Forensic Dentistry and Microbial Analysis of Bite Marks (PDF 398KB)

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Forensic Dentistry and Microbial Analysis of Bite Marks
Forensic Dentistry and Microbial
Analysis of Bite Marks
By Darnell Kennedy, Forensic Biology, PhD Candidate, University of Otago, Dunedin, New Zealand
Humans have used their teeth as both tools and
weapons since the dawn of time. Bite marks may be
inflicted during violent altercations in both offensive and
defensive actions. These marks can be used forensically
for law enforcement purposes.
The field of forensic dentistry is “that area of dentistry
concerned with the correct management, examination,
evaluation and presentation of dental evidence in criminal
or civil legal proceedings”. 1 The field consists of two
primary areas. The first is disaster victim identification
or identification of people who have become casualties
as a result of a crime. The second is the identification,
examination and evaluation of bite marks which occur
during sexual assaults and child abuse. 2
A bite mark may be defined as having occurred as a
result of either a physical alteration in a medium caused
by the contact of the teeth, or a representative pattern
left in an object or tissue by the dental structures of an
animal or human. 3 A prototypical human bite mark is
described as being a circular – or oval – patterned injury
consisting of two opposing symmetrical, U-shaped
arches separated at their bases by open spaces.
Along the periphery of the arches can be a series of
abrasions, contusions and/or lacerations indicative of
the size, shape, arrangement and distribution of the
contacting surfaces of the biting dentition. 3
Historical Bite Mark Cases
Salem Witch Trials
The fi rst reported incident of bite mark identifi cation occurred in
1692 in what is now commonly referred to as the Salem Witch
Trials. Reverend George Burroughs was accused of soliciting
young women into witchcraft by pinching, choking and biting his
victims. It was reported that, during the trial, Burroughs’ mouth
was pried open and his teeth were compared not only with the
teeth marks on several injured victims present, but also with
others in the courtroom.
Judges readily accepted this presentation of bite mark evidence
to substantiate the allegations and, at the conclusion of the trial,
Reverend Burroughs was convicted of witchcraft by the Court of
Oyer and Terminer and was hanged on August 19, 1692.
The Cheese Thief
The fi rst bite mark case to be reported as an American judicial
opinion was the 1954 Texas case of Doyle v. State. 4 This particular
case involved a bite mark left in a piece of cheese which was
found at the scene of a break and enter at a grocery store.
The investigating sheriff of the case approached the suspect,
who happened to be in custody for an unrelated offence,
requesting he voluntarily bite into a piece of cheese. The suspect
complied and later a fi rearms examiner photographed and made
plaster casts of both pieces of cheese. The fi rearms examiner
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Salem Witch trials
and a dentist then analysed both exhibits. The defendant was
convicted as a result of the damning testimony of these two
experts who believed that both pieces of cheese had been bitten
by the same set of teeth.
Wayne Boden Murders
The Canadian judicial system was presented with its fi rst bite mark
case in 1972 in the Alberta Supreme Court. More commonly
referred to in the tabloid press as ‘The Vampire Rapist’, this case
was the fi rst in which bite marks in human skin were used to
identify the perpetrator of a bite. 5 Also noteworthy is the fact that
this particular case was the fi rst in which bite mark evidence from
multiple cases could be linked to a single offender.
Wayne Boden sexually assaulted and murdered four young
women over a 16-month period, including one in a city some
distance away from the other victims. His ‘calling card’ or
‘trademark’ was to leave bite marks on his victims, particularly to
their breasts. Two days following the discovery of the last victim’s
body, Boden was apprehended as a possible suspect.
This last victim, a 33-year-old high school teacher named
Elizabeth Porteous, had suffered bite marks to one of her breasts
and her neck.
The police enlisted the services of a local orthodontist,
Gordon Swann, in an effort to prove that the marks on Porteous’
breasts and neck were Boden’s bite marks. At the time there was
nothing in the Canadian forensic literature on bite mark evidence.
The orthodontist then wrote to the FBI seeking their assistance.
In response, the FBI referred him to an expert in England.
Armed with this knowledge, the orthodontist then conducted a
detailed examination of these injuries in conjunction with models
and wax impressions of Boden’s dentition. His analysis indicated
29 points of similarity between the injuries on the victim and
the suspect’s dentition, thus providing enough evidence with
which to positively conclude that the bite marks were infl icted
by the accused.
