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Bite Mark In Forensic Analysis

What Is Bite Mark?       

Over the past decades, the concept of comparing the mark made by the dentition of an individual in the skin of another individual has been well accepted by forensic odontologists, law enforcement officers, and the jurisdiction system. Indeed, there is a rapidly growing body of case study and research material, which have proper documentation on the validity of bite mark comparisons. Nevertheless, these cases probably represent a very small percentage of the total number in which this type of evidence exists but is not recognised by the investigating officer or pathologists.

A bite mark is a circular or oval (doughnut or ring-shaped) patterned injury consisting of two opposing (facing) symmetrical, U-shaped arches separated at their bases by open spaces. Following the periphery of the arches are a series of individual abrasions, contusions or lacerations reflecting the size, shape, arrangement, and distribution of the class characteristics of the contacting surfaces of the human dentition.


Figure 1. Human bite marks in a victim of homicide. A scale is used to measure the size of the bite mark.

Any circular or semicircular or short linear mark with indentation should be considered as a possible bite mark. Marks caused by various implements may mimic a bite mark. Interpretation and presentation of a bite mark is as follows:

  1. Resistance and elasticity of the tissue.
  2. The degree of curvature of the body surface.
  3. Lapse of time.

 Bite marks may be made in variety of ways. They are :

  1. Direct tooth pressure.
  2. Skin pressed against the teeth by the tongue which may produce an outline of the palatal surfaces of the upper incisors and canines.
  3. Scrapping teeth over the skin as may occur when the victim is struggling violently – this produces a series of parallel marks or wounds and is often associated with bites on the nipple.

Types Of Bite Mark      

In the content of bite mark analysis, teeth are essentially a tool which exhibit unique and often highly individual characteristics. Teeth or tooth marks are basically tool marks which represent the impressions or indentations striations or other markings left by a harder material in a softer substance.

Aggressive Type:

The teeth are used as a weapon and there is no suck mark where the bite is said to be forceful and rapid.

Sexual Type:

Sexually oriented bite marks are often sadistic and typically appear to have been inflicted slowly and deliberately with suction applied to the tissue. The teeth are used to grip during sucking. The resultant injury exhibits central and/or peripheral suck marks and linear abrasions, which produced the characteristics of reddening, caused by the incisal angles of anterior teeth with good definition of both the gross and individual characteristics of the teeth. The amount of distortion allows an opinion as to whether the person being bitten was active or passive when the bite was being inflicted.

Child Abuse Cases:

Bite marks most nearly resembling tool marks are seen in child abuse victims and represent the manifestations of primal rage by the attacker against the victim. Both types of bite marks have been documented in the child victims of single assaults by other children as young as two years old. While these cases probably represent sadistic behaviour and/or primal age, the entire question of the mental state component of the bite mark requires further study.

Human                       

Ovoid or elliptical pattern. Canine areas are not unduly pronounced, with indentations broader and more blunt in appearance than dogs, cats and rodents. Petechiae caused by sucking are only seen in human bite marks.

Animal

Animal teeth tend to puncture deeply and tear the tissue whereas human bites are blunt and more superficial and caused abrasion rather than tearing. Animal bites are marks made by non-human vertebrates possessing teeth, most mammals, reptiles (crocodiles and alligators) and some fish (sharks and rays).

Dogs: Narrow squarish arch anteriorly, prominent pointed marks produced by canines.

Cats: Small rounded arch with puncture marks made by canines. The bite is often associated with scratch from claws.

Rodents: Small bites with long grooves caused by the central incisors.

Insect

Insects are armed with fangs with which they can deliver a bite or sting that may leave their predators numb for some time. Although some bites are harmless, there are other insects that have high level of toxin in their sting. The most common reaction to an insect bite is swelling, causing pain and itching. However, some insect bites and stings can lead to an allergic reaction that might be potentially life-threatening. Identifying them, more so if the insect was a venomous one.

