Determination of the rate of release of intra-oral mercury vapor from amalgam

Shedding Novel Photophysical Insights Toward Discriminative Detection of Three Toxic Heavy Metal Ions and a hazard class 1 nitro-explosive By Using a Simple AIEE Active Luminogen

In this work, we introduced a simple aggregation-induced emission enhancement (AIEE) sensor (PHCS) which can selectively detect and discriminate three environmentally and biologically imperative heavy metal ions (Cu2+, Co2+ and Hg2+) and a hazard class 1 categorized nitro-explosive picric acid (PA) in differential media. By virtue of its weak fluorescence attributes in pure organic medium owing to the synergistic operation of multiple photophysical quenching mechanisms, the molecular probe showcased highly selective 'TURN ON' fluorogenic response towards hazardous Hg2+ with a limit of detection (LOD) as low as 97 nM. Comprehensive investigation of binding mechanism throws light on the cumulative effect of probe-metal complexation induced chelation enhanced fluorescence (CHEF) effect and subsequent AIEE activation within the formed probe-metal adducts. Noteworthily, the probe (PHCS) can be readily used in real water samples for the quantitative determination of Hg2+ in a wide concentration range. In addition, the probe displayed modest colorimetric recognition performances to selectively detect and discriminate two essential heavy metal ions (Cu2+ and Co2+) with a LOD of 96 nM and 65 nM for Cu2+ and Co2+ respectively, in semi-aqueous medium. Intriguingly, based on high photoluminescence efficiency, the AIEE active nano-aggregated PHCS displayed a remarkable propensity to be used as a selective and ultra-sensitive 'TURN-OFF' fluorogenic chemosensor towards PA with LOD of 34.4 ppb in aqueous medium. Finally, we specifically shed light on the interaction of PHCS hydrosol towards PA using some unprecedented techniques, which helped uncover new photophysical insights of probe-explosive molecule interaction.

100 years of high GEM concentration in the Central Italian Herbarium and Tropical Herbarium Studies Centre (Florence, Italy)

Up to 1980s, the most used preservative for herbaria specimens was HgCl₂, sublimating at ambient air conditions; ionic Hg then reduces to Hg⁰ (gaseous elemental mercury, GEM) and diffuses throughout poor ventilated environments. High GEM levels may indeed persist for decades, representing a health hazard. In this study, we present new GEM data from the Central Italian Herbarium and Tropical Herbarium Studies Centre of the University of Florence (Italy). These herbaria host one of the largest collection of plants in the world. Here, HgCl₂ was documented as plant preservative up to the 1920s. GEM surveys were conducted in July 2013 and July and December 2017, to account for temporal and seasonal variations. Herbaria show GEM concentrations well above those of external locations, with peak levels within specimen storage cabinets, exceeding 50,000 ng/m³. GEM concentrations up to ~7800 ng/m³ were observed where the most ancient collections are stored and no ventilation systems were active. On the contrary, lower GEM concentrations were observed at the first floor. Here, lower and more homogeneously distributed GEM concentrations were measured in 2017 than in 2013 since the air-conditioning system was updated in early 2017. GEM concentrations were similar to other herbaria worldwide and lower than Italian permissible exposure limit of 20,000 ng/m³ (8-hr working day). Our results indicate that after a century from the latest HgCl₂ treatment GEM concentrations are still high, i.e., the treatment itself is almost irreversible. Air conditioning and renewing is probably the less expensive and more effective method for GEM lowering.

Gaseous Elemental Mercury and Total and Leached Mercury in Building Materials from the Former Hg-Mining Area of Abbadia San Salvatore (Central Italy)

Mercury has a strong environmental impact since both its organic and inorganic forms are toxic, and it represents a pollutant of global concern. Liquid Hg is highly volatile and can be released during natural and anthropogenic processes in the hydrosphere, biosphere and atmosphere. In this study, the distribution of Gaseous Elemental Mercury (GEM) and the total and leached mercury concentrations on paint, plaster, roof tiles, concrete, metals, dust and wood structures were determined in the main buildings and structures of the former Hg-mining area of Abbadia San Salvatore (Siena, Central Italy). The mining complex (divided into seven units) covers a surface of about 65 ha and contains mining structures and managers' and workers' buildings. Nine surveys of GEM measurements were carried out from July 2011 to August 2015 for the buildings and structures located in Units 2, 3 and 6, the latter being the area where liquid mercury was produced. Measurements were also performed in February, April, July, September and December 2016 in the edifices and mining structures of Unit 6. GEM concentrations showed a strong variability in time and space mostly depending on ambient temperature and the operational activities that were carried out in each building. The Unit 2 surveys carried out in the hotter period (from June to September) showed GEM concentrations up to 27,500 ng·m-3, while in Unit 6, they were on average much higher, and occasionally, they saturated the GEM measurement device (>50,000 ng·m-3). Concentrations of total (in mg·kg-1) and leached (in μg·L-1) mercury measured in different building materials (up to 46,580 mg·kg-1 and 4470 mg·L-1, respectively) were highly variable, being related to the edifice or mining structure from which they were collected. The results obtained in this study are of relevant interest for operational cleanings to be carried out during reclamation activities.

Long term changes in health complaints after removal of amalgam restorations

OBJECTIVE

Concerns over adverse effects of mercury released from dental amalgam sometimes lead patients to request removal of their amalgam restorations. Several studies report improvement of subjective health after removal of amalgam restorations, but the mechanisms are unclear. The aim of this paper is to present data on long term changes in intensity of health complaints after amalgam removal in a group of patients with health complaints self-attributed to dental amalgam. Data from the five years follow-up in a clinical trial are presented and related to potential determinants of change.

MATERIALS AND METHODS

Patients previously referred to a specialty unit for health complaints attributed to amalgam restorations were included in the study. The 20 participants who were allocated to the treatment group had all amalgam restorations removed and replaced with other dental restorative materials. Intensity of health complaints was calculated from questionnaire data and personality variables were measured by MMPI-2.

