Root canal therapy is needed when the pulp (nerves and blood vessels) of teeth have become invaded by bacteria. This condition leads to hyperemia (excess blood in the pulp), irreversible pulpitis (pulpal infection and death) and then abscess (infection in the surrounding bone). Symptoms include pain, swelling, and increased sensitivity to hot and cold.

Treatment involves removal of all organic tissue from inside the tooth (including any bacteria) and filling the inside of the tooth with a rubberized material known as Gutta Percha. This prevents bacteria from ever inhabiting the space again and allows for maintaining the tooth in place as opposed to extraction. The treatment can take anywhere from 1-2 or more visits, but generally will require only one appointment.

After  root canal treatment, a tooth generally needs to be protected with a crown.  The main benefit of  root canal therapy  is that you are able to keep the tooth versus extraction.  Although extraction is cheaper, the space left behind will require a bridge or implant, which can be more expensive than the root canal therapy. 

The rest is up to you.  The restored tooth can remain healthy as long as its roots are nourished by the surrounding tissues.  Good oral hygiene at home and regular dental visits can help prevent tooth decay and gum disease.  Modern root canal therapies are more than 95% successful.  If you take good care of it, the restored root canal treated tooth could last a lifetime.