Does dental amalgam have a future in restorative dentistry?

It is estimated that 180 million Americans carry 1.4 billion restored teeth. Most of these restorations are made with amalgam, which is 50% elemental mercury (Hg) by weight [1]. Amalgam has had such extensive use in dental restorations due to them being the least expensive filling material [2] and having a long-lasting nature. A study showed that after 14 years, just 13% of the 320 restorations looked at had been lost [3], displaying why amalgam fillings have been used so widely for over a century [4]. However, concerns have been raised over the safety and sustainability of the use of dental amalgam, primarily in its release of elemental mercury to both humans and the environment. The extensive use of dental amalgam and the concerns about its safety and environmental sustainability make the question of whether we should continue to use dental amalgam in the future an important one. Dental amalgam should be phased out due to their negative environmental impacts and their contribution to raised levels of mercury in the blood (which when combined with other factors can cause even more problems). Alternatives for amalgam are readily available and have been used for 30 years, making this transition relatively smooth considering the scale of use of amalgam.

The WHO Consensus statement on dental amalgam concludes that dental amalgam is considered a safe and effective material for the use in restorative dentistry, but components of dental amalgam, in individual cases, cause side effects or allergic reactions [5]. The final opinion on dental amalgam by the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) for the European Commission also concludes that the current evidence does not prevent the use of amalgam in restorative dentistry, but the use of the material should be reviewed in individual cases, particularly whether the patient is pregnant or has an allergy to mercury or other components of amalgam [6]. The work completed by the SCENIHR is based upon the safety concerns that dental amalgam may have on patients and dental professionals. The conclusions drawn are highly credible due to the extensive research into the toxicology of mercury including the differing effects of elemental and inorganic mercury, both of which can be released into the mouth through both inhalation of mercury vapours (primarily in the case of elemental mercury) and the ingestion of inorganic mercury. The study has explored numerous potential health issues that the increased levels of mercury in the body due to dental amalgam can cause, however, in many of these conclusions into the effect of dental amalgam into a specific health problem, only one or two studies have been referenced, meaning that the report’s ability to fully assess all of the proposed impacts of dental amalgam would be limited. The report also identifies the need for further research, particularly in areas concerning the neurological effects of inorganic mercury released from dental amalgam and the impact that genetic variation as a result of multiple alleles (forms of a gene) being able to occupy one locus in different individuals (genetic polymorphism) have on the effect of mercury on individuals making is useful in exploring any adverse neurological effects amalgam may have but less so for more subtle impacts on individuals that the release of mercury from silver fillings may have. The report is credible and has substantiated conclusions based upon reviewed evidence. The lack of exact knowledge on the subtle and hard to identify the neurological effects of dental amalgam has upon individuals with multiple fillings and the increased levels of mercury in the blood of babies whose mothers had multiple fillings means that the conclusion that the choice of filling should be based upon the circumstances of the individual well informed, at least when looking at the potential impact of patients and dental professionals.

The decision on whether amalgam should continue to be used in restorative dentistry should not just consider the impact on patients and dental professionals, but the environment. Views on the release of amalgam or even elemental mercury from amalgam fillings into the environment through a variety of ways identify that, while there is evidence that mercury release from amalgam has harmful effect on the environment, the levels of mercury release due to dental amalgam are insignificant compared to that released from industrial pollution, and this level can be reduced with correct methods concerning the disposal of amalgam [7]. The report shows no bias as it presents the evidence concerning the effects of dental amalgam on the environment without a vested interest and the conclusion is based upon evidence from peer-reviewed studies. While in terms of the damage to people in general, there is little evidence to support the total banning of dental amalgam, the release of mercury shows a greater threat  when it comes to the environment, thus a decision on whether continuation of the use of dental amalgam in the way that we do is appropriate should be made in reference to the different ways in which dental amalgam has an impact on people and the environment. The Minamata Convention on mercury signed by 140 countries including the United Kingdom and the United States has set out to reduce the use of dental amalgam through a number of ways such as setting national objectives to reduce its use and discouraging insurance companies that favour amalgam restorations [16]. Similarly, a directive in the EU placed restrictions on the use of amalgam on deciduous (baby) teeth or persons under 15 years of age. These actions show that something is being done to slowly reduce the use of amalgam in restorative dentistry.

