A root canal is usually done in two appointments, though it can be done in one long treatment. Generally it takes around an hour and a half altogether, and the first appointment is usually around thirty minutes.
The procedure is done to clean and remove infected pulp tissue within a tooth. The tooth generally becomes infected through a crack, which gradually erodes away the tooth enamel, and it leaves the inside of the tooth exposed to everything that goes into the mouth. As there are a lot of nerves inside the tooth, this can become extremely painful and a root canal is needed to clean out, and to remove the nerve from the tooth, before filling it back up and protecting it once again. As with any operation, there are potential risks involved, and things can and do go wrong, but generally this is a really safe procedure. It is not painful as some people suggest that it is, as the mouth is numbed so that you cannot feel a thing.