Even with a crown, a new cavity can develop at the border of the tooth and the crown, in the same way a cavity can form at the edge of a filling. A cavity is caused by dental plaque buildup leading to tooth decay. If the decay spreads beneath the crown or deeply into the tooth, the nerve tissue becomes inflamed and painful. Should bacteria from the decay reach the nerve itself, root canal therapy or removal of the tooth is necessary to clear the infection. Root canal therapy in a crowned tooth involves drilling a small hole into the crown to remove the infected nerve and surrounding tissue in the tooth roots.
The gums around a crowned tooth can recede with time, exposing part of the root and leading to hot or cold sensitivity, or both. Gum recession is often associated with excessively forceful tooth brushing. Areas of gum recession are particularly susceptible to developing plaque buildup, which can lead to a painful gum infection.

Contact your dentist as soon as possible if you develop a toothache in a crowned tooth. Whether the crown is new or established, a dental professional can investigate the cause of the pain and intervene, if necessary. Early diagnosis and treatment of problems in a crowned tooth offers the best chance of saving the tooth.