To pick up where I left off in the previous article about tooth wear appliances, a posterior pivot is the opposite of an anterior bite plane. This appliance only has occlusion on the posterior teeth and displays no anterior occlusion whatsoever. The concept of a posterior pivot is about supporting the jaw joint during clenching and translation in patients with symptomatic temporomandibular joints. This appliance is commonly named the Gelb appliance, after Harold Gelb who used this appliance to treat joint pain in his patients.
Conceptually the goals of this appliance are to keep the posterior teeth in occlusion at all times to reduce joint loading both in clenching and excursions. In other words, the appliance is used to prevent any posterior disclusion from anterior tooth contact. The challenge of this appliance design is that it has the potential to increase muscle activity in both clenching and excursions. In addition, if you have a patient that is grinding their teeth, their molars are receiving seven to nine times more bite force than the anterior teeth. Placing an appliance that has only posterior occlusion will now place all the force on the posterior teeth, especially high on the molars with the potential for damage to the teeth opposing the appliance.
Besides the risk of excessive muscle activity and high posterior bite forces, there are additional risks to a posterior only appliance, they are the eruption of the non occluding anterior teeth, or intrusion of the posterior teeth, resulting in a posterior open bite – the exact opposite risks of an anterior bite plane. Having described the risks, these appliances have been effective for patients with significant joint pain at making them more comfortable. The challenge is that because they are more comfortable patients wear the appliance 24 hours a day and invariably get eruption of the anteriors or intrusion of the posteriors or both. A safer design is to use a full coverage appliance with occlusal contact on all the teeth in clenching, and built in posterior interferences, minimal anterior contact, in excursions. Soft full coverage appliances with no anterior guidance can fill this role nicely in some patients.