In breathing set

Breathing set

*Scuba set, used underwater*Rebreather, reprocesses exhaled air*Surface supplied diving, fed from the surface*Self-contained breathing apparatus, used out of water, worn by rescue workers, firefighters, and others*Spacesuit, used in space...

s, a mouthpiece is a part that the user grips in his mouth

Mouth

The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....

, to make a watertight seal between the breathing set and his mouth. It is composed of a short flattened-oval tube that goes in between the lip

Lip

Lips are a visible body part at the mouth of humans and many animals. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech...

s, with on its free end a flange that fits between the lips and the tooth

Tooth

Teeth are small, calcified, whitish structures found in the jaws of many vertebrates that are used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are embedded in the Mandible bone or the Maxillary bone and are...

 and gums

Gingiva

The gingiva , or gums, consists of the mucosal tissue that lies over the mandible and maxilla inside the mouth.-General description:...

. On the flange there are two projections with enlarged ends, which are gripped between the teeth. Most sport diving scuba sets use a mouthpiece rather than a fullface mask.

In many industrial breathing sets and a few scuba sets (e.g. the Siebe Gorman Salvus

Siebe Gorman Salvus

The Siebe Gorman Salvus is a light oxygen rebreather for industrial use or in shallow diving. Its duration on a filling is 30 to 40 minutes. It was very common in Britain during World War II and for a long time afterwards...

, and a 1980s model of double-hose diving regulator made by Nemrod

Nemrod

Nemrod was a Spanish firm that made scuba gear and spearfishing equipment. It ceased operating in the late nineties and was dismembered by the year 2000.-External links:*...

), the mouthpiece also has an outer rubber flange that fits outside the lips and extends into two straps that fasten together behind the neck. That makes the mouthpiece more airtight and watertight, and helps to keep the mouthpiece in if the user lets his lips or jaws get slack through unconsciousness or absent-mindedness or being preoccupied with work.

A mouthpiece in the mouth prevents clear speech

Gag

A gag is usually a device designed to prevent speech, often as a restraint device to stop the subject from calling for help. This is usually done by blocking the mouth, partially or completely, or attempting to prevent the tongue, lips, or jaw from moving in the normal patterns of speech. They are...

; as a result, many work divers, and many people who use a breathing set on land (e.g. firefighter

Firefighter

Firefighters are rescuers extensively trained primarily to put out hazardous fires that threaten civilian populations and property, to rescue people from car incidents, collapsed and burning buildings and other such situations...

s), use a fullface mask.

In breathing sets with two wide hoses

In a loop of wide breathing tubes like in a twin-hose aqualung or some rebreather

Rebreather

A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where...

s, the word "mouthpiece" is sometimes taken to mean the whole of the rigid assembly between the two flexible tubes.

Godel mouthpiece

In the 1960s a mouthpiece assembly of this sort (for a double-hose aqualung

Aqua-lung

Aqua-Lung was the original name of the first open-circuit free-swimming underwater breathing set in reaching worldwide popularity and commercial success...

), called a "Godel mouthpiece" was made, which had a snorkel attached, and a valve so the diver could breathe from the aqualung or from the snorkel.