You can never get rid of all the bacteria in your mouth. However you can take steps to control and disrupt the bacteria so that it does not attack your teeth and cause dental health issues such as tooth decay. To do this make sure to brush your teeth twice a day, floss daily and reduce the number of times each day that you consume fermentable carbohydrates.
Some mouthwashes reduce bacteria in your mouth. This can help prevent decay. Chewing sugarless gums, especially those with xylitol, can help reduce the number of bacteria that cause cavities and increase the flow of saliva. Also you need to make sure that you visit your dentist regularly. The dentist can find and treat any decay before it causes larger dental issues.