RESULTS

At the follow-up five years after the amalgam removal was completed, intensity of general health complaints was significantly reduced (p=.001), but the symptom load was still high. The reduction was significantly correlated with concentration of mercury in urine at pre-treatment. There were no significant correlations with personality variables.

CONCLUSIONS

Removal of amalgam restorations was followed by a long term reduction of general health complaints, which was associated with mercury concentration in urine before amalgam removal. Additional studies are needed to confirm the potential mechanisms for the observed reduction.

Mercury toxicity and treatment: a review of the literature

Mercury is a toxic heavy metal which is widely dispersed in nature. Most human exposure results from fish consumption or dental amalgam. Mercury occurs in several chemical forms, with complex pharmacokinetics. Mercury is capable of inducing a wide range of clinical presentations. Diagnosis of mercury toxicity can be challenging but can be obtained with reasonable reliability. Effective therapies for clinical toxicity have been described.

Mercury exposure and risks from dental amalgam in the US population, post-2000

Dental amalgam is 50% metallic mercury (Hg) by weight and Hg vapour continuously evolves from in-place dental amalgam, causing increased Hg content with increasing amalgam load in urine, faeces, exhaled breath, saliva, blood, and various organs and tissues including the kidney, pituitary gland, liver, and brain. The Hg content also increases with maternal amalgam load in amniotic fluid, placenta, cord blood, meconium, various foetal tissues including liver, kidney and brain, in colostrum and breast milk. Based on 2001 to 2004 population statistics, 181.1 million Americans carry a grand total of 1.46 billion restored teeth. Children as young as 26 months were recorded as having restored teeth. Past dental practice and recently available data indicate that the majority of these restorations are composed of dental amalgam. Employing recent US population-based statistics on body weight and the frequency of dentally restored tooth surfaces, and recent research on the incremental increase in urinary Hg concentration per amalgam-filled tooth surface, estimates of Hg exposure from amalgam fillings were determined for 5 age groups of the US population. Three specific exposure scenarios were considered, each scenario incrementally reducing the number of tooth surfaces assumed to be restored with amalgam. Based on the least conservative of the scenarios evaluated, it was estimated that some 67.2 million Americans would exceed the Hg dose associated with the reference exposure level (REL) of 0.3 μg/m(3) established by the US Environmental Protection Agency; and 122.3 million Americans would exceed the dose associated with the REL of 0.03 μg/m(3) established by the California Environmental Protection Agency. Exposure estimates are consistent with previous estimates presented by Health Canada in 1995, and amount to 0.2 to 0.4 μg/day per amalgam-filled tooth surface, or 0.5 to 1 μg/day/amalgam-filled tooth, depending on age and other factors.

Effects of bleaching on mercury ion release from dental amalgam

The chemical reactions that take place at the amalgam surface when exposed to bleaching agents are not well-understood. It is known, however, that mercury ions are released from dental amalgam when bleached. We hypothesized that increasing concentrations of hydrogen peroxide are more effective than water at increasing mercury ion release from dental amalgam. We prepared dental amalgam discs (n = 65) by packing amalgam into cylindrical plastic molds and divided them into 13 equal groups of 5 discs each. The discs in each group were individually immersed in either 0%, 3.6%, 6%, or 30% (w/v) hydrogen peroxide at exposure periods of 1, 8, 48, and 168 hrs. Samples were taken for mercury ion release determination by inductively coupled plasma mass spectrometry. There were significant increases in mercury release between control and all other hydrogen peroxide concentrations at all exposure times (p < 0.05).

Biomarkers of kidney integrity in children and adolescents with dental amalgam mercury exposure: findings from the Casa Pia children's amalgam trial

Mercury is toxic to the kidney, and dental amalgam is a source of mercury exposure. Few studies have evaluated the effects of dental amalgam on kidney function in a longitudinal context in children. Here, we evaluated urinary concentrations of glutathione S-transferases (GSTs) alpha and pi as biomarkers of renal proximal and distal tubular integrity, respectively, and albumin as a biomarker of glomerular integrity in children and adolescents 8-18 years of age over a 7-year course of dental amalgam treatment. Five hundred seven children, 8-12 years of age at baseline, participated in a clinical trial to evaluate the neurobehavioral and renal effects of dental amalgam in children. Subjects were randomized to either dental amalgam or resin composite treatments. Urinary GSTs alpha and pi, albumin, and creatinine concentrations were measured at baseline and annually in all subjects. Results were evaluated using linear regression analysis. GST-alpha concentrations were similar between treatment groups and in each sex and race (white vs. non-white) group in each follow-up year. GST-pi levels tended upward over the course of follow-up by four- to six-fold. This increase was seen in all groups irrespective of the treatment, race, or gender. Females had GST-pi levels approximately twice those of males at all ages. Albumin concentrations were constant throughout the follow-up period and did not differ by treatment, although females had 39% higher albumin levels than males. Additionally, we found no significant effects of amalgam treatment on the proportion of children with microalbuminuria (>30 mg/g creatinine). These findings are relevant within the context of children's health risk assessment as relates to the safety of mercury exposure from dental amalgam on kidney function. These data also provide normative values for sensitive indices of renal functional integrity that may serve in the evaluation of children and adolescents with renal disorders.

A Scandinavian tragedy

This paper briefly reviews the logic surrounding the controversial banning of dental amalgam by the Norwegian government. The very small contribution from dentistry to environmental mercury pollution and the significant advantages of amalgam as a dental restorative are emphasised.

The contribution of dental amalgam to urinary mercury excretion in children

BACKGROUND

Urinary mercury concentrations are widely used as a measure of mercury exposure from dental amalgam fillings. No studies have evaluated the relationship of these measures in a longitudinal context in children.

OBJECTIVE

We evaluated urinary mercury in children 8-18 years of age in relation to number of amalgam surfaces and time since placement over a 7-year course of amalgam treatment.

METHODS

Five hundred seven children, 8-10 years of age at baseline, participated in a clinical trial to evaluate the neurobehavioral effects of dental amalgam in children. Subjects were randomized to either dental amalgam or resin composite treatments. Urinary mercury and creatinine concentrations were measured at baseline and annually on all participants.

