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Brazilian Journal of Oral Sciences
Piracicaba Dental School - UNICAMP
EISSN: 1677-3225
Vol. 5, Num. 19, 2006, pp. 1193-1197
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Brazilian Journal of Oral Sciences, Vol. 5, No. 19, October-December 2006, pp. 1193-1197
Human bite mark identification
and dna technology in forensic dentistry
Ricardo Henrique Alves
Silva1*,Jamilly de Oliveira Musse2*, Rodolfo Francisco H. Melani3*, Rogério Nogueira Oliveira4*
1DDS, MSc, PhD's Degree Student
(FOUSP)- Professor in Forensic Dentistry and Legal Medicine (UNIP)
2DDS, Master's Degree Student
3DDS, MSc, PhD - Social Dentistry Department
4DDS, MSc, PhD - Social Dentistry Department
*Dental School São Paulo University (FOUSP)
Correspondence to: Ricardo Henrique Alves da Silva Rua Minas Gerais, 12-67, Parque Paulistano, CEP: 17030-511 - Bauru SP - Brazil, E-mail: ricardohenrique@usp.br
Received for publication: September 14, 2006
Accepted: December 15, 2006
Code Number: os06034
Abstract
A significant field of study and analysis in Forensic
Dentistry is the recognition and interpretation of marks and
injuries produced for human bites in foods founded in crime scenes
or in the human skin. In this way, the knowledge of the
anatomical particularities of human dentition and distribution in the
dental arcs can supply subsidies of real value to forensic
scientist, sometimes, the only elements on which can count the
expert. Particularly, in bite marks found in the skin, generally
resultant of rapes, fights, assaults, abuses and child violence,
this evidence can mean the crime resolution, assuming a
decisive role in the criminal identification. In this direction, the
DNA technology can be used in the recovery of the genetic
material, through the saliva deposited in the skin, after the production
of a bite mark, due to the fact that dental impression can
be adulterated easily and showing problems on expert
analysis. This literature review aimed to stand out the importance of
the recognition of these injuries in practical skillful of the
dentist, being emphasized the use of the DNA technology in the
briefing of crimes.
Key Words: bite marks, DNA, saliva
Introduction
Historically, the dental professional was organize as
time passed by. It was first executed by healer and doctors
and then it was relegated to charlatans, until it found
a professional segment that would dedicate to
it1.
The emersion of Forensic Dentistry, as a discipline, in
Brazil, just happened in curriculum edition established by
Decree nº 19.852, edited in 19312:
"1st Year anatomy, physiology, histology and
microbiology, metallurgy and applied chemistry.
2nd Year dental practice
(1st chair), hygiene and forensic dentistry, dental prosthesis, dental technique.
3rd Year dental practice
(2nd chair), pathology, applied therapeutics, buco-facial prosthesis, orthodontics
and pediatric dentistry."
Since, this Dentistry' specialty has been in
continuous development and it has shown, lately, a
remarkable professional and scientific maturity.
By the time, oral conditions analysis has been presented
as a crucial tool to the forensic investigation team
members when solving identification problems and it has been
helpful to Criminal and Civil
Justice3.
One of the possibilities in Forensic Dentistry field is
related to the human identification process, such as in cases
which involve the study of bite marks. Bite can be defined as
the mark made by human or animal teeth in the skin of
alive people, cadavers or unanimated objects with
relatively softened consistence4.
Besides the agent identification, bite mark analysis, in
a forensic investigation, can elucidate the kind of
violence and the elapsed time between its production and
the examination. It can show if the bite was produced intra-vitam or post-mortem and, in case of several bite
marks, identify the sequence of them4.
Therefore, by observing, analyzing and interpreting, the
bite marks constitute a important medical-judiciary proof in
some cases of offense and help in suspects' exclusion or point
out the culpability elements5.
However, bite marks do not embody all the requisites of
an ideal identification method (unicity,
immutability, practicability, classificability), but it can represent, in
some cases, the unique signs of real value to criminal
investigation6.
Fulfilling these requisites, we can state that the
immutability characteristic is not much preserved in bite marks,
especially when acting on human skin. Moreover, the practicability
may not be so easily verified because of involved
technical knowledge.
And, when referring to human identification, nowadays,
there are three kinds of identification using oral characters.
Two of them have been used a long time ago and behave
as primary responsibilities of the expert. The first one
is denominated comparative dental identification and
involves a comparison between intra-vitam and post-mortem registers (x-ray, clinical promptuary). The second one, which
is composed by the reconstruction of
post-mortem dental profile, is used in the cases in which there is no suspicion
of the person or his/her descendents. The third kind works
on the application of the modern techniques of DNA, in
order to establish the identity7.
