A crown is needed when your tooth has either broken or a large, existing filling has new decay around it.  Crowns are also recommended after most root canals because the tooth has become weakened and needs reinforcement.  Dental anesthetic is commonly used for your comfort.  The tooth is prepared with a hand piece making sure that all ideal measurements are made to ensure proper fit of the crown.  An impression of your tooth is taken to be sent to a dental lab.  A temporary crown is made from plastic to keep you comfortable while your permanent crown is being made by a dental artist.