Lesson 4 Forensic Dentistry
Pre-lesson Reading
Forensic Science
Forensic science is the scientific examination of evidence in a criminal investigation.
Forensic Dentistry or Odontology
Forensic dentistry or forensic odontology is a branch of forensic science which deals with the
collection, evaluation and proper handling of dental evidence in order to assist law enforcement
officers and to assist in civil and criminal proceedings.
Major Services of Forensic Dentistry
a) Identification of deceased persons through dental remains;
b) Bite mark analysis, determining or ruling out possible suspects in crimes using the bite marks
left on a victim or other object; and
c) Examination of oral-facial structures for determination of injury, possible malpractice or
insurance fraud.
Data to be collected for forensic dentistry include
a) Bite mark on victim’s body or objects;
b) Postmortem odontogram;
c) Shape, colour and arrangement of teeth; and
d) Unique changes due to dental surgery or accidents.
On-line studying
Forensic dentistry
http://www.forensicdentistryonline.org/forensichomepage.htm
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Lesson 4 Forensic Dentistry
Worksheet 4.1 Making a bite mark
You are given a washed apple. Make a bite mark on it similar to the picture shown below. Compare
your teeth bite mark with your partner’s. What are the differences between the two sets of teeth bite
marks?
Differences between teeth bite marks:
1.
2.
3.
4.
5.
6.
7.
8.
The shape or curvature
No. of tooth marks
Horizontal diameter
Vertical diameter
Depth of depression
Distances between two tooth marks
Orientation of each tooth mark
Other reasonable answers
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Lesson 4 Forensic Dentistry
Worksheet 4.2 Dentitions of Humans and Animals
Dentition of Humans
Dentition refers to the number and arrangement of different types of teeth in a mammal. The
following shows the number and key features of each type of teeth in human adults.
Tooth type
Incisors
Canines
Premolars
Molars
Total
Upper
Number jaw
of teeth Lower
2
1
2
3
16
2
1
2
3
16
jaw
General feature
Front teeth
All have thin
edges
Square shaped
Cone-shaped
Single rooted
Two cusps
Single rooted
Single rooted
Function
Multiple
rooted
Used for biting
into food
incisor
Square
4 and 5 cusps
Largest teeth
in jaw
Used for tearing
food
canine
Used for
grinding food
premolar
Used for
grinding food
molar
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Dental formula
Dentition can be represented by a dental formula, which shows the numbers and types of teeth on
each side of the upper and lower jaws. For example, the dental formula of a human adult is:
i
2 1
2
3
2123
, c , pm , m or simply
2 1
2
3
2123
Try to do the following calculation with the dental formula!
Total number of teeth on each side
= 2 x (2+1+2+3) = 16
Total number of teeth of adult human
= 16 x 2 = 32
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Dentition of different animals
The dentitions of different animals vary according to their diets. In order word, biologists can
predict whether an animal is meat-eating (carnivores) or plant-eating (herbivores) by studying the
dentition of an animal. Similarly, forensic scientists can make use of an animal bite to determine the
identity of an animal.
1. Carnivores
Carnivores feed mainly upon meat, their dentitions are characterised by well-developed sharp
canines for catching preys and shearing meat. The premolars and molar are strong and blade-like to
perform cutting and chewing actions.
The following diagrams show the dentition of a dog.
Dental formula:
Try to work out its dental formula.
3142
[note that the upper and lower dentitions are unequal]
3143
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2. Herbivores
Herbivores feed mainly on plant matter. Most herbivores have no or very small canines but they
usually have a big diastema (gap) between incisors and premolars for easy manipulation of plant
matter during chewing. The premolars and molar are ridged for grinding and crushing fibrous plant
materials.
The following diagrams show the dentition of a sheep. Try to work out its dental formula.
Dental formula:
0033
[note that the upper and lower dentitions are unequal]
3133
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Worksheet 4.3 Which of the following is an omnivore?
Humans are described as omnivores whose primary food sources include both plants and animals.
Which of the following dentitions belongs to an omnivore? Explain your answer.
Explanation:
Answer: C

Canines are pointed for tearing meat;

A diastema between incisors and premolars for manipulation of plant matter for grinding;

Premolars and molars have cusps and relatively flat surfaces for crushing and grinding vegetables;
and thus, this animal is possessing features for eating both plant and meat.
Remarks:
A: Horse; B: Hyena; C: Black bear; D: Sea lion.
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Lesson 4 Forensic Dentistry
Worksheet 4.4 Animal attack
On Sunday, Jenny went on a picnic in the countryside. She was attacked by an animal and her hand
left a bite mark shown below:
Which of the following animals may cause the bite? Circle it out and explain your answer.
Fruit Bat
Dog
Monkey
Cat
http://www.freedigitalphotos.net/images/Dogs_g59-Greyhound_p132.html
(Arvind Balaraman)
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Explanation:
Answer: Monkey.

The diameter of the bite mark is about 1/2 of point finger.
of a fruit bat.
It is bigger than the bite mark
The sizes of teeth are bigger than those of a fruit bat but smaller than
those of a dog.

The canine marks are not very deep and prominent, it should not belong to a dog or a cat.

