Mercury Toxicity and Management

Dr.Alok Misra

M.D.S.

Conservative- Dentistry and Endodontics

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MERCURY TOXICITY

INTRODUCTION

Silver amalgam has been in use as a restorative material since the beginning

of the nineteenth century. Unlike any other plastic dental filling material, it has

been in continuous clinical use for more than 160 years. Yet the safety of dental

amalgam for both the dental patient and the dental personnel has been questioned

intermittently since the inception of the use of this material. The controversy

relates to the important component of the dental amalgam, that is, mercury.

The seemingly constant pronouncements about the toxic effects of mercury

and the suggested links between dental amalgam and disease have confused and

frightened the general public. While there is no scientific evidence whatsoever to

support such claims, they continue to fuel the anti-amalgam fire. Jones has arqued

that the media is not the place to present preliminary research results, especially

when they involve an emotionally charged subject such as mercury poisoning.

HISTORY [Amalgam Wars]

Controversy is not new for amalgam. The foundation for the earliest

recorded amalgam war were laid around 1833. The Crawcour brothers, then

exiled from France for dental practice irregularities started a thriving practice in

New York city using a silver coin-mercury mixture called Royal Mineral

succedaneum. However, there was no attention to the proper mercury alloy ratios

or to the type of alloy being used. For the most part, the alloy mixed with the

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mercury was prepared by filling silver coins whose composition was considerably

variable. After a few years of the unscrupulous and inept work of the Crawcours

and their followers, disastrous side effects started to appear. In many cases, the

inconsistency in materials and techniques led to slow setting amalgams that

released mercury from the unset mass into unprotected dentinal tubules. Although

there were no reported cases of patient deaths, there were several cases of pulp

death.

In 1843, the American Society of Dental Surgeons condemned the use of

all filling materials other than gold, thereby igniting the first amalgam war.

The question of amalgam composition was finally settled in 1895 by Dr.

G.V. Black, who after years of scientific research on amalgams, demonstrated the

proper quantitative and qualitative mixture of mercury in amalgam to make an

effective restorative material.

The second amalgam war was started by a German chemist, professor

Alfred Stock in the mid 1920s when. Stock claimed to have evidence showing

that mercury could be absorbed from dental amalgams and that this led to serious

health problems. Stock reported that nearly all dentists had excess mercury in their

urine. He reported that mercury levels in urine of 7 patients with amalgam ranged

from 0.1 to 40 g/L but failed to record any mercury urine levels before

restorations were placed. Stocks work was later questioned: even Stock, in 1934,

repudiated his earlier analyses.

Following these controversies, a dramatic health history was reported. A

17-year-old girl, withdrawn, totally lacking in energy, even suicidal sought

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treatment. When she became ill, she began to hyperventilate and started

withdrawing from life and eventually dropped out of school. She was sent to

psychiatrists, internists and cardiologists without results and became progressively

sicker. A detailed case history recorded by a dentist disclosed that her symptoms

had begin 6 months earlier, after the placement of several dental amalgam

restorations. A mercury evaluation and biochemical tests were done. The amalgam

restorations were removed and within days all symptoms cleared.

Interestingly, one of the arguements is that if mercury was the cause of the

patients problem, she would feel much worse rather than much better

immediately following the removal of her amalgam restorations.

The current controversy, sometimes termed the Third Amalgam War

began primarily through the seminars, writings and videotapes of H.A. Huggins, a

dentist from Colorado Springs. He was convinced that mercury released from

dental amalgam was responsible for a plethora of human diseases affecting the

cardiovascular and nervous systems. Patient claimed recoveries from multiple

sclerosis, Alzheimers disease and other afflictions as a result of removing their

amalgam fillings.

In 1991, the General American public was widely exposed to the

controversy when it was reported by a major television program (60 minutes). In

response to numerous public questions, although the experts agreed dental

amalgam research was needed and should continue, they concluded that there was

no basis for claims that dental amalgam was a significant health hazard.

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Amalgam controversy in Western countries

The use of dental amalgam has been strongly debated in Sweden, Germany,

the United States and Canada.

The Public Health Department in Berlin has initiated the withdrawal of r-2

containing amalgam from the German market. The German authorities have

further recommended that amalgam restorations be avoided in patients with kidney

complaints and in children under 6 years of age who, they claim, are generally

believed to have a higher mercury sensitivity.

