Restorative dentistry

	During initial dental examination to relieve general anxiety, especially in patients with sensitive soft tissues or teeth
	During removal of provisional crowns or bridges
	Occlusal adjustment of crowns, bridges or natural teeth
	During insertion of metrix bands or wedges between teeth prior to the placement of a restoration

Periodontics and dental hygiene

	During initial periodontal examination, especially in patients with inflamed, sensitive soft tissues and teeth with deep periodontal pockets
	For scaling, curettage and root planing because N20-02 helps develop a degree of soft-tissue analgesia
	In the management of necrotizing ulcerative gingivitis
	While using ultrasonic instruments to remove calculus from teeth
	During periodontal surgery

Oral and maxillofacial surgery

	During lengthy surgical procedures
	During management of abscesses requiring incision and drainage for pain control
	Management of postoperative complications, such as localized osteitis (dry socket)
	During suture removal, although not generally required

Endodontics

	Cellulitis and pericementitis to raise the pain reaction threshold
	Occasionally during placement of a rubber dam clamp on the neck of an endodontically involved tooth
	To gain access to the pulp chamber so that an intrapulpal injection may be administered
	Instrumenting canals following extirpation of pulpal tissues
	Filling of root canals

(Discomfort is generally nonexistent in most patients during the last two procedures. Only in exceptional cases N₂0-0₂ may be required.)

Fixed prosthondontics

	During impression taking process to reduce the gag reflex and elevate the pain reaction threshold
	Removal of provisional crowns and bridges
	During trial and adjustment of cast crowns and bridges after provisional prostheses have been removed

Removable prosthondontics

	Preparation of abutment teeth (only in those patients who experience tooth sensitivity or anxiety)
	Occlusal adjustment and impression taking
	Fitting of immediate dentures

Nitrous oxide-oxygen sedation is sometimes used during orthodontics and pediatric dentistry, keeping in mind the limitation that inhalation sedation, to be effective, requires a cooperative patient willing to don the nasal hood and to breathe through his nose.

As noted above, the technique of inhalation sedation with nitrous oxide and oxygen possesses many significant advantages over other techniques of pharmacosedation. The following is a summary of these advantages. 

ADVANTAGES

1. The principal advantage to the use of nitrous oxide-oxygen is the rapidity with which the sedation takes effect. The onset of action of inhalation sedation is less than 20 seconds which is almost equal to that of intravenous medications. Compare this to the 30-minute onset period for oral or rectal sedation.

2. Inhalation sedation provides peak clinical action within 3 to 5 minutes which permits titration. In most other techniques of sedation peak clinical effect does not develop for as long as 60 minutes. Titration is the ability to administer small, incremental doses of a drug until the desired clinical action is obtained. The ability to titrate a drug is a great safety feature in the sedation technique, for it allows the drug administrator to exercise control over the actions of the drug preventing medical emergencies due to overdose.

3. The degree of sedation achieved in inhalation can be deepened or lightened very easily from moment to moment. No other technique of sedation gives this much control to the administrator over the clinical actions of the drug.

4. Another advantage of inhalation sedation is the variability of duration of action at the discretion of the administrator. If a sedation technique has a relatively fixed duration of clinical activity, the dentist has to tailor his dental treatment to this limitation. N₂0-0₂ sedation does not have this limitation giving him the flexibility of planning the procedure which may take a minute or three to four hours.

5. Recovery from sedation is obtained rapidly with a full return to presedative psychomotor capacity. Because nitrogen oxide is not metabolized by the body, the gas is rapidly and virtually completely eliminated from the body within 3 to 5 minutes. Recovery from other forms of sedation may take longer than 2 to 3 hours. Inhalation sedation obviates the need for the patient to be accompanied to the dental appointment; he can drive and return to normal activities following treatment. Occasionally, patients experience lingering mental fuzziness or headaches, usually after extended, higher N₂0-0₂ dose use.

6. Another advantage of inhalation sedation is the ease of administration. No injection is required to obtain the effect. The patient merely breathes through his or her nose.

7. Inhalation sedation with nitrogen oxide-oxygen is safe with very few side effects. No serious complications have been reported in millions of cases where inhalation sedation is used.

8. N₂0-0₂ sedation has no adverse effects on the liver, kidneys, brain, or cardiovascular and respiratory systems. Because nitrous oxide is not biotransformed anywhere in the body and enters and exits unchanged almost entirely through the lungs, its use is not contraindicated by dysfunction of these organs. Further, the use of nitrous oxide is not contraindicated in patients with diabetes or seizure disorders. There are no known allergies to nitrous oxide.

