Forensic DentistryForensic Dentistry• We will focus on a specific element of forensic

dentistry – specifically, bitemark analysis– Here, a dentist is required to compare the

impressions and bruises left in the skin by one person biting another to a suspect’s teeth.

• However, another important element of forensic dentistry involves the identification of human remains by comparing dental charts to the teeth of the victim– This latter component of forensic dentistry has only

been around for about 50 or so years. Why?

WHAT IS A BITEMARK?WHAT IS A BITEMARK?• Bitemark:

– A physical alteration in a medium caused by the contact of teeth.

– A representative pattern left in an object or tissue by the dental structures of an animal or human.

• Cutaneous Human Bitemark:– An injury in skin caused by contacting

teeth (with or without the lips or tongue) which shows the representational pattern of the oral structures.

WHY ARE BITEMARKS USEFUL?WHY ARE BITEMARKS USEFUL?• We can use bitemarks to carry out

bitemark analysis. i.e. a comparison of a known person’s dentition to a patterned injury which appears consistent with a bitemark

• This type of comparison is used to confirm or eliminate the identity of a suspect in relation to the bitemark.

A Crash Course in DentistryA Crash Course in Dentistry1. 3rd Molar (wisdom tooth) 2. 2nd Molar (12-yr molar) 3. 1st Molar (6-yr molar) 4. 2nd Bicuspid (2nd premolar) 5. 1st Bicuspid (1st premolar) 6. Cuspid (canine/eye tooth) 7. Lateral incisor 8. Central incisor 9. Central incisor 10. Lateral incisor 11. Cuspid (canine/eye tooth) 12. 1st Bicuspid (1st premolar) 13. 2nd Bicuspid (2nd premolar) 14. 1st Molar (6-yr molar) 15. 2nd Molar (12-yr molar) 16. 3rd Molar (wisdom tooth) 17. 3rd Molar (wisdom tooth) 18. 2nd Molar (12-yr molar) 19. 1st Molar (6-yr molar) 20. 2nd Bicuspid (2nd premolar) 21. 1st Bicuspid (1st premolar) 22. Cuspid (canine/eye tooth) 23. Lateral incisor 24. Central incisor 25. Central incisor 26. Lateral incisor 27. Cuspid (canine/eye tooth) 28. 1st Bicuspid (1st premolar) 29. 2nd Bicuspid (2nd premolar) 30. 1st Molar (6-yr molar) 31. 2nd Molar (12-yr molar) 32. 3rd Molar (wisdom tooth)

Please note: When you look at the tooth chart, you are looking into a person's mouth with the jaws open. You're facing the person, so their upper right jaw will be on the left of this image.

Bitemark AnalysisBitemark Analysis

• In a bitemark comparison, you are looking for and matching unique features between the bitemark and exemplar castings. These features may include:– Gaps– Rotation (angle)– Size of teeth (e.g. width at tip)– Width from tooth to tooth (e.g. cuspid to

cuspid)

Evidential Value of BitemarksEvidential Value of Bitemarks• By establishing the uniqueness of the biter's teeth and

then applying those unique properties to the bite pattern, a degree of confidence relating the biter's teeth to the injury pattern is described.

• This opinion can range for excluded ( the suspect did not do the biting) to likely and without a doubt (the bite was witnessed and there is not question the suspected biter inflicted the bite).

• Despite the unique nature of the position and arrangement of the human teeth, it is usually easier to rule out a suspect as a potential biter than it is to include a suspect as a potential biter.

Visual Index of Bitemark SeverityVisual Index of Bitemark Severity

Range of Bitemark SeverityRange of Bitemark Severity• 1) Very mild bruising, no individual tooth marks present, diffuse• arches visible, may be caused by something other than teeth – low• forensic significance• 2) Obvious bruising with individual, discrete areas associated with• teeth, skin remains intact, moderate forensic significance• 3) Very obvious bruising with small lacerations associated with• teeth on the most severe aspects of the injury, likely to be assessed• as definite bitemark, high significance• 4) Numerous areas of laceration, with some bruising, some areas of• the wound may be incised. Unlikely to be confused with any other• injury mechanism and a high forensic significance.• 5) Partial avulsion of tissue, some lacerations present indicating• teeth as the probable cause of the injury. Moderate forensic• significance.• 6) Complete avulsion of tissue, possibly some scalloping of the• injury margins suggested that teeth may have been responsible for• the injury. May not be an obvious bite injury – low forensic• significance

How are bite marks analyzed?How are bite marks analyzed?There are over 20 different methods of bitemark analysis.The most common used are:1.Comparing an acetate overlay manually fabricated from study models

to a life size photograph of the wound.2.Comparing study models to a life size photograph of the wound3.Comparing an acetate overlay manually fabricated from bites in wax

to a photograph of the wound 4.Comparing an acetate overlay manually fabricated from x-rays of

radiopaque material placed in a wax bite to a life size photograph of the wound.

