We have all seen folks that seem to have a fairly prominent chin.
Sometime's that's all it is, is a prominent chin and no other factors exist.
Other times however the cause for the prominence is due to a misalignment of teeth.
This misalignment is called a class III occlusion of more
commonly known as an underbite.
In a classic occlusion, or bite, your top teeth are supposed to
protrude out over your bottom teeth slightly as shown in the top picture below.
In the underbite situation things are reversed and your bottom teeth
protrude out further then your top teeth, as shown in the bottom right picture below.
Some people have lived their entire lives in this condition (my wife's Grandfather)
and haven't suffered any ill effects at all.
Others have suffered tremendously from poor chewing ability, pain and
popping in their TMJ joint, headaches, etc.
With surgery this condition is correctable (my wife, passed down from Gramps)
and within a very short period of time return to full function and look.