A mouthguard (also known as a mouth protector, mouth piece, gumshield or nightguard) is a protective device for the mouth that covers the teeth and gums to prevent and reduce injury to the teeth, arches, lips and gums. Mouthguards are most often used to prevent injury in contact sports, as a treatment for bruxism or TMD, or as part of certain dental procedures, such as tooth bleaching.

Mouthguards may be used as splints to treat temporomandibular joint disorder and bruxism. A thin acrylic mouthguard appliance is often used during tooth bleaching. It might even be used to straighten your teeth (Invisalign).