David M. Kaffey, DDS
1) It may be that the cement holding the crown became weak & if so, then the crown will be recemented.
2) Or your tooth under the crown may have decayed or
3) The core of the prepared crown may have broken.
Any defects must be fixed before recementing the crown - it is important that the crown be recemented properly without any voids in the marginal seal to prevent leakage & future decay under the crown.