An intraoral discluder for preventing chronic tension headaches, common migraine headaches, and temporomandibular disorders that are caused or perpetuated by chronic activity of the temporalis muscle. The discluder includes a trough, contoured to encompass at least one maxillary or mandibular incisor, from which extends a protruding platform, for engagement by the opposing incisors. The trough can be retained on the teeth by any adaptable material than can flow around the teeth and then maintain its shape. Once in place in the wearer's mouth, one or two opposing incisors will come into contact with the platform prior to the upper and lower posterior and/or canine teeth coming into contact, regardless of the position of the mandible, thereby reducing the intensity of the activity of the temporalis muscle. In addition, a special post on the discluder's platform is engageable directly with one or more opposing incisors, to act as a stop and thereby inhibit excessive retrusive movement of the mandible and urge the mandible toward a more protrusive position. This can reduce the intensity of undesired clenching, and it can enhance the size of the wearer's pharyngeal airspace, thereby reducing the incidence and severity of snoring.