Teeth with large restorations or fractures, or those that have had root canals, benefit from having crowns placed on them for protection and strength. Crowns are also placed on implants to restore esthetics and function. (NB: The terms crown and cap are often used interchangeably.)
In the event that a patient is missing teeth and would like to have something done to replace them, one option is bridgework. Bridges are multiple crowns attached to each other and cemented in the mouth so that they cannot be removed.