The Joint Protective Telescopic Appliance

Occasionally, when a TMJ needs maximal protection, a telescopic appliance is indicated.  A telescopic appliance is composed of an upper and a lower appliance connected on each side by a tube and rod (telescopic) mechanism.  When the rod bottoms out in the tube, these telescopic components form a rigid bar that acts like a straight arm to prevent the condyles from moving any further backward, even when the mouth is open.  In this manner, a telescopic appliance can provide a zone of absolute protection for a damaged TMJ, unlike single arch appliances which only protect the TMJs when you bite down far enough to engage their inclines.  
One advantage of telescopic appliances is that they distribute the forces needed to protect the TMJs evenly among all the upper and lower teeth.  This feature prevents directional tooth pressures that can cause inadvertent tooth movement in single arch or partial coverage appliances.
Another advantage of telescopic appliances is that they do not interference with normal tongue posture, because the telescoping mechanisms rest between the teeth and the cheeks, well away from any potential contact with the tongue. Studies have shown that anything that interferes with tongue posture affects jaw posture.
When telescopic appliances are used for TMJ protection, the length of the telescopic components is not set to hold the lower jawbone further forward than its natural bracing position, just to prevent it from retruding excessively during sleep.  In this way, they work like joint protective stabilization appliances, but they protect the joint with mechanics that are more effective and controllable.  In addition, telescopic appliances can also include a variety of different bite surfaces to create special orthopedic effects, such as pivoting to relieve inflammation or a flat front bite plate to reduce the force of nocturnal clenching or grinding. 
A basic telescopic appliance costs $1300.   A telescopic appliance with microadjustable features costs $1500.