9. Since the patient remains conscious during N₂0-0₂ sedation, the patient is able to follow directions and can cooperate during the procedure. Also the patient's protective reflexes remain functional to help prevent aspiration.

DISADVANTAGES

Although there are no significant disadvantages associated with nitrous oxide-oxygen inhalation sedation the following factors should be considered:

1. The initial cost of the equipment and the continuing cost of the gases are relatively high.

2. Since nitrous oxide is not a potent agent, there will be a small percentage of patients in whom the technique will fail to produce the desired clinical action. N₂0 should never be administered with less than 20% 0₂.

3. Chronic exposure to high amounts of N₂0 by dental personnel has the potential to cause infertility and congenital abnormalities in women and decreased mental performance and manual dexterity. 

Cautions and Contraindications

In the use of N₂0 - 0₂ there are two potential problems to consider_hypoxia and excitement. The former can be avoided as long as the percentage of oxygen administered with nitrous oxide is greater than 20%. Newer machines provide a delivery system that requires a minimum 25% to 30% oxygen before the nitrous oxide will flow. This is an important safeguard. Excitements can be prevented by avoiding too deep a sedation. Again, this can be achieved by providing a maximum of 50% to 70% nitrous oxide.

When assessing patients for the administration of N₂0-0₂ conscious sedation, there are a few conditions or patient profiles that may provide a contraindication for its use. Chief among these are patients with chronic obstructive pulmonary disease (COPD) (e.g., emphysema, chronic bronchitis) because of the potential effect of administering a gas mixture enriched with 0₂, many of whom have chronically elevated C0₂ blood levels. Whereas the usual stimulus for breathing in a healthy person is an increase in the blood CO₂ level, the stimulus for breathing in patients with COPD is a lowered blood 0₂ content. The use of N₂0 with 0₂ during inhalation sedation raises the oxygen saturation of the blood resulting in the loss of the stimulus and apnea may result. Nitrous oxide with oxygen may be appropriate for patients with mild to moderate disease, but the use in patients with severe condition must be carefully evaluated.

Chronic obstructions or acute upper respiratory tract infectious conditions may pose contraindications in inhalation sedation techniques. Blocked nasal passages (i.e., common cold, allergies) or chronic mouth breathing prevent effective use of this drug system. Any infectious respiratory condition (i.e., common cold or cough, tuberculosis, infectious bronchitis) will contaminate the tubing and breathing apparatus. Although there are disposable nose pieces and many newer units allow for regular sterilization of this part of the equipment, it still poses an infection control problem in many offices.

Several conditions that involve confined air spaces may be adversely affected by use of nitrous oxide. One characteristic of this anesthetic is that it diffuses into any air-containing body cavity, generally replacing nitrogen. Because nitrous oxide diffuses into an air space faster than nitrogen moves out, there is a temporary increase in either the size of the air space or the pressure in the space, depending on the rigidity of the walls. The middle ear is particularly affected by the pressure increase caused by this phenomenon. Nitrous oxide use may be contraindicated for patients with a history of middle ear or tympanic membrane problems or blockage of the eustachian tubes, even if caused by a head cold. Along the same lines, sinus congestion or blockage, either acute or chronic, may subject a patient to more pressure and discomfort.

Gastrointestinal distention is another possibility. This may be a factor in patients who vomit when higher concentrations of nitrous oxide are administered. It may be contraindicated for a patient with a bowel obstruction. The degree to which this phenomenon will occur is influenced by the concentration of nitrous oxide, the duration of its use, and the vascularity of the air space. The first two of these are under the control of the clinician.

There are few absolute contraindications to the use of nitrous oxide-oxygen form of sedation. There are, however, certain categories of patients on whom this technique of sedation would not work as well. For example, patients with compulsive personalities and those suffering from claustrophobia usually would avoid this form of sedation. The person with the compulsive personality will consciously or subconsciously fight the effects of the drugs, whereas the claustrophobic person will avoid the use of nasal hood or face mask used in the administration of gaseous agents. Similarly, children with severe behavioral problems will not be good candidates for inhalation sedation drug technique because a degree of patient cooperation is required for this technique to be successful.

