Air-teeth

"" was the apparent nickname for a breathing apparatus employed by humans at least during that Dalek invasion of the Solar System which was countered by Space Army. Jeff, Andy and Mary Stone once used them on the Moon.

The nickname was derived from the devices' positioning on the human body. They were engineered so that they fitted behind the wearer's gums. They contained solid oxygen, which was converted to a usable gas upon contact with the warmth of the mouth. (DAN: Battle for the Moon)
 * ''This device is always referred to with inverted commas in the narrative, indicating it's not the formal name.