How to fix underbite, protruding jaw, move lower jaw backwards naturally | Prognathism jaw exercises How to fix underbite, protruding jaw and move lower jaw backwards naturally | Prognathism jaw exercises. If your jaw protrudes, it’s known as prognathism. This trait is sometimes called extended chin or Habsburg jaw. It can be caused by a genetic or inherited condition or an underlying medical condition. Prognathism can cause malocclusion of the teeth, which happens when your teeth aren’t aligned