What is Amalgam and how is it used?
Amalgam is a material used in dentistry to restore teeth that have been damaged by decay (caries). This procedure is known as a "filling", whereby the caries is removed and the resulting space in the tooth is "filled" by one of various available materials.
Amalgam is a a mixture of silver and mercury. Essentially, the mercury allows the small silver particles to be more easily manipulated and slightly liquid so that the space in the tooth can fully filled. Without mercury, the silver would amount to a powder and could not be permanently packed as a filling material in the tooth.
Why use amalgam?
Many dentists prefer amalgam fillings because they are considered easier to place. This is because even if the tooth is wet, for example from saliva in the mouth, it does not affect the amalgam. On the contrary, white or "composite" fillings need a dry environment because they chemically "stick" to the tooth and this bond is severely impaired by moisture. The other argument for amalgam fillings is that they are long lasting. This is supported by numerous studies which have shown fillings lasting as long as 30 years. Similar studies of composite "white" fillings had originally not shown the same longevity. However, it is very important to note that composite fillings only started to be placed in the 80's and did not become widely used until the 90's. Finally, more advanced chemical composition of the fillings as well as improved understanding of the techniques necessary to properly place them have been developed in the last ten years. Therefore, to properly compare the longevity of amalgam to composite, it will be necessary to see how the composites placed in the last few years perform over the next three decades. In fact, the latest continuous studies of amalgam/composite longevity (which now track over 100 thousand amalgam and over 90 thousand composite fillings) have found the two materials to be equal in longevity.
Concerns about mercury safety
The main concern about amalgam comes from the fact that it contains mercury, which is a known toxic substance. The majority of published studies have shown that a certain amount of mercury can and does leak from the fillings into the bloodstream. Most of the mercury exposure occurs through vaporized mercury which occurs when amalgam is first placed or when amalgam fillings are taken out. However, although blood levels of mercury can increase due to amalgam fillings, numerous amalgam studies in the U.S. have not shown any correlation between these elevated levels of mercury and any diseases. A study, however, is only as good as its investigation protocol, because without strict protocols studies can be no more useful than anecdotal accounts. On this issue, there is definitely some controversy. For example, an outside advisory panel to the FDA said in a 13-7 vote that the conclusions FDA's report on amalgam safety (which stated that amalgam was safe) were unreasonable based on the available research and that further research was necessary. In Europe, however, the scientific evidence has pointed towars the possibility of amalgam-associated health effects. For example, a systematic review (a scientific examination of available studies for scientific soundness and credibility) by the Freiburg University Institute for Environmental Medicine, found that "mercury from dental amalgam may lead to nephrotoxicity, neurobehavioural changes, autoimmunity, oxidative stress, autism, skin and mucosa alterations or non-specific symptoms and complaints", that "Alzheimer's disease or multiple sclerosis has also been linked to low-dose mercury exposure", and that "removal of dental amalgam leads to permanent improvement of various chronic complaints in a relevant number of patients in various trials." . In light of information such as the above, some countries such as Austria and Germany have imposed restrictions prohibiting the use of amalgam in children and pregnant women. In Norway, the use of dental amalgam was banned in 2008.
In summary, it is absolutely impossible to say with certainty that dental amalgam is safe. However, there has not been any direct evidence to show that amalgam causes any specific diseases.
The other amalgam issues
While the mercury concerns are a matter of debate, several other disadvantages of amalgam are often overlooked.
The first one is that because amalgam does not bind to the tooth structure, it relies on mechanical retention only. The shape of the preparation of the tooth allows the amalgam to stay in. To ensure the correct shape, the preparation of the tooth is much larger than what is needed for a white filling, very often necessitating the removal of healthy tooth structure. For example, if a tooth has cavities on its side (in the area where it touches the teeth next to it), but not on its top (the area that is used to chew), the top of the tooth still needs to be drilled and filled with amalgam, whereas a white filling can be limited to the decayed area only. This means that although an amalgam filling may last a long time, once it does need to be replaced, there is usually not sufficient tooth structure left to allow a replacement amalgam filling. In general, if an amalgam filling needs replacement, the tooth will need a crown, whereas a properly placed composite (white) filling can be replaced several times without enlarging its size. Furthermore, amalgam fillings can stain the gums or the inside of the cheeks or tongue. This is known as an "amalgam tattoo" and although probably not dangerous, can certainly be unsightly. Finally, an amalgam filling, because it does not bind to the tooth, often acts as a wedge, causing cracking of the tooth over time. This is because the amalgam filling is often in the area where there is a lot of pressure from its opposing tooth and when biting, the pressure by the opposing tooth pushes on the amalgam, which then pushes down into the tooth. This is why many amalgams fail due to cracking of the filling or even of the whole tooth. On the other hand, the white filling holds the tooth together (because it is chemically bonded to tooth) and absorbs the pressure of the opposing tooth. Therefore, white fillings often wear down over time. Because of the much higher cost of a crown to repair a cracked tooth than of a second white filling to repair an old white filling, I consider white fillings to be a more cost-effective long-term means of preserving teeth.
Should you replace your amalgam fillings with white fillings?
If your amalgam fillings are intact, they should not be replaced. The act of drilling out an old amalgam filling actually releases more mercury than the filling would release over its entire lifespan. If you suffer from a disease that is claimed to be linked to amalgam, there is little chance that removing fillings will help you because the mercury has already accumulated in your body. However, it is strongly recommended that if your amalgam fillings are cracked, broken, have decay underneath (diagnosed via x-ray or in your mouth by your dentist), they should be replaced as soon as possible to prevent further damage to your teeth and it is strongly recommended that they be replaced with white fillings if possible.
The danger of mercury from amalgam fillings is not signficant, nor is it completely negligible. However, it has many other disadvantages and its main advantage of durability has been eclipsed with the advent of modern white filling materials and techniques. Therefore, for any patient considering new fillings or needing to replace old fillings, white fillings are the preferred material. I recommend white fillings to all of my patients except in the rarest of cases.