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Note this special guest post submitted by Maddaz A. Hatter, D.D.S. Thanks Dr. Hatter!

Also, on an almost-completely-unrelated note, skeptical dentist, haberdasher extraordinaire, and sometime-guest-blogger Grant Ritchey recently moderated debate between SBM regular Clay Jones, and pediatrician-who-has-yet-to-be-coerced-into-blogging-with-us Raymond Cattaneo, about the pros and cons of firing families who refuse to vaccinate according to the recommended schedule. I’m told Clay wins the debate through a swift blow to the throat, but it happens at the very end so you’ll have to listen to the whole thing! Located at the Prism Podcast via this tasteful and refined link.

In England during the 1700s and 1800s, felt hats – very fashionable at the time – contained trace amounts of mercury, and many of the workers in the hat factories that produced them succumbed to mercury poisoning over time. Symptoms of mercury poisoning include dementia and other neurological complications, from whence came the term “Mad as a Hatter.” We’ve known for quite a while that quicksilver in large enough quantities does not do a body (or brain) good.

This brings up a point. It seems that a recurring theme at Science Based Medicine is that we are always defending what legitimate health care providers want to put into a human body to prevent, cure, or manage disease, or to improve health or quality of life. Conversely, we critique those who want to put things in us that are of no demonstrable benefit or which may cause harm. To wit: vaccines – good, coffee enemas – not good. Fluoride (at appropriate doses) – good, colloidal silver – not good. This is an ongoing tug-of-war that will likely continue until our sun supernovas and consumes our planet, after which all arguments will probably be moot.

In the dental field, the two biggest battles we seem to continually wage deal with the safety of fluoride and the use of dental amalgam. Fluoride and fluoridation has been written about many times before on Science-Based Medicine. I have also discussed it several times on my podcast, The Prism Podcast, but I’ve never written about amalgam fillings before. Harriet Hall wrote an excellent SBM post on the matter way back in 2008, but after all these years it’s probably time to revisit the topic.

Amalgamology 101

Dental amalgam is the most commonly used filling material for decayed and broken teeth and has been for over one hundred and fifty years. While its use is decreasing due to more cosmetically-pleasing filling materials, concerns over toxicity, improved reimbursement from insurance companies for alternative materials, and other factors, it is still placed in over one billion teeth worldwide per year.

Dental amalgam contains approximately 50% mercury and is mixed with silver, copper, tin, and other metals to form a plastic (i.e. moldable) mixture which is then condensed into the cavity where it hardens. There has long been a concern that the mercury contained within a filling (although chemically bound to silver and other metals) could be released and cause a multitude of diseases and conditions, such as multiple sclerosis, Alzheimer’s disease, kidney disease, as well as a host of other maladies affecting every known body system. In fact, Norway, Sweden, and Denmark have banned its use due to concerns about environmental disposal and in Sweden, also for health concerns. The population of patients in which the greatest concern is expressed is pregnant women and children under the age of six, where toxic threshold levels may be lower than in adults. Countries such as the United States and Canada have not banned amalgam’s use in these groups, but have issued warnings for potential toxicity issues and uncertainties about its possible effects. The Food and Drug Administration (FDA) states: “There is limited clinical information about the potential effects of dental amalgam fillings on pregnant women and their developing fetuses, and on children under the age of 6, including breastfed infants”, while the Canadian Dental Association (CDA) says on their website: There is no scientific evidence of ill effects [on pregnant women or children], although mercury is known to cross the placenta.”

So, is dental amalgam safe to use in the expecting mother or young child? If there are uncertainties surrounding the effects of mercury on this susceptible population, is it ethical for a dentist to recommend dental amalgam as a filling material to his or her patients? What about everyone else? Are amalgam fillings a legitimate choice for restoring a tooth? Do the risks justify the benefits?

Dental amalgam: A brief history

Dental amalgam reportedly was first used by a man named Su Kung in China around 659 CE. More recently, in 1528, a German physician named Johannes Stokers recommended amalgam as a dental filling material. Fifty years later, in 1578, Li Shihchen chronicled a dental mixture of 100 parts mercury with 45 parts silver and 900 parts tin for filling teeth. It is unknown how well or how long any of these restorations lasted as there was little follow up care or record keeping at that time. Moreover, the means by which dental decay was diagnosed and removed was quite primitive by today’s standards. But there probably weren’t a lot of malpractice attorneys around then either, so why not try it out?

The next major historical reference to silver–mercury amalgam was recorded in 1826, when a Frenchman by the name of Traveau described a “silver paste” filling material, produced by mixing silver coins with mercury. In 1833, the Crawcours brothers in the US introduced their “Royal Mineral Succedaneum,” a fancy sounding name for a mixture of shaved French silver coins and mercury, mixed into a paste, and placed in the cavity. Up until that point, the most commonly used filling material was gold foil, which was hammered into the cavity with a mallet. It was (and is) a great filling material, but it was (and is) more expensive and more difficult to place than other materials and is thus rarely used nowadays. Dental amalgam was offered as an inexpensive, easy to place filling material in those days of primitive dentistry (the first dental school in the US did not open until 1840).

