Sedation Dentistry

Sedation methods in dentistry include inhalation sedation (using nitrous oxide), oral sedation, and intravenous (IV) sedation. Inhalation sedation is also sometimes referred to as Relative Analgesia.
Sedation dentistry refers to the use of pharmacological agents to calm and relax a patient prior to and during a dental appointment. The pharmacological agents usually belong to a class of drugs called sedatives, which exert their action by depressing the central nervous system, specifically those areas concerned with conscious awareness.

There are different degrees of central nervous system depression, each corresponding to a level of relaxation which ranges from minimal, moderate, to deep sedation. In general, minimal sedation refers to a patient who has reduced anxiety but is readily responds to verbal or physical stimulation. With moderate sedation the patient is even more relaxed, and will respond to pursposeful stimulation. In deep sedation, the patient may not exhibit any signs of consciousness and therefore be unresponsive to stimulation.
Sedation by pharmacologic methods may be obtained by two general routes. The Enteral route involves absorption of medication across enteric membranes which line the alimentary canal from the oral cavity, through the digestive tract, ending in the rectum. This route includes medications that are either swallowed, absorbed through the mucosa of the oral cavity, or inserted rectally. The Parenteral route involves the administration of sedative drugs other than absorption across enteric membranes (outside of the alimentary canal). These methods include intravenous, inhalation, intramuscular, and submucosal administration, among others.
 
Conscious Sedation
Procedural sedation is defined as "a technique of administering sedatives or dissociative agents with or without analgesics to induce a state that allows the patient to tolerate unpleasant procedures while maintaining cardiorespiratory function. It was previously referred to as conscious sedation.

Nitrous Oxide
Nitrous oxide, commonly known as happy gas or laughing gas, is a chemical compound with the chemical formula N2O. At room temperature, it is a colorless non-flammable gas, with a pleasant, slightly sweet odor and taste. It is used in surgery and dentistry for its anesthetic and analgesic effects. It is known as "laughing gas" due to the euphoric effects of inhaling it, a property that has led to its recreational use as a dissociative drug. It is also used as an oxidizer in rocketry and in motor racing to increase the power output of engines. At elevated temperatures, nitrous oxide is a powerful oxidizer similar to molecular oxygen. For example, nitrous oxide in a test tube will re-ignite a smoldering splint.

Nitrous oxide has been used for anesthesia in dentistry since the 1840s. The most common use is as a 50:50 mix with oxygen, commonly known as Entonox or Nitronox delivered through a demand valve, and frequently used to relieve pain associated with dental treatment.
Professional use can involve constant supply flowmeters which allow the proportion of nitrous oxide and the combined gas flow rate to be individually adjusted. Nitrous oxide is typically administered by dentists through a demand-valve inhaler over the nose that only releases gas when the patient inhales through the nose.

Because nitrous oxide is minimally metabolized, it retains its potency when exhaled into the room by the patient and can pose an intoxicating and prolonged-exposure hazard to the clinic staff if the room is poorly ventilated. Where nitrous oxide is administered, a continuous-flow fresh-air ventilation system or nitrous-scavenging system is used to prevent waste gas buildup.
Nitrous oxide is a weak general anesthetic, and so is generally not used alone in general anesthesia. In general anesthesia it is used as a carrier gas in a 2:1 ratio with oxygen for more powerful general anesthetic agents such as sevoflurane or desflurane. It has a MAC (minimum alveolar concentration) of 105% and a blood:gas partition coefficient of 0.46. Less than 0.004% is metabolised in humans.

Intravenous Sedation
Intravenous Sedation is a method of administering drugs directly into the bloodstream in order to diminish consciousness to a patient. There are various levels of sedation. Conscious sedation has three levels: level 1: awake and calm (no evidence of drowsiness); level 2: awake but sedated (slowed or slurred speech); level 3: asleep but easily aroused (verbally). Deep sedation has: level 4: asleep but difficult to arouse (shake, shout); and level 5: asleep and unarousable (except by surgical stimulus).