Abstract: An intraoral appliance to be worn for the diagnosis and treatment of temporomandibular joint dysfunction. The appliance has upper and lower members which fit respectively on the person's maxillary and mandibular arch. The lower member has an upward projection which makes low friction gliding contact against a smooth surface located anteriorly on the upper member. This maintains vertical clearance between the maxillary arch and the mandibular arch and ensures free horizontal movement of the mandible to allow it to assume a position wherein the masticatory muscles are allowed to relax. Wearing the appliance for a period of time relieves the symptoms of acute and/or chronic headaches which result from temporomandibular joint dysfunction.