Historically, despite Swedens recent decision to ban the use of mercury in

industry, the major cause of mercury contamination in the food chain was the use

of methyl mercury coated seed. Eggs, fish and other Swedish foodstuffs were

found to have higher mercury levels than identical products produced in other

European countries. It is worth noting that Sweden, to date, is the only European

country that plans to prohibit the use of dental amalgam. Swedens motives for

examining the possible discontinuation of dental amalgam are based entirely on

environmental concerns, and not on the potential health hazard to dental patients.

After intensive studies and discussion a scientific panel appointed by

Swedish Medical Research Council concluded that

- Mercury released from dental amalgam does not, according to the available

data, contribute to systemic disease.

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- No significant effects on the immune system has been demonstrated with the

amounts of mercury which may be released from amalgam fillings.

- Allergic reactions to mercury from amalgam fillings have been demonstrated,

but are extremely rare.

- In a very small number of individuals, local reactions, such as lichernoid

reactions of the mucosa, may occur adjacent to amalgam restorations as well as

adjacent to dental restorations made of other materials.

- There are no data to support the belief that mercury released from dental

amalgam gives rise to teratological effects.

- The possible environmental consequence resulting from handling dental

amalgam can be controlled by proper waste management.

- Available data do not justify discontinuing the use of mercury containing

dental amalgam fillings or recommending their replacement.

The story from the National Health Service in the United Kingdom is the

same. In response to a question raised in Parliament, Mr. Hayhoe, the secretary of

state for social services, stated: In our opinion, the use of dental amalgam is free

from risk of systemic toxicity and only a few cases of hypersensitivity occur.

Mercury in the environment and food chain

Mercury is a naturally occurring element with 30,000 to 150,000 tons being

released into the atmosphere by the degassing of the earths crust and the oceans.

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Mercury has been used in preparations such as diuretics, antibacterial agents,

laxatives, skin antiseptics and other ointments. Presently, workers in more than 60

industries are occupationally exposed to mercury. These industries include

factories producing chlorine, caustic soda, insecticides and fungicides as well as

those involved in the manufacture of neon lights, paper and paint.

Mercury enters the food chain by inadequate and improper disposal of

wastes into oceans, lakes and stream where microorganisms methylate inorganic

mercury to the more toxic methyl mercury. Methyl mercury is then rapidly taken

up by plankton algae and is concentrated in fish via consumption by these

organisms. From the aquatic environment, methylmercury becomes incorporated

in the terrestrial environment by species feeding on the aquatic organisms.

The earliest indication that methyl mercury was an environmental hazard

came from two episodes in Minamata Bay and Nigata, Japan from 1953 to 1960.

In both episodes, the fish were contaminated by mercury from factories using

mercuric chloride catalyst in the manufacture of vinyl chloride and actaldehyde.

Several deaths were reported in these episodes.

Major incidents of human poisoning also occurred from the inadvertent

consumption of mercury treated seed grain in Iraq, Pakistan, Ghana and

Guatemala. The most catastrophic outbreak occurred in Iraq in 1972. Iraq having

imported large quantities of seed treated with methyl mercury fungicide

distributed the grain for planting. Despite official warnings, the grain was ground

into flour and made into bread. As a result, 6,350 victims were hospitalized and

500 died.

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Chemical forms of mercury

Mercury exists in three major chemical forms

These forms are.

1. Elemental mercury (mercury vapor)

2. Inorganic mercury or salts of mercury.

3. Organic mercury (organomercurials)

Elemental mercury is the most volatile of the three and exposure to it is

usually occupational. Chronic exposure can result from mercury in the ambient air

after accidental spills and poorly ventilated workrooms or laboratories. Mercury

vapors can have toxic effects and can be an occupational hazard in dentistry.

Inorganic mercury or mercury salts can exist as monovalent mercurous or

divalent mercuric salts. Mercury salts can be irritating and acutely toxic.

Organic mercury is highly absorbed from the gut. The alkylmercury salts

are the most toxic, with methylmercury being the most common form of these

salts. Organic mercury components are not a hazard in dentistry but can be an

environmental hazard.

Absorption bio-transformation, distribution and elimination of mercury

The metabolism of mercury is dependent on the chemical form of mercury

and the route of exposure.

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Absorption efficiencies for different forms of mercury.

