An internal filling placed inside a dead tooth. The root is not removed. Normally, a tooth has canals and a chamber that contain vital nerve tissues and blood vessels. Sometimes the tissues can die due to trauma or can become infected by bacteria from tooth decay. When this happens, dead tissues or infected tissues have to be cleaned out and the canals have to be plugged completely. Basically, the root canal therapy consists of cleaning the canals and a chamber and filling the canals so that bacterial cannot travel from mouth into the body.