The most common complaint among patients using full dentures is always, “My upper palate holds very well, it suctions up, but my lower palate keeps coming out, it pops out when I eat.” There are two very clear anatomical reasons for this. First, the upper jaw has a very large, hard, and immobile “hard palate” surface where the prosthesis sits; when the prosthesis is placed in this large area, it prevents air leakage from the edges, creating excellent negative pressure (suction effect). In the lower jaw, however, the area where the prosthesis can sit is limited to only a narrow horseshoe-shaped bony protrusion, and its surface area is about one-quarter of that of the upper jaw. The second and most dynamic reason is the presence of a huge “tongue” tissue in the very center of the lower jaw, and when swallowing or speaking, the mucosa and muscles (especially the muscles of the floor of the mouth) at the edge of the lower jaw constantly move, propelling the prosthesis upwards.
