In modern machines there is a sort of "double mask" where the outside mask is connected to a vacuum machine to suck away the waste gas - you wouldn't want your dentist to get a face full of N2O... The white inside mask, which is placed over your nose, comes in lots of yummy scents - vanilla, strawberry, and mint!

The twin tubes running to the mask are for "gas in" and "gas out". The "gas out" line is attached to the vacuum machine, while the "gas in" line is attached to the RA (short for relative analgesia) machine. The inner mask is attached to the "line in", you breathe out through a one-way valve in the inner mask, and the exhaust gas is collected inside the outer grey mask (pictured to your right) and sucked into the vacuum machine.
 
The grey "outer mask" ensures that your dentist doesn't leave work with a headache

What are the advantages?

  • Happy gas works very rapidly - it reaches the brain within 20 seconds, and relaxation and pain-killing properties develop after 2 or 3 minutes.
  • The depth of sedation can be altered from moment to moment, allowing the person who administers the gas to increase or decrease the depth of sedation. Other sedation techniques don't allow for this. For example, with IV sedation, it's easy to deepen the level of sedation, but difficult to lessen it. Whereas with gas, the effects are almost instant.
  • Other sedation techniques have a fixed duration of action (because the effects of pills or intravenous drugs last for a specific time span), whereas gas can be given for the exact time span it's needed for. It can also be switched off when not needed and then switched on again (though to avoid a roller-coaster effect, you shouldn't do this too abruptly).
  • There's no "hangover" effect - the gas is eliminated from the body within 3 to 5 minutes after the gas supply is stopped.