An oral cyst is an unexpected fluid-filled sac in or around the mouth that can be caused or aggravated by an infection in the pulp area of the tooth, overly irritated or injured tissue in the mouth or an impacted wisdom tooth. Symptoms include a lump inside of the mouth or along the jawbone or pain near the teeth. Some cysts are painless, while others that become infected or abscessed can become red, swollen and very painful. While oral cysts are not cancerous, it’s important to have a dentist examine any cyst that forms, especially if it does not go away.