The requirement for relining occurs when bone and tissues change due to shrinkage. Possible causes may be:
bite position, existing teeth and acrylic base(s) must be in good condition
and not worn or stained to provide a reline procedure. An impression of your
oral tissue is taken inside your denture(s) to provide a working model. New
acrylic base material is added to your denture to produce a correct fit. The
appearance of your dentures will not change.
Denturists in most cases have no way of trying the denture(s). The procedure is similar to relining. The difference being is that, a rebase replaces all the pink-acrylic denture base material. The existing teeth remain in the exact same place.
for rebase procedure: