An interocclusal appliance is formed from a single polymer material composition as one unitary piece or from multiple polymer material compositions as a two-piece preform. The two-piece preform includes a base material and an impression material that has a softening point lower than the base material. Teeth are received into the heat-softened impression material, so as to contour the impression material. A portion of the impression material also may contour to a portion of the user's palate. In certain embodiments, substantially no polymeric material contacts the front surfaces of the front teeth, leading to greater comfort and better air flow between front teeth. In still another embodiment, the appliance fits over front teeth only and no polymeric material contacts the maxillary molars.