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Mercury is one of the most poisonous metals we know of. It passes effortlessly through most of the body's barriers and once there, is almost impossible to remove.[1,2] Mercury affects the brain, damages the kidneys, inhibits the endocrine system, impairs immune functioning, destroys many types of cells upon contact, affects mood, and may cause autism and Alzheimer's.

A pressing question for dental workers of both genders is: Are dentists, dental assistants, and dental hygienists at a higher risk of mercury poisoning due to the preparation of dental amalgams in the workplace?

A Threat to the Central Nervous System

Elemental mercury vapor escaping from the dental amalgam poses a serious threat to the central nervous system. Elemental mercury is small and lipophilic, and is therefore easily absorbed by the lungs, enters the blood stream, and passes through the blood-brain barrier and binds to brain tissue.[3,4] One study confirms that even small amounts of elemental mercury is sufficient to precipitate symptoms:

"The central nervous system (CNS) is the critical target organ of elemental mercury
(Hg°), and evidence from studies of dental professionals suggests statistically significant exposure-effect associations between CNS-related declines and urinary Hg concentrations less than 4 ug/g creatinine."[5]

Mercury seems to accumulate in the brain even more than in the kidneys, whose job it is to collect toxins from the blood: "mercury levels originating from dental amalgam surfaces and retained in tissues are higher in brain regions and thyroid than those measured in renal cortex."[6]

Neurological disturbance and its symptoms

Because elemental mercury, inorganic mercury, and methylmercury all cause damage to the CNS, there is a long list of studies demonstrating the ways this damage manifests itself among patients with amalgams and the dental workers who install them.[7,8] One study found that people with amalgams showed a higher rate of symptoms such as mood disturbance, impaired motor function, and reduced cognitive ability. They discovered "convincing new evidence of adverse behavioral effects associated with low Hg0 exposures within the range of that received by the general population."[9]

But of course the risk is higher for dental staff. Depression, irritability, memory loss, reduced motor function and cognitive impairment are all frequently found among people with occupational mercury exposure, including dentists. Some even speculate that low-level mercury poisoning is the cause of the well-known high rate of suicide and mental disturbance among dentists.[10]

The EPA (which is much more forthcoming about the effects of mercury than the FDA), lists these symptoms associated with mercury exposure: "tremors; emotional changes (e.g., mood swings, irritability, nervousness, excessive shyness); insomnia; neuromuscular changes (such as weakness, muscle atrophy, twitching); headaches; disturbances in sensations; changes in nerve responses; performance deficits on tests of cognitive function. At higher exposures there may be kidney effects, respiratory failure and death."[11]

One study found high rates of polyneuropathies, visual impairment, and Carpal Tunnel Syndrome among dentists with chronic mercury exposure.[10,12] Another study found that long-term elemental mercury exposure is associated with CNS effects, "particularly memory loss, depression, and anxiety"[13]. Yet another study found that dentists scored worse in the categories of "short-term nonverbal recall and heightened distress generally, and particularly in categories of obsessive compulsion, anxiety and psychoticism"[14]. Dentists exposed to mercury also do worse in neurological and reflex tests such as finger tapping, hand steadiness, visual tracking, and so on.[9] In fact, a well-known study (even the EPA acknowledges it) found that in neurobehavioural tests the dentists' "performance decreased as the exposed dose (product of the TWA of air mercury concentrations and the years of exposure) increased"[15]

Kidney damage and more

The kidneys are heavily burdened by mercury in all its forms. Dental staff is at risk of developing kidney disease due to mercury poisoning. Dentists have been shown to be significantly more likely to have disorders of the kidney.[16,17] It's also known that dentists and dental assistants show reduced functioning of the thymus gland, which affects hormone levels.[18]

In addition, mercury cripples the immune system, by inducing apoptosis (cell death) in white blood cells. Mercury is also known to inhibit respiration bursts, which is an important method cells use for fighting harmful bacteria and foreign bodies.[19]

High mercury levels have also been correlated with autism and Alzheimer's.[20,21]

But this list could go on and on. Let's focus on the situation in the dental office.

Contamination in the dental office

Dentists, dental assistants, and dental hygienists are at a high risk of mercury poisoning not only when amalgams are prepared, but every time an amalgam is agitated. Whole offices are contaminated. Floors, the sides and folds of dental chairs often have high levels of mercury particulates that are easily ingested or inhaled. This study gives a failing grade to the majority of offices:

"One hundred and twenty two (67.8%) of the 180 surgeries visited had environmental mercury measurements in one or more areas above the Occupational Exposure Standard (OES) set by the Health and Safety Executive. In the majority of these surgeries the high levels of mercury were found at the skirting and around the base of the dental chair. In 45 surgeries (25%) the personal dosimetry measurement (ie in the breathing zone of dental staff) was above the OES."[17]

The TWA (Time Weighted Average) for mercury vapor is set to a legal maximum of 0.05 mg/m3 in the dental offices of the US. This is a measurement of how much mercury is in the air, averaged over a work day. One study concludes however, that as a legal limit of mercury exposure, it is far too generous: "The general philosophy now appears to be that these are very much limits: all efforts should be made to control the concentration within the working environment to at most one-quarter of these values."[21]

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REFERENCES - See our complete list of sources

1. Rowland AS, Baird DD, Weinberg CR, Shore DL, Shy CM, Wilcox AJ. The effect of occupational exposure to mercury vapour on the fertility of female dental assistants. Occup Environ Med. 1994 Jan; 51(1):28-34.