5. Comparing an acetate overlay manually fabricated from a photocopy of study models to a life size photograph of the wound.

Sample AnalysisSample Analysis

http://forensic.to/webhome/bitemarks/

Sample AnalysisSample AnalysisBitemark : Upper Jaw Distance Suspect; Upper Jaw Distance

Cuspid to cuspid Cuspid to cuspid

38mm 42mm

 

Bitemark: Distance Suspect: : Distance

Tooth 6 to Tooth 10 Tooth 6 to Tooth 10

 44.25mm 39.65mm

Angle: + 14.5 Degrees Angle: + 12.52 Degrees

ACETATE OVERLAYSACETATE OVERLAYS

• Most of these techniques involve the fabrication of an acetate overlay

• An acetate overlay is an outline of the biting edge of someone’s teeth as traced onto and seen on a clear transparency

• These include tracing from dental models, photographs, wax bites, photocopies.

COMPUTER PROGRAMSCOMPUTER PROGRAMS

• Have been developed to overcome some of these problems

• Theoretically they can;– Correct for distortion– Generate the overlay objectively– Carry out the comparison objectively– Reproduce the overlay

CRITISISMS OF BITEMARK ANALYSISCRITISISMS OF BITEMARK ANALYSIS

In recent years it has been questioned as a reliable scientific tool. This is based on:

1. Numerous methods of fabrication2. Relies on manual fabrication3. Subjective element in fabrication4. Subjective element in comparison5. Distortion which occursAs a result of this it has been suggested that

bitemark analysis using acetate overlays are inaccurate, subjective and non-reproducible

The Accuracy of Skin as a Substrate for a BitemarkThe Accuracy of Skin as a Substrate for a Bitemark• The threshold variable in bitemark analysis is the fact

that, in cases of physical assault having skin injuries, the anatomy and physiology of the skin, and the position the victim was in affects the detail and shape of the bitemark.

• There is one article from the early 1970's that showed how the positioning of the test bite on a bicep varied whether the arm was flexed or pronated.

• What is significant is that there is no way to experimentally control or establish the amount of positional variation in an actual bitemark case.

• The bottom line is that skin is usually a poor impression material. No significant  tests have been published on this subject since 1971 in the odontology literature.

Consider the FollowingConsider the Following

Outlines of the same set of teeth. The different perimeter shapes depend on how far the teeth are pressed into the test substrate.

Stories our teeth tell…Stories our teeth tell…• This is an example of

dental erosion.  Notice on the palatal surfaces of the teeth (i.e. facing inside the mouth) that enamel has been lost.  This can be caused by a number of different conditions, such as anorexia, chronic alcoholism and gastric problems.  Each causes repeated vomiting, which causes acid erosion of the teeth.

• This individual has very pronounced staining visible on their lower teeth.  It was also present on their upper teeth, but this has been covered by some (very poor) porcelain crowns or caps.  This staining has been caused by the anti-biotic tetracycline which was taken when the teeth were developing

• This slide shows the tooth wear associated with pipe-smoking.  Individuals found with wear of this sort are likely to have smoked a pipe and this information could be useful to the police in narrowing the search for antemortem records.

• In this image we can see a wear facet on the upper and lower teeth.  This individual is an electrician who wore his teeth by using them to strip electrical wire.  This is a common finding in such professions, and a similar wear pattern can often by seen in seamstresses who hold pins between their teeth.

• The quality and/or type of dentistry can often tell us where an individual received that treatment.  This can prove valuable information in the search for antemortem records.  This work was performed in Russia and is a classic example of the type of dentistry performed in the former Soviet Union.  Note that the porcelain has been lost from 3 units on this individual.

• The staining on this individual's lower teeth have been caused by cigarette smoking.  This finding can be useful to help include or exclude individual when determining an identity.  The yellow material adhered to the teeth is dental calculus - this shows that this individual does not practice good oral hygiene or visit their dentist often.