Lesson 4
Forensic Dentistry
1
Activity 4.1 Making a bite mark
Can you tell the differences of these bite marks?
2
The shape or curvature
No. of tooth marks
Horizontal diameter
Vertical diameter
Depth of depression
Distances between two
teeth
Orientation of each tooth
Other reasonable answers
3
Activity 4.2
Dentitions of Humans and
Animals
Human jaw
Source: FreeDigitalPhotos.net
http://www.freedigitalphotos.net/images/Human_body_g281-Skulll_p18256.html
(Photographer: Luigi Diamanti)
4
Shapes of teeth
incisor
canine
premolar
molar
5
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
6
Dentition of Dogs
7
Dentition of Sheep
8
Wolf’s Jaw
Source: http://en.wikipedia.org/wiki/File:Kentwolf.jpg
9
Sheep’s Jaw
10
Activity 4.3
Which one is an Omnivore?
11
Black Bear’s Jaw
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)
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.
12
Activity 4.4
Animal attack
On Sunday, Jenny went on a picnic in the countryside. She
was attacked by an animal with the bite mark shown below:
13
Which animal causes the bite?
A. Fruit bat
B. Dog
C. Monkey
D. Cat
Source:FreeDigitalPhotos.net
http://www.freedigitalphotos.net/images/Dogs_g59-Greyhound_p132.html
(Photographer: Arvind Balaraman)
14
Bite marks
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.
15
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 with
a bite mark on it.
16
Are they bitten by the same person?
17
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.
18
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.
19
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.
20
Option 1
Type I error > Type II error
Type 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.
21
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.
22
Further reading: Creating Computer Generated
Exemplars of Suspect Dentition
Source: http://www.forensic.to/webhome/bite marks/#CreatingComputerGeneratedExemplarsofSuspectDentition
1. Using software like photoshop
2. Create images with angular distortion
3. Apply correct scale in both x and y direction
4. Outline the edges to create hollow volume overlay
5. Metric analysis, e.g. arch width (distance from one
cuspid across to the other cuspid), rotational
position, intertooth spacing, tooth width and
thickness, curvatures of biting edges, wear patterns
and unusual dental anatomy
23
The Most Famous Bite Mark
Case of the Twentieth Century
Ted Bundy
Former Law Student
Bundy Bite Mark
Comparison
Note the Yellow
Ruler in the Bite
Mark Photo
Source: Zeno’s Forensic Site
http://www.forensic.to/webhome/
24
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.
25