A well-designed science project starts with background research on the topic of investigation. Read magazine and journal articles, books and websites on the importance of personal hygiene to learn what scientists already know about good hygiene habits. Pose a question about some aspect of personal hygiene that you want to know more about. For example, "Which toothpaste is most effective at whitening teeth or removing plaque?"; or "Which mouthwash -- or soap or hand sanitizer -- is best at removing bacteria?"
A scientific prediction is based on facts established by other researchers in the field to form a hypothesis about the results the scientist expects from testing. Take into account the information you gained from the research and make an educated guess about the answer to the question. For example, "I think Brand X will clean the teeth better than Brand Y because it contains fluoride as recommended by dentists"; or, "Anti-bacterial soap will remove more bacteria during handwashing than regular soap."
For a reliable scientific test, you need to control all the variables except one to isolate that one factor as the cause of any differences in results. Design a standard testing procedure for each subject so that each one uses the same kind of toothbrush, brushes or washes the same way for the same amount of time and uses the same amount of toothpaste, mouthwash, soap or hand sanitizer. Change only the type or brand of cleansing agent used in each test for an accurate comparison of the results of each. Use plaque-disclosing tabs, a dentist's tooth shade chart or a glowing gel that reveals germs on the hands to assess the effectiveness of the cleaning treatment. Take before and after pictures to illustrate the difference in cleanliness with and without treatment.
Scientific knowledge is only useful if someone can benefit from it so scientists need to communicate their findings to colleagues and the general public.
To create a science fair display board, write a summary of the background research, question and hypothesis. Describe the variables and testing procedures in detail. Create graphs and charts to illustrate the change in color or bacteria or plaque presence before and after washing or brushing. Arrange all the pieces neatly on the display board. Be prepared to clearly explain to visitors and judges what you learned about the importance of personal hygiene and the best methods at ensuring cleanliness. Some experiments, such as hand washing and checking results with glowing bacteria revealer gel and an ultraviolet light, lend themselves to allowing you to have your viewers try it for themselves at your table during the science fair.