Science Projects on Teeth Bacteria

The human mouth is home to many types of bacteria.

Bacteria are single-cell microorganisms so tiny that to view a single one you need a microscope. They have no cell nucleus and reproduce rapidly, forming visible colonies. Bacteria play an important part in human health and outnumber human cells by 10 to one. Most of the bacteria in our bodies are beneficial or harmless, not pathogenic (disease-causing). Beneficial bacteria (normal flora) form a protective barrier on our skin and are necessary for digestive health. The human mouth provides a favorable environment for bacteria because of its supply of nutrients and saliva. The normal flora synthesizes vitamins and assists with our immunity system. Bacteria in the mouth can also cause decay, gingivitis, periodontal disease and other conditions..

Supplies

A microscope will help examine the bacteria cultures from your teeth.

The experiments on teeth bacteria can be performed sequentially or concurrently. Wait about two hours after eating to perform the experiments and do not brush your teeth. For the experiments, you will need:

Sterile petri dishes, 6 or more per person

Agar, 125 ml per person

2-quart pan of hot water between 170 and 190 degrees F.

Potholder or tongs

Sterile exam gloves, up to 5 pairs per person

Sterile cheek swabs, 6 or more per person

Compound or stereo microscope, optional

Blotter paper

Sterile scissors

Fine-tip permanent marker

Sterile tweezers

Various new tubes of toothpaste, four or more per person

Various new bottles of mouthwash, four or more per person

Small sterile glass cups, enough for each person to have one for each toothpaste or mouthwash tested

Paper towels

Used, damp toothbrush, one per person

Bleach, 1 cup per person

Plastic trash bag

Preparing Petri Dishes

Prepare the petri dishes before starting the experiments.

Prepare the petri dishes by melting the agar in the hot water until it liquefies. Remove the agar from the water using the tongs or potholder and let it cool to 110 to 120 F. Wash your hands and put on the sterile exam gloves. Open the cover of the petri dish just enough to pour the agar to fill the petri dish 1/2 to 2/3 full (10 to 13 ml.). Do not touch the petri dish with the bottle or your hand, and try not to breath on it. Replace the cover on the petri dish immediately after filling to prevent contamination. Gently tilt the petri dish to coat the bottom evenly and let it stand an hour before using. Label one petri dish as the control and set it aside. Excess petri dishes can be stored in the refrigerator upside down.

Teeth Bacteria Cultures

Use a zigzag motion to rub the bacteria onto the surface of the agar.

Wash your hands and put on sterile exam gloves. Swab some of your teeth with the sterile cheek swab. Open another petri dish and lightly swipe the surface of the agar in a zigzag pattern. Rotate the dish one quarter turn and swipe again in a zigzag pattern.

Close the petri dish immediately. Label the petri dish with your name if others are joining you in the experiment.

Store the petri dishes in a dark cabinet at room temperature and do not disturb for three to seven days. Do not open the petri dishes and examine them for bacteria colonies appearing in round dots. Compare your petri dish with the control and with other students' dishes. Examine the bacteria colonies under the microscope if available.

Dispose of used petri dishes by filling them with bleach, closing the lid, placing them in a plastic bag and throwing them away.

Do Toothpaste and Mouthwash Kill Bacteria?

Are toothpaste and mouthwash effective in oral hygiene?

Wash your hands. Put on the exam gloves. Cut the blotter paper into small squares, called sensitivity squares. Label each square with the name of one of the toothpastes or mouthwashes you will be testing. For each petri dish you will use, label one square of blotter paper as blank. Use the tweezers to handle the squares.

Add one sample of toothpaste or mouthwash to be tested to each glass cup and label the cups. Soak the labeled blotter paper squares in the appropriate toothpaste or mouthwash. Remove excess or spills with the paper towels.

Four samples can be tested in each petri dish. Use as many petri dishes as you desire.

Start the process for teeth bacteria cultures above. After rubbing the swab in a zigzag pattern, place the blank sensitivity square in the center of each petri dish with the other sensitivity squares scattered around it. Continue the process of growing teeth bacteria cultures. After three to seven days, remove the petri dishes from the cabinet and examine them.

Is any toothpaste effective at stopping the growth of bacteria? Does the toothpaste contain an antibacterial ingredient? Is any mouthwash effective at stopping the growth of bacteria? Does the mouthwash contain an antibacterial ingredient? What happens to the beneficial bacteria in the mouth when using toothpaste or mouthwash?

Dispose of used petri dishes by filling them with bleach, closing the lid, placing them in a plastic bag and throwing them away.

Human vs. Dog

Have an adult help obtain the teeth bacteria from a dog.

Wash your hands and put on exam gloves. Repeat the steps for growing teeth bacteria cultures above, using swabs from you own teeth and those of a dog. Have adult supervision for this and use extreme care.

Have you heard the human mouth is "dirtier" than that of a dog? Is this true?

Dispose of used petri dishes by filling them with bleach, closing the lid, placing them in a plastic bag and throwing them away.

Is Your Toothbrush Clean?

We use a toothbrush to clean our teeth, but is the toothbrush clean?

Wash your hands and put on exam gloves. Repeat the steps above for growing teeth bacteria cultures, but swab the toothbrush instead of your teeth.

Is your toothbrush "clean"? Should you let your toothbrush touch the toothbrush belonging to someone else in the toothbrush holder? Should you share a toothbrush? Can you think of ways to sterilize a toothbrush?

Dispose of used petri dishes by filling them with bleach, closing the lid, placing them in a plastic bag and throwing them away.

References

• Home Science Tools: Bacteria Science Project Guide
• The Virtual Museum of Bacteria: What Are Bacteria?
• The Virtual Museum of Bacteria: Bacteria Are Needed for Life
• Todar's Online Textbook of Bacteriology: The Normal Bacterial Flora of Humans