The chins of males tend to be longer and wider than those of females, with a squarer base, and to project outward more than female chins. Male jawlines tend to extend outward from the chin at a wider angle than those of females, and to have a sharp corner at the back.
The chin can be reduced in length either by bone shaving or with a procedure called a "sliding genioplasty", where a section of bone is removed. The jaw can be reshaped through jaw reduction surgery; sometimes this is done through the mouth. The (chewing muscles) can also be reduced to make the jaw appear narrower.
The biggest risk in these procedures is damage to the mental nerve that runs through the chin and jaw; other risks include damage to tooth roots, infection, nonunion, and damage to the mentalis muscle that controls the lower lip and is at the edges of the chin.