The details of the link established between Boden and the
last victim sparked investigators from other law enforcement
agencies to review the previous three unsolved cases that
exhibited overlapping traits. The forensic odontologist from the
fourth case was asked to perform an analysis on the bite marks
on one of these earlier victims.
Darnell Kennedy is a final year PhD student at the University
of Otago, Dunedin, New Zealand. She has a BSc and
PGDipSci, both in Biochemistry, from Otago. She has had
a life-long interest in law enforcement and developed a
passion for science at high school. Embarking on a career
in the forensic science field she hopes will enable her to
combine her two passions. Darnell gave a presentation
in the Biological Criminalistics session at the ANZFSS
International Symposium in September 2010 in Sydney.
She is hoping to launch her forensic career in Australia
where she intends to move upon completion of her PhD.
© Darnell Kennedy retains exclusive copyright of this article and no
part may be reproduced in any form or by any means, electronic or
mechanical, including photocopying, recording or by any information
storage and retrieval system, without prior permission in writing from her.
The bite marks from both cases exhibited similarities and,
as a result, police interviewed Boden in relation to the three
unsolved homicides. Boden provided detailed confessions to
all three and was sentenced to life imprisonment. He died in
custody in 2006, from skin cancer.
Ted Bundy
Perhaps the most highly publicised bite mark case in United
States judicial history, and possibly the catalyst for the surge
in the use of bite mark evidence in courts around the United
States during the 1980s, was the case involving serial killer
Theodore (Ted) Bundy.
Bundy was convicted of two counts of fi rst-degree murder
in 1979 and was sentenced to death. The principal items of
evidence that resulted in Bundy’s murder convictions included
the identifi cation testimony of a key witness who placed him at
the scene of the crime moments before the murders and the
expert analysis of teeth marks found on the body of the one of
the murder victims. 6
Ted Bundy
About the Author
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Forensic Dentistry and Microbial Analysis of Bite Marks
Ted Bundy having dental impressions made. Photo reproduced with the
permission of the State Archives of Florida
Dental evidence in the trial of Ted Bundy. Photo reproduced with the
permission of the State Archives of Florida
Ted Bundy’s dental impressions. Photo reproduced with the permission of the
State Archives of Florida
The examination of the bite mark on one of the victims by a
forensic odontologist involved the comparison of dental casts
of Bundy’s teeth to the photographed indentations in the
victim’s fl esh. During his testimony the odontologist asserted
that the indentations on the victim’s body were made by Bundy.
The testimony included commentary on the uniqueness of the
human dentition and how the variability between individuals is
such that the technique of bite mark comparison is capable of
providing identifi cation with a high degree of reliability.
One of the issues Bundy argued during an appeal of his murder
convictions was the trial court’s ruling which permitted the
testimony of the dental expert who analysed the bite mark.
The defence contended that the comparison techniques used
during the bite mark analysis were not acceptable standards of
comparison and had not been established as reliable. Ted Bundy
was unsuccessful with his appeal and the original ruling was
sustained. He sat imprisoned on death row for 10 years before
being executed in the electric chair on 24 January 1989 at Florida
State Prison in Starke, Florida.
Increasing Understanding of the Forensic
Value of Bite Marks, Victim and Biter
Demographics and Types of Crime
The number of bite mark cases reported globally prior to the
1950s was relatively low with most occurring in Europe or Japan.
However, the number of reported bite mark cases worldwide
surged in the 1970s, with many of these from the United States.
During the years preceding the formal recognition of bite mark
analysis as a branch of forensic odontology, appreciation of the
potential value of bite mark evidence by forensic personnel at the
crime scene or in the autopsy room was slow. Once high-profi le
criminal cases, such as Ted Bundy’s demonstrated the evidentiary
importance of bite marks, law enforcement personnel, coroners,
pathologists and dentists were educated to carefully document
bite marks for subsequent analysis.
Anatomic Location
In 1983, a study was conducted to focus primarily on discerning
the anatomical locations of the bite marks, the sex and age of
victims sustaining these injuries, and the types of crime in which
these injuries featured. 7 The main aim for this type of research
was to provide prior knowledge of where these injuries were
most likely to be found in order to assist with their initial detection.
