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Rebecca's Science Project, 8th Grade


Awards Earned:

2nd Place, 8th Life Science, PCA Science Fair

Photograph of Rebecca's Science Project
Problem to be Solved:

Which mouthwash kills the most oral bacteria?


The mouthwash containing sodium fluoride will work the best because it is an oxidizing agent, which kills bacteria and prevents more sulfur compunds from generating. It differs from the mouthwashes containing zinc, which simply decrease the concentration of sulfur compounds, and the antiseptic mouthwashes that can cause your mouth to be dry.


Listerine - antiseptic mouthwash.
Act - sodium fluoride mouthwash. 
Diabet-Aid - cetylprindinium chloride mouthwash
Lavoris - zinc chloride mouthwash


Gather materials. On the back of a petri dish, trace a quarter four times using a marker. Two hours after two people have eaten, have them rinse their mouths with water. They will rinse their mouths so that they are wet. Swab the back of their tongues with separate cotton swabs. Then gently wipe the area inside of separate circles with the separate cotton swabs. Have them rinse out their mouths with one of the mouthwashes with the directed amount and for the directed amount of time (from the bottle instructions). Then have them rinse out their mouths with water. Again swab the back of their tongues and swab inside the area of another pair of circles. Label each circle on the petri dish to identify before and after circles. Tape the petri dish together so that it is sealed. Four days after the experiment, take a picture of the petri dish and record and compare the amount of bacteria grown. Record the amount of dots and the sizes of the dots, or record the size of the mass grown. Do the experiment with each of the four mouthwashes. Then repeat the procedure with all four mouthwashes again, but with another pair of people.


The zinc chloride mouthwash Lavoris had the least amount of bacteria growth and thus worked best. The sodium fluoride affected bacteria from one person, but not the other. In further experimentation, I would use each mouthwash for two consecutive weeks instead of just once.

Biblical Application:

Do you not know that your body is a temple of the Holy Spirit, who is in you, whom you have received from God? You are not your own; you were bought with a price. Therefore honor God with your body (1 Corinthians 6: 19-20). You need to take care of your body because it is the temple of God, therefore it belongs to God. Jesus even sacrificed Himself to pay for our sins, so we need to give our life to God and glorify Him with our bodies. Since you do not own your body, you need to take good care of it. Personal hygiene and cleanliness play a significant role in caring for your body. Therefore, caring for your mouth is important.

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