The first step in analysis of a bite mark is to determine whether the injury is a bite mark. If it is then it must be determined whether the injury was caused by human teeth (Lane, 1992). Some of the things an investigator might look for are the presence of suction marks (unique to humans) and marks from the front incisors, canines and premolars but not the molars (Lane, 1992).
Second, the investigator should determine whether the bite marks are consistent with the time of the crime. For example, bite marks which have begun to heal are not consistent with a crime which occurred only a few hours before the examination. These wounds may not be related to the crime under investigation.
Finally, the investigator must determine whether the bite marks are of the quality which would be useful for comparison purposes. If it is determined that the marks are human in origin and related to the crime then processing of the marks came begin. At this point dental casts can be made. Casts can be made of the wounds and/or a suspect’s teeth.
If the injuries in the form of bite marks are recent they should be swabbed for DNA from saliva left in the wound (Innes, 2002). The wound(s) should be photographed using digital imaging equipment such as a digital camera (Bowers, 2004).
Forensic Odontologists most often receive evidence in the form of a photographs or images stored on computer disc. The use of digital photography allows the odontologist to reduce the margin of error found with traditional analysis of photographs (Bowers, 2004).
The following is from Dr. C.M. Bowers website found at www.forensic.to/webhome/bitemarks/.
The advantages of using digital photography in imaging software are:
“Digital images provide accurate means of measuring (the) physical parameters of crime scene evidence. The use of digital images and software allow for the correction of common photographic distortion and size discrepancies. Digital images and software help eliminate examiner subjectivity. Digital images when used with software such as Photoshop allow for better control of the image visualization through the use of features such as zoom. When digital photography is used in combination with digital imaging software the procedures used to compare bite marks are standardized leading to the reproducibility of the results between examiners. Finally, images can be electronically stored and transferred as needed (Bowers, 2004).”
To compare dental profiles like the one described in the Ted Bundy case Dr. Bowers recommends the use of the software program Adobe Photoshop. This program can be used to create transparent overlays which can be laid over the bite marks. (See www.forensic.to/webhome/bitemarks/ for more detail on this subject.)
Bite marks which are examined a significant time after they occurred can be examined using alternative photographic methods. Photographic film and lenses which pick up ultraviolet light can be used to make images of the tips of the penetrated area (Gengre, 2002). Photographic film which is sensitive to infrared light can “see through skin” showing damage to the underlying tissue. Both if these types of photography are difficult to use in the field because they require very specific handling and the use of specialized lenses (Lane, 1992) (Gengre, 2002)
Sometimes the bite mark is on a corpse. In this case where decomposition is already in progress the Dorian method can be useful in showing the underlying damage. The Dorian method is to incise the bite mark (Gengre, 2002)
Bite mark analysis can be used with impressions made in foodstuffs and other materials which show the form, shape and size of teeth. In 1984 a man named Aurther Hutchinson was convicted of murder, rape and aggravated burglary. He was convicted on several pieces of class evidence such as blood stains and shoe prints. His dental impression left in a piece of cheese put him at the scene of the crime (Innes, 2000).
Percy Michaels, a forensic odontologist was able to determine the source of a bite mark even though the two subjects were identical twins. Two female twins and a male had engaged in consensual rough sex several months before Dr. Michaels became involved. During the encounter one of the twins bit the male on the buttock. Some time later one of the sisters developed HIV. The male also later tested positive. Dr. Michaels needed to determine which twin bit the man. Was it the HIV positive sister? If so she may have committed a crime in that she bit the man knowing she was positive for HIV. If the other sister, who was not positive for the virus, was the creator of the bite mark then the man may have contracted the disease from another source (Genge, 2002).
Dr. Michael’s used film sensitive to ultra violet light to photograph the bite mark (ultraviolet light is at the far end of the blue spectrum of light and can show underlying tissue damage even months later (Saferstein, 2004). Dr. Michaels then compared the image to detailed X-rays of each of the twin’s dentition.
Even though they where identical twins seven points of difference were found by Dr. Michaels. From this it was determined that the HIV positive sister could not have bitten the man (Genge, 2002).