Teeth and Digestion
1. Why Do We Need Teeth?
Teeth help us CHEW (break down) food into smaller pieces.
'Chewing is the FIRST step of digestion. Without teeth, you could only eat soft or liquid food.'
Functions of Teeth:
- Cutting food into pieces.
- Tearing food (especially meat).
- Grinding food into a paste.
- Helping us SPEAK clearly (try saying 'th' without your front teeth!).
2. Types of Teeth
A human adult has FOUR types of teeth. Each type has a DIFFERENT shape and function.
| Type | Shape | Function | Number in Adults |
|---|---|---|---|
| Incisors | Flat and sharp (like a chisel) | CUTTING food | 8 (4 top, 4 bottom) |
| Canines | Pointed and sharp (like a cone) | TEARING food | 4 (2 top, 2 bottom) |
| Premolars | Flat with RIDGES | CRUSHING and GRINDING | 8 (4 top, 4 bottom) |
| Molars | Large and flat | GRINDING food into fine paste | 12 (6 top, 6 bottom) |
Dental Formula:
'Adults have 32 teeth in total: 8 Incisors + 4 Canines + 8 Premolars + 12 Molars.'
Incisors:
- Located at the FRONT of the mouth.
- Flat, sharp edges — like a CHISEL.
- Used for BITING into an apple or cutting food.
Canines:
- Located NEXT to the incisors (one on each side).
- Long, POINTED — like a SPEAR.
- Used for TEARING food (especially meat).
- 'Also called EYE TEETH because they are under your eyes!'
Premolars and Molars:
- Located at the BACK of the mouth.
- Broad, FLAT surfaces with ridges.
- Used for CRUSHING and GRINDING food.
- Molars are LARGER than premolars.
3. Milk Teeth and Permanent Teeth
Milk Teeth (Deciduous Teeth):
- Start appearing at about 6 MONTHS of age.
- Total: 20 teeth (10 in each jaw).
- These are TEMPORARY — they fall out.
Permanent Teeth:
- Start appearing at about 6-7 YEARS of age.
- Total: 32 teeth (16 in each jaw).
- These are PERMANENT — they LAST a lifetime.
- 'Milk teeth fall out because the permanent teeth underneath push them out.'
| Age | What Happens |
|---|---|
| 6 months | First milk teeth appear |
| 2-3 years | All 20 milk teeth are present |
| 6-7 years | Milk teeth start falling out |
| 12-13 years | Most permanent teeth have come in |
| 17-25 years | Wisdom teeth (last molars) appear |
4. Structure of a Tooth
Parts of a Tooth:
| Part | Description |
|---|---|
| Crown | The PART visible above the gum |
| Root | The part INSIDE the jawbone (not visible) |
| Enamel | The HARDEST substance in the body — covers the crown |
| Dentine | The layer BELOW the enamel — yellowish |
| Pulp | The INNERMOST part — contains nerves and blood vessels |
| Gum | Pink flesh that surrounds and supports the teeth |
'ENAMEL is the HARDEST substance in your entire body — even harder than bone! But it can be damaged by ACIDS from sugar.'
5. Dental Care — Keeping Teeth Healthy
The 2-2-2 Rule:
- Brush 2 times a day (morning and night).
- For 2 minutes each time.
- Visit the dentist 2 times a year.
Good Habits for Healthy Teeth:
| Do | Don't |
|---|---|
| Brush twice daily | Eat too many sweets |
| Use a fluoride toothpaste | Chew hard objects (pens, ice) |
| Floss between teeth | Drink too many sugary drinks |
| Rinse mouth after meals | Use teeth to open bottles |
| Eat crunchy fruits (apple, carrot) | Skip brushing before bed |
| Visit the dentist regularly | Ignore bleeding gums |
What Causes Tooth Decay?
- Plaque — a sticky layer of BACTERIA on teeth.
- Sugar — bacteria feed on sugar and produce ACID.
- Acid — acid eats away the ENAMEL → CAVITY (hole in tooth).
- Pain — if the cavity reaches the PULP, it hurts!
