The future of dental amalgam: a review of the literature. Part 2: Mercury exposure in dental practice

This is the second article in a series of seven on the future of dental amalgam. It describes the means of exposure to mercury which can occur in dental surgeries from the storage of mercury, preparation and placement of dental amalgam restorations, polishing dental amalgam restorations, the removal of amalgam fillings and the storage of waste amalgam. It also reports on the monitoring of dental practices and studies on the mercury air levels in dental surgeries and blood and urine levels in dentists and their staff. Also, studies which compare these levels with the health and neurobehaviour of dentists and their staff are included. In addition, it discusses post-mortem studies of the mercury levels in body organs in dentists and controls. It then recommends methods for the safe handling of mercury and dental amalgam. Finally, it discusses the issues surrounding the release of mercury into the environment from dental practices and industry.     

Dental care using silver amalgam

Dental amalgam is the most widely used filling material in dentistry. In our country there are an estimated 40 million amalgam fillings in place. The mercury present in these fillings has caused health concerns over the last 160 years that amalgam has been used in decayed teeth. The fears have always proven to be unjustified and no harmful effects have ever been demonstrated in dental patients. Mercury can be found in several forms. In dentistry, only the metallic form is used, while inorganic and organic compounds are also present in the environment. The metallic form is absorbed in the human body mostly through the lungs. Once mercury reaches toxic levels inside the body, it will interfere with cell metabolism. Most important among the target organs are the brain, the liver and the kidneys. Elimination occur through urine and feces. Mercury is universally found in blood and urine. The concentration depends on absorption by air, water, nutrition, medication (including dental fillings) and occupational hazards. There are four kinds of objectives to dental amalgam: oral galvanism, toxicity, allergenicity and ecological grievances. Disorders from oral galvanism are difficult and delicate to evaluate as the actual currents are very small. Furthermore, no significant difference can be found in current intensity between patients with and without complaints. Finally patients with complaints often present other oral disorders, the treatment of which most often eliminates all complaints that could be attributed to oral galvanism. Toxicity is dose dependent. Industrial safety rules indicate that the amount of mercury absorbed from dental amalgam fillings is far below the safety level. HgB and HgU levels in patients with amalgam fillings are situated well below the acceptable levels. Allergic disorders are observed in patients with amalgam fillings but far less than expected in view of the wide spread use of dental amalgam. The problem of mercury spilling from dental amalgam fillings into the environment will be resolved by strict legislation in the near future. In this context, it can be stated that the use of dental amalgam is safe and justified. Furthermore, it is also advisable as no other material can meet the actual dental needs as efficiently as can dental amalgam.     

Mercury exposure from dental amalgam fillings: absorbed dose and the potential for adverse health effects

This review examines the question of whether adverse health effects are attributable to amalgam-derived mercury. The issue of absorbed dose of mercury from amalgam is addressed first. The use of intra-oral Hg vapor measurements to estimate daily uptake must take into account the differences between the collection volume and flow rate of the measuring instrument and the inspiratory volume and flow rate of air through the mouth during inhalation of a single breath. Failure to account for these differences will result in substantial overestimation of the absorbed dose. Other factors that must be considered when making estimates of Hg uptake from amalgam include the accurate measurement of baseline (unstimulated) mercury release rates and the greater stimulation of Hg release afforded by chewing gum relative to ordinary food. The measured levels of amalgam-derived mercury in brain, blood, and urine are shown to be consistent with low absorbed doses (1-3 micrograms/day). Published relationships between the number of amalgam surfaces and urine levels are used to estimate the number of amalgam surfaces that would be required to produce the 30 micrograms/g creatinine urine mercury level stated by WHO to be associated with the most subtle, pre-clinical effects in the most sensitive individuals. From 450 to 530 amalgam surfaces would be required to produce the 30 micrograms/g creatinine urine mercury level for people without any excessive gum-chewing habits. The potential for adverse health effects and for improvement in health following amalgam removal is also addressed. Finally, the issue of whether any material can ever be completely exonerated of claims of producing adverse health effects is considered.     

Psychologic factors in the etiology of amalgam illness

Eleven patients with amalgam illness aged 33-50 years were investigated by psychodynamic methods. Six of them, all women, were dental nurses and hygienists exposed to amalgam/mercury both from their own dental fillings and occupationally. Four men and one woman were exposed only to amalgam/mercury from their own fillings. Assays of mercury in urine samples and in the ambient air during work routines involving the heaviest exposure indicated that the exposure was far below the levels at which even subclinical symptoms could be indicated by psychometric tests. The psychologic investigation indicated that the symptoms of amalgam illness were psychosomatic. All patients had experienced important psychic traumata in close connection with the first appearance of symptoms. It can be concluded from the psychodynamic dialogues that they had not been able to mourn for a loss in an adequate manner and that the body had been forced to symbolize the great pain in their souls.     

