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Symptoms of Hg Exposure and Reversibility

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Regarding the clinical signs of mercury vapour exposure, it is important to distinguish between large acute exposures and those of long-term, low-level chronic exposure, known as micro-mercurialism. For acute exposure, Prof. Moore's assertions may be valid, but the assumption that the symptoms are reversible by removing the person from the source of the mercury, is limited and not necessarily the case. Intention tremor must be regarded as indicative of serious neurological damage and is not always reversible. Micromercurialism is characterised by many symptoms, the earliest of which are subclinical and neurological (43). Mercury vaporizes continuously from dental fillings, and this is intensified by chewing, tooth brushing and hot liquids (45, 48). After mastication or tooth brushing ceases it takes almost 90 minutes for the rate of vaporisation to decline to the lower pre-chewing level. Also, the greater the number of fillings and the larger the chewing surface area, the larger the mercury exposure (48). Thus, the average individual is on a roller coaster of mercury vapour exposure during the day. Breakfast will cause the release rate to increase and just as the rate is slowing again, it is time for the mid-morning coffee break. Lunch, the evening meal and bedtime snacks all contribute to the daily exposure to mercury from dental fillings. Even the manufacturer, Caulk Company, has listed on their Material Safety Data Sheet, many of the symptoms of micromercurialism: "Section VIII - Control Measures, Inhalation, Chronic: Inhalation of mercury vapour over a long period may cause mercurialism, which is characterized by fine tremors and erethism. Tremors may affect the hands first, but may also become evident in the face, arms, and legs. Erethism may be manifested by abnormal shyness, blushing, self consciousness, depression or despondency, resentment of criticism, irritability or excitability, headache, fatigue, and insomnia. In severe cases, hallucinations, loss of memory, and mental deterioration may occur. Concentrations as low as 0.03 mg/m3 have induced psychiatric symptoms in humans. Renal involvement may be indicated by proteinuria, albuminuria, enzymuria, and anuria. Other effects may include salivation, gingivitis, stomatitis, loosening of the teeth, blue lines on the gums, diarrhoea, chronic pneumonitis and mild anaemia. Repeated exposure to mercury and its compounds may result in sensitisation. Intrauterine exposure may result in tremors and involuntary movements in the infants. Mercury is excreted in breast milk. Paternal reproductive effects, and effects on fertility, have been reported in male rats following repeated inhalation exposures. "The Caulk Co. also warns that mercury may be a skin sensitizer, pulmonary sensitizer, nephrotoxin and neurotoxin, and further cautions that the number of amalgam restorations for one patient should be kept to a minimum.

The above symptoms are not new. Even the dental industry has given warnings to the dental profession regarding the dangers of inhaling low levels of mercury vapour over a long period. "Mercury Contamination in the Dental Office. A Review" (The NYS Dental Journal, November 1979, pp 457-458), stated..."The symptoms of mercury poisoning from chronic inhalation develop gradually and thus, may be difficult to notice. With the exception of tremor, the symptoms may be ignored by the victim or attributed to other causes. This lack of awareness is particularly likely in the case of erethism, a condition characterized by irritability, outbursts of temper, excitability, shyness, resentment of criticism, headache, fatigue and indecision.

Erethism is the most difficult manifestation of mercury poisoning to evaluate, especially if tremors are absent, and its symptoms may be attributed to anxiety or neuroasthenia. Other general symptoms associated with mercury poisoning include weakness, unusual fatigue, loss of weight, loss of appetite, insomnia and gastrointestinal disturbances.

A condition known as micromercurialism, is said to account for psychological changes observed in persons frequently exposed to low concentrations of mercury in the air, concentrations found in the majority of dental offices surveyed. The syndrome is characterized by: decreased productivity, loss of memory, loss of self confidence, depression, fatigue and irritability.

In a study (46) which exposed rats to 0.3mg/m Hg for 4 hours a day for two weeks it was found that viable brain tubulin decreased between 41% to 75%. How would this compare to a lifetime of chronic exposure? What are the implications for those individuals that are near that "thin red line" going over to Alzheimer-like dementia, whose brain tubulin is already compromised. Does the dental association only consider mercury toxicity effects on the totally healthy, or should we consider the cumulative effects in the medically compromised of what is universally acknowledged to be a potent neurotoxin?

 

 

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