks.
Bite marks are frequently seen on the victims of attack - especially in cases of sexual assault.
Bites are also seen in cases of child abuse. This vital evidence often goes unrecognised by the
untrained person. Any roughly semicircular bruise between 4 and 5cm diameter should be treated
as suspicious and the opinion of a forensic odontologist sought early in the investigation. He will
not only give an opinion, but be able to supervise the photography of the bite mark using different
light sources to demonstrate the bite to advantage.
It will also be the function of the forensic odontologist to record an impression of the bite, take
dental impressions of any suspects, be prepared to make a comparison and, if necessary, to
present the evidence in court as an expert witness.
The forensic odontologist will also be able to recognise and record bite marks in other substances
such as foodstuffs (apples, cheese, chocolate), leather (key rings and belts) and wood (pencils).
The shape of the bite mark can give useful clues about the person who caused it and may lead to
the implication or exclusion of an individual under investigation.
For example; A sex-attacker punched his victim and then threatened to kill her. In the struggle he
bit her on the breast. A forensic odontologist took an impression of the bite mark which later
convinced a jury that the accused was, indeed, the attacker. He was convicted and sentenced
accordingly.
Post-mortem Identification
The most common role of the forensic dentist is the identification of deceased individuals. Dental
identification of humans occurs for a number of different reasons and in a number of different
situations. The bodies of victims of violent crimes, fires, motor vehicle accidents and work place
accidents, can be disfigured to such an extent that identification by a family member is neither
reliable nor desirable. Persons who have been deceased for some time prior to discovery and
those found in water also present unpleasant and difficult visual identifications. Dental
identifications have always played a key role in natural and manmade disaster situations and in
particular the mass casualties normally associated with aviation disasters.
Many people are familiar with the concept of dental identification; it is frequently mentioned on
television news. But the nuances and complexities of the process are rarely understood. The
central dogma of dental identification is that post-mortem dental remains can be compared with
dental records, including written notes, study casts, radiographs, etc, to confirm identity. Clearly,
individuals with numerous and complex dental treatments are often easier to identify than those
individuals with little or no restorative treatment. The teeth not only represent a suitable
repository for such unique and identifying features, they also survive most post-mortem events
that can disrupt or change other body tissues.
The forensic dentist produces the post-mortem record by careful charting and written
descriptions of the dental structures and x-rays. Once the post-mortem record is complete, a
comparison between these and dental records can be carried out. A range of conclusions can be
reached when reporting a dental identification. The American Board of Forensic Odontology
recommends that these be limited to the following four conclusions:




Positive identification: The antemortem and post-mortem data match in sufficient detail,
with no unexplainable discrepancies, to establish that they are from the same individual.
Possible identification: the antemortem and post-mortem data have consistent features
but, because of the quality of either the post-mortem remains or the antemortem
evidence, it is not possible to establish identity positively.
Insufficient evidence: The available information is insufficient to form the basis for a
conclusion.
Exclusion: the antemortem and post-mortem data are clearly inconsistent.
Unlike fingerprints there is no minimum number of concordant features that are required for a
positive identification. A single tooth can be used for identification if it contains sufficient unique
features. Equally, a full-mouth series of radiographs may not reveal sufficient detail to render a
positive conclusion. The discretion of identification lies with the odontologist who must be
prepared to justify the conclusions in court, surely the ultimate in peer-review.
Dental Profiling
When dental records are unavailable and other methods of
identification are not possible, the forensic dentist can often produce a
"picture" of the general features of the individual. This process is
known as post-mortem dental profiling. A dental profile will typically
provide information on the deceased's age, ancestry background, sex
and socio-economic status. In some instances it is possible to provide
additional information regarding occupation, dietary habits, habitual
behaviours and occasionally on dental or systemic diseases.
The forensic dentist will often work with a forensic anthropologists to
help in identification of an individual or the development of a profile
from remains. The determination of sex and ancestry can be assessed
from skull shape and form. Generally, from skull appearance, forensic
dentists can determine race within the three major groups: Caucasoid, Mongoloid and Negroid.
Additional characteristics, such as cusps of Carabelli, shovel-shaped incisors and multi-cusped
premolars, can also assist in determination of ancestry. Sex determination is usually based on
cranial appearance, as no sex differences are apparent in the morphology of teeth. Microscopic
examination of teeth can confirm sex by the presence or absence of Y-chromatin and DNA
analysis can also reveal sex.
In developing a profile dental structures can provide useful indictors to
the individual's chronological age. The age of children can be
determined by the analysis of tooth development and subsequent
comparison with developmental charts. Conclusions are usually
accurate to approximately ±1.5 years. While eruption dates can be
used in determining sub-adult ages, these are highly variable and the
actual developmental stages of the teeth are more accurate.
Other features can be useful in individualising a profile. The presence
of erosion can suggest alcohol or substance abuse, an eating disorder or even hiatus hernia
while stains can indicate smoking. Unusual wear patterns may result from pipe stems, cigarette
holders, hairpins, carpet tacks or previous orthodontic treatment. The quality, quantity and
presence or absence of dental treatment may give an indication of socio-economic status or
likely country of residence.
Because of the resistant nature of dental tissues to environmental assaults, such as incineration,
immersion, trauma, mutilation and decomposition, teeth represent an excellent source of DNA
material. When conventional dental identification methods fail, this biological material can
provide the necessary link to prove identity.
Bite Marks
Forensic odontologists may also work backwards matching the bite marks on objects found at a
scene to a suspect. They develop the skill of comparing dental impressions taken from a
person's mouth to bite-mark impressions on the skin (or possibly the bones) of a victim. There
are many factors to consider, including matching for striations, whorls, indentations, pitting, and
abrasions, and often this is done through computer-enhanced photography. They can also
analyse bite marks on food in cases where a perpetrator might have taken a bite out of
something in the victim's home and left it behind. An example is given below. What experts
seek are a sufficient number of points of similarity between the evidence and a suspect to be
able to say with a reasonable degree of certainty that this is the perpetrator.
However, bite marks left on foodstuff offer a three-dimensional impression, which is superior to
the two-dimensional impression often left on skin. A bite might penetrate the skin, but often only
leaves bruising—and sometimes the blood marks of a bruise are mistaken for the impression of
a tooth. Conversely bite marks might be dismissed as simple bruising. Some bites are forceful
enough to leave a good impression, others are not.
The physical characteristics of both the bite mark wound and the
suspect's teeth include








