Many patients with paralyzing injuries or medical conditions retain the use of their cranial nerves, which control the eyes, jaw, and tongue. While researchers have explored eye-tracking and speech technologies for these patients, we believe there is potential for directly sensing explicit tongue movement for controlling computers. In this paper, we describe a novel approach of using infrared optical sensors embedded within a dental retainer to sense tongue gestures. We describe an experiment showing our system effectively discriminating between four simple gestures with over 90% accuracy. In this experiment, users were also able to play the popular game Tetris with their tongues. Finally, we present lessons learned and opportunities for future work.