Similar studies have been conducted since this time to update
and augment previous fi ndings. 8, 9 However, common to each
study were the following observations:
1. Bite marks are found on almost all areas of the body.
2. It is common to fi nd more than one bite mark on a victim,
often in different anatomical locations.
3. Bite marks occurred primarily in sex-related crimes,
child abuse cases and cases involving physical altercations
of various types.
4. Female victims are most commonly bitten on the breasts,
arms and legs in descending order of frequency, and males
most frequently bitten on the arms, back and hands.
5. Patterns of distribution of bite marks are discernable and
variable and are based in part by the type of crime involved,
the age and sex of the victim, whether the bite mark is on the
victim or the attacker and the sex and age of the perpetrator.
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Mould of maxillary (upper) teeth
The mandible area of a human skull
Anatomy of the Typical Human Bite Mark
on Skin
Adult human dentition consists of 32 teeth, each of which varies
in terms of its size, shape and function. The full complement of
teeth comprises two incisors, one canine, two premolars and
three molars in each upper and lower quadrant.
The characteristic oval-patterned injury that results from the
action of biting will typically only reveal several of the anterior
teeth in each arch, namely the canines and the incisors.
A very frequent observation noted during bite mark investigations
is that the mandibular (lower) anterior teeth are exhibited more
clearly than the maxillary (upper) teeth. While numerous schools
of thought exist as to the reason governing such a phenomenon,
the most common proposal is that the mandibular jaw is capable
of movement during bite infl iction whilst the maxillary is not.
Odontologists recognise a variety of characteristics within
a bite injury that enable them to classify this injury as such.
These vwariations of bite mark patterns are defi ned as class
and individual characteristics. Class characteristics are features
that distinguish a human bite mark from other patterned injuries.
Individual characteristics are secondary level features within a
bite mark injury that represents individual tooth variations.
Bite mark dynamics can be infl uenced by many factors.
These can be variations that occur during bite infl iction with
both the perpetrator and victim infl uencing the resulting injury
in a contrasting manner. Furthermore, variations can also occur
during the recording and preservation of the evidence in addition
to any external or environmental infl uences.
Contentious Issues Surrounding Bite Mark
Analysis
Bite marks often represent the only physical evidence found on
a body. Consequently, the assessment of bite mark evidence
provides the basis of the testimony presented by a forensic
odontologist during criminal proceedings and the weight
placed on this type of evidence can have severe consequences
for suspects.
Despite the continued acceptance of bite mark evidence in
courts around the world, some experts in the fi eld are conceding
that the scientifi c basis supporting many of the assumptions
made by forensic odontologists is weak. The new level of judicial
scrutiny surrounding scientifi c evidence has highlighted the
defi ciencies plaguing bite mark analysis, and has thus created
hotly-debated areas of contention within the fi eld of forensic
dentistry. While Ted Bundy’s appeal arguments were deemed to
be without merit back then, the issues on which he based his
appeal are now at the forefront of the present-day debate.
Uniqueness of Human Dentition – the Debate
Rages
Bite mark analysis is centred on two assumptions: The fi rst
is that the dental characteristics of the teeth involved in biting
are unique among individuals, and second, that this asserted
uniqueness is registered in the material that is bitten.
A forensic odontolgoist identifying an individual from their
dentition will use dental x-rays and records to classify features
such as dental restorations and root morphology. Contrastingly,
identifying a person from a bite mark rests on an assumption
that because the dentition can exhibit endless variations,
this confers individual uniqueness. The major pitfall with this,
and consequently the catalyst for what is now an intense
debate in forensic odontology, is that this assumption has yet to
be validated.
Historical studies that attempted to establish the uniqueness of
human dentition did not address the accuracy of how various
dental characteristics used to establish uniqueness are recorded
in a bite mark in human skin. The most recent study that
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Forensic Dentistry and Microbial Analysis of Bite Marks
Figure 1 Figure 2a Figure 2b
Figure1. This bite mark injury was sustained in an incident that occurred a couple of days prior to being analysed by forensic dentists in Dunedin, New Zealand.
