Basic 8 · Science · Mammalian Tooth
The Mammalian Tooth
In this topic you will identify the parts of a mammalian tooth, describe the types of teeth and discuss the functions of incisors, canines, premolars and molars.
By the end of these notes you should be able to:
- Identify the parts of a mammalian tooth
- Describe milk and permanent sets of teeth
- Explain the functions of different types of teeth
What you already know
- Digestive system of humans
Copy everything that has a blue line on its left into your notebook. The other parts are for reading.
Lesson 1
- Strand
- Systems
- Sub-strand
- Mammalian Tooth
- Indicator
- B8.3.1.1.1 – Identify parts of a mammalian tooth
Introduction
Your teeth are living parts of your body, and the outer layer is the hardest substance you have.
1. External Parts
| Part | Position | Description |
|---|---|---|
| crown | above the gum | the part you can see |
| neck | at the gum line | joins crown and root |
| root | inside the jawbone | anchors the tooth |
2. Internal Parts
| Layer | Description | Function |
|---|---|---|
| enamel | hard, white, non-living covering of the crown | protects the tooth |
| dentine | bone-like layer under enamel | supports enamel, forms the tooth's bulk |
| pulp cavity | soft inner space | contains nerves and blood vessels |
| cement | thin layer on the root | holds the tooth in the socket |
| periodontal fibres | fibres between tooth and bone | absorb shock |
Blood vessels in the pulp bring food and oxygen to the living cells of the tooth. Nerves there detect pain, heat and cold. That is why a hole deep in a tooth causes such strong pain. Enamel has no living cells and cannot repair large damage, so a cavity needs to be treated by a dentist.
3. Enamel: Nature's Armour
Enamel is mainly made of calcium compounds. It is harder than bone, and it is the hardest substance in the body. Fluoride in toothpaste helps it to resist acids. However, enamel can chip if you open bottles or crack very hard objects with your teeth, which is a habit you should avoid.
4. Teeth in Other Mammals
All mammals share the same basic tooth structure, although tooth shapes differ with diet. Elephants' tusks are very long incisors, which are made mainly of dentine. This is why the ivory trade has threatened elephants, and why elephants are protected by law in Ghana. Scientists can work out how an animal lived just by studying its teeth, even from ancient fossils.
New words
- crown
- The visible part of a tooth.
- enamel
- The hard outer covering of the crown.
- dentine
- The bone-like layer of a tooth.
- pulp
- The soft centre with nerves and blood vessels.
Summary
- A tooth has a crown, neck and root.
- Enamel, dentine, pulp and cement form the layers of the tooth.
- Nerves and blood vessels keep the tooth alive.
Class activity: Label the Tooth
- Draw a section through a tooth.
- Label six parts.
- State the function of each.
You need: Mammalian jaw model, Printed tooth diagram, Hand mirror
Exercises
Answer in your exercise book first, then check your answers.
1. The visible part of a tooth is the…
- A. crown
- B. root
- C. pulp
- D. cement
Show answer
Answer: crownAbove gum.2. The hardest part of the body is…
- A. enamel
- B. bone
- C. dentine
- D. nail
Show answer
Answer: enamelHardest.3. The pulp contains nerves.
- A. True
- B. False
Show answer
Answer: TruePain.4. The bone-like layer of a tooth is ______.
Show answer
Answer: dentineLayer.5. Name three layers of a tooth.
Show answer
Answer: Enamel, dentine and pulp.Any three.6. Why does a deep cavity cause pain?
Show answer
Answer: It reaches the pulp, which contains nerves.Structure.
Lesson 2
- Strand
- Systems
- Sub-strand
- Mammalian Tooth
- Indicator
- B8.3.1.1.1 – Identify parts of a mammalian tooth
Introduction
Open your mouth and look in a mirror. You will see teeth of different shapes, each of them suited to a different job.
1. Four Types of Teeth
| Type | Shape | Position | Number in an adult |
|---|---|---|---|
| incisors | chisel-like | front | 8 |
| canines | pointed | beside incisors | 4 |
| premolars | two-cusped | behind canines | 8 |
| molars | broad with cusps | back | 12 |
2. Two Sets of Teeth
Humans have two sets of teeth during life. The milk or primary teeth begin to appear at about 6 months, and a child has 20 of them by about the age of three. They begin to fall out around the age of six, when permanent teeth push up. An adult has 32 permanent teeth, including four wisdom teeth, which may appear in late teens or later, and may never appear at all. Children have no premolars in their milk set.
3. Dental Formula
Scientists write a dental formula for one half of the mouth, showing upper and lower teeth. For adult humans, it is I 2/2, C 1/1, PM 2/2, M 3/3. Multiply the total by two: (2 + 1 + 2 + 3) × 2 = 16 for the top row, and the same for the bottom row, which gives 32. For a child, the formula is I 2/2, C 1/1, M 2/2, giving 20 teeth.
Dental formula
An animal has the formula I 3/3, C 1/1, PM 4/4, M 2/3. How many teeth does it have?
- Upper half: 3 + 1 + 4 + 2 = 10.
- Lower half: 3 + 1 + 4 + 3 = 11.