RESULTS

Treatment groups were comparable in baseline urinary mercury concentration (approximately 1.5 microg/L). Mean urinary mercury concentrations in the amalgam group increased to a peak of approximately 3.2 microg/L at year 2 and then declined to baseline levels by year 7 of follow-up. There was a strong, positive association between urinary mercury and both number of amalgam surfaces and time since placement. Girls had significantly higher mean urinary mercury concentrations than boys throughout the course of amalgam treatment. There were no differences by race in urinary mercury concentration associated with amalgam exposure.

CONCLUSIONS

Urinary mercury concentrations are highly correlated with both number of amalgam fillings and time since placement in children. Girls excrete significantly higher concentrations of mercury in the urine than boys with comparable treatment, suggesting possible sex-related differences in mercury handling and susceptibility to mercury toxicity.

The effect of hydrogen peroxide concentration on metal ion release from dental amalgam

OBJECTIVES

The aim of this study was to investigate the effect of hydrogen peroxide (HP) concentration on metal ion release from dental amalgam.

METHODS

Dental amalgam discs (n=25) were prepared by packing amalgam into cylindrical plastic moulds (10 mm diameter and 2 mm height). The discs were divided into five equal groups and each group was immersed in 20 ml of either 0%, 1%, 3%, 10% or 30% HP solution for 24 h at 37 degrees C. Samples were taken for metal ion release determination (Hg, Ag, Sn and Cu) using inductively coupled plasma mass spectrometry (ICP-MS). The surface roughness of each disc was measured before and after bleaching.

RESULTS

The differences in concentration of metal ions released after treatment with 0% (control) and each of 1%, 3%, 10% and 30% HP were statistically significant (p<0.05). Metal ion release for the elements (Hg, Ag, Sn and Cu) increased with exposure to increasing concentrations of HP. Surface roughness measurements of the samples before and after treatments with HP solutions were not significantly different (p>0.05).

CONCLUSIONS

Exposure to HP bleaching agent was associated with increased metal ion released from dental amalgams compared to treatment with a control solution. Ion release was in proportion to the peroxide concentration tested, with the highest concentration associated with the greatest metal ion release for all elements investigated.

The effect of carbamide peroxide treatment on metal ion release from dental amalgam

OBJECTIVES

There is concern that hydrogen peroxide generated by tooth bleaching agents may cause enhanced metal ion release (including mercury) from dental amalgam following contact. The aim of this in vitro study was therefore to investigate the effect of a carbamide peroxide (CP) based tooth bleaching gel on metal ion release from dental amalgam.

METHODS

Dental amalgam discs were prepared according to the manufacturers' instructions. These were treated with either a 10% carbamide peroxide (CP) gel or a 0% CP gel for 24h. Discs were carefully wiped with cotton wool before immersion in distilled water (20 ml) for 24h at 37 degrees C. Following immersion, water samples were taken for metal ion release determination (Ag, Cu, Hg and Sn) using inductively coupled plasma mass spectrometry methods. The specimens were further evaluated for surface changes using scanning electron microscopy (SEM) and Talysurf surface roughness measurements.

RESULTS

The differences in concentration of metal ions released after treatment with the 10% CP gel and a placebo gel treatment were not statistically significant (p>0.05). For example, mercury release following treatment with the 10% CP gel and the 0% CP gel was found to be 1.17(0.5) and 0.57(0.1)microgcm(-2), respectively. Roughness measurements for samples treated with the 10% CP gel and 0% CP gel were 2.23(0.47) and 1.74(0.16)microm, respectively, again showing no significant difference between groups (p>0.05). SEM images of the amalgam surfaces showed no apparent differences between treatments.

SIGNIFICANCE

Treatment with a 10% CP gel did not significantly enhance subsequent metal ion release from dental amalgams compared to a control gel, contradicting previously published studies.

Disinfectants' effect on mercury release from amalgam

BACKGROUND

Mercury environmental discharge is under increased scrutiny by the U.S. Environmental Protection Agency (EPA). Dental amalgam should be processed properly to prevent an additional environmental burden. Some processing agencies require that submitted amalgam be noninfectious. Investigations have demonstrated that oxidizing disinfectants mobilize mercury from amalgam into solution and add mercury to the environmental burden if it is disposed of improperly. The authors conducted a study to evaluate the effect of representative disinfectants on amalgam mercury release.

METHODS

The authors sized a high-copper spherical amalgam alloy to match that typically found in dental unit suction traps. They exposed 20 grams of the alloy to several disinfectant solutions and evaluated the filtered supernatant solution for mercury content.

RESULTS

Chlorine disinfectant materials discharged the most mercury ions, followed by bromide, iodophor, peroxide/peracetic acid and phenolic disinfectants. The quaternary ammonium compound did not discharge mercury ions above the detection limit (0.2 parts per billion) into solution.

CONCLUSIONS

A quaternary ammonium compound did not mobilize mercury ions into solution when used as a disinfectant agent for amalgam. Chlorine disinfectants mobilized mercury ions the most, followed by bromide, iodophor, peroxide/peracetic acid and phenolic disinfectants.

CLINICAL IMPLICATIONS

Dentists are obligated to be good environmental stewards and should follow practices that reduce environmental mercury release. Dental personnel should be aware that oxidizing disinfectants mobilize mercury ions into solution, which will be added to the environment if they are processed improperly. If required by processing, dental personnel should consider the different oxidizing effects of commonly used disinfectants.

