This is a fun experiment for parents and teachers to show kids how fluoride helps protect teeth against tooth decay. The Canadian Dental Association recommends adult supervision for this activity. 

Background

Eggshells and teeth both have something in common; they can be weakened by acid. When you put an egg in vinegar, it attacks the shell similar to how your teeth are vulnerable to weak acid attacks.

*Note for teachers: You might like to create a checklist for the following steps on your blackboard or on paper handouts to involve your whole class in this activity in this EggSperiment.

Purpose

This experiment shows how you can help lock in the calcium in an eggshell – and your teeth – by protecting them with a fluoride toothpaste.

Time Needed

This experiment can take 5 or 6 days so if this is being done at school, start on a Thursday or Friday afternoon.

Materials

• Crest for Kids Cavity Protection Sparkle Gel toothpaste
• Paper towel
• Teaspoon
• Plastic wrap
• Marker or pen
• Clear nail polish
• Glass measuring cup (500 ml / two cups)
• Three or four eggs without cracks – fresh or hard boiled*
• Table vinegar

*NOTE: You’ll only need one egg for the experiment but you might want to use 3 or 4 eggs just in case one egg gets dropped.

Preparation

1. Let the egg warm to room temperature
2. Empty the tube of toothpaste into the measuring cup.
3. Remove any air bubbles in toothpaste by patting it down with a teaspoon.
4. Wash your hands and the egg with warm water and dry using a paper towel
5. Mark one side of the egg with a small “X” using a pen or marker to show the side that will not be covered (protected) by the toothpaste.
6. Cover the mark with the nail polish to protect it from the coming vinegar.
7. Horizontally, place the egg  into the measuring cup to cover half the egg with toothpaste. But make sure the bottom of the cup doesn’t touch the egg.
8. Use plastic wrap to cover the cup and put it in a safe place. Place it in room temperature for 4 days.

Acid Attack

1. After 4 days, use the teaspoon to carefully remove the egg and rinse off the toothpaste with some warm tap water.
2. Let the egg dry overnight.
3. On the next day, pour enough vinegar into the measuring cup that will submerge the egg
4. Carefully place the egg into the vinegar solution
5. You and your students will see gas bubbles quickly begin to form and rise from the unprotected side of the egg. The shell is being attacked by acid.
6. Leave the egg in the vinegar until the side with the “X” softens. This could take between 7 and 13 hours. You can leave it overnight and record the number of hours the egg spent in the vinegar.

Results

1. After the egg has been in the vinegar for at least 7 hours, you can check if the unprotected side has softened by using your finger to tap it very lightly
2. When finally soft, carefully remove the egg and wash it with warm water.
3. Holding the egg, you can now tap the unprotected side (side with the “X”)  and compare the weak shell with the protected side, which should be much harder.

The fluoride in the toothpaste helped to make the eggshell strong, protecting it from the acid in vinegar. Fluoride is a mineral found in nature. It makes the hard, outer layer of teeth (called enamel) stronger. – Canadian Dental Association

We hope you and your kids learned something about enamel and the importance of protecting your teeth with fluoride! 

Source: http://www.cda-adc.ca/en/oral_health/teaching_resources/eggsperiment.asp