After a new denture has been inserted, it remains in the mouth quite nicely due to the fact that the shape of the inside of the denture base conforms closely to the shape of the gums. Unfortunately, the longer you wear the denture, the more your gums change underneath it, and the looser it gets.  In order to restore the retentive qualities of the denture, and to prevent the production of flabby gum tissue under it, you should have the denture professionally relined at least every two years. 

There are actually three types of denture relines: Hard, Soft and Temporary.

Hard reline

This is the kind of reline that should be done on all full dentures every two years.  The dentist removes some of the plastic from the inside of the denture, and then fills the denture with a soft material (think of soft putty) which, when replaced in the mouth, conforms to the contours of the tissues, and then hardens to a rubbery consistency.  When the denture is removed, the denture now contains an accurate impression of the shape of the gums.  The denture is sent to the lab, and the impression material is replaced with pink, hard acrylic in exactly the same shape as the original impression material.  When returned, the denture now conforms to the contours of your mouth and should make maximum contact with the tissues producing maximum suction. 

Soft reline

Occasionally, a patient finds that he cannot wear the denture because his gums are too tender, and keeps getting sore spots.  In cases where the patient is unable to wear ordinary dentures because of tender gums, the denture can be relined with a material that remains somewhat pliable for a year or two before it needs replacement.

Temporary relines (Therapeutic relines)

Frequently, by the time a patient with an old denture finally shows up at the dentist's office looking for a new denture, the dentures have not been serviced for such a long time that the gums are in terrible condition.  They may be red, swollen and quite misshapen.  Relining the old denture, or building a new one using impressions taken while the gums are in such poor condition would lead to a denture that would simply perpetuate the problem with the new appliance.  

When faced with situations like this, a dentist will frequently resort to a temporary, or palliative (medicated) reline material to allow the inflammation to subside.  This reline makes the denture fit much more tightly, and is usually soft and pliable.  It will not last more than a few months, but the patient wears it for a few weeks until the gums return to a more normal state.  After this happens, then the patient is ready for his new denture.