Malnutrition degrades activities of daily living （ADL） for the elderly. In order to maintain their ADL, it is important to prevent the frailty cycle from developing by activating nutrient absorption. Nutrient absorption is affected by the degree of food digestion, and so mastication function should be maintained at a level that allows foods with various textures to be taken. For aged persons suffering from mastication disorders due to general muscle weakness in association with aging, food may be softened to a texture that does not require mastication. Over time, mastication function might degrade through disuse. Therefore, the bite force essential for mastication should be strengthened up to the normal level. A 15-week program of exercise by clenching with the maximum possible force using a specially fabricated elastic plate was designed and applied to six residents wearing dentures in a nursing home. Chronological changes in bite force and masseter muscle activity were investigated periodically.
Before the exercise, none of the subjects exhibited vertical force during clenching, but force in either the anteroposterior or lateral direction was observed for all subjects. EMG did not exhibit continuous activity but spastic activity for all subjects. Four weeks later, bite force in the vertical dimension as well as the horizontal dimension appeared for all subjects. The continuous aspect of EMG activity was observed instead of the spastic aspect for all subjects.
It is concluded that the designed biting exercise strengthened the bite force and thus improved mastication ability.

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