Childhood urine mercury excretion: dental amalgam and fish consumption as exposure factors

The authors investigated the effect of amalgam fillings and fish consumption on urine mercury level (UHg), in children aged 4-8 years old inclusive. Using a sample of 60 children, we found that children with amalgam fillings had significantly higher UHg levels than children without amalgams (geometric mean=1.412microg Hg/g versus 0.436 microg Hg/g, respectively, P = 0.0001). Subjects with reported higher fish consumption also had significantly higher UHgs (P = 0.004). Univariate analyses provide evidence of an association between elevated UHg level and young age (P = 0.009), short height (P = 0.024), and low weight (P = 0.049) in children with amalgam chewing surfaces. We also found a negative correlation between urine mercury and age (-0.378), height (-0.418), and weight (-0.391). A multiple logistic regression model shows that the presence of amalgam fillings leads to increased odds of high UHg in children (OR=47.18), even after adjusting for high fish consumption (OR=8.66) and height (OR=11.36).

Surface analysis of dental amalgams by X-ray photoelectron spectroscopy and X-ray diffraction

OBJECTIVES

It is important to characterize the surface of dental amalgam in order to understand the process of mercury release from amalgam restorations in the oral cavity. The mercury evaporation occurs not only from the newly made restoration but also from the set material.

METHODS

The surfaces of four different types of amalgams, which had been well set, were analyzed with X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) and the relationship between surface compositions and mercury release was studied. Fresh amalgam surfaces as well as aged surfaces, which were stored for 30 days in air, were investigated using XPS and the chemical states of amalgam components and oxygen were studied. The aged surfaces were also characterized with XRD and grazing angle XRD.

RESULTS

With increased oxidation, the surface contents of tin and oxygen were increased in all amalgams. In contrast, the surface contents of copper and mercury were decreased. An increase of zinc or indium content were observed in zinc or indium containing amalgams, respectively. A surface layer enriched with indium and oxygen was clearly detected by XPS but not with grazing angle XRD.

SIGNIFICANCE

The thickness of the enriched surface layer is estimated to be in the order of few nanometer, which is approximately equal to the analysis depth of XPS. In addition, the presence of metallic elements, like tin and zinc, that readily form a stable oxide layer at the surface suppress the release of mercury.

Placental transfer of mercury in pregnant rats which received dental amalgam restorations

Mercury vapor released from one, two and four amalgam restorations in pregnant rats and mercury concentrations in maternal and fetal organs were studied. Dental treatment was given on day 2 of pregnancy. Mercury concentration in air samples drawn from each metabolism chamber with a rat were measured serially for 24 h on days 2, 8 and 15 of pregnancy. On each day of pregnancy, the amount of mercury in 24 h air samples was in proportion to the amalgam surface areas. Linear regression analysis showed relatively high correlation coefficients between the mercury content and amalgam surface areas, and the coefficients were statistically significant. A highly significant correlation was also found between the number of amalgam fillings and their surface areas. Mercury concentrations in major maternal organs with one, two and four amalgam fillings tended to increase with the increasing amalgam surface areas. Spearman's rank correlation test revealed significant correlations in the brain, liver, kidneys and placenta but not in the lung. Furthermore, significant correlations were also found between the mercury concentrations in all maternal organs and the amount of mercury in 24 h air samples on day 15 of pregnancy. Mercury concentrations in fetal brain, liver and kidneys were much lower than those of the dams but liver and kidneys showed positive correlations between the mercury content and maternal amalgam surface areas. Similar correlations were observed between the mercury concentrations in fetal organs and the amount of mercury in 24 h air samples on day 15 of pregnancy. In fetal brain, no significant correlations were found between either maternal amalgam surface areas or the amount of mercury in 24 h samples on day 15 of pregnancy but significant uptake of mercury was found in the samples from the dams given four amalgam fillings. The results of the present study demonstrated that mercury vapor released from the amalgam fillings in pregnant rats was distributed to maternal and fetal organs in dose-dependent amounts of the amalgam fillings.

Influence of amalgam fillings on Hg levels and total antioxidant activity in plasma of healthy donors

In order to evaluate the influence of specific factors on mercury (P-Hg) levels and antioxidant power (P-FRAP) in human plasma, 26 healthy donors were examined by a dentist, their plasma analyzed for Hg by atomic absorption spectrometry and for total antioxidant activity by FRAP method. Hg plasma concentration was found to be correlated with the number of amalgam fillings, suggesting that Hg released from fillings is a source of Hg in non-occupational exposed subjects. P-FRAP correlated negatively with P-Hg suggesting a pro-oxidant role of the Hg released from amalgam fillings. Though age by itself was not significantly correlated with P-FRAP, when considered together with P-Hg in multivariate analysis, it was found to be a major related cofactor. Multivariate analysis showed no influence of fish consumption or cigarette smoking on P-FRAP.

Factors influencing total mercury levels among Lebanese dentists

The aim of the current study is to examine the various factors, which contribute to high levels of mercury (Hg) in the hair of Lebanese dentists. The survey, which was carried out on ninety-nine dentists in the greater Beirut area, included a structured questionnaire designed to provide information about the parameters that influenced their occupational exposure to Hg. These included: precautionary measures, dental fillings, work habits and lifestyle of the tested dentists. The study showed that two of the four investigated precautionary measures had a significant effect on Hg level. The results revealed that, at the 95% confidence levels, Hg concentration in hair was significantly lower among the dentists who always used gloves and masks. Multiple regression analysis showed that the use of masks (P = 0.055) had significant effects on mercury accumulation in hair. In addition, dentists who saw more than eight patients per day had marginally higher mercury levels in their hair than those who did not. Since it was shown that precautionary measures could limit exposure to Hg concentration, then the use of protective measures needs to be emphasized.

Effects of gallium and mercury ions on transport systems

Mercury was previously shown to exert toxic effects by influencing ion channels and transporters in the kidney and brain. Gallium alloys were suggested as less toxic restorative materials. To compare the toxicity of gallium ions with those of mercury ions, we applied gallium nitrate Ga(NO3)3 (0.1-100 microM and mercuric chloride (HgCl2) (0.001-10 microM) to Xenopus oocytes expressing mammalian ion channels and transport proteins. Mercury (10 microM) inhibited the K+-channels ROMK and HERG, the phosphate transporter NaPi-3, the amino acid transporter rBAT, the cation transporter OCT-2, and the osmolyte transporter BGT. It activated the I(Ks)-channel but did not affect the Na+-channel ENaC, the anion channel NaPi-1, and the glucose transporter SGLT-1. Gallium was without significant effect on the channels and on SGLT1, NaPi-3, and rBAT, but inhibited BGT and OCT-2. In conclusion, both Hg2+ and Ga3+ may exert toxic effects on transport systems, which may partially explain their cytotoxic effects.

