Root canals become necessary to save a tooth when its root becomes damaged due to an injury or a large cavity which leaves it infected or inflamed. In order to treat the problem, the dentist first has to numb the tooth and then make an opening reaching from the crown to the pulp chamber. Using special files, he then cleans out the infection and unhealthy pulp inside the canals, irrigates them, and shapes them so as to make room for the filling material. In order to protect the canals from contamination and further infection, they are typically filled with a permanent material known as gutta-percha. The focus is now turned toward rebuilding the tooth and the first step is to seal the opening with a temporary filling material that is placed on top of the gutta-percha until a permanent filling or crown is prepared. Made to look like a natural tooth, this crown is then placed on top of the tooth and, if needed, is supported by the insertion of a post into the root next to the gutta-percha. The crown is then cemented into place and the procedure is completed.