AskDefine | Define amalgam

Dictionary Definition

amalgam

Noun

1 an alloy of mercury with another metal (usually silver) used by dentists to fill cavities in teeth; except for iron and platinum all metals dissolve in mercury and chemists refer to the resulting mercury mixtures as amalgams [syn: dental amalgam]
2 a combination or blend of diverse things; "his theory is an amalgam of earlier ideas"

User Contributed Dictionary

see Amalgam

English

Pronunciation

a*mal"gam

Translations

a combination of things
alloy containing mercury

Swedish

Noun

amalgam

Extensive Definition

Amalgam is a commonly used dental filling that has been used for over 150 years. It is a mixture of mercury with at least one other metal. Currently, dental amalgams are composed of about 40% mercury, and 60% powder where the powder is made up of silver (~62%), tin (~26%), copper (~10%), and zinc (~2%). Amalgam has many advantages over other restorative material, such as low cost, strength, durability, and bacteriostatic effects. Its main disadvantages are poor aesthetics on anterior teeth and the known toxicity of mercury. Concerns about possible detrimental health effects from the low levels of mercury released from amalgam have resulted in a decline in the routine use of amalgam in recent years.

History of use

The earliest instance of amalgam use as a a dental restorative material is not well established, but it has been reported that a silver paste was used to restore a tooth in as early as 659 A.D. in China. In modern times, amalgam was placed by Auguste Taveau in France as early as 1826, although he had developed it in 1816.
The Crawcour brothers, two Frenchmen, brought amalgam to the United States in 1833, and in 1844 it was reported that fifty percent of all dental restorations placed in upstate New York consisted of amalgam. Prior to this, dentists had been restoring teeth using filling material such as stone chips, resin, cork, turpentine, gum, lead, and gold leaf. The renowned physician Ambroise Paré (1510 – 1590) had used lead or cork to fill teeth.
Over the next fifty years, many different metal combinations were tried, including the use of, among other things, platinum, cadmium, antimony and bismuth. In 1895, G. V. Black published a dental amalgam formula that provided for the most clinically acceptable performance, and his recipe remained unchanged for virtually seventy years.
In 1959, Dr. Wilmer Eames suggested a modification to the mercury-to-amalgam ratio, recommending it be dropped from 8:5 to 1:1. The standard formula was again changed in 1963, when a superior amalgam consisting of a high-copper dispersion alloy was introduced. Although it was initially believed that this superiority was due to dispersion strengthening of the amalgam, it was later discovered that the improved strength of the amalgam was, in fact, a result of the additional copper forming a copper-tin phase that was less susceptible to corrosion than the tin-mercury phase in the earlier amalgam. This union of tin-mercury, now known as the gamma-2 phase, contributes to failure and is ideally allowed to rise during condensation of the amalgam while it is being placed in a tooth, to subsequently be removed when the amalgam is carved to achieve proper occlusal anatomy and functional occlusion.

Modern use as a dental restoration

Amalgam is an "excellent and versatile restorative material" and is used in dentistry for a number of reasons. It is inexpensive and relatively easy to use and manipulate during placement; it remains soft for a short time so it can be packed to fill any irregular volume, and then forms a hard compound. Amalgam possesses greater longevity than other direct restorative materials, such as composite;. On average, most amalgam restorations serve for 10 to 12 years, whereas resin-based composites serve for about half that time. However, with recent improvements in composite material science and a better understanding of the technique-sensitivity of placement, it should be noted that this difference is decreasing.
The cost benefit analysis of the use of amalgam is often compared to that of resin-based composites because it would be the latter material that would generally be used as an alternative should the amalgam analysis prove unfavorable. There are many reasons why amalgam enjoys greater overall longevity than that of resin-based composites. Among these reasons are that composites are technique sensitive and require "extreme care" and "considerably greater number of exacting steps" in their proper placement. On the other hand, amalgam is "tolerant to a wide range of clinical placement conditions and moderately tolerant to the presence of moisture during placement.
Another important issue is the environment at the tooth-restoration margin. Whereas the elemental composition of amalgam serves as a bacteriostatic agent, TEGMA, the basic constituents in many resin-based composites, actually "encourages the growth of microorganisms." Because of this, recurrent marginal decay underneath resin-based composites "requires almost immediate removal, whereas those underneath amalgam restorations progress much more slowly."
Recurrent marginal decay is a very important factor in restoration failure, but more so in composite restorations. In the Casa Pia study in Portugal (1986-1989), 1,748 posterior restorations were placed and 177 (10.1%) of them failed during the course of the study. Recurrent marginal decay was the main reason for failure in both amalgam and composite restorations, accounting for 66% (32/48) and 88% (113/129), respectively. Polymerization shrinkage, the shrinkage that occurs during the composite curing process, has been implicated as the primary reason for postoperative marginal leakage.
It is for these reasons and more that amalgam has been substantiated as a superior restorative material over resin-base composites. The New England Children's Amalgam Trial (NECAT), a randomized controlled trial, yielded results "consistent with previous reports suggesting that the longevity of amalgam is higher than that of resin-based compomer in primary teeth and composites in permanent teeth. Compomers were seven times as likely to require replacement and composites were seven times as likely to require repair.
There are circumstances in which composite serves better than amalgam; when amalgam is not indicated, or when a more conservative preparation would be beneficial, composite is the recommended restorative material. These situations would include small occlusal restorations, in which amalgam would require the removal of more sound tooth structure, as well as in "enamel sites beyond the height of contour."
Removal and replacement of amalgam restorations has traditionally been considered when "ditching" is present on the edges of the restoration. Ditching is "a deficiency of amalgam along the margin, preventing the margin of the cavity preparation from being flush... An area of ditching is also commonly referred to as a submarginal area and it requires removing tooth structure or replacing the amalgam to correct the situation."

