Fiona M. Collins, BDS, MBA, MA, FPFA
In the 1700s and 1800s, various “dental amalgam” formulations were introduced. Toward the end of the 19th century, G. V. Black developed a dental amalgam that consisted of a silver, tin, copper, and zinc alloy mixed with mercury.1 Modern dental amalgam proved to be durable, wear resistant, technique tolerant, relatively inexpensive, and it has been used extensively for well over a century.2–4 Depending on location and circumstances, declines in amalgam use have occurred to varying degrees. By 1991, dental amalgam was used for around 50% of restorations placed in the United States, compared to 75% of restorations 15 years earlier.5 Dental amalgam is used more frequently for the underprivileged, who also suffer from a greater burden of oral disease.6 It is still selected for its low cost, durability, and tolerance of placement under suboptimal conditions in low- and moderate-income countries.7 Several factors have been associated with the gradual decline in its use.
Dental materials, esthetics, and minimally invasive dentistry
Advancements in dental materials have resulted in products that offer highly esthetic restorations as well as high bond strength and compressive strength. This makes them suitable for use in anterior and posterior teeth, including stress-bearing areas. Patient demand for esthetic restorations has also increased. While a 2014 Cochrane review found that the risk of failure was 89% greater for resin-based composite than for amalgam restorations (minimum follow-up of three years; p<0.001), it was noted that the evidence was of low quality.8 In an evaluation of more than 6,200 resin-based composite and amalgam restorations placed by more than 200 dentists in a dental practice setting (mean follow-up of almost two years), no differences were found for failure rates based on the restorative material.9 A 2011 World Health Organization report also noted that resin-based composite and dental amalgam restorations performed similarly.10 If moisture tolerance is required, resin-modified glass ionomers are available and less technique-sensitive than other alternatives to amalgam.
Minimally invasive dentistry is an additional factor, as it promotes prevention and non- or less-invasive care, thereby supporting the use of materials that minimize or avoid unnecessary removal of tooth structure. As such, direct restorative materials that rely on bonding or self-adhesion to tooth structure would be preferred over dental amalgam, which typically relies on the removal of tooth structure for mechanical retention (unless an amalgam bonding technique is used).
The controversy over health
Mercury vapor release from amalgam restorations has been stated to result in neurological, autoimmune, developmental, and organ-specific diseases and conditions.11 However, numerous studies and reviews support the safety and efficacy of amalgam in children and adults.12–14 Hypersensitivity and allergic reactions are possible.15 The utility and safe use of dental amalgam from a health perspective is supported by the US Food and Drug Administration, American Dental Association, and FDI World Dental Federation.16–18
Globally, concern over mercury release into the environment as a result of human activity has been a significant factor in declining amalgam use. When mercury released into the environment becomes methylated, fish bioaccumulate the methylmercury, whereby it enters the food chain.19 In the US, it was estimated in 2003 that 50% of the mercury entering publicly-owned treatment works originated in dental facilities.20 In addition, publicly-owned treatment works were found in an EPA study to effectively remove 90% of the dissolved and solid mercury in influent wastewater with the remaining 10% being released, further highlighting the need for environmental protection.21 Globally, dental amalgam was estimated to account for 270 to 341 metric tons of mercury in 2010, representing 10% of mercury used.7
While mercury is present naturally, mercury release by human activity is controllable. Dental amalgam–related mercury pollution can be reduced in essentially two ways: by reducing the amount of amalgam used and by reducing the amount of mercury released from dental amalgam into the environment. In Scandinavia, voluntary agreements, guidelines, recommendations, and limitations were introduced in the 1990s.7 Subsequently, mercury products including dental amalgam were banned and eliminated in Norway and Sweden. Similar programs have been applied in other countries, and limitations on the use of dental amalgam were introduced across the European Union on July 1, 2018.22
There is agreement globally on the need to reduce mercury pollution from all sources, including dental amalgam. The Minamata Convention on Mercury, also known as the Minamata Treaty, was adopted in 2013 and ratified in 2017.23 This treaty calls for the phasing down of products containing mercury and the promotion of alternative nonmercury products across all industries. Its objective is to protect the environment, ultimately protecting health. Eight measures are related to phasing down dental amalgam use, while a ninth measure addresses the use of best practices to reduce environmental release of mercury. Countries must select at least two measures for implementation (table 1).
Table 1: Measures for phasing down amalgam use and environmental protection, 2013 Minamata Convention on Mercury
Setting national objectives aiming at dental caries prevention and health promotion, thereby minimizing the need for dental restoration
Setting national objectives aiming at minimizing its use
Promoting the use of cost-effective and clinically effective mercury-free alternatives for dental restorations
Promoting research and development of quality mercury-free materials for dental restorations
Encouraging representative professional organizations and dental schools to educate and train dental professionals and students on the use of mercury-free dental restoration alternatives and on promoting best management practices
Discouraging insurance policies and programs that favor dental amalgam use over mercury-free dental restorations
Encouraging insurance policies and programs that favor the use of quality alternatives to dental amalgam for dental restorations
Restricting the use of dental amalgam to its encapsulated form
Promoting the use of best environmental practices in dental facilities to reduce releases of mercury and mercury compounds to water and land
Source: Minamata Convention on Mercury, 2013. Part II:p41.
