Depending upon the surgery you can encounter with problems like nerve injuries to TMJ problems but only if you won't take any adequate care post surgery.
The plus point after orthognathic surgery is that your teeth won't be wired with elastics so you can do slight jaw exercies to help you not suffer from TMJ problems. Also take special care of your diet by eating soft non sticky food...For more info visit the link...http://www.identalhub.com/dental-how-to-straighten-teeth-without-wearing-braces-762.aspx