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The materials required for this science fair project:
- 8 agar petri dishes prepared with agar
- 8 disinfected swabs
- 1 bottle of disinfected water
- 4 toothbrush
- 1 participant
- 1 cup and water
- 4 types of toothpaste – Colgate, Sensodyne, Aquafresh and Crest
- 1 marker pen


1. For this science fair project, the independent variable is the brand of toothpaste used - Colgate, Sensodyne, Aquafresh and Crest. The dependent variable is the rate of bacteria growth in the petri dish. This is determined by measuring the size of the bacteria colony using a ruler. The constants (control variables) are method of brushing the teeth, the type of toothbrush used, the length of time for which the teeth is brushed, the room temperature, the amount of sunlight and the ingredients in the petri dish.

2. The 8 petri dishes that are prepared using agar are stored in a refrigerator. The petri dishes are brought to room temperature before the start of the experiment by taking them out of the refrigerator and allowing them to attain  room temperature.

3. The science project will be conducted over 4 days using a different  brand of toothpaste each day. The same type of toothbrush, for the same length of time and the same method of brushing the teeth will be used on all 4 days of testing.

4. On the first day of the experiment the Colgate toothpaste will be used by the participant. First, the participant is asked to rinse his mouth for 5 seconds and to then spit out the water. This is repeated 3 times.

5. The sterilized swab is first made damp using the sterilized water.  The swab is rubbed over the front and back teeth of the participant and then rolled on the surface of the petri dish. The cover is closed and the petri dish is marked “Colgate –before”. The petri dish is kept in a cool shady place for the bacteria to colonize.

6. The participant will then brush his teeth using the Colgate toothpaste according to the requirement set out in procedure 3. After brushing his teeth, procedure 5 is repeated again and the petri dish will be marked “Colgate - after “.

7. Procedures 4, 5 and 6 are repeated on the second day using the Sensodyne toothpaste, on the third day using the Aquafresh toothpaste, and on the fourth day using the Crest toothpaste.

8. The diameter of the bacteria colony is measured after 5 days and recorded in the table below. .

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Complexity level:
Project cost ($):
Time required:
1 hour to prepare, 4 days for science fair project
Material availability:
Easily found
Safety concerns:

The bacteria should be destroyed before being disposed of. Pour some bleach into the petri dish to kill all the bacteria before disposal.