In this analysis, some obstacles are always present
when working with human bite marks, which leads to a
discussion on the analysis precision and the violation of citizen's
rights (proofs against yourself)8.
Therefore, the present work intends to display
some applications of DNA technology in human identification
by studying the bite marks in Forensic Dentistry.
Bite mark production mechanism
The bite mark mechanism is the result of teeth pressure
on skin, described as force combination. It starts with
mandibular closure, followed by suction of skin (as a negative
pressure) and action, in the opposite direction, thrusted by the
tongue; hence, we would have its projection on teeth incisor
and lingual surfaces9.
In general, when a person bites an object, the superior
teeth hold the object while the inferior ones cut it. The mark left
by the superior teeth, however, is extremely relevant in order
to provide information such as: dental alignment, size and
shape of dental archs10.
Bite mark is, in general, circular or ovoid, and can have
an appearance similar to sweet dough, like a doughnut or
the dental arch may be registered as horseshoe shape
patches11. Moreover, human adult dentition consists of 32 teeth
and each one of them has its own size, shape and features.
Human dentition is unique and individual due to extractions,
bad alignment, bad positioning, bad development, spaces,
dental fractures, restorations and other numerous
factors10.
The series of characteristics goes from benign
wastage, observed just after the injury, up to a picture of
infection observed days or weeks later. The signs and
symptoms include laceration, erythema, lymphadenopathy, fever,
pain and purulent collection12.
Therefore, the action of the dental arch on the skin
may produce many kinds of lesions, as the dental elements act
as incisive instruments or even
incisive-cut13.
The evidence of a bite mark is usually crucial to
establish that two subjects have been involved in a violent contact
in a crime scene14.
The greatest challenge is Forensic Dentistry are bite
marks found in human skin, because of the distortion
presented and the time elapsed between the production and
the analysis15.
Moreover, many factors can affect the structure of the
lesions produced by bite marks, which include: applied force,
bite duration and movement between tissues and
teeth3. However, our main focus in this paper is the possibility of DNA recovery through saliva deposited on skin after a bite mark or
from object surface7,16.
Using DNA in bite mark
identification
Techniques involving DNA in Forensic Dentistry offers
a new tool when traditional identification methods fail due
to the effects of heat, traumatism or autolytic
processes17, as well as in distortions and difficulties in analysis.
There are many biological materials that can be used
to execute DNA typing, being the most common blood,
semen, bones, teeth, hair and saliva18.
The field of human genetics was revolutionized when
Watson and Crick described the DNA structure as a double helix
in 1953.The acknowledgement of the genetic code
universality in alive organisms has been essential to the
development and application of the genetic
technology19.
Thus, with the molecular biology advance, the DNA
analysis in forensic samples has been increasingly used in
human identification processes20.
Due to this abundance of material, the use of the
technique based on PCR (Polymerase Chain Reaction) has
acquired great importance in DNA post-mortem analysis in forensic cases.
Polymerase Chain Reaction is an enzimatic amplification of
a specific DNA sequence, aiming millions of copies
production from this sequence in a test tube, which was first
described by Kary Mullis, in the late 1980's, and enabling a new
strategy of gene analysis though a simple and fast method,
excusing all the laborious stages of genic
cloning21.
The method using PCR enables the distinction of a
subject among the other ones with a high level of reliability,
starting by 1ng (nanogram), equivalent to a single part in a
billion grams, of the DNA target16,22.
When treating of forensic samples, the DNA study is
usually done through the analysis of regions of short tandem
repeats (STR), which can be defined as DNA hypervariable
regions that present tandem repeats of fragment that have from
two until nine pairs of bases (pb)23.
The most valuable STR's to human identification present
a higher polimorfism (larger alleles amount), smaller size,
greater heteozygosity frequency (higher than 90%) and low
mutation frequency23.
In order to perform human identification, it is more
interesting to use the molecular markers that have great variability
within the population. In other words, high level of
polimorfism, enabling that the probability of two people that present
the same alleles gets smaller.
And, when we wish to identify a subject that comes from
a certain population, the study of different markers in
that population is necessary, in order to know what the
present alleles are and how often they appear, with the purpose
of defining the best markers to be used.
Besides the genomic DNA, inside the cell nucleus, it is possible to use mitochondrial DNA. This organela has
a number that ranges from 100 to 10,000 copies per cell,
enabling the material analysis with limited amounts and also
DNA samples partially degraded24.
