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Amalgam (dentistry)
Encyclopedia
Amalgam is an alloy containing mercury. The term is commonly used for the amalgam employed as material for dental fillings, which consists of mercury (50%), silver (~22-32% ), tin (~14%), copper (~8%), and other trace metals. In the 1800s, amalgam became the dental restorative material of choice due to its low cost, ease of application, strength, and durability.
Recently however, its popularity has diminished somewhat. Concern for aesthetics, environmental pollution, and the availability of improved, reliable, composite materials have all contributed. In particular, concerns about the toxicity of mercury
have made its use increasingly controversial. Due to a worldwide plan to phase out the use of mercury, Norway, Denmark, and Sweden have deliberated in 2009 a ban of mercury dental amalgam in their countries.
, and in 1844 it was reported that fifty percent of all dental restorations placed in upstate New York
consisted of amalgam. However, at that point the use of dental amalgam was declared to be malpractice, and the American Society of Dental Surgeons
(ASDS), the only US dental association at the time, forced all of its members to sign a pledge to abstain from using the mercury fillings. This was the beginning of what are known as the first dental amalgam war.
The war ended in 1856 with the rescission of the old association. The American Dental Association
was founded instead in 1859, which has strongly defended dental amalgam since from allegation of being too risky from the health standpoint.
The ratio of the mercury to the remaining metallic mixture in dental amalgam hasn't been always 50:50. It was as high as 66:33 in 1930. Relative ratios between the other metals used in dental amalgams has been also highly variable. Conventional (or gamma 2)-amalgams have 32% silver and 14% tin, and they are most susceptible to corrosion due to their low copper content. Non-gamma-2 dental amalgams have been developed that however were found to release higher levels of mercury vapor compared with traditional amalgams. Amalgam is the dental material that has the strongest tendency to create galvanic currents and high electric potentials as they age. The rate of mercury release with the corrosion is accelerated when the amalgam filling is in contact with old restorations or couples with gold artifacts present in the mouth.
Mercury has properties of a bacteriostatic agent
whereas TEGMA (constituting some older resin-based composites) "encourages the growth of microorganisms".
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.
, Sweden
and Denmark
have already implemented a total mercury ban, and all other industrialized countries are following their lead with the same focus on the principle of precaution and the principle of substitution but a slightly longer path. "Satisfactory alternatives to mercury in products are available, and it is therefore fitting to introduce a ban," said Norwegian Minister of the Environment Erik Solheim. "Composite fillings have now become so strong that the Danish National Board of Health says that we can expand the ban to also include amalgam fillings", said the (Danish) Minister of Health Jakob Axel Nielsen to TV Avisen.
Controversy over the mercury component of dental amalgam dates back to its inception, when it was opposed by the United States dental establishment, 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 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 cost
s 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.
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."
There is strong evidence that a certain percentage of lichenoid lesions
are caused by amalgam fillings.
Recently however, its popularity has diminished somewhat. Concern for aesthetics, environmental pollution, and the availability of improved, reliable, composite materials have all contributed. In particular, concerns about the toxicity of mercury
Mercury poisoning
Mercury poisoning is a disease caused by exposure to mercury or its compounds. Mercury is a heavy metal occurring in several forms, all of which can produce toxic effects in high enough doses...
have made its use increasingly controversial. Due to a worldwide plan to phase out the use of mercury, Norway, Denmark, and Sweden have deliberated in 2009 a ban of mercury dental amalgam in their countries.
History of use
In 1833 the Crawcour brothers, two Frenchmen, brought amalgam to the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, and in 1844 it was reported that fifty percent of all dental restorations placed in upstate New York
New York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
consisted of amalgam. However, at that point the use of dental amalgam was declared to be malpractice, and the American Society of Dental Surgeons
American Society of Dental Surgeons
The American Society of Dental Surgeons was the first national dental organization formed in the United States of America. The formation of the ASDS was preceded by the formation of the Society of Dental Surgeons of the City and State of New York when fifteen dentists came together in New York...
(ASDS), the only US dental association at the time, forced all of its members to sign a pledge to abstain from using the mercury fillings. This was the beginning of what are known as the first dental amalgam war.
The war ended in 1856 with the rescission of the old association. The American Dental Association
American Dental Association
The American Dental Association is an American professional association established in 1859 which has more than 155,000 members. Based in Chicago, the ADA is the world's largest and oldest national dental association and promotes good oral health to the public while representing the dental...
was founded instead in 1859, which has strongly defended dental amalgam since from allegation of being too risky from the health standpoint.