Figure 2a and 2b. A historical child abuse case (also in Dunedin) where forensic dentists were asked to review this child’s foot to determine (a) whether this was
a bite mark and (b) whether it was possible to identify an individual from this injury. Photos courtesy of Professor Jules Kieser
attempted to fi nally shed some light on the uniqueness of human
dentition used dental casts to produce bites on unembalmed
human cadavers. What authors concluded from this study was
that it was diffi cult to distinguish a bite from individuals with
similarly-aligned dentitions. 10
Accuracy of Bite Marks in Human Skin
Bite mark impressions can be found in inanimate objects such
as food stuffs, however it is the bite marks on human tissue
that comprise the majority of bite mark investigations. The main
challenge in forensic dentistry is the analysis of bite marks in
human skin and this can be primarily attributed to the fact that a
bite injury is subject to much distortion.
The appearance of bite marks in human skin can be infl uenced
by tissue distortion due to the mechanical properties of the skin.
These properties are related to the underlying collagen and
elastic fi bres in addition to other structures such as proteoglycans
(molecules found in the connective tissue of the human body).
The composition of these underlying structural components
varies across different locations on the body. To illustrate this
simply, the underlying tissue in the back varies signifi cantly to that
of the breast; therefore the degree of tissue distortion possible at
each site may differ greatly.
Bite mark deformation which is infl uenced by its anatomical
location has fl ow-on effects on the registration of both class and
individual tooth characteristics. In addition, movement of the
victim during bite infl iction would increase this distortion.
This lack of understanding about the degree of distortion
infl uencing a resulting bite injury creates unexplained variables
that have the potential to weaken testimony in court.
Current research investigating the biomechanics of skin to
explain the distortion inherent in bite mark injuries is aimed at
bridging some of the discrepancy that is observed between a
dentition and the resulting injury. 11
Another diffi culty facing forensic dentists is the changes that
occur to an injury as a result of the human healing processes.
Again, this is also a poorly understood area and – because the
healing process is swift – this results in rapid loss of evidence if
the injury is not reported immediately (Figure 1).
Figures 2a and 2b show the foot of a child who had sustained
physical abuse. Forensic dentists were called in to assess
what may have been a bite injury to the left foot in the hope of
implicating someone for the abuse. Figure 2b of the underside
of the foot illustrates how the healing process can make such a
determination extremely diffi cult to make.
DNA and its Emerging Role in Forensic
Dentistry
Forensic science is based on the premise that: ‘...every contact
leaves a trace’ and this is certainly true of cases involving bite
marks. Body fl uid traces recovered from a crime scene can
potentially contain DNA which, like fi ngerprints, has the highest
evidentiary value. In the bite mark analytical fi eld, attempts to
provide a more objective mode of analysis resulted in the
usefulness of saliva as a source of DNA.
The advent of the dideoxynucleotide termination method of
sequencing DNA in 1977, followed by the development of
polymerase chain reaction (PCR) in 1983, has seen DNA
technology take an irreplaceable position in the forensic sciences.
The application of DNA technology to forensic problems was
fi rst attempted in 1985 and, since that time, thousands of cases
around the world have been solved through the use of DNA-based
technology. Using DNA analysis, it is possible to establish the
origin of a sample that is isolated from biological materials such
as blood, semen, hair roots, tissue, teeth, bone and saliva.
The fi rst successful isolation of DNA from both saliva and
saliva-stained materials occurred in 1992 and was the work of
David Walsh and colleagues. 12 Researchers were aware that
saliva contains sloughed epithelial cells (tissues which form a
thin protective layer) from the inner surface of the lips and oral
mucosa, all of which were potential sources of DNA. The team
proposed a methodology to enable the extraction of DNA from
this fl uid. This provided the bite mark analytical fi eld with an
objective form of evidence, if successfully obtained.
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Numerous enzymes from a variety of sources are present in
saliva. Carbohydrates, esterases, proteolytic enzymes and
other catabolic enzymes are produced by the salivary glands,
oral microorganisms and leukocytes (white blood cells).
Of concern to the successful recovery of DNA from saliva
was the action of nucleases also present in saliva. DNA not
encased within intact cells is liable to degradation by these
enzymes, which has severe effects on both the quality and
the quantity of salivary DNA evidence.
Bacteria in the Oral Cavity
In addition to the proteins, glycoproteins and enzymes secreted
by various glands and cells in the oral cavity, saliva contains
a large population, both qualitatively and quantitatively,
of microorganisms that have been washed or mechanically
removed from their various ecological niches in the mouth.