The use of sedation in the pregnant woman requires many considerations. In general, it is desirable to avoid all unnecessary drugs during pregnancy, especially during the first trimester to avoid the possibility of spontaneous abortion or harm to the fetus. During the second trimester, drugs may be used if necessary, again with caution. The best course of action may be to avoid all elective dental treatments during the first and last trimester of pregnancy. However, if the dental treatment is necessary and anxiety reduction or mild pain control are needed, the safest and most recommended technique is inhalation sedation with N₂0-0₂. Nitrous oxide is not metabolized in the body, has virtually no effect on most organ systems, and it is rapidly and totally removed from the body within 3 to 5 minutes. All of these properties make this technique superior to all other techniques.

In the final analysis, the clinician and the patient have to weigh the risks and benefits of undergoing or postponing dental treatment during pregnancy.

INDICATIONS

The primary indications for the use of inhalation sedation are, of course, the management of fear and anxiety related to dental procedure, the management of gagging and the management of medically compromised patient. Nitrous oxide has become a primary tool of dental office conscious sedations procedures. When nitrous oxide is properly administered, the patient remains conscious with the protective reflexes intact, providing anxiety relief coupled with analgesia.

The major patient indication for the use of N₂0-0₂ conscious sedation is for the medically compromised patient. Again, the chief advantage of this technique lies in the fact that the patient receives significantly higher amount of 0₂ during the procedure, with a minimum of 30% to a high of 50% to 70%. In a patient with cardiovascular disease oxygen deficit in the myocardium is likely to exacerbate the signs and symptoms of the disease, possibly leading to ischemia (lack or reduction of blood or oxygen to an organ or body part.) N₂0-0₂ sedation would avoid such a condition.

Similarly, patients with respiratory or cerebrovascular disease may also be safely sedated with N₂0-0₂. Neither hypertension nor cardiac arrhythmias pose any specific contraindication to its use. Diabetes mellitus does not represent a contraindication to the use of N₂0 - 0₂. There has never been a reported allergy to N₂0.

Complications from inhalation sedation

Although there are few side effects and complications associated with the use of inhalation sedation, the following deserve a mention and a brief discussion.

Expectoration

The patient should be discouraged from expectorating through the use of an aspirator. In the dental office in which the aspirating system does not function well, the patient may need to spit on occasion. If the patient bends forward to do so, the patient is likely to bump his head on the cuspidor while bending over because he may be disoriented due to the effect of nitrous oxide. This can be avoided with the assistant guiding the patient properly. In the dental office where the high volume suction apparatus is available this problem will not arise because all foreign material, blood, and saliva are rapidly and effectively removed from the patient's mouth.

Excessive Perspiration

The patient may become somewhat flush during the administration of nitrous oxide-oxygen. This is brought about by the peripheral vasodilating properties of nitrous oxide. Usually perspiration can be disregarded unless it is accompanied by a loss of color (pallor), a dropping blood pressure, and increased heart rate_all conditions which may result in potentially serious problem. In this situation the flow of nitrous oxide should be terminated, 100% oxygen administered, the patient placed into a supine position with the legs slightly elevated and the steps of basic life support initiated.

Behavioral Problems

Patients who become too deeply anesthetized may develop disassociation, with emotionally disturbing dreams and psychic distortion and reactions. Titration and verbal monitoring of the patient can prevent this potentially serious complication. A decrease in the level of nitrous oxide by approximately 5% to 10% will minimize oversedation. Behavioral problems are also present in patients with authoritarian type of personality, for they are afraid to lose control and will fight the effect of sedation. Other patients receiving inhalation sedation will talk excessively. Again, this problem may be alleviated by decreasing the concentration of nitrous oxide, by 5% to 10% per minute.

Shivering

Some patients develop shivering at the end of the sedative procedure when the nitrous oxide has been terminated and the patient is receiving 100% oxygen. This is explained by the fact that nitrous oxide produces peripheral vasodilation. Management of the patient during this reaction is purely symptomatic. The patient should be reassured that within a few minutes after the procedure is terminated body will return to its normal level.

Nausea and Vomiting

Of all the potential side effects and complications associated with the administration of nitrous oxide-oxygen inhalation sedation, this is the most frequently mentioned and most bothersome to patients. It generally occurs in patients who consume a heavy meal prior to their dental appointment. Monitoring the patient during the procedure is a major means of detecting nausea at the time when it may still be treated and vomiting prevented. Nausea can be effectively managed by reducing the nitrous oxide concentration by approximately 5% to 10%. If the nausea still persists, nitrous oxide should be decreased by an additional 5 to 10 percent.

