This is used to correct the jaw deformities in non-growing patients. For example, if the lower jaw is too far behind the upper jaw, then the lower teeth are also too far behind the upper teeth. In order to line up the teeth, you need to move the lower jaw forward and get the teeth to move with it.
Teeth have to be surrounded by bone for blood supply and nourishment. They can be moved around within the confines of the jawbone, but not outside of it. If more movement is needed, then you have to move the jaw. Braces are used to straighten the teeth within each jaw and then surgery is performed to line up the jaw, which will align the teeth.
Some people who need jaw surgery refuse to have it. Sometimes a compromised treatment can be done to align the teeth, but the jaw and face will remain incorrect. If you decide on a compromised treatment, then you must realize that you will not obtain an excellent result.