The ratio of the mercury to the remaining metallic mixture in dental amalgam hasn't been always 50:50. It was as high as 66:33 in 1930. Relative ratios between the other metals used in dental amalgams has been also highly variable. Conventional (or gamma 2)-amalgams have 32% silver and 14% tin, and they are most susceptible to corrosion due to their low copper content. Non-gamma-2 dental amalgams have been developed that however were found to release higher levels of mercury vapor compared with traditional amalgams. Amalgam is the dental material that has the strongest tendency to create galvanic currents and high electric potentials as they age. The rate of mercury release with the corrosion is accelerated when the amalgam filling is in contact with old restorations or couples with gold artifacts present in the mouth.
Longevity and other advantages
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".Mercury has properties of a bacteriostatic agent
Bacteriostatic agent
A bacteriostatic agent or bacteriostat, abbreviated Bstatic, is a biological or chemical agent that stops bacteria from reproducing, while not necessarily harming them otherwise. Depending on their application, bacteriostatic antibiotics, disinfectants, antiseptics and preservatives can be...
whereas TEGMA (constituting some older resin-based composites) "encourages the growth of microorganisms".
Recurrent marginal decay is a very important factor in restoration failure, but more so in composite restorations. In the Casa Pia study in Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
(1986–1989), 1,748 posterior
Commonly used terms of relationship and comparison in dentistry
There are numerous commonly used terms of relationship and comparison that refer to different aspects of teeth and are frequently utilized in articles about dentistry...
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
New England
New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...
Children's Amalgam Trial (NECAT), a randomized controlled trial
Randomized controlled trial
A randomized controlled trial is a type of scientific experiment - a form of clinical trial - most commonly used in testing the safety and efficacy or effectiveness of healthcare services or health technologies A randomized controlled trial (RCT) is a type of scientific experiment - a form of...
, yielded results "consistent with previous reports suggesting that the longevity of amalgam is higher than that of resin-based compomer
Dental composite
Dental composite resins are types of synthetic resins which are used in dentistry as restorative material or adhesives. Synthetic resins evolved as restorative materials since they were insoluble, aesthetic, insensitive to dehydration, easy to manipulate and reasonably inexpensive...
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
Commonly used terms of relationship and comparison in dentistry
There are numerous commonly used terms of relationship and comparison that refer to different aspects of teeth and are frequently utilized in articles about dentistry...
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.
Dental amalgam toxicity controversy
NorwayNorway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
, Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
and Denmark
Denmark
Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...
have already implemented a total mercury ban, and all other industrialized countries are following their lead with the same focus on the principle of precaution and the principle of substitution but a slightly longer path. "Satisfactory alternatives to mercury in products are available, and it is therefore fitting to introduce a ban," said Norwegian Minister of the Environment Erik Solheim. "Composite fillings have now become so strong that the Danish National Board of Health says that we can expand the ban to also include amalgam fillings", said the (Danish) Minister of Health Jakob Axel Nielsen to TV Avisen.
Controversy over the mercury component of dental amalgam dates back to its inception, when it was opposed by the United States dental establishment, 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 people are unaware of the mercury in fillings, and this lack of informed consent
Informed consent
Informed consent is a phrase often used in law to indicate that the consent a person gives meets certain minimum standards. As a literal matter, in the absence of fraud, it is redundant. An informed consent can be said to have been given based upon a clear appreciation and understanding of the...
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 cost
Externality
In economics, an externality is a cost or benefit, not transmitted through prices, incurred by a party who did not agree to the action causing the cost or benefit...
s 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
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
, restricted in Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
and Finland
Finland
Finland , officially the Republic of Finland, is a Nordic country situated in the Fennoscandian region of Northern Europe. It is bordered by Sweden in the west, Norway in the north and Russia in the east, while Estonia lies to its south across the Gulf of Finland.Around 5.4 million people reside...
, and a committee of the US Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
(FDA) has refused to ratify assertions of safety.
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."
There is strong evidence that a certain percentage of lichenoid lesions
Lichen planus
Lichen planus is a chronic mucocutaneous disease that affects the skin, tongue, and oral mucosa. The disease presents itself in the form of papules, lesions, or rashes. Lichen planus does not involve lichens, the fungus/algae symbionts that often grow on tree trunks; the name refers to the dry and...
are caused by amalgam fillings.
External links
- Video showing Mercury vapour escaping from a filling
- Position Paper on Amalgam Fillings, National Council Against Health Fraud