In the oral cavity, movement of the tongue in relation to palatal shape is important for smooth speech and swallowing activities. The present study analyzed adaptation of tongue force in relation to palatal shape based on measurements of tongue force (amount of force exerted by the tongue against the palate) and its action point (center of contact pressure). As a first step, methods for estimating the amount of tongue force and its action point were investigated based on palatolingual contact pressure as measured by a force-sensor-mounted palatal plate. Next, tongue force and its action point were measured in six healthy adults with an essentially symmetric palatal shape and with no speech or swallowing disorders. Results showed that during speech and swallowing, the action point of tongue force corresponded to the central aspect of palatal shape. Furthermore, palatolingual contact pressure was measured using a different force-sensor-mounted palatal plate that caused midline asymmetry in palatal shape. During speech, the action point of tongue force corresponded to the central aspect of the asymmetric palatal shape, but during swallowing, tongue force differed between symmetric and asymmetric palatal shapes at 107 and 341 gw, respectively. These findings show that the tongue moves in relation to the central aspect of palatal shape during speech and swallowing in order to adapt to changes in palatal shape, but that tongue force adaptation differs between speech and swallowing activities.
