An underbite is when someone's lower teeth stick out past their upper teeth when their mouth is closed. Normally, your top teeth should slightly overlap your bottom teeth, like a lid fitting over a box. With an underbite, it's reversed: the bottom teeth jut forward beyond the top ones.

You can see underbites in both people and animals. Bulldogs are famous for their underbites, which give them their distinctive pushed-in face and protruding lower jaw. In people, an underbite happens when the lower jaw grows longer than the upper jaw, or when the upper jaw doesn't grow forward enough.

Some underbites are barely noticeable, while others are quite pronounced. A severe underbite can make chewing difficult or affect how someone speaks. Orthodontists can often correct underbites using braces, special appliances, or sometimes surgery, especially if treatment starts while someone is still growing.

The opposite condition, where upper teeth stick out too far past the lower teeth, is called an overbite. Both are types of malocclusion, which means the teeth don't line up properly when biting down.