The angles of curvature of the bite marks are similar to those of human teeth. (Both
humans and monkeys are primates)
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Lesson 4 Forensic Dentistry
Worksheet 4.5 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 by 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.
Clue: A piece of bitten sandwich
Now, you are the forensic scientist responsible for examining the teeth bites on the sandwich
(murderer’s bite mark) and match it with the bites from two suspects (suspects A & B*).
You are given some apparatus: transparencies, markers, a ruler, scissors, grid papers and a
contractor. You may suggest to your teacher other apparatus if necessary. Design a scientific test to
achieve the purpose and seek your teacher’s advice before carrying out your test to find out the
murderer.
*The teacher may ask the students to prepare the samples for other groups according to Appendix I
during their planning time.
Your solutions should answer the following questions:
1.
2.
3.
4.
5.
Referring to the bite marks, what information/ data would you collect, measure and compare?
What is your equipment list?
What factors do you need to control in order to make the experiment a fair test?
How is your test performed?
What are the limitations of your test?
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Task: Designing a fair comparison for bite marks
1. Evidences to be collected, measured and compared
1.
To outline the bite mark of cucumber over the transparencies
2.
To use overlay method to compare the curvature of the bite marks from the murderer and suspects
3.
To measure the width of each tooth, width of tooth gaps, distance and angle between two teeth
2. Equipment list
1.
Transparencies
2.
A pair of scissors
3.
Markers (a different colour for each sample)
4.
A ruler
5.
A contractor
6.
3. Factors to be controlled to make it fair
1.
Width of marker head should be the same.
2.
When measuring the distances between two teeth (or two gaps), their mid-points are used.
4. Outline of procedure
1.
Select a piece of bitten cucumber from the sandwich. Put it over a piece of transparency.
2.
Label the transparency.
3.
Use a fine marker to trace the outline of each tooth bite mark.
4.
Match the murderer’s bite mark with those of the suspect by comparing the overall curvature.
5.
When a pair of similar bite marks are found, identify some key features of the bite marks for
comparison, e.g. measure the width of each tooth, width of diastemas, distance between two teeth
and angle of rotation of some teeth.
6.
Record the results of measurement and comparison systematically (using a table).
5. Limitations of my test
1.
The bite marks show only the positions of a few teeth instead of all teeth.
2.
The bite marks give only two dimensional images instead of three dimensional ones.
3.
The shape of the bite mark may be influenced by many uncontrollable variables such as sliding of
bread and other food ingredients.
4.
The tracing of outline of each tooth is subjective.
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Task: Designing a fair comparison for bite marks
6. Results
a) Matching of curvature by overlay method
Suspect A
Suspect B
X

Murderer
b) Further comparison
Measurement
Murderer
Suspect A
Suspect B
7.0 mm
6.5 mm
7.0 mm
2.6 mm
2.6 mm
2.6 mm
Distance between right canine and left 2 incisors / mm
2.15 mm
2.15 mm
2.15 mm
Distance between left canine and right 2nd incisors / mm
2.15 mm
2.15 mm
2.15 mm
Tooth gap between two front incisors / mm
2.5 mm
3.0 mm
2.5 mm
Width of right and left front incisors / mm
3.0, 3.0
3.0, 3.0
3.0, 3.0
53.0o
54.5o
53.5o
Distance between 2 front incisors / mm
Distance between 2 canines / mm
nd
Angle between 1st right premolar and 1st right incisor
7. Conclusion- Who is the murderer?
Suspect B shows positive results in all the comparison items.
Suspect B is the murderer.
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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8. Follow-up Questions
Question 1
Apart from the bite marks, what evidences can be collected from the sandwiches for investigation?
1.
DNA from saliva of murder;
2.
Blood stain of the murderer, if any;
3.
Other trace of food to review the diet the murderer was eating; and
4.
The ingredients of sandwich may help finding the source of sandwich.
Question 2
In a scientific test, there may be two types of error as shown below:
Type I error: you incorrectly release the true murderer
Type II error: you mistake a good person for a murderer
As a forensic scientist, which of these two types of errors must be eliminated? Explain your answer.
Answers (open-ended):
Option 1
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.
Option 2
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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Note:
Activity 4.5
Preparation of Murderer Sample and Suspect Samples
Steps for making Murderer Sample
1. Put a piece of ham and two pieces of cucumber between two pieces of bread with edges
removed.
2. The ‘murderer’ makes a deep bite on the sandwich so that bite marks will be left on all the
ingredients. Label the sample as ‘MURDERER’.
Steps for making Suspect Samples
1. Prepare another set of sandwiches. Several suspects make deep bites on the 4 sides of the
sandwiches. (Refer to photo “04” of Snapshots). Make sure that the bite marks will be left
on all ingredients.
2. Label the sample as ‘A’, ‘B’, “C” and “D”, etc.
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Lesson 4 Follow-up Activities
Extended Reading:
1. Computer Aided Analysis of Bite Mark
http://www.forensic.to/webhome/bitemarks/#CreatingComputerGeneratedExemplarsofSuspectDenti
tion
2. The Most Famous Bite mark Case of the Twentieth Century
http://www.forensic.to/webhome/bitemarks1/
http://crime-scene-processing.suite101.com/article.cfm/the_capture_of_ted_bundy
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