[abstFig src='/00280006/05.jpg' width='300' text='The headset type intraoral interface' ] An extra degree of freedom to human body movement could assist people in a variety of tasks. To this end, we have previously proposed a human-ability extension system through a supernumerary limb. The system comprises of a manipulator that acts as a third arm, a feedback device that displays its status, and an interface that allows for its hands-free operation. Herein, we present this novel, intraoral interface that utilizes tongue motions and expiratory pressure. In contrast to the conventional intraoral interfaces that suffer from a lack of degrees of freedom and stability, our advanced interface is equipped with inertial measurement units and a pressure sensor to solve these problems without sacrificing the ease of use. The proposed interface is utile not only in our ongoing “Third Arm” project, but also in various other applications. We conclude with experimental evaluation of the system’s usability and its efficacy for human-ability extension systems.