Bitemark Analysis and Comparison

After the evidence is collected from a patterned injury, a process is available to assist in the analytical and procedural steps. The Bitemark Evidence Flow Chart provides a pathway to direct the patterned injury investigator through a structured series of decisions that help avoid unsupported methods and/or opinions (Figure 4). Using scientific methodology, the examination of bitemark evidence can be divided into four basic steps:

  1. Examine the pattern to determine if it is a bitemark.
  2. If the pattern is a bitemark, determine its evidentiary value.
  3. If there is high evidentiary value, examine the suspect dentitions.
  4. If the suspect dentitions are unique to each other, a comparison may be possible, after which an opinion may be reached.
Figure 4. Bitemark Evidence Flow Chart.
Used with permission from Dr. Robert Wood.

The first step, the analysis phase, tests the injury against the known definition of what characteristics represent a bitemark. The investigator then compares the patterned injury to that definition. While certainly subjective, applying a restrictive definition can guide the forensic odontologist in the right direction. The definition for establishing a patterned injury as a bitemark which offers the most complete description follows:

Human Bitemark – human teeth created the pattern.

Criteria: The pattern demonstrates class characteristics of human teeth. A circular, or oval or curvilinear pattern or patterned injury consisting of two opposing arches, often, but not always, separated at their bases by space. Individual marks, abrasions, contusions, or lacerations may be found near the periphery of each arch. The marks present should reflect the size, shape, arrangement, and distribution of the contacting surfaces of human teeth. Either the maxillary or mandibular arch, or both arches, can be identified and the midline of each arch should be visible or determinable. Some of the marks made by individual teeth can be recognized and identified based on their class characteristics and/or location relative to other features. The size and shape of each arch visible is consistent with the size and shape of the human dentition.4

Below are examples of patterned injuries with the bitemark definition inserted below the caption. The restrictive definition must be employed during the observer’s subjective interpretation while deciding whether or not the injury is a human bitemark. Compare the images to the definition, inserted directly below the image sets, and try to determine if the injury pairs meet the criteria of the definition. (NOTE: Each pair of injuries demonstrated is NOT from the same case nor are they linked to each other in any way.)

EXAMPLE 1
Human Bitemark – human teeth created the pattern.

Criteria: The pattern demonstrates class characteristics of human teeth. A circular, or oval or curvilinear pattern or patterned injury consisting of two opposing arches, often, but not always, separated at their bases by space. Individual marks, abrasions, contusions, or lacerations may be found near the periphery of each arch. The marks present should reflect the size, shape, arrangement, and distribution of the contacting surfaces of human teeth. Either the maxillary or mandibular arch, or both arches, can be identified and the midline of each arch should be visible or determinable. Some of the marks made by individual teeth can be recognized and identified based on their class characteristics and/or location relative to other features. The size and shape of each arch visible is consistent with the size and shape of the human dentition.

Do the two injury patterns above conform to the definition such that they can be described as human bitemarks?

These two injuries do appear to meet the definition of a human bitemark in skin.

EXAMPLE 2
Human Bitemark – human teeth created the pattern.

Criteria: The pattern demonstrates class characteristics of human teeth. A circular, or oval or curvilinear pattern or patterned injury consisting of two opposing arches, often, but not always, separated at their bases by space. Individual marks, abrasions, contusions, or lacerations may be found near the periphery of each arch. The marks present should reflect the size, shape, arrangement, and distribution of the contacting surfaces of human teeth. Either the maxillary or mandibular arch, or both arches, can be identified and the midline of each arch should be visible or determinable. Some of the marks made by individual teeth can be recognized and identified based on their class characteristics and/or location relative to other features. The size and shape of each arch visible is consistent with the size and shape of the human dentition.

Do the two injury patterns above conform to the definition such that they can be described as human bitemarks?

There are some characteristics present in these injuries as required by the definition but they are certainly less clear than those seen in example 1.

EXAMPLE 3
Human Bitemark – human teeth created the pattern.

