I do not know if anyone has experienced this, but I had a root canal for a tooth, and a day after it was completed I began to develop painful hives that do not go away. They keep on multiplying. I have gone to several doctors and they say that it could not be from the root canal, but have no explanation. They have done allergy testing, which comes back normal. I am in a lot of pain with this. Has anyone ever experienced this, or know if it is possible to be allergic to the tooth that was done.