Bacteria Teeth Kids Science Fair Projects

Jason
Grade 5

PROBLEM
The purpose of my experiment is to see if the amount of bacteria on your teeth changes if you brush your teeth for 1 minute or if you brush your teeth for two minutes.

Hypothesis
If you brush your teeth for two minutes there will be fewer bacteria on your teeth than if you brush your teeth for one minute.

Materials

• 18 sterile Petri dishes
• 2 bottles of nutrient agar
• 18 sterile swabs
• Masking tape
• Toothbrush
• Toothpaste
• Distilled water
• Timer

Experiment
First, I prepared 18 sterile Petri dishes by filling them with nutrient agar. I labeled them with a zero, one or two. I stored the dishes in the refrigerator until it was time to use them.

For each session, before I brushed my teeth, I wet a sterile swab with distilled water and swabbed my molars on the bottom left side of my mouth. I took the swab and inoculated the agar in the Petri dish labeled “0”. Then, I put toothpaste on my toothbrush, set the timer for one minute and brushed my teeth. After one minute, I rinsed my mouth and swabbed my molars on the bottom left side of my mouth with a wet sterile swab and inoculated the agar in the Petri dish labeled “1”. I then brushed my teeth for 1 more minute and swabbed the same teeth with a wet sterile swab and inoculated the Petri dish labeled “2”. I repeated this session a total of 6 times when I would normally brush my teeth.

I kept the Petri dishes upside down at room temperature. Bacteria growth was visible after 2 days.

WHAT I WOULD DO DIFFERENTLY NEXT TIME
Next time, I would take more samples in case some of them didn’t grow. I also would like to see if eating sugar right before you brush your teeth makes a difference in how much bacteria is in your mouth. Finally, I would buy a black display board and not try to paint a white one black. Paint makes it warp and it won’t stand up.