Criteria: The pattern demonstrates class characteristics of human teeth. A circular, or oval or curvilinear pattern or patterned injury consisting of two opposing arches, often, but not always, separated at their bases by space. Individual marks, abrasions, contusions, or lacerations may be found near the periphery of each arch. The marks present should reflect the size, shape, arrangement, and distribution of the contacting surfaces of human teeth. Either the maxillary or mandibular arch, or both arches, can be identified and the midline of each arch should be visible or determinable. Some of the marks made by individual teeth can be recognized and identified based on their class characteristics and/or location relative to other features. The size and shape of each arch visible is consistent with the size and shape of the human dentition.

Do the two injury patterns above conform to the definition such that they can be described as human bitemarks?

These two cases contain some required characteristics but fall short of meeting the criteria of a bitemark.

EXAMPLE 4
Human Bitemark – human teeth created the pattern.

Criteria: The pattern demonstrates class characteristics of human teeth. A circular, or oval or curvilinear pattern or patterned injury consisting of two opposing arches, often, but not always, separated at their bases by space. Individual marks, abrasions, contusions, or lacerations may be found near the periphery of each arch. The marks present should reflect the size, shape, arrangement, and distribution of the contacting surfaces of human teeth. Either the maxillary or mandibular arch, or both arches, can be identified and the midline of each arch should be visible or determinable. Some of the marks made by individual teeth can be recognized and identified based on their class characteristics and/or location relative to other features. The size and shape of each arch visible is consistent with the size and shape of the human dentition.

Do the two injury patterns above conform to the definition such that they can be described as human bitemarks?

These two injuries lack the required criteria to be termed “human bitemarks.”

Once a patterned injury has reached the threshold to qualify as a human bitemark, the second step is to determine its evidentiary value. The evidentiary value is determined by comparing the descriptors of the bitemark definition to the patterned injury. In reality, the frequency of high quality bitemarks seen in violent crime is somewhat low. However, in the rare instance where a high quality bitemark does exist, it still may not be a case that would go to the comparison stage. The suspect dentitions must also be considered.

Once a patterned injury is determined to be a high quality bitemark, the investigator must then look at the suspect dentitions, which is the third step in the analysis process. The more unique the suspect dentitions are when compared to each other, the greater the potential to differentiate between them and the bitemark (Figure 5). Should more than one suspect dentition have similar teeth in size and arrangement (i.e., orthodontically aligned teeth of similar arch and individual tooth size), it would not be possible to differentiate between those individuals’ dentitions when comparing them to a bitemark. Therefore, per the Bitemark Evidence Flow Chart above, the case would not go to the comparison phase.

Figure 5.
Suspect dentitions in a case with distinctively different dentitions.

Even more rare are those cases where there is a human bitemark of high evidentiary value and the suspect dentitions are uniquely different when compared to each other. In those cases, the forensic odontologist can proceed to the comparison, which is the fourth step. Each suspect dentition is compared to the bitemark and a separate opinion is given for each set of teeth.

The ABFO Bitemark Terminology Guidelines5 define possible results of a bitemark comparison as only three choices:

  • Excluded – the suspect dentition could not have created the injury
  • Not excluded – the suspect dentition or similar dentitions could have created the injury
  • Inconclusive – insufficient information exists to form a conclusion either way

Further, the ABFO Standards state that biter identity is not sanctioned. As previously explained, the distortion that occurs during the act of biting human skin cannot be measured or quantified. Additionally, the lack of statistical databases for the determination of an error rate and the mathematical probability linking a suspect dentition to a bitemark are precisely the reasons the ABFO does not sanction that biter identity can be established. The bitemark evidence must only be used as a part of the total evidence presented in a case. In many bitemark cases, the only questions asked are: (1) is the patterned injury a human bitemark and, if so, (2) is it an adult or child bite? There is no attempt at comparing the bitemark to any suspect dentition. The analysis stops after the first step.

Using the methodology of the Bitemark Evidence Flow Chart, if a determination is made that there is a human bitemark of high evidentiary value AND the suspect dentitions are distinctly unique when compared to each other, a comparison may be possible.

There are several different methods that are used in a comparison step. The overlay method, (see Case 2: Figures 6-7) is the most frequently used comparison technique. The biting edges of the suspect dentition are outlined and transferred to an exemplar. The exemplar is then overlaid onto the bitemark image. Both the exemplar and bitemark image should be of life-sized dimension.

Other comparison techniques include:

  • wax exemplars of suspect dentitions compared to the bitemark
  • direct comparison of dental stone models to nearly life-sized images of the bitemark
  • metric analyses