Which Brand of Toothpaste Will Reduce the Most Bacteria?

For this science fair project I am willing to determine which toothpaste is most effective when it comes to removing bacteria
Amina Alwan
Grade 7


For my hypothesis, I believe that Crest toothpaste is most effective because it is a popular brand that seems effective. However, the amount of bacteria varies from person to person, but my best guess would be Crest.


The purpose of this Science Fair Project is to determine which toothpaste is most effective when it comes to removing bacteria. The research question I was going to answer with the results of the experiment is which toothpaste removes the most bacteria. The research I conducted to learn more about toothpaste helped me to further understand bacteria and why you have to brush every morning and night. Toothpaste has been around for centuries and it has gone through many phases of change to what it is today. Toothpaste usually contains fluoride which is found naturally in some foods such as tea and fish. Fluoride has been used for about 50 years in cleaning teeth and has shown to be effective in removing bacteria. Another thing contained in toothpaste is humectants. Humectants give toothpaste it's texture and it keeps it moist so it doesn't dry out. Some certain kinds of toothpaste have stripes and how manufacturers achieve this is simple. First, they make the colours in different tanks at the factory. From their different tanks, the coloured stripes are pumped into pipes at the filling machine. The coloured stripes are brought together with the white toothpaste in even parts. Then all three are pumped into the toothpaste tube to form perfect stripes all the way through.


Ever since we were young we were told to brush our teeth in the morning and at night. We were told that if we didn’t brush our teeth our teeth would get dirty, it would rot, you would get cavities, etc. But we were never told how these changes when we don’t brush our teeth happen which is something I will look into. Brushing teeth often help in the prevention of gum disease and when you refuse the bacteria starts building up in between your teeth which brings me to my next point, flossing. Flossing is very much needed in preventing any type of dental diseases from the food and sugar stuck in between our teeth and only takes a few minutes every day. And so, Flossing would pick out all of the gunk in between one's teeth and reach in places where a toothbrush can't. Bacteria is a living thing, it eats, moves, reproduces, etc. And so, bacteria feeds on the sugar that’s in our mouth and this bacteria, which is the most common one is called Streptococcus mutans. This type of bacteria is very harmful to our oral hygiene and may cause tooth decay. But Streptococcus mutans is not the only harmful bacteria, there are over 700 kinds of different bacteria found in peoples mouths. Most are not that harmful but another harmful bacteria that is often not taken lightly is Porphyromonas gingivalis. 


This bacteria can cause tooth pain and even tooth loss, and it’s said to be linked to periodontitis. Periodontitis is said to be an urgent and growing disease and can cause damage to the bone of the teeth, and it causes extraordinary pain and may just lead to tooth loss. By the time you have a strain of bacteria in your mouth you most likely won't fully get rid of it. However, by managing good oral health you can control the amount of bacteria in your mouth by brushing and flossing.

Brushing your teeth should take up to 2 mins while flossing should be done in between all teeth. This is the most effective way to maintain healthy teeth.



The controlled variables are the method of brushing the teeth, the type of toothbrushes used, the length of time for which the teeth are brushed, the room temperature, the amount of sunlight and the amont of agar in the petri dish

The manipulated variable would be the amount of bacteria after the expirement ends.

The independant variable would be the bacteria on the teeth before the expirement starts each morning.



1. Four kinds of toothpaste: Colgate, Sensodyne, Aquafresh, and Crest will be used each morning

2.  A petri dish with agar would be used each morning to store the bacteria

3. The mouth would be rinsed three times with water then a swab would be rubbed under teeth then stored in the petri dish then labeled- before

4. Normal brushing would be procced, then when done swab would be rubbed under teeth and placed in a petri dish and labeled- after

5. Continue for four days with each toothpaste


My hypothesis was incorrect, Crest toothpaste was not the most effective toothpaste.


The materials I will use in this Project are: 

  • 8 Petri dishes with agar
  •  8 disinfected swabs
  •  1 bottle of disinfected water
  •  4 toothbrushes
  •  1 cup with water
  •  4 kinds of toothpaste – Colgate, Sensodyne, Aquafresh, and Crest
  •  1 marker 


For this Science fair project, Colgate toothpaste reduced the most bacteria when used. My hypothesis was incorrect, Crest toothpaste was not the most effective toothpaste. What I learned was popularity doesn’t determine the quality of the toothpaste. This experiment can help modern society in the choosing of a good effective toothpaste. So, if you want a change in toothpaste and looking for good effective toothpaste, Colgate is the one to get.


The results show that all the Petri dishes with bacteria samples taken after brushing with toothpaste had a smaller amount of bacteria growth. The petri dish with “Colgate – after” toothpaste had the smallest sized bacteria amount.


Sources Of Error

My hypothesis was incorrect


Much thanks to:
CIS judges
CYSF for selection
and parents for help with my experiment