Dental amalgam toxicity controversy

Dental amalgam is a source of low-level exposure to elemental mercury, and concerns have been raised about whether this poses a health hazard, for example migraines, erethism, and multiple sclerosis. As of 2008, the use of dental amalgam has been restricted in Sweden, Norway and Finland, and a committee of the US Food and Drug Administration (FDA) has refused to ratify assertions of safety. In recent years evidence of serious toxic effects, for instance 25 studies of 5821 patients reviewed in "Effects of Amalgam Removal on Health", by Mats Hanson, plus a later study by Wojcik, Godfrey, Christie, Haley (2006).
The most recent source of controversy has been from a December 1990 episode of the CBS news program 60 Minutes. This resulted in a nationwide amalgam scare, and additional research into mercury release from amalgam. The following month, Consumer Reports published an article criticizing the content of the broadcast, stating that it contained a great deal of false information and that the ADA spokesperson on the program was ill prepared to defend the claims .
The American Dental Association Council on Scientific Affairs has concluded that both amalgam and composite materials are considered safe and effective for tooth restoration, and The National Institutes of Health (NIH) has stated that amalgam fillings pose no personal health risk, and that replacement by non-amalgam fillings is not indicated. Recent random clinical trials have also established that amalgams are safe, finding no evidence of neurological harm or deleterious renal effects associated with their use in children after examining a period of 5–7 years following treatment. Both these trails were published in the same issue of the JAMA. So was however also an editorial by Prof. Herbert Needleman commenting on these two articles explicitly advising against using them as evidence of dental amalgam safety. He says:
“It is predictable that some outside interests will expand the modest conclusions of these studies to assert that use of mercury amalgam in dentistry is risk free. This conclusion would be unfortunate and unscientific. The conclusions that can be extrapolated from these 2 studies are constrained by several factors.” .
Because mercury is a regulated waste in some countries, its disposal can be costly.

See also

References

amalgam in Arabic: ملغمة
amalgam in Min Nan: A-má-káng
amalgam in Catalan: Compàs d'amalgama
amalgam in Czech: Amalgám
amalgam in Danish: Amalgam
amalgam in German: Amalgamfüllung
amalgam in Modern Greek (1453-): Αμάλγαμα
amalgam in Spanish: Amalgama
amalgam in Esperanto: Amalgamo
amalgam in Persian: ملغمه
amalgam in French: Amalgame (métallurgie)
amalgam in Galician: Amálgama (química)
amalgam in Italian: Amalgama
amalgam in Hebrew: אמלגם
amalgam in Dutch: Amalgaam
amalgam in Japanese: アマルガム
amalgam in Norwegian: Amalgam
amalgam in Norwegian Nynorsk: Amalgam
amalgam in Polish: Amalgamat
amalgam in Portuguese: Amálgama de prata
amalgam in Russian: Амальгама
amalgam in Slovak: Amalgám
amalgam in Slovenian: Amalgam
amalgam in Serbian: Амалгам
amalgam in Finnish: Amalgaami
amalgam in Swedish: Amalgam
amalgam in Turkish: Amalgam
amalgam in Ukrainian: Амальгама
amalgam in Chinese: 汞齊

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