Effectiveness of Mouthwash
Megan DiGuiseppe
Academy of Notre Dame
Purpose
The purpose of this experiment was to
test the effectiveness of Listerine
Antiseptic, a mouthwash that contains
alcohol, and Crest Pro-Health, a
mouthwash that does not contain alcohol,
on oral bacteria. Not only was the
effectiveness of each mouthwash
observed, but also how long each rinse is
effective.
Background
 The active ingredients in Listerine Antiseptic are eucalyptol,
methyl salicylate, thymol, and menthol. Ethanol (grain
alcohol) is 26.9% of the product’s concentration
 The active ingredient in Crest Pro-Health is 0.07%
cetlyperadium chloride, which is a bacterial agent that
attracts the bacteria in your mouth.
 The oral cavity is home to hundreds of bacteria, viruses,
protozoa, and fungi. However, of all the types of microbes,
bacteria are the most numerous.
 It has been estimated that there are over 100 million
bacteria in every milliliter of saliva.
Hypothesis
The hypothesis was that Listerine
Antiseptic mouthwash will kill the most
oral bacteria immediately after use and
be effective the longest because of the
active ingredient of alcohol.
Materials
 Listerine Antiseptic
Mouthwash
 Crest Pro-Health Mouthwash
 32 Easy Gel Total Count
agar vials and treated Petri
dishes
 Sterile cotton swabs
 Sterile 20 ml measuring cups
 Tap water
 Incubator
 Timer
Procedure
1.
Subjects rinsed with 20ml of tap
water for 30 seconds
8.
The subjects again swabbed the
inside of their cheeks
2.
The inside of the subjects’ cheeks
were swabbed
9.
3.
The swabs were mixed with the
agar vials and the mixtures were
poured into the dishes
The swabs were mixed with agar
vials and the mixture was poured
into the dishes
10. Waited 30 minutes
11. Their cheeks were swabbed once
4.
Subjects rinsed their mouths with
20ml of Listerine Antiseptic
mouthwash for 30 seconds
5.
The inside of the subjects’ cheeks
were swabbed
6.
The swabs were mixed with the
agar vials and the mixture was
poured into the dishes
7.
Waited 30 minutes
more and the mixtures were
poured into the dishes
12. The dishes were incubated for 48
hours and the bacterial colonies
were counted
13. The entire procedure was repeated
again a week later using the Crest
Pro-Health mouthwash
Variables
 Independent Variable: The brand of mouthwash
 Dependant Variable: The number of bacterial colonies
after each swabbing
 Control: The swabbing after the mouths were rinsed
with tap water
 Constants: The amount of mouthwash and water,
source of water, rinsing time, incubation time,
Graphs and Data
Graphs and Data
Summary Graph
Problems and Limitations
 The results are limited because they only apply
to high school-aged, Caucasian girls.
 Because this experiment used human subjects,
there were some minor timing and participation
problems.
Further Studies
 The same experiment could be conducted again using
different brands of mouthwashes or toothpaste.
 The effectiveness over a longer period of time could be
tested.
 This experiment could also be repeated using people of
different ages, ethnicities, and gender
Conclusion
The first part of the hypothesis that Listerine
would kill more bacteria immediately after use was
rejected; however, the portion of the hypothesis
that Listerine would be effective the longest was
supported.
Work Cited

Arnold, P. (2010, July 22). Mouth Bacteria. It’s a Jungle in There. American Journal . Retrieved from
http://www.brighthub.com/science/genetics/articles/45935.aspx

Bowers, C. (2010). Mouthwash Review: Crest Pro Health Rinse Vs. Listerine Antiseptic. Retrieved
from Associated Context, Inc. website:
http://www.associatedcontent.com/article/243129/mouthwash_review_crest_pro_health_rinse.html?cat
=5

Colihan, K. (2008, October 7). Mouthwashes really do fight bad breath. WebMD Health News.
Retrieved from http://www.webmd.com/oral-health/news/20081007/mouthwashes-really-do-fight-badbreath

Gutundo, P. (2010). Mouth Bacteria . Retrieved from http://ezinearticles.com/?MouthBacteria&id=1818508

Halitosis treatments: Using mouthwashes and mouth rinses to get rid of bad breath. (2010). Retrieved
from Animated-Teeth website: http://www.animated-teeth.com/bad_breath/t5_halitosis_cures.htm

Listerine Antiseptic Mouthwash: Original . (n.d.). Retrieved from McNeill-PPC Inc.: Johnson and
Johnson Healthcare Products Division website: http://www.listerine.com/product-original.jsp

A mouthful on mouthwash. (n.d.). Retrieved from PlantetRx website:
http://www.planetrx.com/library/articles/index.cfm/ID/25037

Mouthwash. (2008). Retrieved from Cosmetic Dentistry Guide website:
http://www.cosmeticdentistryguide.co.uk/articles/mouthwash.html

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