Perspectives from a recent survey
Among respondents in a 2017 electronic national survey in the United States, 38% of more than 1,500 general dentists and 44% of 700 pediatric dentists had not placed amalgams in the prior year. A further 33% and 31%, respectively, reported low usage, which was defined as using amalgam for 1% to 30% of restorations.6 No use or low use of amalgam was more likely for dental professionals who identified dental amalgam to be unsafe, in pediatric offices with few patients on government assistance, and among general dentists concerned for the environment. Among the last of these groups, individuals were five to seven times more likely than nonenvironmentally conscious colleagues to agree with mandatory requirements for amalgam separators. Dentists frequently placing amalgam and those who believed amalgam to be unsafe were also more likely to agree with mandatory use of amalgam separators. Less than a quarter of respondents believed that amalgam should be banned. Survey limitations included potential bias due to use of a commercial database and a low response rate.
Agency Final Ruling
The Environmental Protection Agency (EPA) Final Ruling on Amalgam Separators came into effect on July 14, 2017.24 It requires use of a certified ISO 11143-compliant amalgam separator with at least 95% efficiency for removal of solids into the amalgam separator containers. Some amalgam separators today offer greater than 99% efficiency. The ruling also addresses the disposal of amalgam, including amalgam in solids in amalgam separators, and mandates the use of an approved amalgam recycler. In addition, oxidizing cleaners and cleaners with a pH of <6 or >8 may not be used to clean evacuation lines, vacuum pump filters, or nondisposable amalgam traps. It should be noted that the requirements for cleaners do not apply to dental unit waterline products.25 Under the Final Ruling, requirements for compliance and one-time compliance reports are provided for dental facilities already discharging wastewater to publicly-owned treatment works (existing dischargers) and new dischargers. Offices already using an amalgam separator are grandfathered in (table 2).25 Depending on location, local regulations, and requirements for wastewater disposal, amalgam separators and cleaners may be more stringent than EPA requirements, which are the minimum. If so, these more stringent requirements must be followed.
Table 2: EPA Final Ruling—compliance and reports
Discharger prior to July 14, 2017
By July 14, 2020
By October 12, 2020
Within 90 days of first discharge
Existing dischargers using amalgam separators prior to June 14, 2017
Grandfathered in until June 14, 2027 if the amalgam separator is still functioning properly and does not need to be replaced
By October 12, 2020
Exemptions: Oral pathology, oral and maxillofacial radiology, oral and maxillofacial surgery, orthodontics, periodontics, and prosthodontics facilities; mobile dental units providing care at multiple locations; facilities where amalgam is not placed and where amalgam is only removed in unplanned or emergency situations
ADA Best management practices
for amalgam waste
The American Dental Association Best Management Practices for Amalgam Waste guideline has recommended the use of ISO 11143-compliant amalgam separators for several years.26 Other recommendations include the use of only capsulated amalgam, using the smallest capsule required, wearing appropriate personal protective equipment when handling amalgam, and segregating and storing contact and noncontact amalgam waste in dedicated containers for recycling and disposal. A full description of the recommendations, along with dos and don’ts, is available in the report, which can be found on the ADA website.
Dental amalgam is an inexpensive and forgiving restorative material that continues to play a significant role globally in the provision of restorative care. While some high-income countries no longer use dental amalgam, other countries do. Declines in use vary considerably. The Minamata Treaty includes measures for the phasing down of amalgam use and environmental protection measures. In the United States, the EPA Final Ruling—as well as state, city, and water district requirements—will reduce the impact of amalgam used, and the ADA Best Management Practices for Amalgam Waste guideline contains measures that will reduce waste amalgam and its environmental impact. Environmental mercury release from all sources, including dental amalgam, must be minimized.
1. Black GV. The physical properties of the silver-tin amalgams. Dent Cosmos. 1896;38:965-992.
2. About Dental Amalgam Fillings. U.S. Food and Drug Administration website. https://www.fda.gov/medicaldevices/productsandmedicalprocedures/dentalproducts/dentalamalgam/ucm171094.htm. Published December 2017.
3. Eley BM. The future of dental amalgam: a review of the literature. Part 1: Dental amalgam structure and corrosion. Br Dent J. 1997;182:247-249.
4. Hyson JM. Amalgam: Its history and perils. J Calif Dent Assoc. 2006;34(3):215-229.
5. ADA Council on Scientific Affairs. Dental amalgam: Update on safety concerns. J Am Dent Assoc. 1998;129(4):494-503.
6. Bakhurji E, Scott T, Mangione T, Sohn W. Dentists’ perspective about dental amalgam: current use and future direction. J Pub Health Dent. 2017;77(3)207-215.