'Remember: SUGAR + BACTERIA = ACID. Acid makes HOLES in teeth. That is CAVITY!'
6. Digestion — An Overview
DIGESTION is the process of breaking down food into NUTRIENTS that the body can use.
'Digestion starts in the MOUTH and ends in the... well, you know where!'
The Digestive System Organs:
| Organ | What Happens Here |
|---|---|
| Mouth | Teeth CHEW food. Saliva mixes with food. |
| Oesophagus | Food moves DOWN to the stomach (like a slide). |
| Stomach | Food mixes with DIGESTIVE JUICES (acids). |
| Small Intestine | Nutrients are ABSORBED into the blood. |
| Large Intestine | WATER is absorbed. Waste is formed. |
| Rectum/Anus | Waste is REMOVED from the body. |
The Journey of Food:
'Bite → Chew → Swallow → Stomach → Small Intestine → Large Intestine → Waste'
- Mouth: You BITE and CHEW the food. Your teeth cut and grind it. SALIVA (spit) mixes with the food and starts breaking down carbohydrates. The food becomes a soft BOLUS.
- Oesophagus: The bolus travels DOWN a long tube called the oesophagus. Muscles push the food down (PERISTALSIS). This takes about 5-10 seconds.
- Stomach: The food mixes with strong DIGESTIVE ACIDS. The stomach CHURNS the food like a washing machine! It stays here for 2-4 hours.
- Small Intestine: This is where MOST digestion happens. The nutrients (carbohydrates, proteins, fats, vitamins, minerals) are ABSORBED into the bloodstream. 'The small intestine is about 6-7 metres long!'
- Large Intestine: WATER is absorbed back into the body. What is left becomes SEMI-SOLID waste (faeces).
- Rectum: The waste is stored here until it is removed from the body through the ANUS.
7. Common Mistakes
- Thinking enamel can grow back: 'Once enamel is DAMAGED by acid, it CANNOT grow back. That is why brushing is so important!'
- Not brushing before bed: 'Brushing at NIGHT is actually MORE important than morning. Food sits on teeth all night — bacteria love this!'
- Calling the small intestine 'small' as if it is short: 'The small intestine is about 6-7 METRES long. It is called "small" because it is NARROW, not short!'
- Skipping the chewing step: 'Digestion starts in the MOUTH. If you don't chew well, your stomach has to work much harder. Always chew food properly!'
8. Key Facts to Remember
- 'Adults have 32 teeth — incisors, canines, premolars, and molars.'
- 'Enamel is the HARDEST substance in the body.'
- 'Sugar + Bacteria = Acid. Acid causes cavities.'
- 'Brush twice a day for 2 minutes each time.'
- 'Digestion starts in the MOUTH and ends at the ANUS.'
- 'The small intestine is where MOST nutrients are absorbed.'
9. Self-Test
Q1: Name the four types of teeth and their functions.
Q2: How many teeth does an adult have? How many milk teeth does a child have?
Q3: What is ENAMEL? Why is it important?
Q4: How does a cavity form in a tooth?
Q5: List the organs of the digestive system in order.
Q6: What is the function of the small intestine?
Q7: Why is it important to brush your teeth at night?
Q8: What is PLAQUE and how is it formed?
Answers:
A1: Incisors (cutting), Canines (tearing), Premolars (crushing), Molars (grinding). A2: Adults have 32 permanent teeth. Children have 20 milk teeth. A3: Enamel is the HARD outer layer of the tooth. It protects the inner parts of the tooth from damage and decay. A4: Bacteria in plaque feed on sugar and produce ACID. The acid eats away the enamel, creating a HOLE (cavity). A5: Mouth → Oesophagus → Stomach → Small Intestine → Large Intestine → Rectum → Anus. A6: The small intestine absorbs NUTRIENTS (carbohydrates, proteins, fats, vitamins, minerals) into the bloodstream. A7: Because food particles sit on your teeth all night. Bacteria feed on them and produce acid that damages teeth. A8: Plaque is a sticky film of BACTERIA that forms on teeth. It forms when food particles mix with bacteria in the mouth.
