Question: Are mouthguards necessary to play water polo?
About the article "Water polo", section "Water polo equipment".

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This gag has two mouthguards, similar to those worn by football and hockey players.
One rests on the lower teeth of the wearer while the other is against the top.
Again, like sports mouthguards, these mouthguards can be softened in boiling water to fit to the mouth of the wearer.
The mouthguards are attached to a front faceplate, like most plug gags, and straps from the front to the back. 
 Dental trauma *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, mixed martial arts, puroresu, rugby, wrestling, football (soccer), American football, Australian football, lacrosse, basketball, figure skating, ice hockey, underwater hockey, field hockey, water polo, skiing, and snowboarding.
Mouthguards may also prevent or reduce harm levels of concussion in the event of an injury to the jaw.
In many sports, the rules of the sport make their use compulsory, or local health laws demand them.
Schools also often have rules requiring their use.
Studies in various high risk populations for dental injuries are repeatedly reporting of a low compliance of individuals for the regular using of mouthguard during activities.
Moreover, even with regular use, effectiveness in prevention on dental trauma is not complete, and injuries can still occur even when mouthguards are used as users are not always aware of the best makes or size, which inevitably result in a poor ﬁt.
Oral medicine *Mouthguards may be used as splints to reduce strain over the temporomandibular joint in temporomandibular joint disorder *To prevent tooth attrition in bruxism *To deliver topical medication (e.g., corticosteroids) for chronic gingival diseases such as mucous membrane pemphigoid.
*As a therapeutic device in the treatment of morsicatio buccarum.
Dental aesthetics *During tooth bleaching *As a night protector of thin porcelain bridges orthodontics *Invisalign, a substitute for brackets and acrylic plates  
The exact origins of the mouthguard are unclear.
Most evidence indicates that the concept of a mouthguard was initiated in the sport of boxing.
Originally, boxers fashioned rudimentary mouthguards out of cotton, tape, sponge, or small pieces of wood.
Boxers clenched the material between their teeth.
These boxers had a hard time focusing on the fight and clenching their teeth at the same time.
Since these devices proved impractical, Woolf Krause, a British dentist, began to fashion mouthpieces for boxers in 1892.
Krause placed strips of a natural rubber resin, gutta-percha, over the maxillary incisors of boxers before they entered the ring.
Phillip Krause, Woolf Krause’s son, is often credited with the first reusable mouthpiece.
Phillip Krause’s invention was highlighted in a 1921 championship fight between Jack Britton and Ted “Kid” Lewis.
Lewis was a school friend of Krauses’ and the first professional to utilize the new technology, then called a ‘gum shield.’ During the fight, Britton’s manager successfully argued that the mouthpiece was an illegal advantage.
Philip Krause was an amateur boxer himself and undoubtedly used his own device before 1921.
There have been other claims to the invention of the mouthguard as well.
In the early 1900s, Jacob Marks created a custom fitted mouthguard in London.
An American dentist, Thomas A. Carlos, also developed a mouth guard at approximately the same time as Krause.
Carlos claimed that he made his first mouthpiece in 1916 and later suggested his invention to the United States Olympian Dinnie O’Keefe in 1919.
Another dentist from Chicago, E. Allen Franke, also claimed to have made many mouth guards for boxers by 1919.
The mouthguard’s relevance was again brought to the center of attention in a 1927 boxing match between Jack Sharkey and Mike McTigue.
McTigue was winning for most of the fight, but a chipped tooth cut his lip, and he was forced to forfeit the match.
From that point on, mouthguards were ruled acceptable and soon became commonplace for all boxers.
In 1930, descriptions of mouthguards first appeared in dental literature.
Dr. Clearance Mayer, a dentist and boxing inspector for the New York State Athletic Commission, described how custom mouthguards could be manufactured from impressions using wax and rubber.
Steel springs were even recommended to reinforce soft materials.
In 1947, a Los Angeles dentist, Rodney O. Lilyquist, made a breakthrough by using transparent acrylic resin to form what he termed an "acrylic splint."
Molded to fit unobtrusively over the upper or lower teeth, the acrylic mouthguard was a distinct improvement over the thick mouthguard worn by boxers.
It meant that the athlete could talk in a normal manner while the mouthguard was in place.
In the January 1948 issue of the Journal of the American Dental Association, the procedure for making and fitting the acrylic mouthguard was described in detail by Dr. Lilyquist.
He immediately received nationwide recognition as the father of the modern mouthguard for athletes.
The first athlete to wear the acrylic mouthguard was a member of the UCLA basketball team, Dick Perry, who modeled the device at a convention of the Southern California Dental Association.
Another early wearer was Frankie Albert, quarterback for the San Francisco 49ers.
In the 1940s and 1950s, dental injuries were responsible for 24-50% of all injuries in American football.
In 1952, Life magazine did a report on Notre Dame football players without incisors.
The article drew a lot of public attention and led to the inclusion of mouthguards in other contact sports.
In the 1950s, the American Dental Association (ADA) began conducting research on mouthguards and soon promoted their benefits to the public.
In 1960, the ADA recommended the use of latex mouthguards in all contact sports.
By 1962, all high school football players in the United States were required to wear mouthguards.
The National Collegiate Athletic Association (NCAA) followed suit in 1973 and made mouthguards mandatory in college football.
Since the introduction of the mouthguard, the number of dental injuries has decreased dramatically.
Mouthguards have become a standard in many sports.
In addition to football, the NCAA currently requires mouthguards in ice hockey, field hockey, and lacrosse.
The ADA shows that mouthguards are extremely effective in preventing facial injury in contact and non-contact sports.
The ADA recommends mouthguards be used in 29 sports: acrobatics, basketball, bicycling, boxing, equestrian, football, gymnastics, handball, ice hockey, inline skating, lacrosse, martial arts, racquetball, rugby football, shot putting, skateboarding, skiing, skydiving, soccer, softball, squash, surfing, volleyball, water polo, weightlifting and wrestling. 
Sports mouthguards (also termed athletic mouthpieces) are plastic dental appliances which can help to protect the hard and soft tissues of the mouth from damage caused by traumatic blows and collisions.
They are also designed to absorb the shock of impact to the head reducing the incidence of concussions (although the typical boil-and-bite mouthguards may not be very effective at this).
Mouth guards are simple half-moons of plastic with a strap on the end which hooks around the face mask so it isn't lost during play.
Fitting a mouth guard is simple: it is placed in boiling water, allowing the plastic to soften.
It is removed from the boiling water, and then placed for a second in cold water.
The cold water dip cools the exterior of the plastic (so that it won't burn the mouth), while leaving the interior of the plastic soft (so that it can be formed).
Then the player puts the mouth piece in his mouth and bites down, leaving an imprint of his teeth and gums.
As the plastic cools, the mold hardens.
The result is a mouth guard specific to one player's mouth. 
Inner tube water polo is a style of water polo in which players, excluding the goalkeeper, are required to float in inner tubes.
By floating in an inner tube players expend less energy than traditional water polo players, not having to tread water.
This allows casual players to enjoy water polo without undertaking the intense conditioning required for conventional water polo.
Surf polo, another variation of water polo, is played on surfboards.
First played on the beaches of Waikiki in Hawaii in the 1930s and 1940s, it is credited to Louis Kahanamoku, Duke Kahanamoku's brother.
Canoe polo or kayak polo is one of the eight disciplines of canoeing pursued in the UK, known simply as "polo" by its aficionados.
Polo combines paddling and ball handling skills with a contact team game, where tactics and positional play are as important as the speed and fitness of the individual athletes.