Underbite is the term used to refer to a common jaw relationship condition, observed in many people. Also known as Class III malocclusion or prognathism, this condition involves the abnormal protrusion of the lower jaw, causing the lower jaw to protrude forward in front of the upper jaw. Thus, on closing the jaw, the lower teeth overlaps the upper teeth, thereby giving the chin and lower jaw teeth a far more prominent appearance on the face.