Wow, as far back as 1976 Dentists were warned of the problem of mercury contamination in their dental offices. This article was published in the Journal of the American Dental Association. - (M.E.)

Journal of the American Dental Association, Vol. 92, June 1976

Mercury toxicity in the dental office:a neglected problem

Donald G. Mantyla, DDS Orson D. Wright, DDS, Salt Lake City

No longer can the dental profession ignore the problem of mercury contamination in the dental office. Even though the effect of mercury poisoning has been observed in industries, in the past it apparently has not been an important concern for dentists. Now the profession must recognize the potential health hazard associated with the use of mercury and contamination of the dental office. Nationally, at least 10% of dental offices are estimated to have air levels of mercury vapor in excess of the threshold limit value (TLV) of 0.05 mg/ma.' (The TLV has been determined to be the level at which workers probably will not be subject to the injurious effects of mercury toxicity.)

The dentist's awareness of this problem is necessary for two reasons:

• The moral responsibility that the dentist has to protect himself and his employees from any source that may be injurious to either his own physical well being or that of auxiliary personnel.
• A legal responsibility, which has been created for the employer-dentist through the enactment of the Occupational Safety and Health Act of 1970. This federal law was passed for the protection of all employees in any business activity.

Government is now concerned with the possibility of occupational exposure to inorganic mercury in dental offices because the dental profession is one of the large users of inorganic mercury. Guidelinesz have been established as to the amounts of mercury vapor levels that are allowable in offices in which mercury is used.

The problem

Mercury toxication is encountered by dentists and employed personnel primarily from two sources: direct absorption into the tissues through contact or handling of mercury and mercury-containing compounds, or inhalation of vapors that are emitted through a volatilization of mercury and mercury-containing substances. Mercury becomes a liquid at -39 C (-38 F) and volatility increases as the environmental temperature rises. The equilibrium concentration of mercury is 2 mg/mi' of air at 25 C (77 F).

There is an increase of volatility of eight times as the temperature rises from 20 C to 50 C.3

Simple procedures such as the condensation of amalgam and the cutting of hardened amalgarns increase the volatility of mercury.

The safe mercury vapor level in ambient air, the TLV, which had been previously established by the American Conference of Governmental Hygienists at 0.1 mg I-Ig/ms of air, has been reduced to 0.05 mg of fairs" Any office that exceeds this limit is considered to be contaminated.

In a recent study of 72 offices in Utah? about I0% were found to have mercury levels greater than the TLV. Three offices had levels as high as 0. 14 to 0.15 mg of air, read at the breathing level. Other offices had carpet and bench contamination too high to register, approximately 300% or more of the accepted TLV (illustration). These studies were conducted using a Bacharach Mercury Analyzer* and were under the direction of the Radiation and Occupational Health Section and coordinated with the Dental Health Section of the Utah State Division of Health.

We note, however, that a high percentage of dentists are consciously using proper techniques and safe practices in the handling of mercury. These dentists are confident that mercury poses few, if any, problems for them.

What are the laws?

According to the Utah Occupational Safety and Health Act (UOSHA) of 1973 (effective Jan 1, 1974 and which follows federal guidelines), any dental office (with paid employees) in which ambient mercury levels are in excess of the accepted TLV of 0.05 mg/mi' is subject to citation, fine, or both. This citation must be posted in a conspicuous location in the office and should state that the office is in violation of the UOSHA law of 1973, in respect to excessive mercury vapor levels. if this violation is not corrected by a stipulated reasonable date, a second fine may be imposed. A maximum fine of $10,000 may be levied. In addition, the office may be closed until the mercury vapor level is reduced below the accepted TLV.6 The director of dental health of the Utah State Division of Health notified every Utah dentist early in 1974 of the regulations of UOSHA. He cited the necessary precautions that must be implemented to meet the law.'

GRAPHIC: Monitoring of 78 dentai offices for mercury contamination. Utah, 1973-1974. Threshold Llmlt Value (.050 mg/M3)

In addition to the state Occupational Safety and Health Act, criteria for recommended standards of occupational exposure to mercury have been proposed by the US Department of Health, Education, and Welfare, National Institute of Occupational Safety and Health (NIOSI-I).8

Employee exposure criteria, as proposed by NIOSH, are even more stringent than those in UOSHA. The NIOSH document states that "Exposure to inorganic mercury is defined as exposure to a concentration of inorganic mercury greater than 40 percent of the recommended level in the workplace." Therefore, any value exceeding this figure creates an environment of mercurial exposure for those in the workplaces.

Medical records of employees must be available for authorized review for at least five years after an employee's last exposure to inorganic mercury.

