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Oral Health Research Restorative Dentistry

What is a safe level of mercury due to dental amalgam? A Canadian descriptive study

This summary is based on the study published in the BMC Oral Health journal: Dental amalgam and urinary mercury concentrations: a descriptive study

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  • Alexandra Nicolae, Community Dental Health Services Research Unit at the University of Toronto
  • Carlos Quiñonez, Community Dental Health Services Research Unit at the University of Toronto
  • Harry Ames, Alberta Dental Association and College


Dental amalgam is a source of elemental and inorganic mercury. The safety of dental amalgam in individuals remains a controversial issue. Urinary mercury concentrations are used to assess chronic exposure to elemental mercury. At present, there are no indications of mercury-associated adverse effects at levels below 5 μg Hg/g creatinine (Cr) or 7 μg Hg/L (urine). The purpose of the present study is to determine the overall urinary mercury level in the Canadian general population in relation to the number of dental amalgam surfaces.

Key Messages

  • The mean urinary mercury concentrations in the general Canadian population are significantly lower than the values considered to pose any risks for health.
  • In Canada, the mumc in people with or without dental amalgam restorations are well below the levels associated with any health risks.
  • In general, the mumcs tend to increase with the number of amalgam surfaces, and appear to be influenced by age and sex.
  • For the same exposure level, organic mercury from food results in an absorption approximately six times greater than the absorption of inorganic mercury from dental amalgam restorations.


Do you have any particular question on this topic? Do you have any comments or suggestions? Email us at oasisdiscussions@cda-adc.ca

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  1. Euan Swan September 20, 2013

    Will the results of this study change your recommendations concerning the choice of restorative material?

  2. Catherine Zacal September 24, 2013

    Has anyone seen the smoking tooth video posted by the IAOMT? I have often wondered how this video of a tooth filled with amalgam supposedly shows a plume of offgassing mercury (?) came to be. Just putting it out there to try to find out how they made this video as it seems quite disturbing. I don’t place amalgams only because I studied in europe and they banned them in Pregnant women and children. Otherwise I am not against amalgams for service and strength but I favour composite for bondability, conservativenessa and perceived cohesion of the tooth, working best in my hands. The debate will be everlasting, I guess it is how and why a dentist chooses a material and then would have to use these reasons to defend the choice, is what it all comes down to.

    1. Catherine Zacal September 24, 2013

      By the way, I am not an IAOMT member just had some exposure to what this group is about. I do not support this group.

      1. David Kennedy, DDS September 25, 2013

        Our Mission

        The fundamental mission of the International Academy of Oral Medicine and Toxicology is to promote the health of the public at large.

        Essentially, the Academy shall continually examine and compile scientific research relating to the biocompatibility of oral/dental materials. This agenda should ensure a more informed use of these materials in clinical practice. Within these confines, the Academy shall:
        Dear Catherine,

        Can you please identify which of our goals you found objectionable and why?

        Accumulate and disseminate SCIENTIFIC INFORMATION;
        Promote FUNDING for relevant research;
        Promote EDUCATION of the public, professional organizations, and other groups, by providing SCIENTIFIC INFORMATION;
        Provide ADVISORY SERVICES if/when required.
        – See more at: http://iaomt.org/about-us/iaomt-history-mission/#sthash.esjIt4h9.dpuf

    2. David Kennedy, DDS September 25, 2013

      Dear Catherine,

      Good to hear that you do not place new mercury/silver fillings especially considering that AII manufacturers warn about us in vulnerable subsets.

      I am the producer/director of Smoking Teeth you referred to. Did you watch the Cliff’s Notes version (8 min) or the full length 30 min? This demonstration by Dr. Roger Eichman was filmed by myself in the library during the IAOMT Scientific session at Oxford England in 2000. The demonstration is very simple and has been done by many using a clear fluorescent light and some kind of reflective background. If you should do this simple demonstration absolutely do not look directly at the 253.7 angstrom light as it can harm your retina.

      Some have questioned the veracity of such a video to which the IAOMT Science Advisory Board prepared a detailed response citing the various laws that are involved and the principles of atomic absorption. I can email that analysis if you desire. Just comment my channel (davidkennedydds) on YouTube and I’ll send it along.

      sadly this was not the first time mercury was measured in substantial quantities coming of “set” mercury/silver dental fillings. The first time I recall was in 1926 when Alfred Stock measured 10 micrograms in his own exhaled breath. At that time the mercury advocates called Dr. Stock bad names and impugned his integrity. This thrash the messenger continued up until 1984 when the NIDR finally acknowledged that mercury is released from set mercury/silver fillings.

      Much has changed since those early days in large part due to the efforts of the IAOMT to bring well designed scientific experiments into the published peer reviewed medical literature. Our early experiments confirmed exposure, intake and increased body burden of mercury in amalgam bearers. In a perfect world nothing more is really needed since there is no “safe” level of exposure to mercury and especially as you noted in vulnerable subsets.

      Next we did a tracer study in sheep to find the distribution of mercury in an animal approximately the same size as a human who chews vigorously. The mercury exited the fillings and in just 30 days had saturated the jawbone and distributed widely throughout the animals body but especially in kidneys and heart. The next study looked at kidney function in sheep and found a dramatic decline in just 60 days. Our follow up study in wild caught monkeys fed a soft diet found the same distribution pattern as sheep and humans and the team of microbiologists found antibiotic resistant bacteria appeared in gut flora in 6 weeks and remained there throughout the remainder of the experiment. Dr. Ann Summers headed that team and her work continues to this day. During the 2010 FDA hearings she reported that the stool of the monkeys had 1 PPM methyl mercury from mercury fillings. While the article alludes to the speculation that certain kinds of mercury are more dangerous than others I see no mention of the fact that bioconversion is well know to occur both in the body and in the environment. It makes absolutely no sense whatsoever to secretly implant a time-release mercury filling in unsuspecting public while deceptively calling them silver.

      Lastly since I suspect you have not kept up with the current Occupational health and safety Information I wish to inform you that is is unlawful for employer to expose employees to any mercury (including removal or polishing old fillings) unless they follow strict and enforceable with criminal penalties the existing regulations summarized below.
      The US Occupational Safety and Health Act (OSHA) requires that:

      When it is reasonable to assume that exposure [to mercury vapor] is likely the employer shall:

      1. Provide employee with informed consent (1987 Right to Know Act)

      2. Provide training in protection and how to avoid exposure.

      3. Provide protective equipment which for mercury includes:

      a. Airway protection

      b. Full skin covering

      e. Eye protection

      4. Institute work practices to minimize release

      5. Engage engineering controls to minimize worker exposure

      6. Monitor both the workplace and employee for mercury

      7. Record steps 1 through 6 in the Hazard Communication Workbook available for unannounced inspection at any time and retained for a minimum of 30 years after each incident of emission.

      If you did not know this the reason falls directly upon the trade association that “accredited” your educational institution. They are stuck in denial and refuse to address the copious amounts of scientific evidence that use of this antiquated filling material has and is causing irreparable harm both to clients and staff.

      I urge you to join with the IAOMT and call for an immediate ban on all future use of mercury in dentistry and also insist on complete OSHA compliance during any removal procedure and protect the patients and staff as well as yourself from mercury.

  3. Peter Olejarz September 26, 2013

    In June of 2012 I needed to replace my old 36MOD amalgam due to fracture. Just prior to that, one of my colleagues purchased a Jerome 405 portable mercury vapor analyzer. My mouth has more than 10 amalgams at this time. Upon arrival to the clinic we took 3 measurement of the mercury levels in my mouth. I must mention that I ceased chewing gum approximately 30 minutes prior to the measurements. The measurements ranged from 15 to 24 micrograms of mercury per cubic meter. Safe levels are quoted at 0.3 micrograms per cubic meter. When the procedure ended i.e. my colleague placed the composite, more than 2 hours later (we filmed the procedure and took photographs, therefore the length), 3 more measurements were taken. They ranged from 5 to 8 micrograms of mercury per cubic meter (I was not chewing during that time and the amalgams were cooler, therefore less mercury emission). Still, the levels were much higher than the safe levels of 0.3 micrograms. Makes me wonder who is right.

