A cavity can be so large that it allows bacteria to inflame tissue in one of the canals in which the roots of our teeth are housed. If the inflammation goes untreated, it creates a pocket of infection (an abscess) that can cause pain or sensitivity when you chew. It may also cause your gums to swell.
Your dentist or a specialist called an endodontist treats an abscess with a root canal—the name most people use for the process of removing the infected material from the canals, then filling them. The job is finished when your dentist places a crown on the tooth or completes some other form of restoration.
Today, given modern dental techniques, root canals are almost always painless. Never hesitate to undergo one if necessary. They can save teeth and stop pain. However, if an infection goes untreated, a root canal may not be enough to save the tooth and remove the infection. In that case, removing the tooth may be the only solution.