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.

The amalgam controversy. An evidence-based analysis

BACKGROUND

There are a number of patients and health care professionals who believe dental amalgam restorations are a factor in a host of diseases and conditions. They have been influenced by anecdotal case reports in the medical and dental literature, research published in the refereed literature and media stories concerning the alleged dangers of amalgam restorations.

METHODS

The author uses an evidence-based approach in analyzing the data both supporting and condemning the continued use of amalgam restorations. He reviewed the articles from both peer-reviewed and non-peer-reviewed sources and evaluated their relevance, research design and statistical analysis, as well as whether the conclusions follow from the data.

CONCLUSIONS

There are numerous logical and methodological errors in the anti-amalgam literature. The author concludes that the evidence supporting the safety of amalgam restorations is compelling.

CLINICAL IMPLICATIONS

Amalgam restorations remain safe and effective. Dentists should educate patients and other health care professionals who may be mistakenly concerned about amalgam safety.

Diagnostic value of a chelating agent in patients with symptoms allegedly caused by amalgam fillings

The chelating agent 2,3 dimercaptopropane-1-sulfonate (DMPS) has been used in a mercury mobilization test for diagnoses in illnesses allegedly associated with the presence of amalgam restorations. DMPS is an accepted antidote to heavy metal poisoning. The aim of the present study was to evaluate the diagnostic value of DMPS in patients with symptoms self-related to their amalgam fillings. The subjects consisted of four groups: 19 healthy controls without amalgam experience; 21 healthy controls with amalgam fillings; 20 patients who claimed symptoms of "mercury poisoning" from dental amalgam; and 20 patients who had amalgam fillings removed because of such symptoms. DMPS (2 mg/kg body weight) was injected intravenously, and urine was collected prior to the injection, 30 and 120 min after the injection, and throughout the next 22 hrs. The samples were analyzed for total mercury by cold vapor atomic absorption spectrophotometry. The total median amounts of mercury excreted over 24 hrs for those with complaints allegedly associated with amalgam and for the healthy controls with amalgam fillings were similar. Persons with amalgam fillings excreted about three times more mercury than those without. The controls, who had never had amalgam fillings, and the subjects who had had their fillings removed excreted median amounts of 8.5 microg and 7.2 microg mercury, respectively. The present DMPS challenge test did not differentiate between patients with or those without complaints self-related to their amalgam fillings but did confirm the higher mercury values in patients with dental amalgam.

Investigation of two mercury vapor collection techniques

OBJECTIVES

The purpose of this investigation was to develop and test two in vitro mercury vapor collection techniques: a closed bottle technique (CB) and an intraoral flow (IOF) technique.

METHODS

Amalgam samples were prepared in acrylic first molars (#30) with standardized Class I preparations. In the CB technique, samples were placed in either a 25, 100 or 500 ml bottle (n = 5). Vapor was analyzed with the Jerome M-411 using a syringe method over a 7 day period. In the IOF technique an impression of the lower right quadrant of a Typodont was taken with PVS impression material leaving a 5 mm space over #30. Samples were analyzed with the Jerome M-411 connected to the impression tray via tygon tubing at the buccal surface. Average mercury vapor release rates and standard deviations were calculated for each method. Data were analyzed by two-way ANOVA followed by Tukey HSD pairwise analysis for significant findings (alpha = 0.05).

RESULTS

Both techniques indicated mercury vapor release was dependent on volume. The largest bottle, 500 ml, yielded a significantly greater (p < or = 0.00) amount of mercury vapor within the CB systems. In the IOF technique, the addition of air flow over the restoration demonstrated a significant increase (p < or = 0.05) in mercury vapor released compared to the sealed IOF technique.

SIGNIFICANCE

A method for mercury vapor analysis was developed for possible intraoral application. The IOF method with direct air flow removes possible saturation effects found in a CB system, while limiting external variables, which may contribute to errors associated with in vivo measurements.

Effects of palladium addition on emission of mercury vapor from dental amalgam

OBJECTIVES

The purpose of this investigation was to test the hypothesis that palladium causes a reduction in mercury emission when added to dental amalgam during condensation.

METHODS

Mercury vapor release was measured in a closed bottle system and an Intraoral Flow device(IOF). Conventional amalgam restorations were modified by addition of various palladium pellets. 1.57 mm diameter palladium pellets with different porosities were fabricated. These pellets were then placed in amalgam restoration using typical condensation and carving procedures. The samples were stored in a closed bottle and mercury measurements were taken from the bottles at 30 min, 1, 3, 5, 24 and 48 h and 7 days after trituration using a Jerome 411 Mercury Vapor Analyzer (Arizona Instrument Corp., Jerome, AZ). The palladium pellets identified as the most effective in mercury vapor reduction were further tested in an IOF device. Data were analyzed by two-way ANOVA followed by Tukey HSD pairwise analysis for significant findings (alpha = 0.05).

RESULTS

The palladium containing amalgams when tested in the closed bottle system yielded significantly lower (p < 0.05) mercury vapor release than the controls. Pellets fabricated with the highest porosity yielded the greatest reduction in overall mercury vapor release. In the IOF device the overall amount of mercury vapor released from the palladium containing amalgams was also significantly less than the control (p < 0.05).

SIGNIFICANCE

Mercury vapor emission from dental amalgam was greatly reduced by adding palladium pellets to amalgam during condensation. These techniques require only slight modifications of the standard operative procedures.

Alzheimer's disease, dental amalgam and mercury

BACKGROUND

Mercury, or Hg, is a neurotoxin that has been speculated to play a role in the pathogenesis of Alzheimer's disease, or AD. Dental amalgam releases low levels of Hg vapor and is a potential source of Hg for a large segment of the adult population.