A study investigating the bacteriology of human bite wounds
observed that the alpha-haemolytic streptococci were the
organisms most frequently isolated from all bite wounds.
The results of this study also showed that most bacteria isolated
from bite wound cultures originated from the normal oral fl ora,
rather than the skin fl ora. 13
The human oral cavity is the gateway to our bodies.
Approximately two thirds of all microorganisms gain entry
through the mouth, and some of these organisms establish
themselves in the oral cavity. More than 700 bacterial species,
of which over 50 per cent have not been cultivated (ie. grown
on culture in a laboratory), have been detected in the oral cavity.
The bacterial species that predominantly inhabit the oral cavity
are from the genus Streptococcus, more commonly referred to
The author examining a sample
as the oral streptococci or ‘strep’. There are different species of
streptococci (eg. Streptococcus mitis, Streptococcus gordonii)
and within each species exist many subgroups, which are referred
to as strains. Oral streptococci tend to be the major colonising
bacteria on the surface of the teeth, however one particular
species, Streptococcus salivarius, is predominant in saliva.
It was assumed that because streptococci are present on the
surface of the teeth, they would naturally be transferred from the
teeth of a biter to the skin of the victim due to the dynamics of the
biting action. Additionally, oral streptococci exhibit a large degree
of genetic diversity within each species, raising the possibility
of people harbouring their own unique strains of streptococci.
This observable variation between the dentition and subsequent
bite marks on skin and the diffi culties in recovering human DNA
raised the possibility of whether a method of ‘fi ngerprinting’
these bacteria would aid in the identifi cation of a suspect.
Recovery of Oral Streptococci from Bite Marks
The concept of recovering oral bacteria from bite marks for
forensic purposes was fi rst proposed in 1984 by Brown and
colleagues from the Department of Oral Biology at the University
of Adelaide, South Australia. 14 Researchers wanted to establish
the survival rates of bacteria on human skin prior to determining
the possibility of a ‘fi ngerprint’ typing scheme for identifying
streptococcal isolates obtained from bite marks.
A minute amount of freshly-collected human saliva was
applied as droplets onto the chest area of human participants.
At predetermined time intervals, an area of the skin was
sampled for viable (live) bacteria, specifi cally Streptococcus
salivarius as it is the major species found in saliva. The rate of
loss of live bacteria was 45-50 per cent per hour with viable
oral streptococci being recovered after 6.25 hours following
application of saliva. In conclusion, these authors acknowledged
that the establishment of a suitable “fi ngerprint” typing scheme
for oral bacteria may provide evidence relating to the identity of a
suspect in such cases.
A decade later, a small research team in the Department of Oral
Sciences at the University of Otago in Dunedin, New Zealand,
decided to investigate the idea of a “fi ngerprint” typing scheme
as proposed by Brown and colleagues. Researchers aimed to
assess the feasibility of utilising a genomic comparison approach
to match Streptococcus isolates recovered from bite marks with
those recovered from the incisor teeth of the biter. 15
This study involved the recruitment of eight participants, none of
whom were using or had used antiseptic mouthwashes or had
received antibiotic treatment in the previous three months,
as these treatments reduce the bacterial numbers in the mouth.
Participants were required to bite themselves in the bicep
region (Figure 3, page 12), with as much pressure as they could
tolerate, without infl icting lacerations. Researchers believed
that it was critical to authenticate the transfer of bacteria from
the teeth to the skin with the resulting self-infl icted bites being
sampled for up to 24 hours after biting.
The proposed genomic comparison approach involved the
successful culture of bacterial strains from the swabs taken of
the experimental bite marks and the mandibular anterior teeth.
Bacterial cells were then isolated from growth media and opened
to release the DNA. A comparison of the bacterial DNA profi les
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Forensic Dentistry and Microbial Analysis of Bite Marks
The methodology involved taking swabbed samples from selfinfl
icted bite marks of 24 participants, and from the mandibular
anterior teeth of those participants.
In contrast to the previous two studies, this study circumvented
the need to culture the samples onto specialised growth media by
processing the samples directly. In accordance with the fi ndings
from the previous two studies, the results obtained indicated a
high likelihood of matching bacterial DNA amplifi ed directly from
a bite mark with bacterial DNA from the teeth responsible for
the bite.
