In this picture, you can see the patient has a back tooth on his left side. The partial denture has a clasp which fastens onto this back tooth. This clasp provides greater stability than the patient will have on his right side, where the partial denture has a “free end extension.”
The flat top of the metal clasps, called a rest seat, is perched solidly on the tooth structure. These rest seats reduce biting force on the gums and bone underneath. The more rest seats on a partial denture, the less damage to the underlying jaw bone over time.
Because every patient’s mouth is unique, no two partial dentures are exactly alike in design or stability.