Science Challenge

Science Challenge

Get involved in our September Science Challenge - Teeth: Why should we brush them?


  • Post-its or a label
  • See through glass/beaker
  • Bowl
  • Cola and lemon juice (not lemonade)
  • 4 Eggs
  • Toothpaste


  1. Write on sticky notes: Cola 1, Cola 2, Juice 1, Juice 2.
  2. Place them in a row on a counter.
  3. Fill two glasses halfway with cola and label.
  4. Fill two glasses halfway with lemon juice.
  5. Carefully place one egg in the bowl. Squeeze a big dollop — about one tablespoon — of toothpaste on top of the egg and gently rub the toothpaste all around with your hands until the egg is completely covered in a thick layer of toothpaste. Repeat with a second egg.
  6. Gently submerge the toothpaste-covered eggs into the liquids: one egg in the glass labelled Cola 1 and the other egg in the glass labelled Juice 1. Wash and dry your hands.
  7. Gently submerge the remaining eggs, without toothpaste on them, in the remaining glasses: one in the glass labelled Cola 2 and the other in the glass of juice labelled Juice 2. Wash and dry your hands. Leave the eggs in the glasses for 12 hours.
  8. After 12 hours, remove the eggs from the glasses one at a time. Rinse them in cool water and pat them dry with the towel. Place each egg by the sticky note of the glass it was in. Are the eggs the same or different colours? Feel the eggs gently. Does one feel stronger or weaker than another?

The Science:

The eggshells represent the enamel (outer coating) on your teeth. Brushing with toothpaste prevents stains and removes food particles that are stuck on your teeth. It also protects your teeth from decay (wearing down). One egg without toothpaste should turn brown and discoloured and the other will soften whereas the eggs covered in toothpaste were protected. When a tooth is worn down, a cavity can form more easily. The fluoride in toothpaste forms a protective coat around your tooth enamel. This helps keep your teeth strong and cavity-free.

Please send a photo in via Class Dojo or bring in your drawings and write-up. Remind your teacher to tell the Science Leader to collect a certificate.

Science of the Month

Choose one of the following topics to investigate:

  1. How many teeth do children have and how many when you grow up?
  2. Find out about the different types of teeth. How many of each to do you have?
  3. Research this question. Do different animals have different types of teeth?

You can also download our Science Challenge as a PDF.