Mercury Skin Lungs GIT

Elemental -- 80% 0.01%

Inorganic -- 80% 7%

Organic -- -- 95 98%

There is evidence that elemental mercury can penetrate skin, but

quantitative data are lacking Ingested elemental mercury vapor readily crosses cell

membranes because of its high diffusibility and lipid solubility. About 80% of

inhaled mercury is absorbed across alveolar membranes into blood stream and

then transported to other tissues. Accumulation occurs in spleen, muscle, glands

such as thyroid gland, salivary gland and tests. The accumulation of mercury, after

exposure is dependent on the close, frequency and duration of exposure as well as

a number of metabolic factors related to the exposed individual. The retention time

of mercury in organs varies considerably, with biologic half-life ranging from a

few days to months. On an average biologic half-life of inorganic mercury is 50-

60 days.

The organs with the longest retention times are the brain, kidneys and

testicles. The kidney especially renal cortex is the main organ of accumulation. In

cases of chronic low level exposure, the critical organ is the brain.

Mercury ions (H+2

) circulate readily in the blood but pass the membrane

barriers of the brain and placenta only with difficulty. In contrast, honionized

mercury (Hg) is capable of crossing through lipid layers at these barriers and, if

subsequently oxidized within these tissues, is only slowly removed.

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The elimination of mercury from the body occurs primarily by the

excretion of Hg++

via the 1) Urine and 2) feces. 3) Exhalation of mercury vapor

accounts for only a small portion of 7%. 4) Perspiration may also have a role

under certain conditions.

All forms of mercury cross the placenta to varying degrees.

Olsonn and Bergman model

Total absorption dose

Hg absorbed in GI tract Hg absorbed in lung

Ingestion absorption Inhalation absorption

Hg2+

in saliva

Hg in oral air

Amalgam fillings

Richardson model

Hg in urine

Distribution, metabolism, excretion

Total absorption dose

Amalgam fillings

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Mercury exposure from various sources

The sources are

- Food

- Fish

- Other (egg etc.)

- Water

- Soil

- Air

- Amalgam

- Drug

Eg: Calomel used in face creams.

Antiseptic agent eg. Merbromin

Diuretics.

Sources of mercury in dental office.

These include

- mercury spills

- expression of excess mercury from amalgam

- leakage from dispensers

- leakage from amalgam capsules during trituration

- mercury vaporization from contaminated instruments placed in

sterilizers.

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- grinding of amalgam during removal of restorations

- amalgam condensation with ultrasonic condensers

- contaminated furnishings of the office

- contaminated amalgamators, cabinets, drains, drapes

- waste containers

Mercury vapor from amalgam

The levels of mercury vapor in the expired air of patients, reported in

different studies varied greatly, as did the methods of measurement. It is observed

that chewing or brushing increases the level of mercury vapor released from dental

amalgam.

It has also been found that certain types of food on the surface of fillings

can influence the rate of mercury release and can either increase of decrease it

Effect Food & drink

No effect

Decrease

Increase

Hot and cold drinks, bread roll, apple.

Mixed lunch, eggs.

Brittle biscuits.

Average stimulation Factors

Gum chewing

Mixed food chewing

Tooth brushing

X 5.3

X 3.7

X 1.9

The mercury levels released as a result of various dental procedures are as

follows.

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Trituration

Placement of amalgam restoration

Dry polishing

Wet polishing

Removal of amalgam under water spray and high volume section

Additional evacuation for 1 minute to remove residual amalgam

dust

1 2 g

6 8 g

44 g

2 4 g

15 20 g

1.5 2.0 g

Corrosion of amalgam

The 2 phase (mercury tin phase) found in low copper alloys renders an

amalgam alloy much more susceptible to corrosion and significantly lowers the

strength of the alloy. Work by Jorgensen suggested that mercury released from the

breakdown of mercury tin phase ( 2 phase) is absorbed by the unreacted

particles in the matrix i.e. phase, resulting in the expansion and protrusion of the

cavo-surface margins. Increased marginal breakdown was associated with the

phenomenon of expansion. Research by Sarkar and Greener clearly established

that the - 2 phase of amalgams was the most electrochemically active phase, and

would undergo selective attack in a stimulated clinical environment.

High copper amalgams contain no 2 phase and thus more resistant to

corrosion than silver tin amalgams. In the corrosion of the high copper amalgams

the most corrosion prone phase is the phase (Cu6 Sn5) and during this process

tin oxide and tin oxychloride corrosion products are formed. The preferential

corrosion of this phase does not therefore release mercury.

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The corrosion of an amalgam may be affected when the amalgam is in

contact with a dissimilar metal forming a galvanic cell.

