A removable partial denture or complete denture that covers and rests on one or more remaining natural teeth, the roots of natural teeth and /or dental implants. A prosthesis that covers and is partially supported by natural teeth, natural tooth roots and or dental implants - called also overlay denture, overlay prosthesis, superimposed prosthesis. An overdenture is a denture that may be supported by soft tissue, bone, the root of a tooth, or a modified tooth. In 1978, Louis Rissin studied the masticatory performance by over denture which is found to be one-third higher than normal denture. Various terms have been used to describe this treatment modality: overlay denture, telescoped dentures, tooth supported dentures, hybrid prosthesis, crown and sleeve prosthesis, biologic prosthesis and superimposing dentures. Patients with a poor prognosis for complete dentures when the palatal vault is high and the ridges slope. When the mandible has a poorly defined sublingual fold space, the floor of the mouth drapes and the tongue falls back, positive retention and stability can be hard to attain.