Dental amalgam has many benefits as a material for use in dentistry. It has been shown to have to be replaced as a result of further decay 7 times less than their composite counterparts [8] and have been shown to last a very long time [3]. However, dental amalgam can release elemental and inorganic mercury into the body. Most of the elemental mercury from amalgam is inhaled into the lungs. Elemental mercury has an 80% uptake rate into lungs due to its solubility in lipids, allowing it to pass through the cell membranes of the capillaries. The main deposit for the mercury is the kidneys, where the mercuric ions’ high affinity to bond with sulfur in proteins causes the accumulation of mercury in the kidneys. 7% of the mercury taken into the body is also deposited at the brain [6], causing mercury poisoning to have neurological impacts as well as physical ones.

A particular concern in the use of dental amalgam is over pregnant women. Mercury is able to enter the placenta and enter the bloodstream of the baby. This has caused concerns when coupled with the evidence showing that exposure to electromagnetic fields has caused an increase in the release of mercury from amalgam fillings, as a study showed that there was a statistically significant difference in the urinary levels of mercury in students who had and hadn’t used mobile phones following an amalgam restoration [9]. Similar results were shown when a group underwent a 7 Tesla MRI scan within 24 hours of the amalgam restoration [10]. Studies have made links between the increasing exposure to electromagnetic radiation and the increasing rate of autism. Considering the electromagnetic waves increase the levels of mercury released from amalgam fillings, the causal mechanism of mercury has been used to explain the increase of autism rates [11]. This provides a reason to limit the use of amalgam restorations, even if this is targeted at certain groups such as pregnant women or children, where amalgam fillings showed a statistically significantly higher level of urinary mercury levels than their composite counterparts [12]. Due to the lack of information regarding the exact effect of mercury on the brain when the doses are not extreme, these studies should not be taken lightly.

However, the study investigating children’s mercury levels, while showing a difference in urinary mercury levels, did not show any statistically significant difference in the neuropsychological or kidney functions between the amalgam and composite resin group [12]. This highlights a key argument in favour of the use of amalgam, there is no evidence to show any adverse health or neurological impacts of the mercury that is released from dental amalgam used in restorations. Adverse physical reactions can occur due to an allergy to amalgam which is seen in two forms: type I (fast onset, swellings, asthmatic seizures, and potentially asphyxiation) and type IV (slow onset, inflammation, dermatitis). It has been shown that kidney diseases and amalgam restorations are not linked in a study of 20,000 people [13].

When looking at the reduction in the use of amalgam, we must look at what would replace it. Composite resin fillings have been used for 30 years as an alternative to amalgam fillings. They can be coloured to look like teeth and have a lifespan of 3-10 years. While these alternatives may not be as durable, resistant to secondary cavities or as cheap as amalgam fillings, they provide an alternative which is constantly evolving to improve its safety and efficacy.

Environmentally, when mercury is discharged into sewage systems, it can get into the water. Elemental mercury in water can be turned into methylmercury by bacteria in the water. Methylmercury can easily enter plankton, putting the organic mercury into the food chain [7]. Biomagnification will occur where the mass of methylmercury in individuals increases as you go up the food chain, causing a magnification of 100,000 times when comparing algae and predators in the same ecosystem [14]. If the predators are eaten by humans, it can cause serious issues as methylmercury is the most toxic form of mercury, meaning that mercury that is present in sewage systems can cause serious harm to people and the environment. A study estimated that from amalgam containing 90,000kg of mercury, approximately 100kg was released into the environment [7]. Another way in which mercury can enter the environment is through the cremation of cadavers. A study estimated that over 170kg of elemental mercury was released into the atmosphere from the cremation of 50,000 bodies [7]. This mercury can stay in the atmosphere for up to 3 years [7] but will eventually fall to the ground through precipitation or other means. While there is a natural mercury cycle which emits 150,000 tonnes of mercury a year [14], the artificial addition of mercury into the atmosphere will also lead to an increase in the levels of terrestrial mercury, causing environmental issues.

While this 100kg is a large amount of mercury, the low solubility of elemental mercury in water would limit the mass of methylmercury formed. The use of dental aspirator kits to remove amalgam from the mouth during the removal of a filling reduces the inhaled amalgam in the process. The amalgam that is in the wastewater can be removed via an amalgam separator. This ensures that amalgam is not distributed into sewers and their use was made law in 2005 [15], showing that we can work from the dental practice to limit the levels of amalgam released into the environment.

Overall, while dental amalgam doesn’t show evidence of adverse physical and mental health effects, nor does it pose a threat to the environment that cannot be reduced, dental amalgam should be reduced in their use. This reduction would not be an immediate change but the phasing out of the use of amalgam would be beneficial for several reasons. While adverse health effects have not been observed, there may be more subtle changes that the mercury from dental amalgam is causing such as slight neurological changes and an increased risk of autism and other complications for newborn babies whose mother had amalgam fillings, this is a field that requires more research. The environmental impacts of mercury from amalgam are real, if insignificant compared to other industries, meaning that considerations have to be made. Limiting the use of amalgam, while maybe not necessary for the safety of people in general, should be encouraged due to their negative effects but ultimately, the possibility of alternatives. Alternatives for amalgam have been being used for thirty years and are constantly improving. If we slowly phase out the use of amalgams in dentistry and replace them with composites and other alternatives, we will be able to reduce the negative environmental effects amalgam has as well as its potentially harmful effects in humans, especially vulnerable groups such as pregnant women.

