There are a number of reasons why you may experience swelling in one or both cheeks. Minor injuries from a fall or blunt force can cause damage to the soft tissues and bones in the face, causing swelling. A minor injury will often heal on its own. Untreated tooth decay leads to infection around the root of the tooth. In severe cases, it leads to a pocket of pus called an abscess. This can also lead to facial swelling. If you have a fever along with the swelling, you need to see your dentist immediately, as this could indicate the infection has spread into your jaw or other parts of the body. Your dentist will treat the abscess by draining it and getting rid of the infection.