The Herbst appliance is an orthodontic appliance used by orthodontists to correct class 2 retrognathic mandible in a growing patient, meaning that the lower jaw is too far back. This is also called bitejumping. Herbst appliance parts include stainless steel surgical frameworks that are secured onto the teeth by bands (steel rings that go around teeth) or acrylic bites. These are connected by sets of telescoping mechanisms that apply gentle upward and backward force on the upper jaw, and forward force on the lower jaw.

https://en.wikipedia.org/wiki/Herbst_appliance