St. Bonaventure College and
High School
Form 4 Biology
Bridging Course 2009-2010
Structure of a tooth
Types of teeth
Dentition and Diet
• Herbivores (e.g. rabbits) are animals that
feed on plants only. Their incisors are
sharp edged for cropping plants. Canine
are either absent or reduced to form a
diastema, a gap for holding grasses.
There are ridged surfaces on the
premolars and molars,
which allow grinding of
tough grasses and plant
tissues.
Carnivores (e.g. dogs) are animals that
feed on other animals only. Their teeth are
adapted for killing prey, tearing flesh and
crushing bones. Their canines are
enlarged, with sharp pointed edges for
piercing and grasping prey. There are
carnassial teeth (modified premolars and
molars), which form a pair of large, sharp
blades for cutting flesh and bones on each
side of the jaw.
Omnivores (e.g. humans) feed on both
plants and animals. Their teeth are less
specialized compared with herbivores and
carnivores as omnivores consume many
types of food including both meat and
plant materials. They usually have all four
types of teeth.
Vocabularies
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jaw
chew
embedded
enamel
calcium phosphate
resistant
decay
pulp cavity
nutrients
cement
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incisor
canine
premolar
molar
chisel-shaped
biting
grinding
cusp
dentition
diet
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herbivores
reduced
absent
carnivores
prey
carnassial
teeth
• omnivores
Questions
1. What is the hardest substance in our
body?
2. What are the functions of the different
types of teeth?
3. What is the function of diastema in
herbivores?
Useful vocabularies to answer
question 2
saliva
alkaline
neutralize
acid
stimulate
secrete
fluctuation
snakes
plaque
food debris
dissolves
tooth decay
cumulative time
Question 2
Leo
pH of
mouth cavity
Nicole
7
6
5
time
breakfast
lunch
afternoon tea
dinner
Question 2
(1) The pH value is restored to around 7
after the meal. How is the restoration
brought about?(2 marks)
Saliva is alkaline and therefore it neutralizes
the acidity in the mouth cavity.
(2) A chewing gum advertisement claims
that its product can help speed up the pH
restoration after meals. Explain how
chewing gum can do so.
(2 marks)
Chewing gum stimulates salivary glands to
secrete more saliva to neutralize the
acidity.
(1) Describe how the pH changes in the
mouth cavity of Nicole differ from those of
Leo.
(2 marks)
The pH in the mouth cavity of Nicole shows
more fluctuation. The pH falls not only at
meal times, but also between meal times.
(2) Explain the difference in (1).
Nicole has snacks between meal times,
while Leo does not.
Describe the occurrence of tooth decay.
(4 marks)
The bacteria in the mouth cavity/ on the
plaque break down sugars in the food
debrisinto an acid.
The acid dissolves the calcium salts in
enamel and causes tooth decay.
Who has a higher chance of getting tooth
decay? Why?
(3 marks)
Nicole. (no mark if explanation is not given)
The cumulative time of experiencing acidity
in Nicole’s mouth cavity is longer.
The pH in Nicole’s mouth cavity is lower.