The prototypical human bite is generally an ovoid or circular bruise pattern that consists of two opposing U-shaped arches separated at their bases by open space (Fig. 26-1). Frequently there is a central area of ecchymosis or contusion between the opposing arches (Fig. 26-2). In many bite marks, individual tooth patterns or the dental signaturedental signature left by the anterior teeth can be seen. If the injury meets these criteria, chances are excellent that it is, in fact, a bite mark. Many factors affect bite mark dynamics and appearance, with both the victim and the biter. Age and race of the victim play an important role in the variation of wound healing and visibility of bites (Wilkes, 1973). The location of the bite will affect its manifestation. Bite marks can be distorted due to the biomechanical properties of skin and underlying tissue (Bush, 2009). Bites on unsupported tissue such as the breast usually are more diffused than bites on tissue that is well supported by muscle or bone. Thin skin such as one finds on the face will generally produce more classic characteristics and individualizing characteristics of the biter’s teeth than the thick skin found on the palms and soles of feet. The actual size of the bite mark will vary with the type of tissue and area where sustained. Unsupported tissue typically produces larger-than-life–sized bite marks. Thin, supported tissue generally produces bite marks smaller in size than the actual dentition that created it.

Factors linked with the perpetrator include the number of teeth, the strength of the biter, and movement during the act of biting. Bites made through clothing sometimes may result in a diffused bruise pattern. Additional variables to consider are time elapsed before the bite is documented and environmental factors such as temperature, humidity, and contamination.

It must be said at this point that there are other blunt force injuries from a variety of instruments that can mimic the appearance of a bite mark; however, this chapter only shows examples of known bites. Ultimately the final determination should be made using the assistance of a qualified forensic odontologist.

Dog bites vary in degree of severity and can be more oblong and even V-shaped. In their least aggressive form, they can appear as a superficial bruise (Fig. 26-3). Similarly, human bites seen and analyzed are often limited to damage of the surface epithelium, dermis, and muscle tissue; or they can appear to be only superficial or predominantly contusions and abrasions. In contrast, the more severe dog bites typically involve punctures and laceration of the skin. Figure 26-4 shows an adult male who was fatally attacked by eight pit bull terriers. Even though there were numerous punctures and lacerations noted at autopsy, the cause of death was asphyxiation, not exsanguination.

The most noticeable difference between animal and human bites occurs as a result of the canine teeth. An examination of canine teeth in most domestic animals reveals that they are proportionally much longer, relative to the other anterior teeth, than are human canines to their adjacent anterior teeth. Figure 26-5 demonstrates the obvious size difference between the canines and anterior incisors in domestic dogs. Similar conditions exist in cougars, bears, and many other animals known to have bitten people. As the longest teeth, the canines create the most damage to the bitten victim. Animal canines typically produce telltale punctures and parallel linear abrasions or lacerations caused by movement of these teeth over the surface of the tissue as the bite occurs. Human canines, also typically the longest of the anterior teeth, do not usually inflict the same extent of damage or leave the same pattern as animal canines.

Both animal bites and human bites can take place either as single or multiple injuries. Some lacerations can be fatal, particularly in areas where large vessels are near the surface of the skin, such as in the neck. The crushing power of even a medium-sized dog’s jaws has also been documented to cause multiple fractures in infant skulls and adult bones as well.

Whatever the severity of the bite, in any emergency department setting, concern for the patient is most important and preempts collection of the bite mark evidence. Only after the victim is stabilized and out of danger is attention to be directed to collecting evidence from the bite mark injury.

For a bite mark to be recognized as a bite, the injury should first meet the criteria previously mentioned that establish its validity as a bite pattern injury. Occasionally only a single arch is represented, such as in the case of a bite to a finger, hand, or foot (Fig. 26-6). If a nurse examiner is unsure whether or not an injury is in fact a bite mark, the assistance of a qualified forensic odontologist should be requested.

Within the classic bite pattern are individual “tooth prints” generally created by the incisal or cutting edges of the six upper and six lower front teeth. Characteristics that may be used to individualize the dental signature to a particular suspect, or rule out others, are most important. Positional relationships of adjacent teeth, rotations, chips and fractures, spacing, and relative height in the dental plane of occlusion are all features that assist the forensic odontologist in the analysis of the bite mark. Some terms generally used to describe the extent of a bite mark injury are petechial hemorrhage, abrasion, contusion, erythema, ecchymosis, indentation, and laceration.

A comparison of a suspect’s teeth to the dental signature left on the skin of the victim can be accomplished by a variety of methods. For several decades, the accepted protocol has included using transparent acetate overlays that indicate the biting edges of the six maxillary and six mandibular anterior teeth (Fig. 26-10). A 1-to-1 (life-sized) photographic print is then created from either a slide, negative, or digital image. The overlay created from the biting edges of the suspect’s teeth is then compared to the pattern injury for consistent features or concordant points (Fig. 26-11). Some odontologists prefer to work at even larger magnifications such as 2-to-1 or even a 3-to-1 for better visualization.