[1] Richardson GM, Wilson R, Allard D, Purtill C, Douma S, Gravière J. Mercury exposure and risks                  from dental amalgam in the US population, post-2000. Sci Total Environ. 2011;409(20):4257–4268.   doi: 10.1016/j.scitotenv.2011.06.035

[2] Glover, L.. 2016. How much does a filling cost? [Online] Available at: https://www.nerdwallet.com/blog/health/medical-costs/how-much-does-a-filling-cost/

[3] Osborne JW, Norman RD, Gale EN. A 14-year clinical assessment of 12 amalgam alloys. Quintessence Int. 1991 Nov;22(11):857-64 PMID: 1812507

[4] FDA. 2019. About dental amalgam fillings. [Online] Available at: https://www.fda.gov/medicaldevices/productsandmedicalprocedures/dentalproducts/dentalamalgam/ucm171094.htm

[5] FDI, World dental association. 1997. WHO consensus statement on dental amalgam. [Online] Available at: https://www.fdiworlddental.org/resources/policy-statements-and-resolutions/who-consensusstatement-on-dental-amalgam

[6] SCENIHR (Scientific Committee on Emerging and Newly-Identified Health Risks), Scientific opinion on the Safety of Dental Amalgam and Alternative Dental Restoration Materials for Patients and Users (update), 29 April 2015.

[7] Chin, G. , Chong, J. , Kluczewska, A. , Lau, A. , Gorjy, S. and Tennant, M. (2000), The environmental effects of dental amalgam. Australian Dental Journal, 45: 246-249. doi:10.1111/j.1834-7819.2000.tb00258.x

[8] Soncini JA, Maserejian NN, Trachtenberg F, Tavares M, Hayes C.. The longevity of amalgam versus compomer/composite restorations in posterior primary and permanent teeth: findings From the New England Children’s Amalgam Trial. J Am Dent Assoc. 2007 Jun;138(6):763-72. PMID: 17545265

[9] Mortazavi SM1, Daiee E, Yazdi A, Khiabani K, Kavousi A, Vazirinejad R, Behnejad B, Ghasemi M, Mood MB. Mercury release from dental amalgam restorations after magnetic resonance imaging and following mobile phone use. Pak J Biol Sci. 2008 Apr 15;11(8):1142-6. PMID: 18819554

[10] Mortazavi SM, Neghab M1, Anoosheh SM, Bahaeddini N, Mortazavi G, Neghab P, Rajaeifard A. High-field MRI and mercury release from dental amalgam fillings. Int J Occup Environ Med. 2014 Apr;5(2):101-5. PMID: 24748001

[11] Gh. Mortazavi, M. Haghani, N. Rastegarian3 S. Zarei, and S.M.J. Mortazavi. Increased Release of Mercury from Dental Amalgam Fillings due to Maternal Exposure to Electromagnetic Fields as a Possible Mechanism for the High Rates of Autism in the Offspring: Introducing a Hypothesis. J Biomed Phys Eng. 2016 Mar; 6(1): 41–46. PMID: 27026954

[12] Ben Balevi, BEng, DDS, Dip EBHC (Oxford), MSc Are Dental Amalgams Toxic to Children? Comment on 2 Recently Published Randomized Controlled Trials

[13] Bates MN1, Fawcett J, Garrett N, Cutress T, Kjellstrom T.. Health effects of dental amalgam exposure: a retrospective cohort study. Int J Epidemiol. 2004 Aug;33(4):894-902. Epub 2004 May 20. PMID: 15155698

[14] Berlin  M.  Mercury.  Handbook  on  the  toxicology  of  metals. Amsterdam: Elsevier Science Publishers, 1986:387-445.

[15] Cash, C. 2016.  Amalgam Separators. [Online] Available at: https://www.isopharm.co.uk/dental/blog/amalgam-separators

[16] United Nations Environment Programme. 2017. Minamata convention on mercury. P.58. [Online] Available at: http://www.mercuryconvention.org/Convention/Text/tabid/3426/language/en-US/Default.aspx

Photo Credits due to: https://www.happysmilesdentistry.co.uk/treatments/amalgam-fillings/

Hamza Khan