 |
|
| ||||||||||||||||||||||||||
|
|
| ||||||||||||||||||||||||||
|
|
|
|
|
| ||||||||
An amalgam is an alloy of mercury. Most metals are soluble in mercury, but some (such as iron) are not. Amalgams are commonly used in dental fillings.
Ammonium has been isolated in amalgam, but not as the pure pseudometal - it decomposes to ammonia and hydrogen.
For centuries dentists have been cleaning out decay and filling cavities, using filling material such as stone chips, resin, cork, turpentine, gum, lead and gold leaf. The renowned physician Ambroise Pare (1510-1590) used lead or cork to fill teeth. Amalgams were the first true standard filling material.
Mercury amalgams are used in dentistry because they are cheap, easy to use, durable, and were widely regarded as safe. They are made by mixing approximately equal measures of mercury and an alloy of silver, copper, tin and other metals. Dental amalgams are sold in self contained capsules so that the dentist, dental technician, and patient are not exposed to mercury vapour during the mixing.
The first people to use amalgams to fill cavities appear to be the French. In 1816 Auguste Taveau developed first dental amalgam from silver coins and mercury. This early amalgam was low in mercury and had to be heated in order for the silver to dissolve at any appreciable rate. Modern dental amalgams are mixed cold.
One obvious disadvantage of using amalgams for fillings is they look unattractive. The material is black (silver if an abrasive toothpaste is used) and can clearly been seen on, and sometimes behind, a tooth. For this reason, amalgam fillings are seldom used in the front teeth. They are, however, still very popular for use in the back teeth, especially since dental amalgams are much tougher wearing than composite fillings.
In 1840 the only official dentist organisation in existence, The American Society of Dental Surgeons, which had promoted mercury amalgams since its inception, had members sign a mandatory pledge promising not to use mercury fillings because of fear of mercury poisoning in patients and dentists. It must be noted that in 1840 dentists mixed the amalgam themselves in their office, making the office a source of poisonous levels of mercury. The American Society of Dental Surgeons however claimed amalgams were toxic in the mouth and should be removed. Such claims have been controversial for over a century because the removal exposes the patient to abundant mercury vapors.
In 1856 the American Society of Dental Surgeons disbanded because dentists who supported the use of amalgams, deserted the ASDS ranks until it had too few members to exist.
In 1859 the ADA formed from dentists who wanted to continue the use of amalgams. Their position is that amalgams were proven to be completely safe and leaked no mercury at all. No such proofs existed in 1859, because the scientific methods of medicine in 1859 was not as advanced, and toxicity of amalgams or exposure to the mixing process could not be proven or disproven. Therefore, no substantial medical studies were funded. The ADA position on the safety of amalgam itself never changed.
In 1895 the multitude of formulas for making amalgam have been standardised:
The gamma-2-phase amalgams contain equal parts, 50% of liquid mercury, and 50% of an alloy powder containing:
Around 1970, the ingredients changed for manufacturing cost reasons to the new non-gamma-2 form:
The gamma-2-free amalgams contain equal parts, 50% of liquid mercury, and 50% of an alloy powder containing:
The possible difference in toxicology between the two has not been studied. Around the 1970s, the gamma-2-free amalgam became common. The leaking of poisonous substances other than mercury has never been tested because of the overfocus on mercury. This was done without having to undergo FDA approval because amalgams are classified as a device, not a substance. Device modification does not need FDA approval. As far as the U.S. Code of Federal Regulations is concerned amalgams are a prosthetic device.
Amalgam Alloy, (a) Identification. An amalgam alloy is a device that consists of a metallic substance intended to be mixed with mercury to form filling material for treatment of dental caries. (b) Classification. Class II (21 CFR 872.3050 (2001)).
This prevented amalgams from undergoing the testing which had been used for all other dental materials invented since.
Most modern governments claim that certain fish in excess quantities are unsafe due to methyl mercury levels (death has been known to occur from mercury contaminated fish). The warnings especially target pregnant women.
The World Health Organization, OSHA, and NIOSH, all agree that mercury is an environmental poison and have established specific occupational exposure limits. The Environment Protection Agency has declared amalgam removed from teeth to be a toxic waste. Even the American Dental Association warns that amalgam filling material is hazardous to dental office personnel before and after its presence in patients' mouths.
Mercury amalgams have been blamed by practitioners of alternative medicine for many (vague) physical problems. They reason that, since mercury is poisonous, so must be anything containing mercury; hence, amalgams are poisonous. This argument however ignores the difference between a metal and an alloy.
Diagnostic methods, such as hair analysis, have been used to convince people their dental fillings are poisoning them. Dentists point out that while there is no denying that, when placing the fillings, both patient and dentist are exposed to a very small amount of mercury and mercury vapour, once the alloy has hardened (which takes less than a minute), the mercury is captured in the filling and cannot get out. It is bound in the alloy.
No alternative medicine has ever proved any evidence of any significant physical problems caused by amalgam fillings. Even among modern dentists who are exposed to the mercury and its vapour on a daily basis, no evidence of mercury poisoning has ever been found beyond the very mildest of subclinical symptoms.
However, some recent research is showing that mercury from amalgams may be affecting some dentists with mild toxicity. A examining the health effects of mercury on dentists was done in the UK and published in the Occupational and Environmental Medicine Journal. This study found that 180 dentists had on average 4 times the urinary mercury excretion levels of 180 people in a control group. Also, dentists were significantly more likely than control subjects to have had disorders of the kidney and memory disturbance. But a direct correlation between urinary mercury levels and the disability was not found. More research needs to be done before a solid conclusion can be reached.
Alternative dentists (also known as holistic, homeopathic, or biological) have advised patients to have all their fillings removed. While they show no evidence that amalgam fillings cause health problems, removing all of them at once can cause problems. Any time a filling is drilled out, there is always risk that the drill will remove too much tooth material, requiring the tooth be restored with a cap. Another risk is that the dentist may drill to far, hitting the pulp and causing an infection, subsequently requiring the tooth to be treated with a root canal. Removal involves drilling in amalgam so more vapors are released than in putting them in. Some alternative dentists use "cold" drills, cooled by a stream of water to help avoid vaporizing the amalgam when drilling. The alternative to amalgam fillings usually selected are composites. The do have drawbacks; they may have to be replaced more often, again causing risk of tooth damage or infection during replacement.
Mercury amalgams have been used in the gold and silver mining process due to the ease with which mercury will amalgamate with them.
After all the usable metal had been extracted from the ore, mercury was poured down a long copper trough which formed a thin coating of mercury on the surface. The waste ore was then poured down the trough, and any gold in the waste amalgamated with the mercury. This coating was occasionaly scraped off and distiled to remove the mercury, leaving behind fairly high purity gold.
The Spanish Empire transported mercury from Almadén across the Atlantic to supply the silver mines of Zacatecas and Potosí.
|
||||
| View Live Article | This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License | |
||
