Facial swellings are usually a sign of a severe infection. Pus has formed and has entered the space between tissues. This may or may not be accompanied by pain, but it is very important to see a dentist straight away to assess the cause, and start any appropriate treatment. Left untreated, swellings may cause hospitalization, especially if they spread to the neck region and start to cause difficulties in breathing.
Treatment may include drainage of the swelling if appropriate (either by a small incision, or by making a small hole in the tooth) and the use of antibiotics. Sometimes, if appropriate and if clinically feasible, the offending tooth may be removed.