Current Research Shows Promising Results
The three projects described above all converged on the same
conclusion, which indicated the strong possibility of utilising
streptococcal DNA to match a bite mark to the teeth of the biter.
With all three studies providing proof of concept that genotypic
analysis of streptococci from bite marks may provide valuable
forensic evidence to corroborate traditional bite mark methods,
it was decided to launch another project.
Figure 3. A participant demonstrating how self-inflicted bite marks were
generated
generated from the bite marks and the teeth of the participants
revealed two interesting observations. Firstly, it was apparent
that there were streptococcal strains that could be matched
between both the bite mark and teeth samples. Secondly,
all the streptococcal profi les for each of the eight participants
were different. This suggested distinct bacterial profi les providing
possible grounds for the development of a microbial genomebased
approach for forensic purposes.
In 2005, a slightly different team, again from the Department
of Oral Sciences at the University of Otago, decided to extend
the approach devised previously by applying different molecular
biology tools to allow greater numbers of oral bacteria to be
analysed more rapidly. 16
In similar fashion to Borgula’s study, swabbed samples were
taken from the mandibular anterior teeth of eight participants,
however, only one of the participants was required to produce
a self-infl icted bite mark. In contrast to the prior study, a sample
of a self-infl icted bite mark was obtained from one individual
whose teeth samples the laboratory investigator did not have.
This element of the study was not revealed to the laboratory
investigator who believed that the two bite mark samples were
from two of the eight participants.
In accordance with the fi ndings of the previous group’s work,
bacterial genotypic profi les from separate individuals did not
match. The laboratory investigator was able to match the
bacterial genotypic profi le obtained from one of the bite marks
with that obtained from the teeth of that biter, thus correctly
identifying the biter. In contrast, the bite mark sample derived
from the ninth participant revealed no genotypic profi le that
appeared in anyway similar to those obtained from the teeth of
any of the original eight participants.
There was a revision in the methodology yet again with a third
study in 2006, again by a group in the University of Otago’s
Department of Oral Sciences. This study aimed to utilise
sophisticated molecular tools to achieve not only a faster
analysis, but a greater resolution. 17
Advancements in DNA Technology
The advancing technology in DNA sequencing has seen the
development of an instrument capable of sequencing DNA
mixtures, which is a limitation of conventional sequencing
technologies. An analogy to illustrate this novel capability would
be a shopping basket of groceries. Currently, when a person
buys groceries, the customer is required to take each item out
of the basket to be scanned individually. This is the same for
conventional DNA sequencing. DNA from different origins has
to be separated and sequenced individually. With the new
sequencing capability, however, it is not necessary to separate
DNA from different origins. Back to the shopping basket –
this means the customer no longer has to take each item out
of the basket. The whole basket could be passed through the
scanner, with the scanner then generating an itemised printout
of the contents of the basket.
In terms of the different strains of streptococci present in the
saliva and on the teeth, this technology provides a means with
which to identify the bacterial composition of these samples.
In other words, it is possible to determine the different strains of
oral streptococci from bite mark and teeth swabs and generate
what is essentially a ‘printout’ of the strains contained within
these samples. So, utilising this new sequencing technology,
more accurately referred to as high-throughput sequencing,
the current research aims to determine whether the streptococcal
DNA sequences from a bite mark can be matched exclusively
to those from the teeth responsible. Described below is a brief
overview of the methodology used.
1. 16 participants were recruited to bite themselves on the
bicep region of one arm.
2. The bite marks and the teeth were swabbed three hours
after the bites were infl icted.
3. PCR was used to amplify streptococcal-specifi c fragments
from four loci.
4. These partial DNA fragments were submitted for highthroughput
sequencing.
5. The sequences from the bites were compared to the teeth
of the biter and the teeth of the other participants.
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An oral bacterial swab
FLX sequencer machines
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Forensic Dentistry and Microbial Analysis of Bite Marks
6. Statistics are being performed to determine the accuracy
with which a bite mark could be correctly matched with the
teeth of the biter.
The criteria for eligibility to participate in this research remained
unchanged from Borgula’s study described earlier. The threehour
time lapse before sampling was an arbitrary time designed
to mimic the delay between an incident and the presentation of
Figure 4. A gel photo showing DNA fragments from streptococci from the
saliva (Sa), skin (S), bite (B) and teeth (T) samples of three participants.
