A mouth guard is a shaped piece of plastic or rubber used to protect the teeth and gums from injury during contact sports activity, such as [[ice hockey|hockey]] or [[American football]]. Another kind of mouth guard, also called a sleep guard or bite guard, is used while sleeping to prevent the grinding of teeth or for other kinds of dental and orthodontic treatment. A mouth guard is worn inside the mouth, between the teeth, and so may only be visible when it is taken out, or the character's mouth is sufficiently [[open mouth|open]].