tooth_mark.jpg
Exact replicas were made to compare to the bite marks found in the investigation.
Bite Mark Identification


Bite mark identification is the means of using a bite mark to identify a suspect or victim in an investigation. Bite marks are normally left on either the victim by the attacker, the perpetrator from the victim of an attack, or on an object found at the crime scene. This is done using dental records including radiographs, ante-mortem which means prior to death and post-mortem photographs and DNA.The identification of bite marks has been instrumental in criminal investigations of homicide, sexual assault, and child abuse cases. Most bite mark cases involve photographs of bite marks on skin or on other substances that are later compared with dental evidence obtained from suspects. This type of comparison makes dimensional accuracy and sizing of the utmost importance. There are different types of bite marks that scientific analysis revealed; A clear impression means that there was significant pressure; an obvious bite signifies medium pressure; and a noticeable impression means that the biter used violent pressure to bite down. The American Board of Forensic Odontology allows digital imaging in bite mark analysis thus creating an easier way in identifying these types bite marks.The identification of bite marks holds such importance because of it's accuracy, no two people have the same dental records therefore allowing for accurate results in crime scene or various other investigations.

A forensic dentist can tell a lot about a person based on their bite mark. If there's a gap in the bite, the biter is probably missing a tooth. Crooked teeth leave crooked impressions, and chipped teeth leave jagged-looking impressions of varying depth and braces and partials in addition leave very distinctive impressions. Once investigators have identified a suspect, they are able to obtain a warrant to take a mold of his or her teeth as well as photos of the mouth. Than they compare transparencies of the mold with those of the bite-mark cast. Also photos of the bite mark and the suspect's teeth are compared to look for similarities.

Ways of Identifying Bite Marks:

Digital Photography: For the photographic reproduction of crime scene evidence forensic protocols demand that a linear scale be placed next to the evidence sample to
shoulderali.jpg
Investigators would measure bite marks to compare once they collected substantial evidence.
make an accurate comparison. This dimensional reference allows the photographic examiner to re-create life-sized graphical reproductions. Photographic distortion is shown by the scale's incremental lines appearing nonparallel and not uniformly shaped. Without rectification, the photographed evidence will not be representative of its true shape and dimension therefore non-helpful in the investigation. The photographic laboratory technician normally has the job of the correction of photographic distortion.


Johansen and Bowers and Sweet and Bowers tested and used the digital imaging program Adobe Photoshop for it's ability to evaluate photographic evidence and comparative analysis. The program was used to correct for certain types of distortion created from misplacement of the linear reference scale and off-angle placement of the camera. This type of analysis used the digital editing program Adobe Photoshop 5.5, a desktop computer, and a flatbed scanner to identify bite marks. Photoshop is a commercially available digital imaging program that aids heavily in this type of investigation. The original evidence photograph was scanned at on a flatbed scanner and then imported into the Adobe Photoshop program. After it was imported into Photoshop, the original image was than adjusted for contrast, rotated to orient the horizontal leg of the scale along the computer screen's x-axis, and later cropped. Lastly, the bite mark is rectified to demonstrate it's actual form and than resized to life size.

While Digital Photography of bite marks is one of the most documented ways of identification, other ways include:
-Comparing a model of a suspect’s teeth to a life-size photograph of the actual bite mark.
-The “fingerprint powder lift” technique which involves dusting the bitten skin with black fingerprint powder and using fingerprint tape to transfer the bite marks onto a sheet of acetate.
-The use of transparent overlays to record a suspect’s biting edges.
-The 2D polyline method includes drawing straight lines between two fixed points in the arch and between incisal edges to indicate the tooth width.
-The painting method entails coating the incisal edges of a dental model with red glossy paint and then photographing the model.
-Simulation of the bite using porcine skin (pigskin) due to it's comparability to human skin and it is considered unethical to bite a human for study in the United States.

Forensic dentists use different terms to describe the types of bite marks:
  • Abrasion - a scrape on the skin
  • Artifact - when a piece of the body, such as an ear lobe, is removed through biting
    BiteMark2.jpg
    Example of the moldings investigators would make for a case involving a bite mark.
  • Avulsion - a bite resulting in the removal of skin
  • Contusion - a bruise
  • Hemorrhage - a profusely bleeding bite
  • Incision - a clean, neat wound
  • Laceration - a puncture wound

How Bite Marks are Recognized

  • Differences in size and shape of teeth for instance when someone has teeth missing or very prominent teeth.
  • A representative human bite mark is described as an elliptical or circular injury that records the specific characteristics of the teeth.
  • The sizes, shapes and pattern of the biting edges of the anterior teeth that are arranged in the upper and lower dental arcades are reported to be specific to that individual.
  • Bite marks with high evidentiary value that can be used in comparisons with the suspects' teeth will include marks from specific teeth that accurately record distinct traits.
  • Class characteristics.


Timeline:

About 1870: Using bite mark evidence began.
1954: Bite mark analysis has been judicially accepted in the United States.
1954: The first published account involving a conviction based on bite marks as evidence was in the case of Doyle vs. State, which occurred in Texas.
1984: The ABFO began making an attempt to diminish the discrepancies and increase the validity of bite mark analysis by creating bite mark methodology guidelines.
F2.small.gif
By using moldings, investigators would compare them to the bite marks found in victims.

Cases:
The first published account involving a conviction based on bite marks as evidence was in the case of Doyle vs. State which occurred in Texas in 1954. The bite mark in this case was on a piece of cheese found at the crime scene of a burglary. The defendant was later asked to bite another piece of cheese for comparison to the one found at the crime scene of the burglary. A firearms examiner and a dentist evaluated the bite marks independently and both professionals concluded that the marks were made by the same set of teeth and therefore the defendant. The conviction in this case set the stage for bite marks found on objects and skin to be used as evidence in future cases.

People vs. Marx occurred in California in 1975. A woman was sexually assaulted and later murdered by strangulation. Although she was bitten several times on her nose. Walter Marx was identified as a suspect and dental impressions were made of his teeth. Impressions and photographs were also taken of the victim's bitten nose. These samples along with other models and casts were evaluated using a variety of techniques, including two-dimensional and three-dimensional comparisons, and acetate overlays. Many experts testified that the bite marks on the woman’s nose were made by Marx and he was later convicted of voluntary manslaughter.

Sources-

Johansen, R. J. and Bowers, C. M. Digital Analysis of Bite Mark Evidence. Forensic Imaging Services, Santa Barbara, California, 2000.

Sweet, D. and Bowers, C. M. Accuracy of bite mark overlays: A comparison of five common methods to produce exemplars from a suspect's dentition, Journal of Forensic Sciences (1998) 43(2):362–367.

Johansen, Raymond J. "Digital Rectification and Resizing Correction of Photographic Bite Mark Evidence." F.B.I. FBI, July 2001. Web. 10 May 2011. <http://www.fbi.gov/about-us/lab/forensic-science-communications/fsc/july2001/bowers.htm>.

Al-Talabani N, Al-Moussawy, ND, Baker FA, Mohammed HA. (2006). Digital analysis of experimental human bitemarks: application of two new methods. Journal of Forensic Science, 51(6), 1372-75.