A reline is the process of replacing the old fitting surface of an older denture with an updated new one ( think of a new sole on a shoe?)
Denture relines are necessary in order to accomplish several goals. These goals include:
Increasing retention and vertical height of old, existing dentures or new dentures that, for one reason or another, have lost retention. Often due to recent extractions or sometimes due to surgical oral procedures.
Relining of old dentures to prolong the necessity of making new dentures.