Amalgam: Fact and fiction

What is amalgam?

Amalgam is a material produced by mixing mercury (a liquid) with another metal. Amalgam used in dentistry is often called 'silver amalgam', because the main metal mixed with mercury is silver powder. Other metals such as copper and tin are usually present.

What is it used for?

Amalgam is used for filling teeth. The decay in the tooth is removed, and the pre-measured amalgam is mixed and then packed into the cavity in the tooth, and shaped to match the original tooth. The amalgam sets hard in about 10 to 20 minutes, and reaches its full strength in 24 hours.

What are the advantages and disadvantages of amalgam? Amalgam has been used in dentistry for more than 100 years, and has therefore been extensively researched. It is very easy to use, is very strong and hard wearing, lasts for many years and is low in cost. The metals in the amalgam also tend to inhibit new decay starting between the filling and the tooth.

However, the colour of the amalgam is silver, grey or black. Many patients find this to be unacceptable. Amalgam does not stick to the tooth, therefore the cavity has to be prepared to prevent the filling falling out. This often means cutting away normal tooth structure.

Is mercury poisonous?

Most chemicals are poisonous if taken in large amounts. However, mercury is only released from amalgam in very tiny amounts. There have been many scientific studies which have examined the possibility of mercury from dental amalgam causing damage to health. None of these have found amalgam to be a problem. There is a very small number of people (probably less than one in a thousand) who are allergic to mercury, and alternative materials have to be used.

National and international health organisations (e.g. the World Health Organisation, the FDI World Dental Federation), have confirmed the safety of dental amalgam, except for patients who are allergic to mercury. In March 1999, the National Health and Medical Research Council of Australia endorsed the report of its Health Advisory Committee on dental amalgam.

The key findings were that there is a lack of convincing evidence of any link between dental amalgam and specific diseases or symptoms, nor is there any evidence of improvements in health upon removal of dental amalgam fillings. The report also said that it would be prudent to avoid placement and replacement of dental amalgam fillings in certain population groups such as pregnant women, children and people with kidney disease. However, such avoidance is based on public health principles of risk avoidance, not on any credible evidence of harm.

What are the alternatives?

Some of the alternatives to amalgam include gold, porcelain and composite resin. Gold is expensive and takes much longer to place than amalgam, as does porcelain. Porcelain can be made to match the tooth colour very closely, but is a very brittle material.

Composite resin, a plastic filled with very fine glass particles, is the most popular alternative to amalgam. Composite resin is tooth coloured and can help to strengthen the tooth, but is difficult to use correctly. A composite resin filling can take twice as long to carry out as an amalgam filling, and if not done perfectly, decay can start and spread rapidly under the filling. Although composite resin is quite strong, it may not be strong enough in very large cavities.

What about the environment?

Some heavily industrialised countries, such as Germany, have experienced environmental problems from industrial, not dental, discharge of mercury into the water ways. There is now a world-wide trend towards a reduction in industrial mercury usage. Waste mercury and amalgam are produced in the dental surgery, but the amounts are relatively small and not an environmental hazard. Many dental surgeries are now voluntarily fitting filters to remove waste amalgam from the water before discharge into the sewer. All surgeries now have special storage facilities for waste mercury and amalgam.

Where can I get more information?

Your dentist will discuss the various filling materials which can be used for your teeth, and guide you to an informed choice. Each of the alternatives has advantages and disadvantages.