The future of dental amalgam: a review of the literature. Part 1: Dental amalgam structure and corrosion

This is the first article in a series of seven on the future of dental amalgam. Dental amalgam is still the most useful restorative material for posterior teeth and has been used successfully for over 100 years. The history of dental amalgam since its introduction in 1819 and the controversies about its use between 1834 and today are described. The composition of the various dental amalgams in clinical use today are then reported. It finally covers the corrosion of amalgams since this is the means by which metals, including mercury, can be released.     

Acute exposure to mercury from amalgam: no short-time effect on the peripheral blood lymphocytes in healthy individuals

Mercury, released from dental amalgam, has been considered to adversely affect the human immune system. This study has been performed in order to evaluate if an acute low-dose mercury exposure, achieved by total amalgam removal in 10 healthy individuals, would affect the immunocompetent cells in human blood when the mercury level in blood and plasma was increasing. Induction of lymphocyte proliferation, measured as spontaneous de novo DNA synthesis, and total T cells, CD4+ T cells, CD8+ T cells, and B cells, was studied prior to and 7, 31, and 48 h after amalgam removal. In addition, the levels of interleukin-6 (IL-6) and C-reactive protein (CRP) in serum/plasma were measured. Despite a significant increase of the plasma mercury levels within 24 h after intervention, no significant influence on the peripheral blood lymphocytes could be detected during the first 48 h. The serum IL-6 levels increased significantly within 48 h after intervention, but were still low and within normal range. No influence on the CRP levels up to 7 d after amalgam removal was detected.     

Mercury and dental amalgam fillings

During 1993-95 a total of 169 patients (112 women, 57 men) with a wide range of complaints associated with earlier or present amalgam fillings were seen by the "Dental Biomaterials Adverse Reaction Unit" in Norway. Most patients had amalgam fillings; 19 had removed all amalgam, and 14 were in the process of replacing the amalgam fillings with other materials. Predominant symptoms were of a subjective and general nature (96% of the patients). Muscle and joint pain, headache, dizziness and feeling exhausted comprised the most common symptoms. Intra-oral pathology was observed in 48%. There was a correlation between the amount of amalgam ("amalgam score") and urinary mercury. Those without amalgam fillings and significantly lower values (median = 1.6 micrograms mercury/g creatinine) than those with amalgam fillings (medians: with amalgam = 3.5 micrograms/g; with partial removal of amalgam = 2.7 micrograms/g). Overall, in the present group of patients, no statistically significant correlation seemed to exist between the type and number of subjective symptoms or objective findings and the urinary mercury. This would indicate therefore that there is no straightforward association between urinary mercury and symptoms in the present group of patients.     

Equilibrium vapour pressure of mercury from dental amalgam under loading conditions

Earlier studies have failed to establish a consensus on the amount of mercury vapour released from dental amalgam restorations. The purpose of this study was to accurately and quantitatively measure the equilibrium mercury vapour pressure from dental amalgam. The vapour pressure was measured using a quartz crystal microbalance as a function of the load from 0-5.4 MPa. Auger spectra were collected of the as-formed and argon ion sputter cleaned dental amalgam surface. For the as-formed surface the mercury vapour density is zero with no load and increases to 0.6 microg m(-3) at 5.4 M Pa. Following cleaning the mercury, vapour density increased to a maximum value of 15 microg m(-3). The Auger spectra of the as-formed surfaces were dominated by features associated with carbon and oxygen. These spectral results in concert with the mercury vapour density measurements indicate that the oxide film on the as-formed surfaces inhibited the release of mercury vapour. The results of this experiment provide an upper limit for the amount of mercury vapour released by dental amalgams. Under conditions simulating the oral cavity this value would be reduced by oxides that form on the surface of dental amalgam restorations.     

