Ability of edentulous human beings to adapt to changes in vertical dimension

The ability of ten edentulous patients and one patient with a full upper removable denture and a full arch (16-26) lower fixed denture to adapt to sudden change of the interocclusal distance was tested. An upper acrylic bite splint was inserted which, on average, increased the vertical dimension of the face by approximately twice the mean interocclusal distance during relaxation. After this procedure all patients quickly acquired an unstrained new postural position of the mandible. Directly after insertion, when instructed to relax, all patients hit the lower surface of the splint. They seemed, however, to need only one such experience to adapt to the increased interocclusal distance. The second time they repeated the procedure none of them touched the splint. Instead a new postural position was established with a mean interocclusal distance of 3.3 mm. This fast re-programming of jaw muscle tonus and length is assumed to be a response to different peripheral receptor discharge converging to the cerebellum and other programming centres. The present study on edentulous patients shows that afferent discharge from periodontal receptors is not a necessary prerequisite. It also confirms that the old concept of consistency of the mandibular postural position (Thompson, 1946) is erroneous.