METHODS

The authors studied 68 subjects with AD and 33 control subjects without AD to determine Hg levels in multiple brain regions at autopsy and to ascertain the subjects' dental amalgam status and history. The subjects were from central Kentucky and Elm Grove, Wis. The authors conducted dental amalgam assessments during the lives of the majority of subjects and in some subjects at the time of autopsy only. The authors also determined three dental amalgam index scores--Event (placement, repair or removal of amalgam), Location and Time In Mouth--in addition to the numbers of and surface area of occlusal amalgam restorations. The authors determined Hg levels in multiple brain regions and performed full neuropathologic evaluations to confirm the normal status of the brain or the presence of AD.

RESULTS

The authors found no significant association of AD with the number, surface area or history of having dental amalgam restorations. They also found no statistically significant differences in brain Hg level between subjects with AD and control subjects.

CONCLUSIONS

Hg in dental amalgam restorations does not appear to be a neurotoxic factor in the pathogenesis of AD. The authors found that brain Hg levels are not associated with dental amalgam, either from existing amalgam restorations or according to subjects' dental amalgam restoration history.

CLINICAL IMPLICATIONS

Dental amalgam restorations, regardless of number, occlusal surface area or time, do not relate to brain Hg levels.

Dental amalgam: update on safety concerns. ADA council on Scientific Affairs

This report of the Council on Scientific Affairs reviews and discusses recent studies concerning the safety of dental amalgam, with an emphasis on studies that have been published since the 1993 review of dental amalgam by the U.S. Public Health Service Committee to Coordinate Environmental Health and Related Programs. The Council concludes that, based on currently available scientific information, amalgam continues to be a safe and effective restorative material.

Mercury levels in plasma and urine after removal of all amalgam restorations: the effect of using rubber dams

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.

Potential side effects of dental amalgam restorations. (I). An oral and medical investigation

The aim of this study was to explore a possible association between health status and self-reported adverse effects related to dental amalgam restorations. A group of 50 consecutive patients (index group), referred for complaints self-related to dental amalgam restorations, was compared with a control group of individuals matched by age, sex and postal zip code. The patients underwent an oral, stomatognathic, medical and clinical chemistry examination. Mercury levels were examined in blood, urine and hair. The results revealed that somatic diseases were more common in the index group (38% versus 6%). Symptoms related to cranio-mandibular dysfunction were reported by 74% of the patients in the index group versus 24% in the control group, and were diagnosed in 62% and 36%, respectively. The oral health status and the number of amalgam surfaces were similar in the 2 groups. No positive skin patch test to mercury was found in any of the groups. The estimated mercury intake from fish consumption, occupational exposure, and mercury levels in blood and urine were also similar and far below levels, where negative health effects would be expected. The correlation between the number of amalgam surfaces and mercury levels in plasma and urine (r=0.43) indicated a release of mercury from dental amalgam restorations in both groups. Since the mercury levels were similar among index patients and controls, mercury was not a likely cause of the impaired health reported by the patients.

Potential side effects of dental amalgam restorations. (II). No relation between mercury levels in the body and mental disorders

A group of 50 consecutive patients, referred for self-reported complaints which they related to dental amalgam restorations, was compared with control patients matched by age, sex and postal zip code. All patients were subjected to a psychiatric examination and a set of rating scales and questionnaires, and the symptoms were related to the mercury levels in blood, urine and hair. A psychiatric diagnosis was established in 70% of the patients in the index group versus 14% in the control group. The prevailing symptoms were anxiety, asthenia and depression. Mercury levels in blood, urine and hair were similar among index cases and controls, and were far below critical levels of mercury intoxication. There was no correlation between mercury levels and the severity of the reported symptoms. Therefore, mercury was not a likely cause of the complaints. Instead, the reported symptoms were part of a broad spectrum of mental disorders.

Mercury vapor release from dental amalgam in patients with symptoms allegedly caused by amalgam fillings

The aim of this study was to determine whether a group of patients with symptoms, self-related to their amalgam restorations, experienced an exposure to mercury vapor from their amalgam restorations that reached the range at which subtle symptoms have been reported in the literature. Furthermore, the aim was to determine whether the mercury exposure for these patients was significantly higher than for controls with no reported health complaints. The symptom group consisted of 10 consecutively selected patients from a larger group, referred by their physicians for investigation into any correlation between subjective symptoms and amalgam restorations. The control group consisted of 8 persons with no reported health complaints. The intra-oral release of mercury vapor was measured between 7:45 a.m. and 9:00 p.m. at intervals of 30-45 min, following a standardized schedule. The mercury levels in plasma, erythrocytes, and urine were also determined. The calculated daily uptake of inhaled mercury vapor, released from the amalgam restorations, was less than 5% of the daily uptake calculated at the lower concentration range given by the WHO (1991), at which subtle symptoms have been found in particularly sensitive individuals. The symptom group had neither a higher estimated daily uptake of inhaled mercury vapor, nor a higher mercury concentration in blood and urine than in the control group. The study provides no scientific support for the belief that the symptoms of the patients examined originated from an enhanced mercury release from their amalgam restorations.

Estimation of mercury dose by a novel quantitation of elemental and inorganic species released from amalgam

Amalgam fillings constitute, after food, the main source of exposure to mercury for the general population. An evaluation of potential health risks has to be based on the dose of mercury released from the fillings. This dose is estimated by a new procedure of mercury speciation which elutes the released elemental and inorganic mercury with solvents of different polarity (paraffin and saline). In vitro tests with spherical amalgam pellets have shown that mercury release into the solvents is linearily correlated to time and amalgam surface area. Doses estimated in volunteers by this method average 4.5 micrograms/day (range 0.3-13.9), as compared to a dose of 3.4 micrograms/day (range 0.1-11.8) measured conventionally in the oral air. The aforementioned dose, combined with the nearly equal mercury uptake from food, is below the acceptable daily intake of 40 micrograms for all forms of mercury.