The controversy: Then and now

After dental amalgam was introduced in the US in the 1830s, many dentists at the time felt that it was an inferior material. The American Society of Dental Surgeons (ASDS), the only existing dental association at the time, labeled its use malpractice and required all of its members to sign a pledge vowing that they would not use the material. This led to the first “Amalgam War”, which raged until the 1850s. After the ASDS folded in 1856, and when the American Dental Association was founded three years later, there was no such ban on amalgam. Because of this tacit approval by the fledgling ADA, as well as advances in dental sciences and techniques in general, dental amalgam became more widely accepted as a filling material and has been used by nearly all dentists worldwide since that time. With very few exceptions, dental amalgam enjoyed nearly a century of unquestioned acceptance, with significant improvements being made in the manufacture, composition, and placement techniques occurring throughout that time period.

In today’s image-conscious society, patients typically want to have their teeth fixed with materials that look natural and realistic. Even so, amalgam will always have a place in the dentist’s arsenal. Amalgam is a useful filling material: it’s cheaper and in some situations longer-lasting than the alternatives. It possesses desirable properties that are especially valued in areas where dentistry is primarily cost driven, such as underserved regions of the world (including parts of the US), in charity clinics, prisons, teaching institutions, and so on. Dental amalgam is less technique-sensitive than composite fillings; it is more forgiving being placed under difficult circumstances or moist environments (for example, when the decay is below gum level or in an area that is difficult to access, such as a wisdom tooth). It requires less skill and training to work with, and can be placed faster than composite (tooth colored) fillings.

This invites the question: since mercury is a known neurotoxin, and since trace amounts of mercury leech out of fillings and find their way into the body, why is its use allowed at all? As with most questions concerning science and technology, medicine, and public policy, there are usually no clear-cut answers. There are too many variables to be controlled, too many risk vs. benefit equations to calculate. An attempt to discuss all possible scenarios whereby mercury’s role in pathological brain development and other neurological and physical issues vs. the use of mercury in commerce and medicine would be exhaustive and require a book, not a blog post. The decision tree in evidence-based dentistry is a complex interaction between the known scientific data, the care, skill, judgment, and experience of the dentist, and the circumstances and preferences of the patient.

A brief mercury primer

Mercury (atomic symbol Hg) can be (but shoudn’t be!) consumed in its elemental state (as a liquid or a vapor), in inorganic salts, and in organomercuric compounds (i.e. bound to carbon). Methylmercury (the organomercuric compound found in fish) is the most toxic and is absorbed through the digestive tract. The phase of mercury found in amalgam is elemental mercury (the liquid element that spills out of a broken thermometer), which is primarily processed in the lungs via inhalation, with very little being absorbed in the gastrointestinal tract. Exposure to mercury compounds can come from a variety of sources; chief among them is fish consumption, but can also occur from environmental exposure, exposure to spills (e.g. a thermometer or light bulb breaking), or from dental amalgam. Symptoms of mercury toxicity include profuse sweating, pink or red skin, desquamation (sloughing) of the skin, ataxia (poor coordination) and loss of balance, dysphagia (difficulty swallowing), other sensory deficits, confusion, peripheral neuropathy, and death.

Daily mercury intake

In the US, the FDA has established an acceptable daily intake for mercury of 0.4 micrograms per kilogram of body weight per day. Research shows that this amount of mercury, consumed for extended periods up to a lifetime, presents a negligible risk of adverse health outcomes in even the most sensitive human populations (pregnant women, developing fetuses, young children, or those with kidney disease, for example). The World Health Organization (WHO) has set a standard of 1.6 micrograms per kilogram of body weight per week, cumulatively less than the FDA figure. Although neither the FDA nor the WHO revise their recommendations downward for pregnant or nursing women, they do recommend reducing the amount and types of seafood in order to minimize mercury absorption and transference to the unborn or nursing child.

Much dental research has been done over the past twenty years in the area of dental amalgam and its effects upon human health. The medical scientific community is now in general agreement that patients with dental amalgam fillings are chronically exposed to mercury (a slight amount of mercury vapor is released from a filling during chewing, tooth grinding, etc.) and that the average daily absorption of mercury from dental amalgam is from 3 to 17 micrograms per day, which correlates to roughly 7-50% of the FDA’s acceptable daily intake (depending on body weight and other variables such as toothbrushing, number and size of fillings, clenching and grinding habits, gum chewing, etc.). To date, studies have shown no correlation between dental amalgam and birth defects or adverse health issues in patients with dental amalgam or in dental health care workers who are exposed to it on a daily basis. The FDI World Dental Federation, the world’s largest dental organization, released a policy paper which emphasized that there is no documented scientific evidence to show adverse effects from mercury in amalgam restorations except in extremely rare cases of mercury hypersensitivity. The American Dental Association’s Principle of Ethics and Code of Professional Conduct explicitly states: “removal of amalgam restorations from the non-allergic patient for the alleged purpose of removing toxic substances from the body, when such treatment is performed solely at the recommendation of the dentist, is improper and unethical.”

