1.    Tthe independent variable of this experiment is the conditions of which the dental retainers are subject to – non brushing, brushing with toothpaste and rinsing with mouthwash The dependent variable is the  amount of bacteria growth in the relevant Petri dish. This is approximately determined by measuring the size of  bacteria growth using a ruler. The constants (control variables) are  room temperature,  amount of sunlight and the ingredients in the Petri dish agar.

2.    Prepare 12 Petri dishes of agar and store them in the refrigerator. Bring them to room temperature before the start of experiment by taking them out of the refrigerator.

3.    The experiment will be performed over the course of 3 days Remember to always follow laboratory safety guidelines and always practice sterile technique when handling microbes. Never have any food or drink at your workstation and always thoroughly wash your hands with disinfectant soap or alcohol before leaving your workstation. Always dispose of used material in a biohazard bag. If none are available, the bacteria should be destroyed with bleach before being disposed of. To do this, you need to ensure that you have proper safety gear (gloves, goggles, etc). Prepare a bleach solution of at least 25% concentration (diluted with 3 parts of water). Soak the petri dishes for 24 hours in the bleach solution before disposal, always being mindful that bleach is corrosive and should be handled with care.

4.     On the 1st day of experiment 4 participants are required to wear their dental retainers continuously for 24 hours without brushing their teeth. After  24 hours, the participants are requested to gargle with water for 10 seconds, and to spit out the water. This simulates conditions where a person does not brush his teeth but merely rinses his mount with water. 
   
5.    Wash a cotton swab with sterilized water. Squeeze dry, then wipe the dental retainers with the washed cotton swab before rubbing the swab gently onto the agar surface in the Petri dish.  Ensure that you cover the entire surface area of the dish (swab in at least 3 directions). This Petri dish is labeled “without brushing”. The Petri dish is then covered and incubated in a cool shaded place for 5 days, allowing the bacteria to colonise.

6.    On the 2nd day, the participants will brush their teeth using toothpaste. Ensure that  a regular bran/type of toothpaste is used - and have the participants use the same toothpaste. Wait for 4 hours after brushing, then repeat procedure 5 with their dental retainers.  Label the petri dishes as “after brushing with toothpaste”. On the third day, the participants will rinse with mouthwash whilst wearing their dentures (use any regular brand, and ensure that they all use the same brand), and then after 4 hours, the procedures in paragraph 5 above will be repeated. Label this batch of petri dishes as “after rinsing with mouthwash” .

7    The diameter of the bacteria colony growth is measured for each batch of petri dishes, after 5 days of incubation, and recorded in the table provided below