Inside every tooth lies the pulp, often called the "nerve". If bacteria reach it, for example through deep decay or a crack, it becomes inflamed. This often causes severe pain, but sometimes the inflammation causes no symptoms at all.
In root canal treatment (endodontics) the inflamed tissue is removed and the fine root canals are cleaned, disinfected and then tightly filled. Digital X-rays help us measure the length of the canals precisely on screen.