Gas, laughing: Nitrous oxide, is a gas that is used in dentistry for its sedative or analgesic properties in the management of fear and anxiety, especially for children and special needs patients. The patient must be able to breathe normally through the nose, or the effectiveness of the gas is greatly reduced. It is contra-indicated for pregnant patients. After administration of the gas, it is important that the dentist provide 100% oxygen to the patient for at least 5 minutes. After this period of 100% oxygen, the patient can then leave on their own. Nitrous oxide is also used as an oxidizer in rocketry and motor racing to increase power output from engines.