Melamed (Sedation: A Guide to Patient Management, Mosby) lists several factors that contribute to nausea in patients during N₂0-0₂ administration:

	The greater the depth of sedation (which in turn is related to the concentration of N20), the greater the incidence of nausea.
	In some patients, the longer the inhalation procedure, the greater the likeli- hood of nausea.
	A more anxious or fearful patient is more likely to feel nauseous under N20-02.
	Some patients are predisposed to become nauseous.
	There is no proven direct correlation between eating (or not eating) prior to the procedure and the incidence of nausea, although most patients are advised not to eat a heavy meal approximately 4 to 6 hours prior to the procedure.
	Frequent changing of the concentration of N20 during sedation increases the likelihood of nausea developing.

Occupational HAZARD

More than the patient, it is the dental office personnel who may be at risk from nitrous oxide. In April 1994, the National Institute for Occupational Safety and Health (NIOSH) issued the following alert: "Workers exposed to nitrous oxide may suffer harmful effects."

N₂0 has been found to affect the woman's ability to conceive. A recent retrospective study of female dental assistants concluded that occupational exposure to high levels of nitrous oxide may adversely affect the ability to become pregnant. Those exposed to 5-9 hours per week of unscavenged nitrous oxide were 59% less likely to conceive during each menstrual cycle than unexposed women. Each hour of exposure to unscavenged N₂0 corresponded to a 6% reduction in probability of conception. For those working with nitrous oxide that had a functioning scavenging system, no decrease in fertility was detected.

In addition, some studies have reported an increased rate of congenital abnormalities among women exposed to N₂0, and an increase in liver, kidney and neurologic diseases among male dentists similarly exposed to inhalation anesthetic.

In 1977, NIOSH concluded that N₂0 exposure resulted in decreased mental performance, audiovisual acuity and manual dexterity. To prevent these effects, a 25 ppm exposure limit was recommended.

To reduce nitrous oxide levels in the dental office, NIOSH recommends the following steps:

1. Set the exhaust ventilation of the nitrous oxide scavenging device to the recommended 45 liters per minute.

2. Maintain equipment; inspect the connectors and test for leakages at frequent regular intervals.

3. Vent the exhaled gases to a safe disposal site outside the building.

4. Use a fan or auxiliary exhaust system to direct exhaled nitrous oxide away from the breathing zone of the operating personnel.

5. Improve circulation in the operatory by opening a window or using a nonrecycling air conditioning system.

6. Use a monitoring system; air sampling equipment is available and relatively in expensive; a badge can be worn on the lapel to detect nitrous oxide levels in the operator's breathing zone.

7. Set conservative limits on the duration and concentration of nitrous oxide expo- sure for each patient.

8. Fit the nasal mask to the patient as well as possible.

9. Minimize patient conversation and mouth breathing.

10. Shut off and secure the equipment after each day's use.

Source: Stach DJ. Nitrous oxide sedation: Understanding the benefits and risks. Am J of Dentistry 1995; 8:47-50.

TECHNIQUE OF ADMINISTRATION

The technique of administration of N₂0-0₂ inhalation sedation is simple enough that a dental technician with minimal training can administer the sedation successfully. The equipment is a compact, continuous flow machine designed to deliver compressed gases under controlled conditions. The success rate of N₂0-0₂ sedation _ if proper technique is followed _ is 90% to 95%. There is a small percentage of patients in whom the technique will fail to produce adequate sedation. Melamed provides a brief description of the technique of N₂0-0₂ administration in the adult cooperative patient:

1. A 6 L/min flow of 100% 0₂ is established, and the nasal hood is placed on the patient's nose.

2. The appropriate flow rate of gas is established while the patient is breathing 100% 0₂.

3. Titration of N₂0 is started, with the patient receiving approximately 20% N₂0.

4. The percentage of N₂0 is increased approximately 10% every 60 seconds until the ideal level of clinical sedation is reached.

5. The planned dental or surgical procedure is completed.

6. Nitrous oxide flow is terminated, the patient receiving 100% 0₂ at a flow equal to the rate established in step 2. Oxygen is administered for a minimum of 3 to 5 minutes or longer if clinical signs and symptoms of sedation persist.

7. The patient may be dismissed from the dental office unescorted if, in the doctor's opinion, recovery from the sedation has been complete.

