Based on the premise that temporomandibular disorders (TMD) are the result of occlusal disharmony, oral appliance therapy was developed to disengage the occlusion, relax the jaw muscles, restore vertical dimension, unload joints, and reposition the TM joint (TMJ). These appliances are made of either hard acrylic resins or soft plastics and polymers. In a literature review on using oral appliances to treat TMD, among the findings was that there is no merit in using soft material to fabricate an oral appliance, but several studies show that hard acrylic splints do decrease muscle activity as determined by electromyography devices. In terms of occlusal design, the flat plane occlusion appears to be most successful. Evidence suggests that a mini-anterior bite plane has very little merit for resolving TMD or headaches. Further, the anterior repositioning splint, which forces the mandible forward, has been used to unload the joint. However, it has been shown that the mandible is a class III lever system and will not fulcrum on any point anterior to the masseter muscle, therefore it is impossible to unload the TMJ using an oral appliance. The anterior repositioning splint does help to alleviate pain from acute internal derangement and is indicated for temporary use. Oral appliances should not be used to treat headaches, but when headaches result in tenderness of the masticatory muscles oral appliances can relieve the muscle pain. Also, oral appliances have a significant placebo effect. When non-occluding splints are used they can be very effective in reducing symptoms. The study concludes that oral appliances are still regarded as useful adjuncts for treating certain kinds of TMD, but the emphasis is entirely on their conservative application.
(Source: Oral Surg Oral Med Oral Pathol Oral Radiol Endod. February 2009;107:212-223)