As of April 1976, state occupational and safety health acts are operational in 23 states and territories: Alaska, Arizona, California, Colorado, Connecticut, Hawaii, Indiana, Iowa, Kentucky, Maryland, Michigan, Minnesota, Nevada, New Mexico, North Carolina, Oregon, South Carolina, Tennessee, Utah, Vermont, Washington, Wyoming, and the Virgin Islands. Nevada and the Virgin Islands operate a safety program only, whereas the health portions of the program are handled under federal jurisdiction. New Mexico and Indiana operate under a dual state and federal jLlI'lSdiC[iO1'l.9

Symptoms of mercury poisoning

Worldwide studies show that several sympmay develop on exposure to mercury, either through direct contact or by inhalation of vapors. Perhaps some undiagnosed conditions in dental personnel in the past could be attributed to mercury toxication. The symptoms are:

• Erthism: A peculiar form of psychic disturbance characterized by self-consciousness, timiclity, embarrassment with insufficient reason, anxiety, indecision, lack of concentration, depression, resentment of criticism, irritability or excitability; these appear to cause a complete change of personality. Other symptoms may include headache, fatigue, and weakness; either drowsiness or insomnia also are characteristic complaints and in more advanced cases there may be hallucinations, memory loss, and general vasomotor disturbances (these may include blushing, excessive perspiration, and dermagraphia).
• Tremor: This is one of the most obvious symptoms of the neurological upset. A fine "intention" tremor of the hands is one of the first signs; the tremor may be demonstrated in the face, arms, or legs. As it progresses, it may develop into convulsions.
• Speech disorders: Slurring of words, slight starnmering, and a difficulty in pronunciation of words are characteristic.
• Alteration of handwriting: A progressively tremulous, irregular, and illegible handwriting often is associated with the tremor.
• Motor and sensory nerve disorders: An unsteady gait, possibly of a spastic nature, has been observed in some patients. Hyperactive reflexes up to five times those in a normal person have been exhibited in patients with chronic mercurialism. Numbness and pain in the extremities may develop in various degrees.
• Eye affections: Two types of changes have been observed including a constriction of visual fields and lens reflex changes. Other defects have been reported in accommodation and muscular balance.
• Oral pathosis: Mercury toxication can manifest itself orally through a gingivitis that may result in an extreme gingival recession and mobility of the teeth.

Safeguards against contamination

Every office should institute proper procedures for the handling of mercury to reduce the hazard of contamination.

Air concentrations should be controlled so the employees are not exposed to mercury vapor levels greater than 0.05 mg determined as a time-weighted average exposure for an eight-hour workday. Air samples must be frequently analyzed. Local health departments are usually equipped to analyze mercury levels in dental offices.

Comprehensive medical examinations should be available to employees both before their employment and annually thereafter. These examinations should specifically emphasize any signs or symptoms of mercury toxication. Urine and blood samples may be taken for analysis.

Employees subject to exposure to inorganic mercury should be inforrned at the beginning of their employment about the hazard, relevant symptoms, emergency procedures, and proper conditions and precautions for the safe use of the material and minimal exposure.

Proper office conditions, work practices, and personal hygiene practices should be observed. Floors, work surfaces, and equipment should be constructed and maintained so mercury will not accumulate or be retained in any area. Mercury spills should be promptly cleaned up, either chemically, mechanically, or through a combination of both. If vacuum cleaners are used (only high-powered industfial cleaners are effective), they should be equipped with mercury vaporabsorbing filters so that they will not disperse mercury-laden dust into the workplace.

Waste mercury, materials contaminated by mercury, or materials combined with mercury should be stored in vapor-proof containers or in chemically treated solutions until proper removal for disposal or reprocessing. Water should be placed in containers of waste amalgam and mercury to minimize contamination. The use of unbreakable plastic containers for storage of new mercury or waste products is recommended. Containers of mercury should be kept covered except when they must be open for use.

Safe techniques should be used including minimal mix procedures to reduce contamination. Mercury should not directly contact any skin surface, including the hands. The cutting and carving of amalgarns, procedures which increase mercury vapor levels, should be done using water spray and evacuation.

Food preparation and eating should be prohibited and smoking should not be permitted in mercury work areas, since oral contamination may occur. Finally, handwashing facilities and materials should be available for proper personal hygiene. Employees should be told of the importance of thoroughly washing their hands before eating or smoking and of the use of good Working techniques in accordance with currently recommended methods of mercury control.

Despite all precautions, mercury emergencies may occur. Spillage of mercury on smooth counter tops may be removed by wiping the counter and brushing the mercury into a container. Mercury falling into cracks and crevices on counter tops and floors may be removed by a combination of mechanical cleansing and chemical dissolution. Mechanical cleansing is self-explanatory. Chemical dissolution is accomplished by use of either a chemical mercury solvent (liquid) or "flower (or flour) of sulphur." Both are available commercially. In the use of either product, the agent should be worked into the crevice as deeply as possible, then wiped out. Carpet spills should be handled immediately since contamination may produce a very high level of mercury vapor—sometimes too high to be measured. Spills should be removed by first vacuuming with a high-powered industrial vacuum. Flower of sulphur should be sprinkled liberally on the spill, brushedand worked into the depth of the carpet, and left in place at least one day. Repeated applications may be necessary.

