That is how acute periradicular abscesses are formed. Clinically, these patients present with swelling and mild to severe pain. Depending on the relationship of the apices of the involved tooth to the muscular attachments, the swelling may be localized to the vestibule or extend into a fascial space. In addition, the patient may exhibit systemic manifestations such as fever, chills, lymphadenopathy, headache and nausea. Since reaction to the infection occurs very quickly, the involved tooth may or may not show radiographic evidence of pathosis - a widened periodontal ligament space or radiolucency.
Treatment involves root canal therapy to remove the source of the infection.
In some cases, incision and drainage may precede the root canal therapy.