Corrosion is limited by three factors,

1. The formation of a pacifying layer of corrosive products on its surface.

2. The formation of additional 1 and 2 phases from the action of the

released mercury on the residual phase (Ag3Sn).

3. The preferential corrosion of the (Cu6Sn5) phase of high copper

amalgams.

Particulate exposure from amalgam

Amalgam particles embedded in oral tissues may manifest clinically as

pigmented molecules that are referred to as amalgam tattoos. Amalgam particles

are present in the tissues in two forms: Very fine, discrete, round black or dark

brown granules of 1.0 m or less in size or as irregular, dark, solid fragments of

various larger sizes. The embedded particles usually elicit no reactions, although

in some cases a mild to moderate chronic inflammatory response occurs.

Monitoring Mercury Levels:

Biologic monitoring for mercury exposure

Because of high individual variations and daily fluctuations, serial

monitoring is recommended to increase the reliability of blood and urinary

concentrations as a measure of exposure to individuals. Blood levels reflect very

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recent exposure since mercury in blood has a short half-life, (destruction by

erythrocytes) estimated to be about 3 days. Urinary monitoring is recommended

for assessing long-term steady state exposure. Analysis of sequential segments of

hair has been advocated for determination of longitudinal exposure to methyl

mercury as hair reflects the blood concentrations of methyl mercury at the time of

formation. But this procedure is not considered valid because mercury vapor may

directly contaminate the hair and not reflect mercury metabolized into the hair.

The range of concentrations of mercury in urine and blood in general

population, (not excessively or occupationally exposed to mercury) is 0 to 20 g/L

and 0 to 1.0g / 100ml respectively. Several surveys have shown mercury levels in

dentists and dental assistants are often at higher levels compared to general public.

Also levels were highest in eaters of fish and farmers using fungicides indicating

that mercury burden is from a non dental source.

100g/m3 Clinical mercurism threshold (LOAEL)

50g/m3 Nephrotoxicity threshold (LOAEL)

25g/m3 WHO industrial threshold (NOAEL)

5g/m3 General public threshold (NOAEL)

1g/m3 Children, pregnant, sick threshold (NOAEL)

Monitoring the mercury vapor levels in dental offices

Monitoring the mercury vapor in the office has to be done periodically.

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The Threshold Limit Value (TLV) is the concentration of mercury vapor to

which nearly all workers may be repeatedly exposed without adverse effects. The

TLV recommended by OSHA is 50g/m3, based on a time-weighted average

during an 8 hours work shift over a 40 hours workweek.

LOAEL Lowest Observed Adverse Effect Level is the lowest level at which

an adverse effect has been observed.

NOAEL No Observed Adverse Effect Level is the level at which adverse

effects have never been observed.

Air Mercury Exposure Hazards

Mercury toxicity

Mechanism of action:

- The elemental mercury gets oxidized into mercuric ion, which has a strong

affinity for the sulfydryl groups of proteins.

- The mercuric ion also combines with other ligands, such as the phosphoryl,

carboxyl, amide and amine groups.

- Within cells mercuric ions act as potent nonspecific enzyme inhibitors and

denaturants of proteins, thus interfering with cellular metabolism and function.

- The mercuric ion has also been shown to alter membrane function and

transport, including the release and uptake of neurotransmitters in the brain.

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Chronic exposure to mercury vapor produces a form of toxicity that is

dominated by neurological effects. The characteristic mercurial tremor appears

as fine trembling of muscles interrupted by coarse shaking movements.

- Psychological and behavioral changes occur. Symptoms may include increased

excitability, loss of memory, insomnia, severe depression, irritability,

excessive shyness and confusion. Other reported symptoms include ataxia,

speech disorders, reflex abnormalities, kidney dysfunction, visual disturbances

and impaired nerve conduction.

- Oral symptoms include gingivitis, excessive salivation, metallic taste, and

loosening of teeth. The triad consisting of increased excitability, tremors and

gingivitis has been recognized as the major manifestation of mercury poisoning

from inhalation of mercury vapor.

- The possible harmful effects from amalgam could be

- neurotoxicity

- kidney dysfunction

- reduced immunocompetence

- birth defects

- general health

But several studies have demonstrated no relationship between the presence

of amalgam fillings and the above mentioned harmful effects.

Dr.Alok Misra

M.D.S.


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Mercury allergy / hypersensitivity

Although poorly understood, mercury hypersensitivity has also at times

been claimed as a potential hazard. This is an immune system response to very

low levels of mercury. It is a type IV or cell mediated delayed hypersensitivity

reaction. However, the number of individuals identified as potentially

hypersensitive is extremely low, and the sensitivity reaction is very mild. Also, it

is not life threatening.

