Laughing gas, or Nitrous Oxide, has anesthetic properties that were discovered by a dentist named Dr. Horace Wells in 1844. He is usually credited with being the father of anesthesia. It is an inert gas that makes the patient feel light headed, less anxious, and also has some anesthetic properties. It takes effect quickly can be adjusted during admisistration and wears off quickly. The main use in dentistry is the reduction of anxiety. It smells good and is administered with a "Mr. Nose" which is a nasal hood that, in our office anyway, is scented with flavors like bubblegum and strawberry. Children especially like the flavors and the bright colors. There are larger sizes for teenagers with more "adult" flavors like vanilla and pina colada.
Nitrous Oxide's main clinical effect is to lessen anxiety. It works really well and is very safe. Its effects are somewhat mild and, in some patients, additional medications may be needed to relieve anxiety or achieve a more cooperative patient. You can't rely on laughing gas alone to eliminate painful sensations, you still need to use local anesthetics for more invasive procedures, but in some cases Nitrous alone will be enough to eliminate the need for local anesthesia. Its effects are generally described as analgesia.
Is Laughing Gas Safe? Yes, when administered to patients correctly. It is always administered with oxygen. In fact "flowmeters" have a fail-safe mechanism that will deliver no less than 35-40% oxygen. That's almost twice the oxygen concentration in room air (which is 21% O2). I personally don't like to use it higher that 50% Nitrous/50% Oxygen. The only complication I sometimes see is a child who has been on it a really long time and gets a little sick to his stomach. Sort of like riding the merry-go-round one too many times.
Do patient's really laugh? Well, usually not. Usually they just feel good and "zone out' a little although they are still responsive and will cary on a conversation with you. Some kids really do get the giggles. When they do, it's hard for them to stop. That gets us giggling too and it's really funny!
By the way, it's also used in race cars to boost engine output.