Upper Dentures are held in place by interfacial surface tension, generally referred to as "suction" or "vacuum" and other important factors such as good base adaptation and border seal.
The same applies for Lower Dentures, but the small support surface area and the pronounced musculature in the lower jaw, reduce the secure grip of dentures, causing displacement of the denture.
Wearing dentures for a number of years causes the underlying surface to resorb, resulting in "shrinkage" of the gum. In worst cases, the "shrinkage" is so severe as to make virtually impossible the construction of stable, satisfactory dentures.
