Abstract: A concealed, resilient and flexible mouth splint for placing in the mouth of an individual around the upper maxillary posterior teeth to affect the tension of the masticator muscles of the individual is disclosed. The device comprises a right channel (22) and a left channel (24) for fitting over the left first molar and the right first molar, respectively. The top side (30A, 30B) of each channel member is molded to conform with the biting surface of the first molars, and each of the left and right channel members (22, 24) are molded to conform to the interior and exterior lateral surface of the first molar. This is a molded palate member (20) which arches between and integrally joins the two channel members, and which conforms with the roof of the mouth of an individual wearing this splint. The biting portion (28A, 28B) includes sufficient material such that the front upper teeth and the front lower teeth are maintained between two (2) and seven (7) millimeters.