What kind of gas anesthesia do they use at the dentist for deep cleaning?

Nitrous Oxide. Bruno, if you are speaking about the mild sedative anesthesia that is most typical for deep cleanings, it would be nitrous oxide. Deep cleanings do not usually require a person to be sedated any deeper than this level. Nitrous oxide is inhaled to "take the edge off" and is flushed completely from the system with oxygen when the procedure is finished. It is elective, not necessary in most cases.