A mouthguard (also known as a mouth protector, mouth piece or gumshield) 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.

An early mouthguard was developed in 1890 by Woolf Krauze, a London dentist to protect boxers from lip cuts and lacerations. The modern mouthguard design started from the work in the 1970s done by Dr. A. W. S. Wood, a Canadian pediatric dentist who was aiming to reduce and prevent injuries to children’s teeth in hockey games.

Mouthguards are used in sports where deliberate or accidental impacts to the face and jaw may cause harm. Such impacts may occur in many sports including: Baseball, Boxing, Martial Arts, Rugby, Wrestling, Football, American Football, Australian Football, Lacrosse, Basketball, Figure Skating, Hockey, Underwater Hockey, Field Hockey, Water Polo, Skiing and Snowboarding. Mouthguards may also prevent or reduce harmful level of concussions in the event of an injury to the jaw.

In many sports, the rules make their use compulsory, by local state health laws. Schools also often have rules requiring their use.

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

Types of mouthguards
Stock or ready made:
Manufactured in a pre-formed shape in various sizes but with nearly no adjustment to fit the user’s mouth. The only adjustment possible is minor trimming with a knife or scissors.

Mouth adapted or "boil and bite":
A thermo-plastic material manufactured in a pre-formed shape in various sizes that can be adapted to fit more closely to an individual’s teeth and gums by heating and molding such as boiling them and then placing in the mouth. Some are now available that incorporate special fins within the fitting zones which increase retention and give an improved fit over traditional boil and bite mouth types. Mouthguards are usually made of Ethylene-vinyl acetate.

Custom made:
An impression of the users teeth is used by specialist manufacturers to create a best-fit mouth protector. The impression may be obtained by specifically designed Home Impression kit from the guard manufacturer that uses dental putty, or from a dentist who will take an upper impression in dental alginate material and use that mould to make a cast model of the teeth from which the mouthguard is then fabricated.

Performance Mouthguards
Recently, high-end mouth guards are being manufactured to enhance athlete performance, by opening up the airways, preventing teeth-clenching and aligning the jaw.