There are different types of dentures, but they share their common function. They replace teeth that have been lost due to cavities or bone loss. The entire mouth is examined and a determination is made as to which teeth will have to be removed, and which will remain. Dentures are fitted to go over or around whatever teeth remain in the mouth, depending on the type.
There is an adjustment period after dentures are placed in the mouth, and it can take some getting used to. But once accustomed to the dentures, all the normal functionality and appearance return and one just carries on as usual. Implants can also be used to further stabilize the dentures.