Wait at least 30 minutes. Here’s why. Believe it or not, sugar doesn’t cause cavities — at least not directly. Sugar feeds cavity-causing bacteria, such as Mutans streptococci (strep throat), and it is those bacteria that directly cause cavities. Sugar contributes to cavities because the bacteria process sugar into demineralizing acids that damage your tooth enamel and cause cavities.  Anytime that we eat sugar, we expose our teeth to these acids. Sugar is like fuel for cavity-causing bacteria. The acid that is produced will break down your enamel, so it would be a mistake to immediately brush your teeth after eating. When you brush your teeth while acid is present, the abrasive brushing grinds the acid into the enamel, causing more damage. Instead, you should swish thoroughly with water to wash away as much acid as possible. After about 30 minutes, it will be safe to brush.  Related Post: Common Acidic Foods That Damage Your Teeth