Abscess, fistula and drainage. Ref.: 66

A dental abscess or phlegmon is the accumulation of pus caused by a bacterial infection and can occur for various reasons, such as due to an untreated cavity or a periodontal problem. Symptoms include severe pain, fever, swelling, inflammation, etc.
If an abscess is not treated, it can cause the infection to spread, or cause a fistula, through which pus drains to the outside.
A drainage consists of creating a small access through the tissues to allow the pus to drain to the outside.
In cases where there is pulp involvement it may be necessary to perform an endodontic procedure to resolve the infection. In cases where the infection persists despite having performed endodontics, it may be necessary to perform an apicoectomy or remove the piece, depending on the case.