After a crown prep procedure, a temporary crown is placed. The cement used is weak to provide easy access for placing your permanent crown.
Permanent crowns are placed with a much stronger cement, however occasionally the seal of that cement can be broken by biting on something hard or sticky.
Should your crown, temporary or permanent come off, you can recement your crown using a paste/gel denture adhesive such as Fixodent or use a temporary cement/temporary filling material kit that is occasionally available at drugstores. It is important that the crown, temporary or permanent, not stay off the tooth for very long as the tooth can become damaged or teeth can shift causing the crown to no longer fit. NEVER USE SUPER GLUE. Super glue is very toxic and can damage the tooth under the crown and the surrounding teeth as well. Call the office to be scheduled for a recement at your earliest convenience.