Teeth contain nerve tissue in their innermost portion. This is why teeth often have to be numbed prior to dental work being performed. If the nerve on the inside of the tooth is injured, it can begin a process from which it cannot heal. This can sometimes cause severe pain and infection. When a tooth reaches this point, it either must be extracted, or it can often be saved with root canal therapy. During this therapy, the canals where the nerve rests are cleaned, shaped, and disinfected to allow placement of a rubberized filling material. If all the canals can be accessed, disinfected, and filled, there is a great chance the symptoms will subside, and the tooth will be saved. Back teeth that receive root canals will need a crown to protect the tooth from future breakage.