Control of Mechanical Impedance in the Orofacial System

− Studies of arm movement have suggested that the control of stiffness may be important for maintaining stability during interactions with the environment. Here we have examined the voluntary control of stiffness in the human jaw. The goal was to determine whether changes in jaw stiffness might be used to maintain jaw position in the face potentially destabilizing mechanical loads. A series of force pulses was applied to the jaw using a robotic device. The loads were designed to disrupt the ability of subjects to maintain a static jaw posture. In all cases, subjects increased the magnitude of jaw stiffness in order to maintain jaw position. A clear effect of the magnitude of the destabilizing load was observed — greater increases in stiffness were observed when larger forces were applied. Moreover, subjects were able to differentially modify stiffness in the direction of the destabilizing load in the case of loads in the vertical direction. The observed change in the relative magnitude of stiffness in different directions indicates some ability to control the pattern of stiffness of the jaw. The results indicate that jaw stiffness can be adjusted voluntarily, and thus may play a role in maintaining stability. Stiffness regulations may similarly provide a means to achieve the differential precision requirements of speech.