Extensibility characteristics of human cheek--visco-elastic properties.

Using a hydraulic bellows system mounted on a maxillary partial denture, continuous force-displacement data were taken in an edentulous area in the maxillary bicuspid-molar region on ten adults. Both loading and unloading force-displacement curves showed three segments. Two visco-elastic properties - hysteresis and relaxation - were consistently evident. The maximum difference in force-magnitude of the hysteresis loop was 1.02 g. A pre-conditioning phenomenon of the cheek tissue, evidence by a reduction of the area of the hysteresis loop, was observed in a series of repeated runs. The significance of the study was that: (1) in some individuals, the cheek could be displaced, by expansion of the molars, up to 1 mm into a second stable position; and (2) the relaxation phenomenon suggests a limited adjustive capacity in cheek stiffness.