Most of us take them for granted, fearing the drill perhaps, but not the fillings themselves. But recently the British Department of Health advised pregnant women not to have amalgam (silver) fillings inserted or removed, reminding us that there have been arguments over the safety of the most popular type of dental fillings since amalgam was invented, more than 150 years ago.
Amalgam, a mixture of metals, was invented by a Parisian, O. Traveau, in 1826. When mixed initially it is soft and can be pushed into a cavity in a tooth. It sets in a matter of minutes, reaching full hardness 24 to 48 hours later. Being cheap and easily used, it quickly became a popular alternative to gold fillings, bringing dental treatment to the masses, and has remained the most commonly used filling material since.
The reason for the argument is that amalgam is comprised of 50 per cent mercury - a liquid metal more toxic than arsenic or lead, the rest being an alloy of silver, tin, copper and zinc. Dentists agree that amalgam fillings leach mercury but pro and anti-amalgam groups disagree over the significance and the effects, if any, this has on the body. The warning to pregnant women follows concerns that mercury in the body may cross into the placenta.
Alternatives to amalgam include gold, porcelain and composites, which are a mixture of plastics and ceramics. Composites and porcelain fillings match tooth colour and are often used on front teeth. Composites, like amalgam, are also pushed into a cavity, while both porcelain and gold fillings must be made in a laboratory from an impression of a cavity and later inserted.
The Case Against
`We're coming to the end of the third amalgam war," says Dr Graeme Hall, one of the leading anti-amalgam campaigners in Europe. Dr Hall, European president of the International Academy of Oral Medicine and Toxicology (IAOMT), welcomes the British Department of Health advice to pregnant women, saying it is "better late than never".
The British Department of Health's Committee on Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) said in April that although there is no evidence to indicate it is harmful, "it may be prudent to avoid, where clinically reasonable, the placement or removal of amalgam fillings during pregnancy". The COT said that studies estimated that one to five micrograms (millionths of a gram) of mercury are released from amalgam fillings but also said it "accepted that exposure of mercury vapour is of greater concern for dentists and their staff than for patients".
What Dr Hall calls "the first amalgam war" was the breaking away of the pro-amalgam American Dental Association from its pro-gold colleagues in the 1850s, in what his organisation calls "The basic controversy . . . between health professionals: one group was concerned that implanting mercury in the body presented unacceptable health risks to the patient; the other group claimed that amalgam was so easy to use that it would permit dentists to treat large numbers of patients cheaply and that this benefit outweighed the possible health risk to the patient."
The second amalgam war, says Dr Hall, was in 1926 when a German chemistry professor, Dr Alfred Stock, proved that mercury leached from amalgam fillings. Now, he says, they are banned in Sweden, restricted in Germany, and will be banned in Austria and Denmark by the year 2000.
Dr Hall says mercury leaches from amalgam fillings constantly, and enters the body when swallowed or when its vapour is breathed. This happens particularly when you chew, drink hot liquids, or smoke. He cites studies which say the amount of mercury released is at least doubled if there are other metals in your mouth, due to battery effects. However, the highest rates of mercury ingestion, he says, occur during, and for approximately 12 days after, inserting or removing amalgam fillings.
Dr Hall cites a number of studies which associate what he calls "chronic mercury poisoning" with a host of illnesses and conditions, including memory loss, anxiety, depression, heart disease, immune system deficiencies and allergies, birth defects, male and female infertility and kidney damage. He says removal of amalgam fillings has led to significant rates of cure or improvement in multiple sclerosis and epileptic cases. He recommends removal of all amalgam fillings for women of childbearing age and for men trying to become fathers.
Another IAOMT member, Dr David Kennedy, says: "Mercury is also associated with depression, suicidal thoughts, nervousness, fits of anger, shyness, and emotional outbursts." He says World Health Organisation figures show amalgam is the highest source of daily mercury consumption, at three to 17 micrograms, while fish and seafood are second at 2.3 micrograms. He says: "Because the effects of mercury poisoning are cumulative and longterm, the only definitely safe exposure is no exposure at all."