7. Lessons from countries phasing down dental amalgam use. Report by United Nations Environment Programme. Available at: https://wedocs.unep.org/bitstream/handle/20.500.11822/11624/Dental.Amalgam.10mar2016.pages.WEB.pdf?sequence=1&isAllowed=y. Published March 2016.
8. Rasines Alcaraz MG, Veitz-Keenan A, Sahrmann P, et al. Direct composite resin fillings versus amalgam fillings for permanent or adult posterior teeth. Cochrane Database Syst Rev. 2014;(3):CD005620.
9. McCracken MS, Gordan VV, Litaker MS, et al. A 24-month evaluation of amalgam and resin-based composite restorations: Findings from the National Dental Practice-Based Research Network. J Am Dent Assoc. 2013;144(6):583-593.
10. Future use of materials for dental restoration. Report by World Health Organisation. Available at: http://www.who.int/oral_health/publications/dental_material_2011.pdf. Published 2011.
11. Dodes JE. The amalgam controversy: An evidence-based analysis. J Am Dent Assoc. 2001;132(3):348-356.
12. Kingman A, Albers JW, Arezzo JC, et al. Amalgam exposure and neurological function. Neurotoxicol. 2005;26(2):241-255.
13. Bellinger DC, Trachtenberg F, Daniel D, et al. A dose-effect analysis of children's exposure to dental amalgam and neuropsychological function: the New England Children's Amalgam Trial. J Am Dent Assoc. 2007;138:1210–1216.
14. Hujoel PP, Lydon-Rochelle M, Bollen AM, et al. Mercury exposure from dental filling placement during pregnancy and low birth weight risk. Am J Epidemiol. 2005;161(8):734-740.
15. McParland H, Warnakulasuriya S. Oral lichenoid contact lesions to mercury and dental amalgam--a review. J Biomed Biotechnol. 2012;2012:589-569.
16. Food & Drug Administration. Update/review of potential adverse health risks associated with exposure to mercury in dental amalgam. Available at: https://www.fda.gov/MedicalDevices/ProductsandMedicalProcedires/DentalProducts?DentalAmalgam/ucm171117.htm.
17. American Dental Association, https://www.ada.org/en/press-room/news-releases/2016-archive/september/american-dental-association-reaffirms-position-on-dental-amalgam and, Statement on Dental Amalgam. Available at: https://www.ada.org/en/about-the-ada/ada-positions-policies-and-statements/statement-on-dental-amalgam.
18. International Dental Federation (FDI). Policy statement. Dental amalgam and the Minamata Convention on Mercury, September 2014, New Delhi, India. Available at: https://www.fdiworlddental.org/sites/default/files/media/documents/6-fdi_ps-dental_amalgam_and_minamata_adopted_gab_2014.pdf.
19. Ward DM, Nislow KH, Folt CL. Bioaccumulation syndrome: identifying factors that make some stream food webs prone to elevated mercury bioaccumulation. Ann N Y Acad Sci. 2010;1195:62-83
20. Vandeven J, McGinnis S. An assessment of mercury in the form of amalgam in dental wastewater in the United States. Water Air Soil Pollut. 2005;164(3):349-366.
21. United States Environmental Protection Agency. Health services industry detailed study. Dental amalgam. https://www.epa.gov/sites/production/files/2015-06/documents/dental-amalgam-study-2008.pdf. August 2008.
22. EU Scientific Committee on Emerging and Newly Identified Health Risks. Final opinion. https://ec.europa.eu/health/sites/health/files/scientific_committees/emerging/docs/scenihr_o_046.pdf4:270-5.
23. United Nations. Minamata Convention on Mercury. https://treaties.un.org/doc/Treaties/2013/10/20131010%2011-16%20AM/CTC-XXVII-17.pdf. Published 2013.
24. Environmental Protection Agency. 40 CFR Part 441. Effluent limitations guidelines and standards for the dental category. Final Rule. Federal Register June 14, 2017.
25. Frequently asked questions on the dental category final rule. Environmental Protection Agency website. https://www.epa.gov/sites/production/files/2017-12/documents/dental-office-category_frequent-questions_nov-2017.pdf. Published November 2017.
26. Best management practices for amalgam waste. Report by the American Dental Association. http://www.ada.org/~/media/ADA/Member%20Center/Files/topics_amalgamwaste_brochure.ashx. Published October 2007.
Fiona M. Collins, BDS, MBA, MA, FPFA, is an international lecturer and published author on a variety of dental topics, including infection control, caries, dry mouth, biofilm, patient compliance, tobacco cessation, opioids, and waste streams. She is the American Dental Association representative to the Association for the Advancement of Medical Instrumentation and is a fellow of the Pierre Fauchard Academy. Dr. Collins graduated as a general dentist from the University of Glasgow and holds master’s degrees from Boston University.