A root canal is a procedure that is usually done on a non-vital (dead) tooth or a painful dying tooth. The tooth is well frozen and the inner tissue of the tooth is removed. An antibacterial agent is used to flush out the inside of the root(s). The root(s) are then sealed in a rubber-like material and a permanent filling is placed. Root canals can be avoided by catching cavities when they are small and hidden. A painful tooth with a large cavity will usually need a root canal or an extraction.