In the United States, amalgam is not regulated as a material by the FDA, but as a prosthetic device. Because of this classification, amalgam is not forced to undergo the same safety testing as is required for pharmaceutical products. In 2009, the FDA issued a ruling that reclassified mercury from a class I (least risk) device to class II (more risk) device. Because of this, a warning label must be enclosed in every package of dental amalgam that reads: “Dental amalgam has been demonstrated to be an effective restorative material that has benefits in terms of strength, marginal integrity, suitability for large occlusal surfaces, and durability. Dental amalgam also releases low levels of mercury vapor, a chemical that at high exposure levels is well-documented to cause neurological and renal adverse health effects.”

Amalgam removal to cure systemic disease

In the 1970s, a dentist by the name of Hal Huggins began advocating for the wholesale removal of amalgam fillings, claiming that mercury toxicity from them cause such illnesses as multiple sclerosis, Crohn’s disease, lupus, arthritis, leukemia, and many, many more. He subsequently lost his dental license for “‘deceptive yet seductive advertising” when conning his patients into replacing their amalgam fillings with other restorative materials, often at great cost to the patient. Since then, the anti-amalgam movement has gained strength and momentum, with entire organizations such as the International Academy of Oral Medicine and Toxicology (with their own journals and conferences) boasting thousands of members. Fortunately for the public, very few dentists are as zealous about removing amalgam fillings as Hal Huggins was, but there is a pervading belief among anti-amalgam dentists that mercury toxicity is a real and serious danger, and they are pushing for legislation to ban amalgam fillings. Dr. John Dodes authored an excellent review of the literature regarding the use of amalgam and the adverse health claims made by amalgam opponents and concluded that “(t)here are numerous logical and methodological errors in the anti-amalgam literature… (and) that the evidence supporting the safety of amalgam restorations is compelling.”

Informed consent in the use of dental amalgam

When choosing a dental material to use when restoring teeth, the dentist (in collaboration with his or her patient, and based upon the most current reliable scientific data) must identify which one will serve the patient best while reducing the probability of any untoward effects. Many factors come into play in this decision making process: the strength, durability, and longevity of the material, cost factors, cosmetic concerns, biological compatibility (i.e. low allergic or hypersensitivity potential), etc. In the case of dental amalgam, the following is accepted as being true: it is strong and durable, it is inexpensive when compared with other dental materials (gold, porcelain, composite), and it is not cosmetically appealing. In the area of health (although it has been shown to not cause medical problems) many patients have a concern in putting a known neurotoxin into their body, and this is a concern not to be taken lightly, especially in pregnant women and children.

When presenting options to a patient, the prudent dentist will objectively explain all risks and benefits, as well as costs, to the patient. Of course, the dentist can offer his or her professional opinion as to what the most favorable option would be, but ultimately the choice is the patient’s, and the dentist must respect this choice. For many, dental amalgam is an acceptable choice and an acceptable risk. For others, the choice and risks are unacceptable, and alternatives are then utilized. Children and women of childbearing age are of particular interest to the prudent dentist, as this subgroup (or the potential unborn child contained therein) is considered to have an increased risk of mercury toxicity if exposed. Further, what are the ramifications and ethical considerations of a mother consenting for her child (born or unborn)? Finally, the dentist must take into consideration the total environmental mercury intake of a person, not just that due to amalgam fillings. For example, if a person consumes a high quantity of fish and other mercury-rich foods, then even a “safe” level of dental amalgam could theoretically push the mercury burden to unsafe levels. Another dilemma in the decision-making process is the almost total absence of randomized controlled studies in this field; our only data come from less robust cohort studies. Even if these studies infer a minimal risk to the unborn or young child, the dentist may find it difficult to confidently assure the mother or father that placing dental amalgams in their child (or pregnant mother) is safe. If there are complications in childbirth, or if the child develops a neurological disorder, will the dentist be held liable?

Conclusion: Dental amalgams balance utility and safety

In the United States, Canada, and in many countries worldwide, citizens pride themselves on the qualities of autonomy, self-determination, self-direction, and freedom of choice, including those decisions involving health care. The regulatory agencies that govern amalgam use in North America (EPA, FDA, ADA, CDA, et.al.) make recommendations that are science based, using high quality research to evaluate the most current data on the safety of amalgam. Balancing the low risk of mercury exposure with the benefits to the general public of such a material is an on-going task, and one the various agencies revisit with regularity, making new recommendations and guidelines as the evidence warrants. To date, they have done an excellent job (in my opinion) with their recommendations, as retrospective studies are confirming their decisions as responsible and accurate; however the RCT “gold standard” studies remain forthcoming. For now, dental amalgam remains a safe and effective restorative material when indicated. If, in the future, studies definitively demonstrate harm being done, the new regulations and guidelines will change to reflect this. Evidence-based dentists will then change their protocols appropriately.

Note: Dental fillings do not actually contain plutonium.