NITROUS OXIDE IN THE DENTAL OFFICE

Nitrous oxide continues to be a valuable agent for the control of pain and anxiety. However, chronic occupational exposure in dental offices not using scavenging systems may be associated with possible deleterious neurological and reproductive effects. This report outlines recommendations for controlling nitrous oxide exposure that were made by an expert panel convened by the ADA.

The safe use of nitrous oxide in the dental office has been an issue the ADA has monitored for many years. In 1977, an ad hoc committee convened by the Association published a report on the potential health hazards of trace anesthetics in dentistry. Also in 1977, the National Institute of Occupational Safety and Health (NIOSH) reported that, by using several control measures, nitrous oxide levels of approximately 50 parts per million were achievable in dental operatories during routine dental anesthesia/analgesia. A few years later, in 1980, the ADA Council on Dental Materials, Instruments and Equipment recommended that effective scavenging devices be installed and monitoring programs be instituted in dental offices in which nitrous oxide is used, and the council indicated that using these methods or devices would assist in keeping the levels of nitrous oxide at the lowest possible level.

NIOSH continued its activities relating to nitrous oxide concentrations in the dental office and, in 1994, published an alert called "Request for Assistance in Controlling Exposures to Nitrous Oxide During Anesthetic Administration." In the same year, NIOSH also reported on field evaluations and laboratory studies evaluating nitrous oxide scavenging systems and modifications in attempts to achieve the current NIOSH- recommended exposure limit of 25 ppm during administration. NIOSH concluded that nitrous oxide levels may be controlled to about 25 ppm by maintaining leak-free delivery systems and using proper exhaust rates, better-fitting masks and auxiliary exhaust ventilation.

In 1995 the ADA Council on Scientific Affairs convened an expert panel to review scientific literature on nitrous oxide and to revise recommendations on controlling nitrous oxide concentrations in the dental office. What follows is an overview of the conclusions reached by that panel.

Assessing the Risk

The administration of nitrous oxide mixed with oxygen is a safe and effective method of managing pain and anxiety in dentistry. Referred to as "relative analgesia," "conscious sedation" or "nitrous oxide sedation," the use of nitrous oxide is increasing in dentistry. Among all dentists, it rose from 35 percent in 1983 to 58 percent in 1991 among pediatric dentists, it increased from 65 percent in 1980 to 88 percent in 1988.

Potential benefits of nitrous oxide sedation are well-documented. The dental care team and the patient benefit from reduced stress and increased comfort. The potential disadvantages of using nitrous oxide sedation are few. For the patient, the production of hypoxia is the most significant potential hazard. Adequate training in the administration of nitrous oxide reduces the potential of hypoxia and other adverse patient outcomes. The most significant hazard for the dental care team is the potential adverse health effect of long-term exposure to nitrous oxide.

Nitrous oxide inactivates methionine synthase, an enzyme essential for the synthesis of DNA and for the metabolism of vitamin B₁₂ , thereby interfering with cellular proliferation. The effects of short-term (acute) nitrous oxide exposure are reversible. Long-term (chronic) exposure to nitrous oxide in sufficient concentrations can produce irreversible, toxic changes, and should be a concern for dental personnel working in environments in which nitrous oxide is administered to patients.

Chronic exposure to nitrous oxide has been associated with reproductive, hematologic, immunological, neurological, liver and kidney disorders. Symptoms are dose-and time-related, with neurological symptoms most frequently reported in cases of chronic abuse (or recreational use).

Chronic exposure to nitrous oxide may produce symptoms that mimic those of pernicious anemia or multiple sclerosis. Among the reported neurological symptoms are loss of ability to concentrate, numbness of the extremities, paresthesia, ataxia, impotence, and loss of bladder and bowel sphincter control. The neurological symptoms are dose-related, increasing in both intensity and number with increased exposure.

Hematologic changes associated with chronic exposure to nitrous oxide are a result of bone marrow suppression. The effects are suggestive of pernicious anemia, a vitamin B₁₂ deficiency disease.

Conclusions and Recommendations of the Expert Panel

Nitrous oxide continues to be a valuable agent for the control of pain and anxiety. However, chronic occupational exposure to nitrous oxide in offices not using scavenging systems may be associated with possible deleterious neurological and reproductive effects on dental personnel. Limited studies show that as little as three to five hours per week of unscavenged nitrous oxide exposure could result in adverse reproductive effects. In contrast, in dental offices using nitrous oxide scavenging systems, there has been no evidence of adverse health effects. It is strongly recommended, therefore, that while there is no consensus on a recommended exposure limit to nitrous oxide, appropriate scavenging systems and methods of administration should be adopted. A protocol for controlling nitrous oxide is outlined below.