Postmortem / Antemortem      

Flesh is elastic and stretches when it is bitten. A bite mark on a body, therefore, is somewhat different from a bite mark on an inanimate surface. A forensic pathologist will note a bruising pattern in the shape of two curved lines facing one another if the bite has been inflicted before death (antemortem). Bites inflicted on muscular tissue make a more distinct pattern than bites found on fatty tissue. Postmortem (after death) bites do not produce bruising. Particularly ferocious bites will produce lacerations.

How Bite Mark Functions As An Important Evidence In Forensic Investigation?       

When dealing with bite mark evidence, there are four basic questions which the forensic scientist attempt to answer:

  1. Is this injury a human bite?
  2. Can this bite mark be individualized with reasonable dental certainty?
  3. Can this bite mark be connected with the time frame of the crime?
  4. Is the bite mark consistent with the type of crime?

An essential component of the determination of the validity of bite mark analysis is that the techniques used in physical comparison between the suspect dentition and physical injury have been assessed and found valid.

The successful evaluation of bite mark evidence depends upon :

  1. Recognition that a lesion is a human bite mark, and
  2. Preservation of the evidence in a form suitable for analysis.

Techniques Of Bite Mark Analysis       

The analysis of a bite mark begins with photographing the evidence in both black and white and in color, and from several angles. It is important to take these photographs within eight hours of the injury being inflicted in the case of a victim. Inflammation tends to blur the pattern after this time if the victim is alive. If the mark is deep enough, then a cast can be made using dental processes similar to those used for making a tooth crown or a bridge in dental procedure.

The next step is to make an image that can be overlaid on the bite mark of a suspect for comparison. The image can be made by manual tracing or by scanning into a computer and using a program that makes a picture on a transparent overlay sheet.

Swabbing of the bite injury is important to recover trace evidence and may be able to obtain the DNA profile of the assailant. Stains of saliva or human cells for a DNA analysis should be collected whenever possible.

Comparison And Identification Of Bite Mark    

A review of published literature on bite marks underscores the significance in specimen examination and evaluation with any obtained templates or known impressions relative to:

  1. The relationship of the jaws.
  2. The form and size and arches.
  3. Missing teeth.
  4. Spacing between teeth.
  5. Presence of supernumery teeth.
  6. Observed rotations of teeth.
  7. The width of teeth.
  8. Presence of special features such as fractures and ridges.

The characteristics of human bites are superficial abrasion and/or sub-surface haemorrhage looking like an arch. They are caused by the incisors, canine and premolars. The abrasions and/or haemorrhage caused by the canine are in a shape of points. If the perpetrator has dentures, additional specific marks can be expected. They differ between bridges, crowns and dentures. Crowns and bridges may have a ceramic surface and partial dentures braces to fix at the teeth. These peculiarities can be responsible for specific wounds and contribute for additional markers for identification.

Conclusion     

The evaluation of bite mark evidence is subjective and based upon the education, training and experience of the examiner. There are basically three possible conclusions:

  1. With reasonable dental certainty the bite mark in the tissue and the exemplar have been left by the same teeth. (This is a high degree of probability that the two bite marks have common origin).
  2. The bite mark in the tissue and the exemplar are consistent. (This is a middle ground conclusion, which means the two bite marks could have a common origin. Because a single discrepancy would exclude the suspect, this is still a meaningful conclusion).
  3. The bite mark in the tissue and the exemplar are not consistent. (This two bite marks do not have common origin).

References      

  1. Brennan, J.C.  2004. Forensic Science: An Illustrated Dictionary. CRC Press. Boca Raton.
  2. Cattone, J.A., Standish, S.M. Outline of Forensic Dentistry. Year Book Medical Publishing. 1982.
  3. Lessig, R., Wenzel, V., Weber, M. Bite mark analysis in forensic routine case work. EXCLI Journal 2006;5:93-102.

Last Reviewed : 19 May 2015
Writer : Salina bt. Hisham
Accreditor : Khoo Lay See