Amalgam tooth fillings and man's mercury burden

Next to nutrition, amalgam fillings represent the main source for exposure of the general population to mercury. Toxicological considerations focus on the dose of mercury resulting from such exposure. Various approaches to estimate this dose are reviewed. Introducing the dose into the known toxicokinetic model for mercury, tissue and blood and urine concentrations related to mercury release from the fillings can be predicted. These agree well with autopsy and in vivo observations. An assessment of the health hazard for individuals with amalgam fillings shows that the combined mercury intake from food and amalgam does not exceed the acceptable daily intake. In addition, blood and urine mercury concentrations of amalgam bearers are below one tenth of the critical values associated with the onset of early symptoms or of subclinical effects attributable to mercury.     

Mercury content in amalgam tattoos of human oral mucosa and its relation to local tissue reactions

Mucosal biopsies from 48 patients with and 9 without amalgam tattoos were analysed with respect to their mercury content, distribution of mercury in the tissue, and histological tissue reactions. The distribution of mercury was assessed by autometallography (AMG), a silver amplification technique. The mercury content was determined by energy dispersive X-ray fluorescence (EDXRF), a multielemental analysis. Mercury was observed in connective tissue where it was confined to fibroblasts and macrophages, in vessel walls and in structures with the histological character of nerve fibres. A correlation was found between the histopathological tissue reaction, the type of mercury deposition, the intensity of the AMG reaction, and the mercury content. Mercury was also found in patients with amalgam dental fillings but without amalgam tattoos.     

Effect of acute ethanol ingestion on prolactin in menopausal women using estradiol replacement

The current study was to answer the question: Is enough mercury absorbed from dental amalgam fillings to produce renal damage? One hundred healthy adults (18-44 years old) filled out health questionnaires and voided urine samples. Urine mercury concentration and N-acetyl-beta-glucosaminidase (NAG) were measured. Subjects were grouped into those having amalgam fillings (N = 66) and those without (N = 34). Median (95% Confidence Interval) urine mercury was 1 (1-2) and 0 (0-0.6) ng/ml (P < 0.01) and median urine NAG was 23 (18-27) and 16 (11-18) units (P < 0.05) in the two groups respectively. People with mercury amalgam fillings excreted slightly more mercury than people without them, and have a very small increase in urinary NAG excretion that is probably of no clinical significance. This dose of mercury absorbed from amalgam appears to be too little to be a public health hazard for renal injury.     

Risk estimation of mercury intake from different sources

Biological monitoring of mercury (Hg) in blood, urine and hair was performed in volunteers with amalgam fillings, in subjects who consumed fish and in Hg-exposed workers. It was found that both amalgam fillings and the consumption of fish burden the organism with Hg in the same order of magnitude. The Hg concentrations in urine in the occupationally exposed group were higher by a factor of about 100 compared to the group with amalgam fillings. No pathological changes were found in the exposed workers. It seems safe to conclude that no health-related problems from Hg are to be expected from amalgam fillings.     

Surface chemistry of a high-copper dental amalgam

In amalgam, mercury is intended to take the form of stable intermetallic compounds. Any mercury leakage must therefore come from free mercury not involved in such compounds. Thus, a knowledge of the exact surface chemistry of dental amalgam is necessary if this phenomenon is to be understood. From XPS and EDS analyses, a model of the surface chemistry of amalgam is proposed which fully characterizes all the phases that are present. The data show the surface to have a composition different from that of the bulk, being comprised of a hydrocarbon deposit and adsorbed water covering the intermetallic phase gamma2 (Sn(6-8)Hg), tin (iv) oxide, and mercury in a free state. After amalgamation, the amount of mercury at the surface decreases with time and eventually attains a constant concentration, where it is all involved in the gamma2 phase, leaving no free mercury. A model is proposed for the surface of amalgam and the changes in this model with time.     