The lanes labelled M indicate the DNA markers and are included to reveal
the length of the DNA fragment. The lanes labelled H2O and EC indicate
water and Escherichia coli (a bacteria of another genus), are to ensure that
only streptococcal DNA is capable of being amplified and are the negative
control samples. The lanes labelled SG and SM indicate S. gordonii and
S. mitis pure cultures from which DNA was amplified from and are the positive
control samples
the victim to the authorities, observed in real cases. Similarly to
Hsu’s study, streptococcal DNA was amplifi ed directly from the
bite mark and teeth swabs to avoid the need for culturing.
Before participants were asked to infl ict the experimental bites
on their arms, a swab of the area of skin where the bite mark
was to be located was obtained. This was to ensure that the
streptococcal DNA being extracted from the bite mark originated
from the teeth and not from the skin. This is exhibited in Figure 4
where there is an absence of a DNA fragment for the skin samples
from the three participants. The design of the DNA primers used
to amplify fragments of DNA is specifi c to streptococcal bacteria
only. This is also evident in Figure 4 with the absence of DNA
bands in the samples containing only water (labelled H2O on
the gel photo, left) and DNA from a bacteria not belonging to the
Streptococcus genus (labelled EC on the gel photo).
The high-throughput sequencing technology generates numbers
of DNA sequences not previously achievable with conventional
sequencing. To illustrate this point, the number of sequences
analysed from the bite mark samples of the 16 participants
ranged from 1700–10,000 for each participant. For the teeth
samples, this range was from 2600–9700 for each participant.
Dealing with data of this magnitude was only going to be
feasible via computational means, so a customised computer
program was written specifi cally for this project. One of the
requirements needed from this program was the ability to
compare the sequences from each of the bite mark samples to
the sequences obtained from the teeth samples to determine the
proportion of shared sequences. Ideally, the greatest proportion
of shared sequences was expected to be between a bite mark
and the teeth responsible.
T1
T2
T3
T4
T5
T6
T7
T8
T9
T10
T11
T12
T13
T14
T15
T16
B1 B2 B3 B4 B5 B6 B7 B8 B9 B10 B11 B12 B13 B14 B15 B16
Table 1. Shown in this table are where the highest proportion of sequence overlap is occurring between the bite samples of the 16 participants (B1-B16) and
their teeth (T1-T16). Green indicates the bite and corresponding teeth samples sharing the highest number of sequences. Yellow indicates where bite and
corresponding teeth do not share the highest number of sequences and blue indicates the bite and non-corresponding teeth samples sharing the highest
number of sequences
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Preliminary Results from the Current
Research
The sequences from each of the bite mark samples were
compared to the sequences for each of the teeth samples
and the proportion of shared sequences were calculated and
entered into a table similar to the one on page 14. The table
has been colour coded to give an overview of how the bite and
the corresponding teeth samples have aligned. From the table,
15 out of 16 bite samples shared the greatest number of
sequences with the teeth responsible.
Currently, researchers are determining the best statistical model
to use in order to predict the probability of success which, in this
case, is the probability of matching a bite mark to the correct
teeth based on streptococcal sequence data.
The Way Forward
There is a demand on the fi eld of bite mark analysis for research
to adhere to more stringent scientifi c regulations in order for
it to be more resilient to scientifi c scrutiny. The foundation on
which this fi eld currently stands is fairly weak in the light of
new levels of scientifi c rigor. The introduction of DNA analysis
provided an objective form of evidence, however the use of this
technology for forensic purposes was subject to a lot of criticism
before it was admitted into judicial hearings. Attempts to resolve
the insecurities and misunderstandings about such evidence
led to intense scientifi c validation by scientists to establish its
worth as a valuable and objective form of forensic evidence.
Today, DNA is the arguably most conclusive form of forensic
evidence and the scrutiny applied to DNA technology during
those founding years has acted to highlight the defi ciencies in the
establishment of other techniques in the forensic fi eld, including
bite mark analysis.
The current project aims to achieve a higher level of objectivity
in terms of evidence analysis in the bite mark analytical fi eld.