the distance from cuspid to cuspid
the shape of the mouth arch
the evidence of a tooth out of alignment
teeth width and thickness, spacing between teeth
missing teeth
the curves of biting edges
unique dentistry
wear patterns such as chips or grinding.
All of these are examined in detail and than compared, preferably in a
blind test in which the odontologist is not aware of which teeth
impressions belong to the suspect. At the very least, the injury pattern
itself should be completely analysed first before looking at the data from the suspect.
Currently, there is no agreement among forensic odontologists about the individuality
(uniqueness) of dentition or the behaviour of human skin during biting. Although these issues
have never been proven scientifically, much research is currently underway in an attempt to
prove the suspicion that each human dentition is unique. The sizes, shapes and pattern of the
biting edges of the anterior teeth that are arranged in the upper and lower dental arcades are
thought to be specific to that individual.
The amount and degree of detail recorded in the bitten surface may vary from case to case.
And, even if it is assumed that the dentition is individual enough to warrant use in forensic
contexts, it is not known if this individuality is recorded specifically enough in the injury. In
situations where sufficient detail is available, it may be possible to identify the biter to the
exclusion of all others. Perhaps more significantly, it is possible to exclude suspects that did not
leave the bite mark.
The complexity of bite marks on skin has made their use a contentious issue in some
jurisdictions.
Use of Bite Marks to Identify Individuals
An oblong piece of chewing gum was found at
the scene of a crime, it appeared to have
impressions of human teeth.
Piece of chewing gum found at crime-scene.
Positive replications of the impressions were
generated using a dental impression material.
The replications were used to compare with
casts of the suspect's teeth.
Positive cast of chewing gum surface.
Corresponding morphological features were
found on cast of the chewing gum surface and
the suspect's teeth. This dental evidence lead to
a subsequent guilty plea on the part of the
suspect.
Casts of the suspect's upper left posterior teeth.
Some common terms used in Odontology:










canines - The third tooth to the left and to the right of the midline of either jaw, situated
between the second incisor and the premolar teeth. Also known as the cuspid.
cementum - A bony substance covering the root of a tooth.
dentine - The dense calcified substance of which teeth are largely composed. It
contains less animal matter than bone, and in the teeth of man is situated beneath the
enamel.
enamel - A hard ceramic which covers the exposed part of your teeth.
eruption - The act of breaking out, appearing or becoming visible, as eruption of the
teeth.
incisors - One of the teeth in front of the canines in either jaw.
milk teeth - first or temporary teeth.
molars - Any one of the teeth behind the incisors and canines.
periodontics - A dental specialty concerned with the histology, physiology, and
pathology of the tissues that support, attach, and surround the teeth, and of the
treatment and prevention of disease affecting these tissues.
premolars - One of the two double-pointed teeth which intervene between the canines
(cuspids) and the molars, on each side of each jaw. Also known as the bicuspid.
Back to Forensic Index Page
Page Design © Ian Hunter.