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Lesson 4

Forensic Dentistry

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Activity 4.1 Making a bite markCan you tell the differences of these bite marks?

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The shape or curvature No. of tooth marksHorizontal diameterVertical diameterDepth of depressionDistances between two teethOrientation of each toothOther reasonable answers

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Human jaw

Source: FreeDigitalPhotos.net

http://www.freedigitalphotos.net/images/Human_body_g281-Skulll_p18256.html

(Photographer: Luigi Diamanti)

Activity 4.2

Dentitions of Humans and Animals

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Shapes of teeth

incisor canine premolar molar

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Human Dentition

Incisors: 2

Canine: 1

Premolar: 2

Molar: 3

Dental formula of a human adult is:i 2/2, c 1/1, pm 2/2, m 3/3

simply 2123

2123

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Dentition of Dogs

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Dentition of Sheep

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Wolf’s Jaw

Source: http://en.wikipedia.org/wiki/File:Kentwolf.jpg

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Sheep’s Jaw

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Activity 4.3 Which one is an Omnivore?

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Black Bear’s Jaw

C.

Canines are pointed for tearing meat;

A diastema between incisors and premolars for manipulating plant;

Premolars and molars have relatively flat surface for grinding plant;

Possessing features for eating both plant and meat.

Source: http://www.michigan.gov/dnr/0,1607,7-153-10363_10856_10890-27479--,00.html

(Department of Natural Resources and Environment, Michigan Government, USA)

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On Sunday, Jenny went on a picnic in the countryside. She was attacked by an animal with the bite mark shown below:

Activity 4.4 Animal attack

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A. Fruit bat B. Dog

C. Monkey D. Cat

Which animal causes the bite?

Source:FreeDigitalPhotos.nethttp://www.freedigitalphotos.net/images/Dogs_g59-Greyhound_p132.html

(Photographer: Arvind Balaraman)

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Monkey

The diameter is about ½ point finger, bigger than the bite mark of fruit bat;

Canine marks are not very deep and prominent, not a dog or a cat;

The curvature is similar to that of human bites. Monkeys and humans are primates and the curvatures of their bites are similar.

Bite marks

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Who is the Murderer?

• A murder case was reported at the Integrated Science Laboratory!

• The body of the laboratory technician was found at the entrance between the IS laboratory and the preparation room. He was struck at the stomach with a piece of broken glass, which might be the cause of the murder.

• Some broken glasses were found in front of the teacher’s bench, alongside with a piece of unfinished sandwich witha bite mark on it.

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Are they bitten by the same person?

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The True Story• Peter was late for school this morning. He had not yet taken his

breakfast when he returned school. During the recess time, he bought a piece of sandwich and entered the IS lab without the permission of the teacher. He wanted to enjoy his breakfast by himself there. While he was eating the breakfast, the apparatus placed on the Teacher’s bench drew his attention. He took up a piece of apparatus but accidentally dropped it on to the floor. He was in a panic because he knew that he made a serious mistake. His piece of sandwich dropped from his mouth on to the floor, too. He attempted to clean up the broken glass and picked up the largest piece. He rushed to the door case because the litter bin was located near it. Just at that moment, the laboratory technician came out of the preparation room as he heard a noise from the laboratory. Unfortunately, Peter collided with the technician with great force. He unintentionally struck the broken piece of glass into the technician’s stomach. The technician stepped backward and hit his head at the wall. He fell to the floor, fainted and later died of excessive bleeding.

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Activity 4.5 Q1: Other evidences from bitten sandwich?

• DNA from saliva of murder;

• Blood stain of murder, if any;

• Other trace of food to review the diet the murder is taking;

• The ingredients of sandwich may help finding the source of sandwich.

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Activity 4.5 Q2: Which should be eliminated, type I or type II error?

• Type I : you incorrectly release the true murderer.

• Type II : you mistake a good person for a murderer.

As a forensic scientist, which of these two types of error is more important? Explain your answer.

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Option 1Type I error > Type II errorType I error has a higher priority than type II

error and Type I error should be eliminated completely. The police should include all potential murderers for the investigation but the criteria for judging a suspect as a murderer should be strict. If so, even if type II is made, we still can make use of other methods and evidences to prove that a suspect is not guilty if he did not commit the crime.

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Option 2

Type II error > Type I error

• Type II error has a higher priority than type I error and Type II error should be eliminated completely. It is not just and acceptable to mistake a good person for a murderer.

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Further reading: Creating Computer Generated Exemplars of Suspect Dentition

Source: http://www.forensic.to/webhome/bite marks/#CreatingComputerGeneratedExemplarsofSuspectDentition

1. Using software like photoshop2. Create images with angular distortion3. Apply correct scale in both x and y direction4. Outline the edges to create hollow volume overlay5. Metric analysis, e.g. arch width (distance from one c

uspid across to the other cuspid), rotational position, intertooth spacing, tooth width and thickness, curvatures of biting edges, wear patterns and unusual dental anatomy

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The Most Famous Bite Mark Case of the Twentieth Century

Source: Zeno’s Forensic Site

http://www.forensic.to/webhome/

Bundy Bite Mark Comparison

Note the Yellow Ruler in the Bite

Mark Photo

Ted BundyFormer Law Student

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Summary• Dentition refers to the number and arrangement of

different types of teeth in an animal. The dentitions of different animals vary according to their diets.

• Bite mark can be used to identify the animal or the person causing the bite.

• Teeth bite mark can be compared by overlay method. Key features include width and rotation of each tooth, teeth gap width, distance between teeth.

• Type I error: you incorrectly release the true murderer.• Type II error: you mistake a good person for a

murderer.