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.

 


Comments

Commenter's Profile Image Stephen Broderson DDS
February 26th, 2014
You have confused the pivot appliance with the Gelb appliance. The May pivot is made at the swallowing/muscle tested vertical with two contacts only- the Mli cusps of the upper first molars. The Gelb appliance is a full posterior contact appliance that is made with the condyle down and forward on the eminentia. Chronic clenching, extraction orthodontia, poor dentistry, bad orthognathic surgery, premature loss of posterior teeth all cause distal superior displacement of the condyles ultimately leading to locking up of the cranial/sacral system. The May appliance with only two contacts at the physiological vertical allows the neural proprioceptive mechanism to reorganize/reprogram-leading to positive clinical changes in the pain dysfunction patient. What one sees in long term wear of both the Gelb and May appliances is mandibular repositioning along with extrusion of the teeth not contacting the appliance-a posterior open bite. Treatment is then done with dental orthopedic appliances to close the posterior bite to support the mandible in the anterior inferior position. These patients have a pathologic centric relation to begin with, and the changes are cranial as well as joint. When the May appliance is made properly, muscle activity is actually REDUCED as one can monitor the wear on the pivots. I have been using these appliances for almost 40 years with great success!! Thank you Willie May