Effect of topical timolol on tissue circulation in optic nerve head

OBJECTIVE: The aim of the present study was to determine whether removal of all amalgam restorations might significantly affect mercury levels in plasma and urine and whether the use of rubber dams might reduce patient exposure to mercury during amalgam removal. METHODS: All amalgam restorations were removed from 18 subjects during a single treatment session in which a rubber dam was used and from 10 subjects when a rubber dam was not used. All amalgam restorations were removed by the same dentist using high-speed cutting, water coolant, and high-volume evacuation. The levels of mercury in plasma and urine were analyzed both before and during the subsequent twelve months after amalgam removal. In order to determine whether removal of all amalgam restorations might cause an exposure large enough to significantly increase the mercury levels in two indicator media for mercury exposure, i.e., plasma and urine, and to determine if the removal might cause a significant decrease in the mercury levels found over time, the one-tailed, paired Students' t-test was used. For each individual, the pre-removal levels were compared with both the levels found in plasma on d 1 and in urine on d 10, and also with the levels found 1 y after removal. Furthermore, in order to examine whether the use of rubber dams had any effect on the mercury levels found after removal, the changes in the mercury levels found were compared between the groups using the Wilcoxon-Mann-Whitney rank sum test. RESULTS: After removal of all amalgam restorations, only the non-rubber dam group showed significant increases in the mercury levels found in plasma (p = 0.012) and urine (p = 0.037). However, one year later, the mercury levels in plasma and urine had sunk significantly below the pre-removal levels for both groups. When the changes in the mercury levels found were compared between the groups, the non-rubber dam group showed a significantly higher increase of mercury in plasma than the rubber dam group the day after removal (p = 0.0010). Compared to the pre-removal mercury levels in plasma and urine, the levels found 1 y after removal of all amalgam restorations were on average 52 +/- 23% (range 4-89%) lower in plasma and 76 +/- 21% (range 20-94%) lower in urine. SIGNIFICANCE: The study showed that dental amalgam had a statistically significant impact on the mercury levels found in plasma and urine in the patients tested, and that the use of a rubber dam during removal of all amalgam restorations significantly reduced the peak of mercury in plasma following removal.     

Occupational exposure to mercury in dentistry and dentist mortality

In response to public concern, Health Canada recently conducted a review of amalgam safety and released a position statement entitled The Safety of Dental Amalgam. Essentially, the department has concluded that the levels of mercury absorbed by the body due to the release of mercury vapor from amalgam restorations, while detectable, do not approach those recognized to cause illness. It has therefore confirmed that amalgam restorations can be used safely in most patients, with some notable caveats. Despite Health Canada's position statement in support of amalgam, patient doubts about amalgam safety remain, including the tenuous hypothesized link between amalgam restorations and specific diseases. This article reviews the available studies of dentist mortality to identify possible links between mercury exposure and negative health effects. A lack of evidence to suggest a detrimental health outcome in dentists who are occupationally exposed to higher levels of mercury than their patients, and are known to have higher levels of mercury in their blood, provides an important reassurance concerning the safety of amalgam. The reviewed data indicates that the 10 leading causes of death in the United States and Canada are the same for both dentist and non dentist population groups, and that the percentage of deaths by the same cause are remarkably similar. By 1975, the year of the most recent U.S. study, the average age at death for white male dentists was about three years higher than for all adult white males. Although suicide standard mortality rates are known to be higher for dentists, suicide deaths have also been shown to be a factor in many other occupations, particularly those where there is easy access to drugs. Although updated actuarial data for dentist mortality are needed, the available data indicate no reduction in the life expectancy of practising dentists, nor any specific or disproportionate rates of disease associated with high mercury exposure. In fact, the available mortality studies are generally optimistic about the health of dentists, which should reassure patients about the safety of dental amalgam.     

Use of a fluorescent method for detection of lymphocyte Fc-receptors]

Studies in both the human and ovine near-term fetus have identified the clustering of physiologic and behavioral parameters into states. In a recent study in the human fetus a considerable decrease was found in fetal urine production during non-rapid eye movement (non-REM) compared with REM sleep. Whether this decrease was caused by decreased renal blood flow or changes in urine concentration is not known. This prompted us to investigate the relation between fetal urine production rate and electrocortical activity in the near-term ovine fetus. We hypothesized that in the ovine fetus urine production and renal blood flow during REM [comparable to low voltage electrocortical activity (LV ECoG)] would be lower than during non-REM [(high voltage (HV) ECoG)]. In eight fetal sheep between 123 and 127 d of gestation (term 147 d), ECoG, renal blood flow, urine flow, and urine osmolality were measured continuously for 6 h on 2 consecutive days. Data were analyzed into HV ECoG and LV ECoG whereafter urine flow, urine osmolality, and renal blood flow data were averaged per state. We found no significant differences in urine flow, urine osmolality, or renal blood flow between the two behavioral states in the ovine fetus. Because these data are in sharp contrast to those found in the human fetus, we conclude that the observed dissimilarities in renal responses between the human and sheep fetus add to the already known differences in behavioral states between the two species.     

Mercury release from amalgam into saliva. An in-vitro study

The aim of the study was to investigate mercury release into salivary fluid and to test whether this release is associated with flow rate, buffer capacity or pH of salivary fluid. Salivary fluid was collected from 18 persons (11 with amalgam fillings, 7 without) and the surface area of the fillings was assessed. Mercury loss in unstimulated saliva was 11.6 ng/min for persons with amalgam and 2.1 ng/min for those without. Multiple regression analysis revealed no association between flow rate, buffer capacity or pH of unstimulated salivary fluid and mercury release.     