Areas in which mercury vapor levels do not exceed 40% of the TLV are not considered potential exposure areas. Records of surveys should be kept as a basis for concluding that air levels are below the 40% TLV.

If an area is considered to be contaminated with inorganic mercury, these requirements should be observed. Employers should monitor environmental levels of inorganic mercury vapor at least every six months. If any time-weighted average exposure is at or exceeds the accepted TLV, immediate steps should be instituted to reduce environmental levels. Samples should be taken every 30 days or as frequently as the department of health desires, until the level has been reduced below the TLV. Records should be maintained for all sampling schedules, including the sampling and analytical methods, type of respiratory protection, and the mercury vapor levels in each work area. These records should be available to each employee so that he can obtain information on his own exposure.

Other precautions often recommended in industry are not practical in the dental office. They include the construction of exhaust systems to prevent recirculation of the mercury vapor, and the incorporation of engineering controls for respiratory protection, as used in industry, to maintain mercury levels at or below the maximum prescribed limits.

Report of two cases

In one office in Utah, exposure to mercury led to mercurial toxication in two dentists, resulting in extreme symptoms of long standing. The two dentists, a father and son, share a small single building with their offices distinctly separated by a reception room which is in the entire middle portion of the building. The younger man was recently graduated from dental school. Both rnen began to notice symptoms of mercurial poisoning about the same time.

In the father, extreme fatigue developed early. This was distinctly noticeable and was more than a tired feeling. There was a pain in the neck. Slight edema of one hand developed and the hand felt hot and hurt a great deal. Some numbness developed later. The impression that the pain was caused by shaking hands when greeting people obviously proved false because the numbness and pain continued even when shaking hands was avoided. Later, an ulceration developed on the father's left leg, with which he operates the foot pedal located below the amalgamator.

The onset of symptoms occurred over a twomonth period in the son. A depressing fatigue developed, followed by a sudden numbness in the toes and feet, with diminishing reflexes in the feet, knees, and legs. A strong metallic taste developed. A few days later, the son noticed tremors in the head and felt sensations similar to electric shocks in his neck when his head was bent forward.

The basic symptoms (numbness, pain in the limbs and neck, a heavy depressing fatigue, diminished reflexes, metallic taste, and tremors) were similar for both dentists.

Some office conditions should be noted. Both dentists share the same ventilation and heating system that might disperse the mercury vapor to both offices. Tests were made for mercury vapor levels in ambient air and at floor levels. Initial ambient air levels ranged as high as 0.150 mg/m3 and levels of carpet readings were so high in some areas that they were unreadable. Urine tests were made for the entire office staff; again, initialhigh levels were obtained. With care and much work, these readings have decreased in more than a year to near normal limits.

Both dentists had used amalgamators that dropped excess mercury onto the counter top or into open containers or trays, thereby increasing contamination. From the counter tops, mercury spilled onto the carpet.

Some of the steps that these dentists took to correct the conditions were removal of mercury from drains where about 1 tablespoonful of mercury had accumulated in each, decontamination of carpets with flower of sulphur brushed into the carpet and not removed for at least a day, replacement and relocation of amalgamators, and refinement of technique.

Fortunately, in nearly 20 months' time, with correction of the office conditions leading to contamination, many of the symptoms have subsided. Although research shows that complete regeneration generally does not take place.1°"5 alleviation of symptoms is possible if the condition is diagnosed at an early date; this will afford as much opportunity for repair as possible. These dentists report that their symptoms are partially alleviated. In the left hand of the father, some residual edema, numbness, and noticeable impairment remained for a long time; this caused discernible difficulty in his playing of a musical instrument. For all practical purposes, this impairment has subsided. The ulceration of the father's leg remained for a year after the contamination was cleared up. The son, still under medication with chelating agents, notes a slight numbness remaining in the lower legs and feet, with diminished but returning reflexes.

Summary

Amalgam has proved to be among the most versatile and durable of all restorative materials used in the treatment of dental disease. If it is handled and controlled properly, problems with its use should not develop.

Safe mercury vapor levels can be maintained if good mercury hygiene practices are exercised. Materials and devices are available for aiding the dentist in adequate mercury control procedures; With the cooperation of each member of the dental team, compliance with all the criteria imposed by governmental regulatory agencies can be accomplished.

These criteria have been established for the health protection of the dentist and his auxiliary personnel. Each practitioner and office staff member should realize the potential hazards associated with mercury, and effect good mercury hygienic measures and control procedures.