All right, so why do you need a root canal? Typically, you need a root canal because of two reasons. Main reason is that the nerve has been traumatized, either by trauma or by infection due to like a cavity. So the bad bacteria gets inside the tooth and more or less causes the tooth to die and cuts off the blood supply one way or another to the tooth.
So once the tooth has become dead and necrotized, there's bad bacteria that are in the booth. The blood supply has been cut off, the body can't heal the inside of the tooth anymore, so it's our job to go in there and kind of clean up the tooth. A good example I like to give is: if you have a candle - you know how the wick's in the middle of a candle, just how the nerve is all the way up and down the whole tooth - you have to take out the wick, clean out the inside of the tooth and put in a rubber filling. And that way your body can clean the infection outside the tooth, and then there's no longer infection in the tooth.