Neurobehavioral effects from exposure to dental amalgam Hg(o): new distinctions between recent exposure and Hg body burden

Potential toxicity from exposure to mercury vapor (Hg(o)) from dental amalgam fillings is the subject of current public health debate in many countries. We evaluated potential central nervous system (CNS) toxicity associated with handling Hg-containing amalgam materials among dental personnel with very low levels of Hg(o) exposure (i.e., urinary Hg <4 microg/l), applying a neurobehavioral test battery to evaluate CNS functions in relation to both recent exposure and Hg body burden. New distinctions between subtle preclinical effects on symptoms, mood, motor function, and cognition were found associated with Hg body burden as compared with those associated with recent exposure. The pattern of results, comparable to findings previously reported among subjects with urinary Hg >50 microg/l, presents convincing new evidence of adverse behavioral effects associated with low Hg(o) exposures within the range of that received by the general population.     

Negative association between reported life events and cardiovascular disease risk factors in employed men: the CORDIS Study. Cardiovascular Occupational Risk Factors Determination in Israel

This article reviews the literature data concerning the immunologic monitoring of animals and cell cultures exposed to mercury compounds. Mercury is present in nature as metallic mercury, mono- and bivalent inorganic compounds, and organic alkyl, aryl and alloxy-alkyl compounds. Methylmercury is most important in terms of environmental exposure while metallic mercury is the most common form to which workers are exposed. The database on immune function disturbances in human induced by mercury compounds is limited. Immunotoxicity assessment in animals, mainly in rodents, with subsequent extrapolation to man, is the basis of human risk assessment. The strength of in vitro immunotoxicity testing lies in studies aimed at unravelling mechanisms of immunotoxicity. These experimental investigations show clearly that mercury compounds can have immunomodulating activity. Mercuric chloride and methylmercury inhibit most of animal and human lymphocyte functions including proliferation, expression of cell activation markers on cell surface and cytokine production. These cells exhibit a greater sensitivity to the immunotoxic effects of methylmercury than to mercuric chloride. Repeated administration of mercuric chloride to rats, mice and rabbits can induce autoimmune response and a membranous nephropathy. In contrast, Lewis rats injected with mercuric chloride do not develop autoimmunity but exhibit immunosuppression. The immunosuppressive effects associated with exposure to chemical substances are often accompanied by increased susceptibility to challenge with infectious agents or tumour cells. Only few reports are available on animal studies of increased mortality connected with exposure to mercury compounds and challenge with infectious agents. It is difficult to establish a relationship between the observed immunomodulatory properties of mercury compounds and their possible carcinogenicity. In fact, the epidemiological studies performed so far failed to bring any conclusive evidence of carcinogenicity of mercury in animal experiments. The induction of renal tumours in male rodents by methylmercury was observed only.     

Helping patients to die--an ethical challenge to nursing care and to its institutional framework]

The objective of this study was to determine fluid-electrolyte changes in male Wistar rats during 90 days of hypokinesia (decreased motor activity) and 15 days posthypokinesia. The animals were divided into two groups: rats subjected to hypokinesia served as experimental animals and rats placed under vivarium conditions served as control animals. The hypokinetic effect was carried out by keeping the experimental rats in small individual cages which restricted all their movements without hindering food and water intake. Determination was made of body weight, fluid consumed and eliminated in urine, sodium and potassium excretion in urine, concentrations of sodium and potassium in urine, the hematocrit level and water content in blood, and plasma concentration of sodium and potassium. During the experimental period body weight, water intake, urinary sodium and potassium content, and water content in blood decreased significantly, while electrolyte excretion in urine, plasma electrolyte concentration, hematocrit content and fluid excretion in urine increased significantly in the hypokinetic animals when compared with the control animals. During the initial seven days of the postexperimental period, water intake increased significantly while hematocrit level, water content in blood, and electrolyte plasma concentration remained markedly higher, and the fluid electrolyte excretion and electrolyte concentration thereof in urine decreased significantly. However, all these changes reverted back to the control level by the end of the post-experimental period. It was concluded that prolonged hypokinesia (HK) and the initial stages of post hypokinesia are associated with significant sodium and potassium changes and water consumption and elimination disturbances.