Dental Amalgam - Restoration Material.

Dental amalgam is the most commonly used dental restorative material used for dental fillings. First introduced in France in the early 19th century, it contains a mixture of mercury with at least one other metal. Amalgam has been the restorative method of choice for many years due to its low cost, ease of application, strength, durability, and bacteriostatic effects. Factors that have led to recent decline in use are a lingering concern about detrimental health effects, aesthetics, and environmental pollution. The health issue concerns the known toxic affects of mercury and whether these are present in the amounts released from the amalgam. The aesthetic issue is because the metallic colour does not blend with the natural tooth colour. This is especially a concern when used on front teeth, but it can be addressed using alternative dental materials. The environmental concerns are regarding mercury emissions during preparation and from waste amalgam upon cremation of deceased individuals.

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Dental Amalgam Filling


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Dental Amalgam filling of 1^st Molar


Composition:

Currently, dental amalgams are composed of 43% to 54% by weight of mercury and the remaining powder is made up of mainly silver (~20-35%) and some tin, copper (~10%), and zinc (~2%).

Gamma 2 Phase Amalgams:

After widespread adoption and wildly varying standards, the multitude of formulas for making amalgams were standardized into the gamma-2-phase amalgam formula in 1895.
The gamma-2-phase amalgams contain approximately equal parts 50% of liquid mercury and 50% of an alloy powder containing:[citation needed]:

* > 65% silver (Ag)
* < 29% tin (Sn) * < 6% copper (Cu) * < 2% zinc (Zn) * < 3% mercury (Hg) The resulting amalgam is composed of the gamma phase (the silver-tin eutectic Ag₃Sn), which reacts with mercury, yielding the gamma-1 phase (Ag₂Hg₃) and gamma-2 phase (Sn₇-8Hg). The gamma phase is prone to corrosion and its mechanical strength is low. The alloy tends to undergo crevice corrosion and form local galvanic cells, due to the potential difference between the gamma-1 and gamma-2 phases.

Around 1970, the ingredients changed to the new non-gamma-2 form, with lower manufacturing cost, greater mechanical strength, and better corrosion resistance. The reduced-gamma-2 amalgams (sometimes referred to as "high-copper" amalgams [44]) contain approximately equal parts 50% of liquid mercury and 50% of an alloy powder containing:

* > 40% silver (Ag)
* < 32% tin (Sn) * < 30% copper (Cu) * < 2% zinc (Zn) * < 3% mercury (Hg) The amalgam alloy is strengthened by presence of Ag-Cu particles. The gamma-2 phase reacts with the Ag-Cu particles to form eta phase Cu6Sn5 and gamma-1 phase. The possible difference in toxicology between the two has not been studied conclusively. Galvanic Shock:

When aluminium foil makes contact with some amalgam fillings, saliva in the mouth can act as an electrolyte. This can generate small electrical currents which are felt through the nerves in the tooth as (often extremely painful) electrical "jolts" or shocks.

Modern Use as 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 when compared to other direct restorative materials, such as composite. However, this difference has decreased with continual development of composite resins.

Amalgam is typically compared to resin-based composites because many applications are similar and many physical properties and costs are comparable.

Longevity:

Amalgam is "tolerant to a wide range of clinical placement conditions and moderately tolerant to the presence of moisture during placement. In contrast, the techniques for composite resin placement are more sensitive to many factors and require "extreme care" and "considerably greater number of exacting steps".

Mercury has properties of a bacteriostatic agent whereas TEGMA (constituting some older resin-based composites) "encourages the growth of microorganisms.". This leads to increased decay underneath older resin-based composites while those underneath mercury 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.

These are some of the reasons why amalgam has remained 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. For example, 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." For cosmetic purposes, composite is preferred when a restoration is required on an immediately visible portion of a tooth.

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:

Controversy over the mercury component of dental amalgam dates back to its inception, when it was opposed by the United States dental establishment,[clarification needed] but it became a prominent debate in the late 20th century, with consumer and regulatory pressure to eliminate it "at an all-time high". Many[clarification needed] people are unaware of the mercury in fillings, and this lack of informed consent was the most consistent issue raised in a recent U.S. Food and Drug Administration panel on the issue by panel members. Environmental concerns over external costs exist as well, as the use of dental amalgam is unregulated at the federal level in, for example, the United States. The WHO reports that mercury from amalgam accounts for 5% of total mercury emissions and that when combined with waste mercury from laboratory and medical devices, represents 53% of total mercury emissions. Separators may dramatically decrease the release of mercury into the public sewer system, where dental amalgams contribute one-third of the mercury waste, but they are not required in the United States. As of 2008, the use of dental amalgam has been banned in Norway, restricted in Sweden and Finland, and a committee of the US Food and Drug Administration (FDA) has refused to ratify assertions of safety.

Scientists agree that mercury amalgam fillings expose the bearers to a daily dose of mercury, but the level and effects of the chronic exposure are disputed. In the 1990s, several governments evaluated the effects of dental amalgam and concluded that the most likely health effects would be due to hypersensitivity or allergy. Germany, Austria, and Canada recommended against placing amalgam in certain individuals such as pregnant women, children, those with renal dysfunction, and those with an allergy to metals. In 2004, the Life Sciences Research Office analyzed studies related to dental amalgam published after 1996. Concluding that mean urinary mercury concentration (μg of Hg/L in urine, HgU) was the most reliable estimate of mercury exposure, it found those with dental amalgam were unlikely to reach the levels where adverse effects are seen from occupational exposure (35 μg HgU). 95% of study participants had μg HgU below 4-5. Chewing gum, particularly for nicotine, along with more amalgam, seemed to pose the greatest risk of increasing exposure; one gum-chewer had 24.8 μg HgU. However, from reviewing medical literature, the World Health Organization states mercury levels in biomarkers such as urine, blood, or hair do not represent levels in critical organs and tissues. Additionally, Gattineni et al. found that mercury levels do not correlate with the number or severity of symptoms. It concluded that there was not enough evidence to support or refute many of the other claims such as increased risk of autoimmune disorders, but stated that the broad and nonspecific illness attributed to dental amalgam is not supported by the data. Mutter in Germany, however, concludes that "removal of dental amalgam leads to permanent improvement of various chronic complaints in a relevant number of patients in various trials."

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 a study has stated that amalgam fillings pose no personal health risk, and that replacement by non-amalgam fillings is not indicated. Recent randomized clinical trials have found no evidence of neurological harm or deleterious renal effects associated with use of amalgam in children after examining a period of 5–7 years following treatment. Both these trials were published in the same issue of the JAMA. Also published in the same journal was an editorial by Prof. Herbert Needleman noting 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.”

The health problems usually focused upon include chronic illnesses, oral lesions, birth defects, mental disorders, autoimmune disorders, neurodegenerative diseases, erethism, and multiple sclerosis. There is strong evidence that a certain percentage of lichenoid lesions are caused by amalgam fillings.

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Posted By: Doc CN

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