Oh no! You've heard the dreaded words "You need a root canal". But there is really no need to worry because root canals are : 1) Painless 2) Get rid of your infection 3) Save the tooth!
Root canals are done under local anesthesia, just a like a filling. They take about an hour and patients report minimal to no discomfort after the procedure.
When the cavity gets large enough where it reaches the nerve, or the tooth gets infected, a root canal is recommended. The nerve is removed with very thin, special files and the cavity is cleaned out and sterilized. The cavity is then filled with special material called gutta-percha, which reduces the chance of bacteria from re-entering and colonizing inside the tooth again.
Most of the time, a crown is recommended after a root canal, since the tooth is no longer strong enoigh to withstand chewing forces, which is 120 pounds of force for an average person!