Why are people afraid of dental amalgam?

Amalgam fillings are a topic often raised by investigative journalists or worried consumers. There are both environmental and aesthetic reasons why the use of amalgam for dental fillings is on the wane or has even been completely discontinued in some countries. Amalgam remains, however, an important alternative for dental fillings. It is presently only used for fillings in the back teeth, because it is not tooth-coloured. Thus the fundamental question must be asked – is amalgam innocuous or outright toxic or somewhere in between?

What is amalgam?

Amalgam is mainly silver and mercury, but it may contain small amounts of other metals such as copper, tin and zinc. One part of metal powder is mixed with one part of liquid mercury to make a paste for filling the cavities. One typical property of mercury is its ability to amalgamate with other metals after mixing to form a hard and homogenous metal alloy; in some senses the new metal is comparable to bronze. The hardening process takes a few hours.

Set amalgam restorations release some mercury into the air, but this occurs very slowly. The fillings also corrode very slowly, but usually the restorations last for many years.

Exposure to mercury from fillings and possible health effects

Metallic mercury is virtually not absorbed at all in the gastrointestinal tract, and the main intake route from fillings is the respiratory route after evaporation of tiny amounts of mercury. The urinary mercury level is slightly higher in individuals who have amalgam fillings. The main exposure to patients happens when they have the fillings inserted or removed.

No health effects have been found in well-designed studies, even in cases when they have been actively sought for. The Scientific Committee on Health and Environmental Risks (SCHER) of the European Union adopted in 2008 a report on the safety of dental amalgams and alternative dental restoration materials for patients and users. Their conclusion was that dental amalgam fillings occasionally cause local effects in the mouth, such as allergic reactions of the gums and to the skin inside the mouth. The claims that the fillings might harm kidneys or have effects on the nervous system or mood are not substantiated by the scientific evidence.

The fact that exposure is highest when several fillings are removed contrasts to the relief of symptoms of patients immediately after their removal. This spectacular effect speaks against rather than for the theory that the symptoms were caused by mercury. For this reason, it is better to leave the amalgam fillings in place unless there is a clear reason to remove them, such as allergy developing to one of the metals in the amalgam. It should be noted that the alternatives are not without occasional side effects such as allergies.

In fact the people who have been exposed to the highest levels are the dentists and dental nurses making the alloys, not the patients. Even here the most important route is exposure to the vapour released when placing or removing the fillings. Improvements of hygiene and ventilating off the vapour have decreased the exposure of the dental personnel.

So why are people afraid?

Probably the most important reason is very simple. There are activist groups who protest continuously against amalgam use, often for very obscure reasons. It also may be difficult to understand why a chemical that is toxic in other places would be safe for long-term use directly in human body. What needs to be borne in mind here is the fundamental fact described in many chapters of this book: it is the amount, not the substance itself that makes something safe. Release of mercury from fillings is miniscule – this is what makes it safe, and furthermore any metallic mercury passing into the digestive tract is not absorbed. In this respect it is not different from many other medical treatments that also would be harmful at higher doses or if administered in an inappropriate way.

There is a great deal of controversy surrounding dental amalgam, but there is no scientific evidence that it will cause any side effects other than relatively rare local effects such as allergies in the mouth.

Notes and references