Sometimes teeth can get infected. This usually happens when a cavity progresses down to the middle of the tooth, causing the nerve within the tooth to die. Teeth that previously had root canals can also get infected even though they don't have nerves any more. The infection can be painful and sometimes causes the gum to swell near the tooth or can be more advanced and cause the cheek to swell or cause swelling underneath the eye or jaw. This oftentimes depends which tooth is involved. Infection and swelling can be dangerous and needs to be evaluated and treated quickly. An abscess is a collection of pus that builds up in the area. Usually the tooth needs to be removed and infection or abscess drained and washed out. Antibiotics are useful but do not replace primary treatment or surgery.