How can you tell of you have an abcess tooth if the root is already dead?

X-ray: A tooth that has already had a root canal can re-abscess and fail. If the tooth never had the root canal to remove necrotic tissue, an abscess can happen because the bacteria is still present withing the canal. A root canal removes the tissue and the canal is sterilized and sealed to prevent further infection. Swelling, a gum boil above the tooth or an x-ray are all verification of an abscess.

See Dentist: See the dentist for evaluation and x-ray imaging of the tooth. It can infect , even if it has had a root canal.