2. Clarkson TW. The three modern faces of mercury Environ Health Perspect. 2002 Feb;110 Suppl 1:11-23.

3. EPA Hazard Summary on Mercury:

4. Takahashi Y, Tsuruta S, Arimoto M, Tanaka H, Yoshida M. Placental transfer of mercury in pregnant rats which received dental amalgam restorations. Toxicology. 2003 Mar 14;185(1-2):23-33.

5. Echeverria D, Woods JS, Heyer NJ, Martin MD, Rohlman DS, Farin FM, Li T. The association between serotonin transporter gene promotor polymorphism (5-httlpr) and elemental mercury exposure on mood and behavior in humans. J Toxicol Environ Health A. 2010 January ; 73(15): 1003-1020.

6. Guzzi G, Pigatto PD. Urinary mercury levels in children with amalgam fillings. Environ Health Perspect. 2008 Jul;116(7):A286-A287.

7. Mutter J, Naumann J. Blood mercury levels and neurobehavior. JAMA. 2005 Aug 10;294(6):679; author reply 679-80.

8. Langworth S, Sällsten G, Barregård L, Cynkier I, Lind ML, Söderman E. Exposure to mercury vapor and impact on health in the dental profession in Sweden. J Dent Res. 1997 Jul;76(7):1397-404.

9. Echeverria D, Aposhian HV, Woods JS, Heyer NJ, Aposhian MM, Bittner AC Jr, Mahurin RK, Cianciola M. Neurobehavioral effects from exposure to dental amalgam Hg(o): new distinctions between recent exposure and Hg body burden. FASEB J. 1998 Aug;12(11):971-80.

10. Ship II, Shapiro IM. Preventing mercury poisoning in dental practice. J Mass Dent Soc. 1984 Spring;33(2):72-4, 80.

11. EPA on Health Effects of Mercury:

12. Shapiro IM, Cornblath DR, Sumner AJ, Uzzell B, Spitz LK, Ship II, Bloch P. Neurophysiological and neuropsychological function in mercury-exposed dentists. Lancet. 1982 May 22;1(8282):1147-50.

13. Heyer NJ, Echeverria D, Bittner AC Jr, Farin FM, Garabedian CC, Woods JS. Chronic Low-Level Mercury Exposure, BDNF Polymorphism, and Associations with Self-Reported Symptoms and Mood. Toxicological Sciences 81, 354-363 (2004). doi:10.1093/toxsci/kfh220

14. Uzzell BP, Oler J. Chronic low-level mercury exposure and neuropsychological functioning. J Clin Exp Neuropsychol. 1986 Oct;8(5):581-93.

15. Ngim CH, Foo SC, Boey KW, Jeyaratnam J. Chronic neurobehavioural effects of elemental mercury in dentists. Br J Ind Med. 1992 Nov;49(11):782-90.

16. Ritchie KA, Gilmour WH, Macdonald EB, et al. Health and neuropsychological functioning of dentists exposed to mercury. Occup Environ Med. 2002 May;59(5):287-93.

17. Ritchie KA, Burke FJ, Gilmour WH, Macdonald EB, et al. Mercury vapour levels in dental practices and body mercury levels of dentists and controls. Br Dent J. 2004 Nov 27;197(10):625-32; discussion 621.

18. Farahat SA, Rashed LA, Zawilla NH, Farouk SM. Effect of occupational exposure to elemental mercury in the amalgam on thymulin hormone production among dental staff. Toxicol Ind Health. 2009 Apr;25(3):159-67.

19. McCabe MJ Jr, Eckles KG, Langdon M, Clarkson TW, Whitekus MJ, Rosenspire AJ. Attenuation of CD95-induced apoptosis by inorganic mercury: caspase-3 is not a direct target of low levels of Hg2+ Toxicol Lett. 2005;155:161-170.

20. Geier DA, Kern JK, Geier MR. A prospective study of prenatal mercury exposure from maternal dental amalgams and autism severity. Acta Neurobiol Exp (Wars). 2009;69(2):189-97.

21. Gelbier S, Ingram J. Public Health. Possible foetotoxic effects of mercury vapour: a case report. 1989 Jan;103(1):35-40.