Mercury release from dental amalgams: an in vitro study under controlled chewing and brushing in an artificial mouth

The release of mercury vapor from class I amalgam restorations prepared in human molar teeth was studied during chewing simulations in an artificial mouth of a bi-axial servo-hydraulic mechanical test system. So that the total mercury released from the restoration over a fixed time could be determined, a closed chamber surrounded the envelope of chewing motion. In addition, the influence of sampling frequency on mercury release was corrected by the use of different sampling frequencies over a fixed time interval of mercury release measurement and extrapolation to zero sampling time. Thus, a combination of a closed environment and an extrapolation method to determine the mercury release under continuous sampling was used to determine the mercury released under normal breathing conditions. The measured mercury release rate data were used to calculate the potential daily mercury dose in a patient due to a single amalgam restoration, following the method previously outlined by Berglund. The mercury release from both a conventional and a high-copper amalgam was evaluated at different age intervals after the restoration was placed in the teeth. The results show that while the age of the amalgam and the amalgam type influence the extent of mercury release during the initial non-steady-state conditions, the steady-state value of mercury daily dose due to a single amalgam filling is 0.03 micrograms/day, which is well below the calculated threshold-limiting value (TLV) of 82.29 micrograms/day considered dangerous for occupational exposure in the United States.

Combined estimation of mercury species released from amalgam

Amalgam fillings constitute, after food, the main source of exposure to mercury for the general population. Banning amalgam would incur huge costs for additional dental treatment. An evaluation of potential health risks must be based on the mercury dose released from fillings. In this study, dose is estimated by a new procedure of mercury speciation which elutes the released elemental and inorganic mercury with solvents of differing polarity. We tested the procedure by incubating spherical amalgam pellets in a mixture of light paraffin oil and saline (0.9% NaCl). Release of mercury into paraffin and saline was linear in relation to both amalgam surface area and exposure time. Measurements with this method were then extended to a group of 21 amalgam-bearing volunteers. The absorbed dose averaged 4.8 micrograms/day compared with 3.7 measured conventionally in intra-oral air from the same persons. With both methods, the dose was significantly correlated to the number of amalgam-covered tooth surfaces. This dose, combined with the nearly equal mercury uptake from food, is far below the acceptable daily intake limit.

The dentist's exposure to elemental mercury vapor during clinical work with amalgam

Continuous measurements of mercury vapor in the breathing zone of the dentist were made under ordinary clinical conditions. Fifty old amalgam fillings were removed and replaced by new ones. The mercury vapor measurements were performed by means of atomic absorption spectrophotometry. On the basis of the type of suction device used, the measurements were divided into seven groups, each of which consisted of a series of measurements. During the cutting, filling, and polishing operations the mean mercury vapor levels in the breathing zone of the dentist were in the range of 1-2 micrograms Hg m-3 air when proper mercury hygiene measures were taken. This is far below the currently valid threshold limit value (30 micrograms Hg m-3 air) in Sweden. The saliva extractor and the dental mirror-evacuator did not influence the mercury vapor levels when used together with the high-volume evacuator. However, when only a saliva extractor was used, the cutting of amalgam fillings caused highly fluctuating mercury vapor levels, which were 2-15 times higher than the threshold limit value.

People with high mercury uptake from their own dental amalgam fillings

OBJECTIVES

To describe people with high mercury (Hg) uptake from their amalgam fillings, and to estimate the possible fraction of the occupationally unexposed Swedish population with high excretion of urinary Hg.

METHODS

Three case reports are presented. The distribution of excretion of urinary Hg in the general population was examined in pooled data from several sources.

RESULTS

The three cases excreted 23-60 micrograms of Hg/day (25-54 micrograms/g creatinine), indicating daily uptake of Hg as high as 100 micrograms. Blood Hg was 12-23 micrograms/l, which is five to 10 times the average in the general population. No other sources of exposure were found, and removal of the amalgam fillings resulted in normal Hg concentrations. Chewing gum and bruxism were the probable reasons for the increased Hg uptake. Extrapolations from data on urinary Hg in the general population indicate that the number of people with urinary excretion of > or = 50 micrograms/g creatinine could in fact be larger than the number of workers with equivalent exposure from occupational sources.

CONCLUSION

Although the average daily Hg uptake from dental amalgam fillings is low, there is a considerable variation between people; certain people have a high mercury uptake from their amalgam fillings.

Human exposure to mercury and silver released from dental amalgam restorations

In 35 healthy individuals, the number of amalgam surfaces was related to the emission rate of mercury into the oral cavity and to the excretion rate of mercury by urine. Oral emission ranged up to 125 micrograms Hg/24 h, and urinary excretions ranged from 0.4 to 19 micrograms Hg/24 h. In 10 cases, urinary and fecal excretions of mercury and silver were also measured. Fecal excretions ranged from 1 to 190 micrograms Hg/24 h and from 4 to 97 micrograms Ag/24 h. Except for urinary silver excretion, a high interplay between the variables was exhibited. The worst-case individual showed a fecal mercury excretion amounting to 100 times the mean intake of total Hg from a normal Swedish diet. With regard to a Swedish middle-age individual, the systemic uptake of mercury from amalgam was, on average, predicted to be 12 micrograms Hg/24 h.

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.

Release of elements due to electrochemical corrosion of dental amalgam

The corrosion pattern of dental amalgam in aqueous media was interpreted theoretically by means of log(ai/a(ref))-pe diagrams. The definitions on which the diagrams were based were given, and their features were described. All sparingly soluble compounds which were expected to be formed in reactions with the solvents considered were listed. All the corrosion products reported in the current literature were found to be formed, and the conditions for their formation were established. It emerged that it was necessary to exclude other sparingly soluble compounds with theoretically might be formed. Two compounds, CuSCN and AgSCN, which have not been reported previously were found to be possible corrosion products. Corrosion products containing mercury compound cannot be formed on amalgam restorations with no metallic contact with other materials.

