an interocclusal appliance includes a maxillary impression preform of a resilient thermoplastic having a low softening temperature , e . g . 36 ° c ., such as an eva copolymer having approximately thirty percent vinyl acetate . the preform is molded over and unitarily bonded to a base having a planar bottom face contacted by mandibular occlusal surfaces . the base is formed of a thermoplastic having a higher softening temperature , e . g . 70 ° c ., with the bond between the preform and base characterized by high shear strength . the preform includes a bight shaped centric relation positioning channel having a thick footing and draft along lingual , buccal and labial walls . the appliance is fitted by immersion in hot water to soften the preform , seating the maxillary arch within the channel and biting , such that the impression of the maxillary dentition embeds in the softened preform . upon cooling , the preform is transformed into a reusable resilient encasement for the maxillary dentition . suitable thermoplastics for implementation as the base include an ema copolymer , blends of ema and eva or tpu or blends of tpu and eva .