A root canal is simply a procedure to remove the nerve and the pulp from inside a tooth. The tooth is then clean and sealed. This is used for teeth that are badly injured or decayed. This procedure does not affect the day-to-day functions of a tooth, only the ability to feel hot or cold. Teeth that would have had to be pulled just a few years ago can now be rescued.
Over the years myths have developed as to how painful and dangerous having a root canal is, but these have been extremely exaggerated. The truth is having a root canal is no more painful than getting a filling.