Treatment for mercury poisoning

- In all cases of suspected mercury poisoning, treatment begins with immediate

termination of exposure. Usually symptoms are reversible.

- Blood and urine analysis is done as soon as possible and are used to monitor

the effectiveness of treatment.

- The affinity of mercury for thiols provides the basis for treatment with

chelating agents. Dimercaprol, penicillamine, and N-acetyl D,L penicillamine

are most commonly recommended for treatment of chronic mercury vapor

exposure.

Dental mercury hygiene recommendations

1. Ventilation: Provide proper ventilation in the work place by having fresh air

exchanges and periodic replacement of filters, which may act as traps for

mercury.

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2. Monitor office: Monitor the mercury vapor level in the office periodically.

This may be done by using dosimeter badges.

3. Monitor personnel: Monitor office personnel by periodic analysis. (The

average mercury level in urine is 6.1 g/litre for dental office personnel).

4. Office design: Use proper work area design to facilitate spill containment and

cleanup.

5. Pre-capsulated alloys: Use pre-capsulated alloys to eliminate the possibility

of a bulk mercury spill. Otherwise store bulk mercury properly in unbreakable

containers on stable surfaces.

6. Amalgamator cover: Use an amalgamator fitted with a cover.

7. Handling care: Use care in handling amalgam. Avoid skin contact with

mercury or freshly mixed amalgam. Avoid dry polishing.

8. Evacuation systems: Use high volume evacuation when finishing or removing

amalgam. Evacuation system have traps or filters. Check, clean or replace traps

and filters periodically.

9. Masks: Change mask as necessary when removing amalgam restorations.

10. Recycling: Store amalgam scrap under radiographic fixer solution in a covered

container. Recycle amalgam scraps through refiners.

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11. Contaminated items: Dispose of mercury contaminated items in sealed bags

according to applicable regulations.

12. Spills: Clean up spilled mercury properly by using bottles, tapes or fresh mixes

of amalgam to pick-up droplets: or use commercial clean up kits. Do not use

household vacuum cleaner.

13. Clothing: Wear professional clothing only in dental operatory.

14. Do not use ultrasonic condensers.

15. Select an appropriate alloy: mercury ratio to avoid the need to remove excess

mercury before packing.

16. Do not eat drink or smoke while working.

Possible alternative materials to dental amalgam

Metal alloys

1. Gold: The only real alternative to amalgam as a material in moderate to large

cavities in cast gold. For small cavities gold foil can be used.

Advantages:

- superior qualities compared to amalgam

Disadvantages:

- Demands high levels of clinical and laboratory skills in fabrication.

- Expensive.

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2. Gallium alloys

Gallium is a metal with similar atomic structure and characteristics to

mercury and has a melting point of 29C. This property has been used to produce

gallium based alloys which can be used in a similar way to mercury based

amalgam. They consist of about 65% gallium and in the commercial products, the

material is supplied in a powder / liquid form. The liquid is an alloy of silver, tin,

indium and gallium.

When set these alloys consist of a number of inter metallic compounds

similar to that seen in mercury based amalgams. These are indium / tin, gallium /

copper and gallium / palladium compounds.

Disadvantages:

- 16 times more expensive compared to amalgams.

- Sticky when mixed, therefore more difficult to pack and special Teflon

instruments are necessary to overcome this problem.

- High level of corrosion

- High level of expansion

- Tooth fracture due to high expansion.

- Toxicology of gallium is unknown.

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M.D.S.


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Tooth colored alternatives

These are:

- Glass ionomer cement

- Composite resins

- Resin modified GIC

- Polyacid modified composites

- Ceramics

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Conclusion

It has been said that we know only what we can measure. We can measure

the mercury given off from amalgam restorations, and we can measure the amount

of mercury present in the environment. And while we have not yet measured any

casual relationship between dental amalgam and disease, we can measure the

superior clinical performance of dental amalgam compared to other restorative

materials. It is possible to clean up our environment without banning the use of

dental amalgam. In the words of the Swedish MRC panel With proper mercury

hygiene measures, mercury emerging from dental amalgam does not per se

represent an environmental hygiene problem. And as Marie Curie once said

Nothing in life is to be feared, it is only to be understood. Let us hope that we

can understand the enigma of amalgam in dentistry and that common sense

prevails.

Documents

Mercury Toxicity and Management