Root canal therapy is often portrayed in pop culture as a painful treatment that should be avoided. In fact, root canals are actually done to relieve pain and infection. With modern anesthetics and techniques, root canals are virtually pain-free. It is actually quite common for patients to fall asleep during root canal procedures because they can take a while to perform!
Root canal therapy is usually needed because the nerve and blood vessels inside a tooth have died and become infected either due to a deep cavity or due to a traumatic injury. The death of these tissues is often, but not always, accompanied by a very bad toothache. The body is unable to remove the dead nerve and vascular tissue inside a tooth, thus, the dentist must remove this tissue during a root canal procedure.
After anesthetizing the tooth, the dentist drills a hole into the centre of the tooth until the root canal system is reached (ie. where the nerves and blood vessels are). Then, a series of files and disinfectants are used to remove this tissue and kill off the bacteria which are present. Finally, a special type of filling material is placed into the root canal system to prevent infection from coming back again.