An in vitro and in vivo study of the release of mercury vapor from different types of amalgam alloys

The aim of the in vitro part of the study was to measure the rate of release of mercury vapor from different types of dental amalgam in air, and in air during cyclic dipping into isotonic saline solution or Fusayama solution. The measurements were carried out by means of the Mercollector/Mercometer system, based on atomic absorption spectrophotometry. Both new (age approximately 2 months) and old (age approximately 1.5 years) amalgam specimens were studied. The variations in the rate of release of mercury vapor in air during cyclic dipping into aqueous media were most pronounced during the first day of the 10-day period studied. In air during cyclic dipping into the aqueous media, the conventional amalgam specimens released mercury vapor at lower rates over the whole period than did the dispersed and single-composition types studied. The aim of the in vivo part of the study was to determine the daily release of mercury vapor from amalgam restorations made of alloys of the same types and batches as those used in the in vitro part of the study. A series of measurements was carried out on each of eight subjects before and after amalgam therapy. None of the subjects was occupationally exposed to mercury. The subjects had to follow a standardized schedule for 24 h, where they ate, drank, and brushed their teeth at predetermined times (Berglund, 1990). The amount of mercury vapor released per time unit was measured at intervals of 30-45 min. Samples of urine and saliva were analyzed formercury.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors influencing mercury evaporation rate from dental amalgam fillings

Factors influencing mercury evaporation from dental amalgam fillings were studied in 11 volunteers. Air was drawn from the oral cavity for 1 min and continuously analyzed with a mercury detector. In six volunteers the median unstimulated evaporation rate was 0.1 ng Hg/s, range 0.09-1.3 ng Hg/s. After chewing gum for 5 min the highest evaporation rate was 2.7 ng Hg/s. Chewing paraffin wax gave only a small increase in evaporation rate. Changes in airflow rates between 1.5 and 2.5 1/min during the 1 min sampling did not change the amount of mercury drawn from the oral cavity. Sampling with different mouthpieces and closed mouth was compared to open mouth sampling with a thin plastic tube. It was found that the latter method could result in lower values for some volunteers due to simultaneous mouth breathing. After placing individual plastic teeth covers in the mouth, the intraoral evaporation of mercury decreased immediately by 89-100% of previous levels. This technique could be used to detect mercury evaporation from separate amalgam fillings or to reduce the intraoral mercury vapor concentration. Rinsing the mouth with heated water for 1 min increased the mean evaporation rate by a factor of 1.7 when the water temperature increased from 35 degrees C to 45 degrees C.

The adverse effects of dental restorative materials--a review

Several materials used in dentistry are described as biomaterials. Owing to the intimate contact of these materials with the oral tissues, they should possess a high degree of biocompatibility. However, some materials may exhibit adverse effects, causing both local and general pathological changes, even though the occurrence seems to be relatively low. It is, therefore, the dentist's responsibility to be aware of the potential adverse effects of these materials and to take precautions to protect the patient form such effects. The purpose of this article is to review the potential adverse effects of some commonly used restorative materials, mainly with regard to patients.

Dental materials for posterior restorations

Assessment of the quality of dental restorations by the Ryge system is described. Generally, the quality of dental restorations is shown to be dependent on the technique sensitivity of the restorative material as well as the skill and experience of the dentist. Concerning biocompatibility, adverse reactions related to amalgam restorations are unlikely or scarce, due to small amounts of released mercury. Resin based restorative materials contain a large number of organic compounds and, as such, the toxic and allergenic potentials are unknown. Gold and ceramics turn out to be the most biotolerable dental materials. Based on studies on longevity, data indicate that the median age of amalgam restorations is 10-12 years, of gold castings 13-14 years and more, and of composite restorations 4 years. Data on longevity of ceramic restorations are sparse. Secondary caries appears to be the most frequent cause for replacement of the different restorations, followed by marginal degradation. Secondary caries account for more failures among the resin based restorations than among amalgam. Reviewing the literature, it appears that amalgam is the best and most economic dental material for routine posterior restorations with reasonable durability. Gold is recommended for complex restorations. Resin based composites may be limited to small restorations where cosmetics is the main aspect, as wear and recurrent caries are main problems. Ceramic restorations comprise aesthetic restorations with excellent biocompatibility, however, data on longevity and marginal adaptation are not encouraging.

Quantitation of total mercury vapor released during dental procedures

An in vitro method is described in which measurements were made of the total amount of mercury vapor released from three types of amalgam during routine dental procedures. It was found that the greatest amount of mercury was released during dry polishing of one amalgam (44 micrograms). Removal of amalgam from a Class I cavity under water spray and high volume evacuation also generated large amounts of mercury as expected (15-20 micrograms). However, under the more clinically relevant conditions of extending evacuation for one minute to remove residual amalgam and mercury after cutting, this value was reduced by approximately 90%. The total amount of mercury generated during placement (6-8 micrograms), wet polishing (2-4 micrograms) and trituration (1-2 micrograms) were also measured. The study showed that dental procedures associated with amalgam do potentially expose the patient and operator to mercury vapor. However, the total amount of mercury released during any procedure was far below the total exposure level calculated from the daily threshold limits established by regulatory agencies for occupational exposure.

Dental amalgam and mercury

The mercury concentrations in blood (HgB) and urine (HgU) samples, and in exhaled air (HgAir) were measured in 147 individuals from an urban Norwegian population, using cold vapour atomic absorption spectrometry. The study aimed to estimate the mercury exposure from the dental restorations, by correlating the data to the presence of amalgam restorations. Mean values were HgB = 24.8 nmol/l, HgU = 17.5 nmol/l and HgAir = 0.8 micrograms/m3. HgU correlated with HgAir, and both HgU and HgAir with the number of amalgam restorations, amalgam restored surfaces and amalgam restored occlusal surfaces. HgB showed poor correlation to HgU and HgAir and the presence of amalgam restorations. A differentiation of the mercury absorption due to exposure from dental amalgams and from the dietary intake, necessitates measurements of both organic and inorganic mercury in the plasma, and in the erythrocytes. The results suggest that individuals with many amalgam restorations, i.e., more than 36 restored surfaces, absorb 10-12 micrograms Hg/day.