Saliva is a very useful DNA source due to the fact of
being collected by painless and non-evasive way, able to be
used even when it is stored in the most different
conditions25. Its composition is 99% of water, has leukocytes (25 to
650,000) and scaled off epithelial cells (6 to
600,000)26.
The amount of saliva deposited on the skin is generally
very little in bite mark cases, making it necessary to use
methods for collecting, whose result in the recovery is the
maximum possible amount of saliva and minimizes any
contamination through the victim's skin
cells22,27-28.
When checking the DNA analysis reproducibility of
collected saliva on the skin, simulating cases that involve bite
marks in 20 samples, the double swab technique showed to
be sensitive and efficient in criminal cases when there
is presence of saliva in bite marks29.
There are studies where 40
ìl of saliva were deposited on the skin of 27 corpses and
100ìl of saliva on the skin of five corpses, making the DNA analysis of all samples
possible16. Studies compared the DNA extraction results in
saliva samples deposited on human skin in a simulation of
bite marks from three different techniques (Organic, Classic
Chelex and Modified Chelex), being the last one more efficient
than the others, but all of them with possibilities of
application27.Comparing saliva collection methods, there is
significant difference between the DNA recovering capacity in
three different techniques: filter paper (17, 4%), the single
swab technique (35,3%) and the double swab technique
(44,6%)22. In another research using bite marks simulated situations
in two experimental series, deposited three samples of
saliva (40 ìl) on the skin of 27 corpses (in 33 different places) and three samples of saliva
(100ìl) on the skin of five corpses (in 12 different places). Saliva was collected using the
double swab technique in times of five
minutes, 24 hours and 48 hours, having proven a decrease in concentration in
the first 24 hours and stability between 24 and 48 hours,
showing successfulness in amplification independent of the time
after the deposit saliva, and absence of any case
of contamination22.
Saliva, in contact with intact skin, maintains itself in
stable conditions and can be recovered, at least, 60 hours after
its deposit30.
In another study, using the DNA analysis by PCR in a
bite mark located in a body that had been submerged in a
river for a 5,5 hour before being found, enough DNA
was recovered from the bitten area, what enabled a genotypical
contribution to identify the
aggressor14.
However, it is not always possible to recover DNA from
a bite mark, due to the fact that it will be subject to a series
of modifications, such as contamination, degradation and putrefaction, depending on the circumstances the body
and/or object were submitted27.
Bite Mark identification: DNA analysis and
genotypical composition of oral bacteria.
The human oral cavity has a large and varied
bacterial community, many of which are unique for this habitat.
There is wide evidence that oral bacteria are transferred during
the human bite act and, in some cases, survive and
multiply, creating infections. Besides, there are evidences
that individuals shelter unique bacterial species stocks in
the oral cavity and that those stocks can be identified
by techniques such bacterial typing and protein
profiles31.
It is important to note that the oral Streptococcus recovery from the skin or objects seems to imply the contact with
oral surfaces or deposit saliva which can lead to evidences
of buccal-envolvement in the injury32.
In a study where 10ìl fresh saliva sample was collected
without stimulation and applied to areas of the upper left quadrant
of the thorax, so that the loss rate of units that make up
the colony and its recovery ranged from 45 to 50% per
hour. They have also noticed that 6, 25 hours after the
saliva deposition, oral viable streptococcus could be
recovered33. In anoher research, volunteers bit their own arms firmly
and the bite marks were sampled in time intervals to
recover isolated viable streptococcus, in order to make a
genotypical comparison with bacteria from the oral cavity. It
was concluded that it is possible to recover bacteria up to
24 hours after the production of the bite, but
identification assertiveness is only possible when compared to
samples acquired from the subjects' teeth responsible for the
bite32. Isolated Streptococcus from recent bite marks can be
listed by PCR and compared to the teeth that were responsible
for the bite. Moreover, they claim it is preferable to recover
the subject's DNA, but such strategy is not always
possible, the recovery of the bacteria derived from the subject's
tooth may enable the link with the suspect of a
crime34.
In conclusions, the knowledge proceeding from
Forensic Dentistry and Molecular Biology has great importance
to the expert practice when we think of a dentist inserted
in forensic investigation team in a bite mark case. It's
necessary to broaden the pertinent studies of the theme, in order
to establish protocols to allow additional tools in
criminal investigation.
It is stated that, in judicial proceedings involving
Dentistry, being Civil or Criminal, it is extremely necessary the
presence of a professional that militates in Forensic Dentistry as
a judicial expert35.
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