A root canal is done to alleviate a patients pain.  This pain can be from
a deep cavity, producing a pulpitis, or inflammation of the tooths pulp
tissue.  The pain can also be from an abscess or infection around the
root tip of the tooth, caused by the pulp of the tooth dying.  The root
canal is done by cleaning out the pulp canals and chamber of the tooth
and filling and sealing it.  After a root canal it my be recommended to
have a crown placed on  a tooth to strengthen it.  Root canals have
about a 85 - 90% success rate, and if it does not work, it can be redone
or repaired surgically.  
Endodontics (Root Canals)