Recommendations For Controlling Nitrous Oxide Exposure

The expert panel identified a number of recommendations that are important to consider in the safe and effective use of nitrous oxide:

• The dental office should have a properly installed nitrous oxide delivery system. This includes appropriate scavenging equipment with a readily visible and accurate flow meter (or equivalent measuring device), a vacuum pump with the capacity for up to 46 liters of air per minute per workstation, and a variety of sizes of masks to ensure proper fit for individual patients.

• The vacuum exhaust and ventilation exhaust should be vented to the outside (for example, through the vacuum system) and not in close proximity to fresh- air intake vents.

• The general ventilation should provide good room air mixing.

• Each time the nitrous oxide machine is first turned on and every time a gas cylinder is changed, the pressure connections should be tested for leaks. High- pressure-line connections should be tested for leaks on a quarterly basis. A soap solution may be used to test for leaks. Alternatively, a portable infrared spectrophotometer can be used to diagnose an insidious leak.

• Prior to first daily use, all nitrous oxide equipment (reservoir bag, tubings, mask, connectors) should be inspected for worn parts, cracks, holes or tears. Replace as necessary.

• The mask may then be connected to the tubing and the vacuum pump turned on. All appropriate flow rates (that is, up to 45 L/min. or per manufacturer's recommendations) should be verified.

• A properly-sized mask should be selected and placed on the patient. A good,comfortable fit should be ensured. The reservoir (breathing) bag should not be over-or underinflated while the patient is breathing oxygen (before administer- ing nitrous oxide).

• The patient should be encouraged to minimize talking and mouth breathing while the mask is in place.

• During administration, the reservoir bag should be periodically inspected for changes in tidal volume and the vacuum flow rate should be verified.

• On completing administration, 100 percent oxygen should be delivered to the patient for five minutes before removing the mask. In this way, both the patient and the system will be purged of residual nitrous oxide. Do not use an oxygen flush.

• Periodic (semiannual interval is suggested) personal sampling of dental personnel, with emphasis to chairside personnel exposed to nitrous oxide, should be conducted (for example, use of diffusive sample [dosimeters] or infrared spectrophotometer).

Source: ADA Council on Scientific Affairs; ADA Council on Dental Practice. 

References

1. ADA Ad Hoc Committee on Trace Anesthetics as Potential Health Hazard in Dentistry. Reports of Subcommittees of the ADA Ad Hoc Committee on Trace Anesthetics as Potential Health Hazard in Dentistry: review and current status of survey. JADA 1977;95(10):787-90.

2. Whitcher CE, Zimmerman DC, Piziali RL. Control of occupational exposure to N₂O in the dental operatory. Cincinnati: National Institute of Occupational Safety and Health, 1977; DHEW publication no. (NIOSH) 77-171.

3. Council on Dental Materials, Instruments and Equipment. Council position on nitrous oxide scavenging and monitoring devices. JADA 1980;101(1):62.

4. Alert: request for assistance in controlling exposures to nitrous oxide during anesthetic administration. Cincinnati: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute of Occupational Safety and Health, 1994; DHHS publication no. (NIOSH) 94-100.

5. Technical report: control of nitrous oxide in dental operatories. Cincinnati: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute of Occupational Safety and Health, Division of Physical Sciences and Engineering, Engineering Control Technology Branch, 1994; DHHS publication no. (NIOSH) 94-l29.

6. Rowland AS, Baird DD, Weinberg CR, Shore DL, Shy CM, Wilcox AJ. Reduced fertility among women employed as dental assistants exposed to high levels of nitrous oxide. N Engl J Med 1992;327:993-7.

SOURCES

American Dental Association. The 1991 survey of dental practice: General characterisitics of dentists. Chicago: American Dental Association, 1992; 11.

Malamed SF. Sedation: A guide to patient management. 2nd ed., St. Louis: CV Mosby, 1989;176.

NIOSH. Controlling exposures to nitrous oxide during anesthetic administration (NIOSH Publication No. 94-100). Cincinnati: U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, 1994.

NIOSH Criteria for a recommended standard: Occupational exposure to waste anesthetic gases and vapors (NIOSH Publication No. 77-140). Cincinnati; U.S. Department of Health, Education, and Welfare, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, 1977.

Trieger N. Pain Control. 2nd ed., St. Louis: CV Mosby, 1994; 75.