be especially difficult in very young children or patients with learning difficulties. Additionally, the drug cannot be used alone; it must be used alongside appropriate methods of behaviour management and local anaesthetic. Therefore, the degree of sedation can depend on the efficacy of behavioural techniques and psychological reassurance from the dentist. Equipment & safety features In the UK, machines used for the administration of inhalation sedation should follow the British Standards and be well-maintained according to the manufacturer's guidance. Equipment Equipment used for inhalation sedation for dentistry include: Gas cylinders Flowmeter Reservoir bag Conduction Tubing Breathing apparatus (Nasal hood or face mask) Safety features Oxygen fail safe mechanism is the most important safety feature of the equipment used in inhalation sedation. Nitrous oxide flow is only allowed via an opened valve when there is flow of oxygen to the system. In any circumstances when oxygen flow is less than 30%, nitrous oxide stops flowing. This prevents the potential delivery of 100% nitrous oxide and it becomes a standard on every sedation unit made today. All nasal hoods should have scavenging ability— provide fresh gas to the patient through one or two hoses while the extra hoses eliminate exhaled gas by the patient via a vacuum system. A pin index safety system prevents incorrectly fitting the two cylinders. In addition, the cylinders are colour coded, which further reduces the risk of incorrect cylinder placement. A diameter index system is also in place to prevent incorrect linking of hoses and stems—the attachment couplings, hoses, and stems are different diameters. Pressure relief devices that dissipate contents of the cylinder to the atmosphere prevent explosion of cylinder due to over-filling. In an emergency, an oxygen flush or emergency oxygen system passes a high flow of high pressure oxygen direct from the source bypassing intermediate meters. Several alarm systems are used to indicate a depleting oxygen supply. Audible alarms are required in Europe and are recommended in the United States. History Nitrous oxide was first discovered by Joseph Priestley in 1772. In 1795, Humphry Davy and surgeon J. B. Borlase experimented with nitrous oxide and the effects of its inhalation. Davy then published a book in 1799 hinting the possible role of nitrous oxide in achieving mild anaesthesia during surgical procedures. In 1844, Dr. Horace Wells carried out an experiment on himself where he had Professor Gardner Quincy Colton administer nitrous oxide to himself prior