    1. David Kennedy, DDS September 27, 2013

      Dear Peter,

      Your findings are consistent with the peer reviewed literature. This was actually where the experiments of the IAOMt started back in 1985. Dr. Murray Vimy teamed up with Professor Fritz Lorscheider of the Calgary Canada medical school to bring peer reviewed evidence into the never ending amalgam debate.

      In making serial measurements he demonstrated that baseline prior to chewing was approximately 5 µg/m3 or about what you found in your mouth. However it is important to note that this can vary considerably depending on the kind of mercury/silver fillings you have and how hard the occlude with the4 opposing teeth.

      Vimy MJ, Lorscheider FL: Serial measurements of intra-oral air mercury; Estimation of daily dose from dental amalgam. J Dent Res 64(8):1072-5, 1985.
      Summary: For this study, serial measurements of Hg concentration in intra-oral air were made during and after chewing stimulation in 35 subjects with occlusal amalgam restorations. Hg concentrations remained elevated during 30 min of continuous chewing and declined slowly over 90 min after cessation of chewing. All subjects received an average daily Hg dose of approximately 20 μg. Dental amalgam Hg makes a major contribution to total daily dose.

  4. Dr. Nestor Shapka DDS September 27, 2013

    I have always found it disturbing that according to Health Canada, a true and unbiased authority on health standards, the maximum acceptable concentration (MAC) for mercury in drinking water is set at only 1 microgram of mercury per liter of water and that any concentration higher than that makes the water unfit for human consumption, and yet dentists and or researchers want us to think/believe that a level of mercury 7 times greater than that amount when present in our bodily fluids is somehow healthy and or safe condition for us. ?????

    The same ????? is true for the Health Canada standards for other mercury containing products. For example, if we look at the product paint, it is considered toxic to be exposed to paint that has more than 0.000005 grams of mercury in it per gram of paint, and yet when we compare this to a mercury amalgam filling, something that is unfortunately “intentionally” meant to be in your mouth, forever, at an astounding 50% mercury by weight, it is “not” considered toxic. Who dreamt this one up?

    Anyone who allows their child to play with a toy that is painted with mercury containing paints therefore, is a negligent care-giver, heaven forbid should their child place that toy in their mouth, but that same parent is considered competent when they allow a dentist to place a 50% mercury containing filling, or worse yet, fillings, in that same child’s mouth. Real intelligent aren’t we.

    It all starts with what conversations that we allow, and as these researchers start their conversation saying that mercury at concentrations of 7 micrograms of mercury per liter in urine – simply because it is what is now found to exist in the average Canadian population at that level – that this is “somehow normal” and or that this also gives them the right to equate or interchange this new normal with the words healthy and or safe. This is not a reflection of any truth, other than the truth that our society has become so toxic, and so complacent on the subject of toxicity, that we start to think that possessing dangerous amounts of mercury and or toxins in our bodies is now “normal” and that they can then publish studies and research papers to justify this argument.

  5. Reza Nouri October 14, 2013

    Are we all open-minded enough to consider the toxicity of the alternative direct restorative material, i.e. resin composite, and discuss it with the same scrutiny and detail?

  6. Michael Doser November 4, 2013

    To the authors,

    Before you proceed with the study, could you please go into detailed research on toxicology of mercury? Because if you will, you will find that urine mercury measure are not a good estimate of potential mercury body burden from amalgams. A lot of people do not excrete mercury as well as others, therefore Hg not showing up in urine in greater levels in greater amalgam surface bearers does not speak of amalgam safety. If anything, it speaks to the contrary because it means Hg is being trapped in tissues instead of excreted.

    Please research the following:


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