- One side: 21.
- Both sides: 21 × 2.
Answer: 42 teeth
4. Caring for Permanent Teeth
Your permanent teeth have to last a lifetime. If you lose one, no new tooth will grow. Protect them when you play active sports, and do not use them to open things. Take care of milk teeth too, because they hold space for permanent teeth.
New words
- incisor
- A chisel-shaped front tooth.
- canine
- A pointed tooth.
- molar
- A broad back tooth.
- dental formula
- A record of the numbers of each tooth type.
Summary
- Humans have incisors, canines, premolars and molars.
- Children have 20 milk teeth, and adults have 32 permanent teeth.
- A dental formula records the teeth in half of the mouth.
Class activity: Mouth Survey
- Use a clean mirror to count your teeth by type.
- Record the numbers.
- Compare with the adult formula.
You need: Mammalian jaw model, Printed tooth diagram, Hand mirror
Exercises
Answer in your exercise book first, then check your answers.
1. Adults have how many permanent teeth?
- A. 32
- B. 20
- C. 28
- D. 36
Show answer
Answer: 32Including wisdom teeth.2. Which teeth are missing in the milk set?
- A. premolars
- B. incisors
- C. canines
- D. molars
Show answer
Answer: premolarsMilk set.3. Milk teeth are replaced by permanent teeth.
- A. True
- B. False
Show answer
Answer: TrueReplacement.4. Children have ______ milk teeth.
Show answer
Answer: 20Primary set.5. Name the four types of teeth.
Show answer
Answer: Incisors, canines, premolars and molars.Types.6. Calculate the teeth from the formula I 1/3, C 0/1, PM 3/3, M 3/3.
Show answer
Answer: Upper 7, lower 10, one side 17, total 34.Formula.
Lesson 3
- Strand
- Systems
- Sub-strand
- Mammalian Tooth
- Indicator
- B8.3.1.1.2 – Discuss the functions of the different types of teeth such as incisors canines premolars and molars
Introduction
Bite into a sugar cane, and then chew on a piece of meat. Each action uses teeth with a different design.
1. Functions of Teeth
| Type | Function | Example of food |
|---|---|---|
| incisors | biting and cutting | apple, sugar cane |
| canines | tearing and piercing | meat |
| premolars | crushing and grinding | groundnuts, chicken |
| molars | chewing and grinding | gari, roasted maize |
The sharp edges of incisors work like scissors. The pointed canines hold and tear food. Premolars and molars have broad surfaces with bumps called cusps, which grind food into small pieces. Chewing increases the surface area of food so that digestive enzymes can work faster, and mixing with saliva makes food easy to swallow.
2. Teeth and Diet in Animals
| Animal group | Examples | Special features |
|---|---|---|
| herbivores | goat, cow | large grinding molars; gap (diastema); no upper incisors in many species |
| carnivores | dog, lion | large canines; sharp carnassial teeth |
| omnivores | humans, pigs | a mix of all types |
| rodents | grasscutter, rat | ever-growing incisors |
3. Reasons for Differences
A goat or cow spends hours grinding tough grass, so it has large flat molars. It uses its lips and tongue with lower incisors against a hard pad in the upper jaw. A dog needs to hold and slice meat, so it has large canines and sharp cheek teeth. Grasscutters have incisors that keep growing because gnawing wears them down. Humans eat many kinds of food, and they have all types of teeth. Teeth show how form relates to function in nature.
4. Teeth and Speech
Teeth also help us to speak. Your tongue presses against them to form sounds such as "t" and "th". Teeth affect appearance and confidence too. A healthy smile matters in social life, so caring for your teeth has benefits beyond eating.
New words
- herbivore
- An animal that eats plants.
- carnivore
- An animal that eats meat.
- omnivore
- An animal that eats plants and meat.
- cusp
- A raised point on a tooth.
Summary
- Incisors cut, canines tear, premolars and molars grind.
- Teeth suit diet: herbivores, carnivores and omnivores differ.
- Teeth also help speech and appearance.
Class activity: Food and Teeth
- Bite and chew a piece of carrot or sugar cane.
- Note which teeth you use.
- Record your observations in a table.
You need: Mammalian jaw model, Printed tooth diagram, Hand mirror
Exercises
Answer in your exercise book first, then check your answers.
1. Which teeth tear meat?
- A. canines
- B. incisors
- C. molars
- D. premolars
Show answer
Answer: caninesPointed.2. A goat is a…
- A. herbivore
- B. carnivore
- C. omnivore
- D. rodent
Show answer
Answer: herbivorePlant-eater.3. Humans are omnivores.
- A. True
- B. False
Show answer
Answer: TrueMixed diet.4. Raised points on teeth are called ______.
Show answer
Answer: cuspsGrinding.5. Why does chewing help digestion?
Show answer
Answer: It increases the surface area of food for enzymes and mixes it with saliva.Digestion.6. Compare the teeth of a dog and a goat.
Show answer
Answer: The dog has large canines and sharp cheek teeth, while the goat has flat grinding molars and lacks upper incisors.Comparison.
Homework
- Draw and label a tooth and explain the functions of all four types of teeth.