Research in forensic odontology has predominantly been directed
at improving the techniques for the traditional morphometric
means of comparing bite marks to dentitions. It is hoped that
the development of this molecular-biology-based tool may
prove feasible and act to corroborate any fi ndings found using
traditional methods.
References
1. American Society of Forensic Odontology. (2007) Introduction
to forensic odontology. In Manual of Forensic Odontology.
(Herschaft, Alder, Ord, Rawson & Smith ed.), 4th edn rev.,
pp. 1-6, Impress Printing & Graphics, New York.
2. Wagner, G. N. (1997). Scientifi c Methods of Identifi cation.
In Forensic Dentistry. (P. G. Stimson and, C. A. Mertz ed.),
pp. 1-36, CRC Press, New York.
3. American Society of Forensic Odontology. (2009). American
Board of Forensic Odontology Diplomates Reference
Manual. Section 3: Policies, Procedures, Guidelines &
Standards.
4. Doyle v. State, 159 Tex. C.R. 310, 263 S.W.2d 779.
5. Swann, G. (1974). The Wayne Boden Murders. International
Journal of Forensic Dentistry, 2(4), 32-42.
6. Bundy v. State 455 So 2d 330 (Fla. 1984): 349.
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of human bite marks in a series of 67 cases. Journal of
Forensic Sciences, 28, 619-621.
8. Pretty, I. A. and Sweet, D. (2000). Anatomical location of bite
marks and associated fi ndings in 101 cases from the United
States. Journal of Forensic Sciences, 45, 812-814.
9. Freeman, A. J., Senn, D. R. and Arendt, D.M. (2005). Seven
Hundred Seventy Eight Bite Mark: Analysis by Anatomic
Location, Victim, and Biter Demographics, Type of Crime,
and Legal Disposition. Journal of Forensic Sciences, 50,
1436-1443.
10. Miller, R.G., Bush, P.J., Dorion, R.B.J. and Bush, M.A. (2009)
Uniqueness of the dentition as impressed in human skin: a
cadavel model. Journal of Forensic Sciences, 54, 909-914.
11. Bush, M.A., Miller, R.G., Bush, P.J. and Dorion, R.B.J. (2009)
Biomechanical factors in human dermal bite marks in a
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12. Walsh, D.J., Corey, A.C., Cotton, R.W., Forman, L.,
Herrin, G.L., Word, C.J. and Garner, D. (1992). Isolation of
deoxyribonucleic acid (DNA) from saliva and forensic science
samples containing saliva. Journal of Forensic Sciences, 37,
387-395.
13. Goldstein, E. J., Citron, D.M., Wield, B., Blachman,
U., Sutter, V.L. Miller, T.A. and Finegold, S.M. (1978).
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14. Brown, K. A., Elliot, T.R., Rogers, A.H. and Thonard, J.C.
(1984). The survival of oral streptococci on human skin and
its implication in bite mark investigations. Forensic Science
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15. Borgula, L. M., Robinson, F.G., Rahimi, M., Chew, K.E.K.,
Birchmeier, K.R., Owens, S.G., Kieser, J.A. and Tompkins,
G.R. (2003). Isolation and genotypic comparison of oral
streptococci from experimental bite marks. The Journal of
Forensic Odonto-Stomatology, 21, 23-30.
16. Rahimi, M., Heng, N.C.K., Kieser, J.A. and Tompkins, G.R.
(2005). Genotypic comparison of bacteria recovered from
human bite marks and teeth using arbitrarily primed PCR.
Journal of Applied Microbiology, 99, 1265-1270.
17. Hsu, L., Power, D.A., Burton, J.P., Hauman, J.H., Tagg, J.R.
and Tompkins, G.R. (2007) Comparison of streptococcal
DNA amplifi ed from human bite marks and teeth by
denaturing gradient gel electrophoresis. New Zealand
Medical Journal, 120, 2-3.
Acknowledgements
I would like to thank my three outstanding PhD supervisors,
Professor Jules Kieser, Dr Geoffrey Tompkins and Dr Jo-Ann
Stanton. Also deserving of my appreciation is Mrs Jenine
Upritchard who is the hub of the Molecular Microbiology Lab in
the Department of Oral Sciences where I am based. I am grateful
to the Foundation for Research, Science and Technology and
the New Zealand Dental Research Foundation for their funding
contributions to this project.
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