Proponents of amalgam have challenged the anti-amalgam camp to prove the links they claim between amalgam and various diseases. Dr Hall says a link between amalgam and lichen planus, a pre-cancerous condition of the mouth, was proven in Berlin in the 1970s, and also says amalgam causes peridontal gum disease. However, he says, it is impossible to prove the link between amalgam and the many other claimed effects. "If the amalgams are removed and you get better, that is not scientific," he says. In order to prove the link "you would have to put them back", he says.
Dr Hall's surgery in Dusseldorf has not used amalgams for 13 years, preferring to use composites of ceramic and plastic. These are as easy to use and last longer, he says. But while he says the materials are not more expensive than amalgam, he admits it takes a longer time to insert them.
When asked why more dentists are not anti-amalgam, especially given that they are exposed to more mercury vapours than patients, he says: "Dentists are not scientists."
The Case For
`Amalgam has worked very well for 150 years. There's no scientific proof that it is harmful," says Prof Robbie McConnell, the head of restorative dentistry at the University Dental School and Hospital in Cork.
Prof McConnell, one of Ireland's leading experts in dental materials, does not subscribe to the amalgam scare stories and says he will only remove amalgam fillings in the extremely rare case of an allergy. "I would find it unethical to remove them for any other reasons," he says, adding that he has only come across one amalgam allergy in 25 years.
Meanwhile the Irish Dental Association, like its American and British counterparts, endorses the view that "all available research worldwide indicates that amalgam is not harmful to health". It says dentists would stop using amalgam if it were found to be hazardous, not least because of concerns for their own health. The association says studies on dental workers show that amalgam "does not cause physical or mental disease" adding: "No government or reputable scientific, medical or dental body anywhere in the world accepts on any present published evidence that dental amalgam is a hazard to health."
The association also notes that fewer teeth need filling these days and many cavities are smaller, suiting other materials. This means amalgam use is declining. Irish people have on average about eight fillings each, most of which are amalgam.
Reacting to the British warning to pregnant women, the association's secretary general, Donal Atkins, says the Committee on Toxicity (COT) found that "there is no evidence that placement or removal of amalgam during pregnancy affects the foetus". He says: "During pregnancy all medical and dental interventions are generally limited to carrying out essential items of treatment only. However, if a pregnant woman has a dental emergency and treatment with dental amalgam is indicated, COT commented that `the benefits far outweigh the hypothetical risk of toxicity'. "
Responding to Dr Hall's criticisms of amalgam, Dublin dental surgeon, Dr Nick Armstrong, questions the association of amalgam with lichen planus. He also says peridontal gum disease is associated with rough edges where fillings meet the gums, rather then with the nature of the fillings themselves. Although acknowledging that mercury does leach out of fillings, he questions the claims of improvement in various conditions following the removal of amalgam, since the amount of mercury in the body increases immediately after a removal. "Instant cures simply can't be true," he says.
The view of the World Health Organisation is that the current weight of evidence finds that dental amalgam is safe and effective. It says amalgam is durable and cost effective and that alternatives "significantly increase the cost of dental care".
Those alternatives generally mean plastic composites, porcelain or gold. In Ireland, the cost of an amalgam filling in private practices is typically in the range of £25 to £40, while composites are in the £50 to £80 range. Porcelain and gold fillings, which need to be made up separately and then fitted, can typically cost upwards of £300.
Composites, or white fillings, are not as good as amalgam, according to Prof McConnell, who says they need to be filled and hardened in little bits because they shrink a little in the process.
As for the amount of mercury that leaches out of fillings, Prof McConnell cites a study in Texas which found that fillings in corpses had only decreased in weight by two per cent over their lifetime. He says much higher doses of mercury are absorbed from fish, particularly big fish such as swordfish and tuna.
But even the pro-amalgam dentists admit its days are probably numbered, though not, they stress, for dental health reasons. The Swedish government has already stopped its use on environmental grounds. Prof McConnell disputes Dr Hall's assertion that this is an outright ban and says the alternatives are so expensive that amalgam use is increasing again there. The old type of amalgam is banned in Germany, he says, and he expects opposition to mercury in the environment will eventually lead to amalgam being banned here too.
He says new resins which do not shrink and do not wear are being developed in the US. "I would think we'll have a new product on the market within five years," he says, predicting this will lead to the use of amalgam in new fillings being phased out. Already, he adds, dental students are being taught new materials in preparation for this day.