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Adults can have 32 permanent teeth: 8 incisors for cutting, 4 canines for tearing, 8 premolars for mashing and 12 molars for crushing. The last molars at the back are the wisdom teeth.

The part of a tooth you can see is the crown. It is covered in enamel, the hardest substance in the body. Under the enamel is dentin, which forms most of the tooth.

In the middle is the pulp, with nerves and blood vessels. The root sits in the jawbone, covered by a bone-like layer called cementum.

Experiment: Which drink attacks an eggshell?

1. Write your question: which drink changes the eggshell most? Predict the order from most to least.
2. Plan a fair test: what will you change (the drink), what will you measure or observe (bubbles, shell feel and colour), and what will you keep the same (size of egg, volume of drink, time, temperature)?
3. Put one egg in each cup and cover it with the same volume of drink. Keep one egg in water as the control.
4. Watch for 5 minutes. Which cups show bubbles on the shell?
5. After 24 hours lift each egg out, pat it dry and compare: is the shell stained, rough, thinner or soft? Record your results in the table and compare them with your prediction.

Drink	Bubbles in first 5 min?	Shell after 24 h (colour, feel)	Rank (1 = most changed)
Water (control)	Your prediction for the most changed egg:
Milk	Your prediction for the most changed egg:
Cola	Your prediction for the most changed egg:
Orange juice	Your prediction for the most changed egg:
Vinegar	Your prediction for the most changed egg:

Questions

1. Label a drawing of a tooth: crown, root, enamel, dentin, pulp.

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2. Explain in your own words how sugar can lead to a cavity. Use the words bacteria, acid and enamel.

3. Name the variable you changed, one you measured and two you kept the same in the eggshell test.

4. Give two things you can do to help your enamel repair itself.

Sources for every fact on this sheet: echoesof.science/school/teeth/sources/

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