Exostosis after root canal. what is that?

May not be related: An exostosis is a benign growth of bone and is usually developmental. It is usually not related to a root canal procedure. There are occasions when an infection around an infected tooth can expand the surrounding bone but that is very rare and almost always in children called garre's osteomyelitis.

Possible cyst: One other possibility may be a residual odontogenic cyst that could be expanding cortical bone over the root of the tooth. A followup film after the root canal has been completed for a few months will either show healing or a possible bony cyst. The cyst (if present) will expand much more quickly than a true exostosis which will expand very slowly.

Exostoses: Exostoses refers to extra bone in the jaw on the cheek side of the teeth. I have never heard of this. Is it possible your had exostoses before the treatment but never noticed it. How long after treatment did you notice this? Is the area tender to touch? Is it hard or soft?Who told you about this? If you are having any swelling or pain, I would see your dentist.

Unrelated: Exostosis is a thickening of bone around the teeth and is not related to root canal therapy.