The association between amalgam dental surfaces and urinary mercury levels in a sample of Albertans, a prevalence study

Association between dental amalgam restoration and urine mercury concentrations among young women: a cross-sectional study

BACKGROUND

The association between dental amalgam fillings and urine mercury concentrations was investigated in this study to assess the health risks associated with dental amalgams.

METHODS

This cross-sectional study included 99 women in their 20s who visited the dental clinic in Daegu, Korea. The 99 participants were composed of 68 subjects who had dental amalgam fillings (exposure group) and 31 subjects who did not have dental amalgam fillings (nonexposure group). Oral examinations were conducted by a single dental hygienist, sociodemographic features were investigated as confounding variables, and urine mercury concentrations were measured using an automatic mercury analyzer.

RESULTS

The mean±standard deviation of the urine mercury concentrations of the exposure and nonexposure groups were 1.50±1.78 μg/g creatinine and 0.53±0.63 μg/g creatinine, respectively. The exposure group showed significantly higher levels than the nonexposure group (p<0.01). The urine mercury concentration significantly increased with an increase in the number of teeth filled with amalgam, cavity surfaces involved, and number of defective amalgam fillings, and according to the latest exposure time (p<0.001). In the multiple regression analysis of amalgam-related factors and urine mercury concentrations after correction for confounding factors, the urine mercury concentration in the group with six or more amalgam-filled teeth, 11 or more cavity surfaces, and two or more defective amalgams was significantly higher than that in the nonexposure group (p<0.001).

CONCLUSION

According to this study, exposure to dental amalgams was confirmed to significantly affect urine mercury concentrations.

Decreased trends of using dental amalgam filling for decayed teeth in Taiwan from 1997 to 2013

Background/purpose

Mercury within dental amalgam has been criticized for the potential toxicity and environmental hazard. Phasing down the use of dental amalgam is the transition for amalgam free dentistry. However, little is known about dental amalgam filling (AMF) in Taiwan. In this study, time trends of AMF were measured by using National Health Insurance Research Database (NHIRD).

Materials and methods

A retrospective study was conducted to analyze the AMF data in registered database compiled by Taiwanese NHIRD from 1997 to 2013. The AMF data were further analyzed according to sex, age, and geographic location, respectively. Time trends of dental visits for AMF and medical expenses for AMF were also evaluated.

Results

The average annual AMF ratio was 8.965% of nationwide population in Taiwan. The prevalence of AMF was significantly decreased both in male and female from 1997 to 2013 (P for trend <0.0001). The decreased pattern of AMF was found by the age stratification (P for trend <0.0001). The significant fall of AMF was also displayed in six districts (P for trend <0.0001). The number of dental visits were ranged from 821,749 in 1997 to 1,313,734 in 2013. However, time trends of dental visits for AMF were significantly decreased (P for trend <0.0001). The medical expenses for AMF were simultaneous significantly decreased from 1997 to 2013 (P for trend <0.0001).

Conclusion

Form the results of this nationwide population-based database, a significant decrease of AMF in Taiwan was observed during past 17 years.

Association between Dental Amalgam Filling and Essential Tremor: A Nationwide Population-Based Case Control Study in Taiwan

Essential tremor (ET) is a common neurological disorder and the most common movement disorder. Low-level occupational exposure to mercury vapor is known to be a crucial factor that increases the risk of tremor. Dental amalgam is one of the main sources of mercury in those who possess amalgam restorations. However, the relationship between ET and amalgam filling (AMF) is not quite clear. The purpose of this study was to investigate the association between AMF and the risk of ET using a population-based administrative databank. The data for this study were sourced from the Taiwanese National Health Insurance Research Database (NHIRD). A retrospective case-control study was conducted using this databank from 2000 to 2013. Case and control groups were matched by sex, age, urbanization level, monthly income, and Charlson comorbidity index using the propensity score method with a 1:1 ratio. In this study, 3008 cases and 3008 controls were included. The results from this nationwide population-based case-control study did not indicate any association between ET and AMF in Taiwan. Although the results were not significantly statistical, the findings may be worthy to be valued.

Quantitative estimation of mercury intake by toxicokinetic modelling based on total mercury levels in humans

Mercury is a toxic metal that can be disseminated into the environment from both natural and anthropogenic sources. Human exposure to the metal stems mainly from food, and more particularly from the consumption of fish and other seafoods. Examining dietary exposure and measuring mercury levels in body tissues are two ways of estimating exposure to mercury. In this study, we utilized a modelling system consisting of three linear toxicokinetic models for describing the fate of methyl mercury, inorganic mercury, and metallic mercury in the body, in order to estimate daily intake of mercury as measured through total mercury concentrations in the blood. We then compared the results stemming from our modelling system to those of the detailed semi-quantitative food frequency questionnaire (FFQ) of the Norwegian Fish and Game (NFG) Study, a project that focused on dietary mercury exposure. The results indicate that toxicokinetic modelling based on blood levels gave higher daily intake values of mercury compared to those of the FFQ. Furthermore, the former had a wider range of estimates than the latter. The properties of the toxicokinetic model or limitations in the dietary exposure assessment could be posited as reasons for the differences between the respective methods. Moreover, the results may have been influenced by sources of mercury exposure that cannot be described as dietary, such as amalgam fillings.

Quantification of Hg excretion and distribution in biological samples of mercury-dental-amalgam users and its correlation with biological variables

This is the first study conducted to quantify the excretion and distribution of mercury (Hg) with time (days) in the biological samples collected from Hg dental amalgam users (MDA). The individuals, with Hg-based dental filling were selected, and their biological samples (red blood cells (RBCs), plasma, urine, hair, and nails) were collected on first, third, and 12th day of fillings. The concentrations of Hg observed in the biological samples of MDA were also correlated with the biological variables such as age, weight, restoration, fish consumption, number, and surface area of fillings. The concentrations of Hg in the biological samples of MDA were found 6-8 times higher than the non-amalgam users (control). The concentrations of Hg in the RBCs (4.39 μg/L), plasma (3.02 μg/L), and urine (22.5 μg/L) on first day of filling were found comparatively higher than the concentrations observed on third day (2.15, 1.46, and 12.3 μg/L for RBCs, plasma, urine, respectively) and 12th day (3.05, 2.5, 9.12 μg/L for RBCs, plasma, urine, respectively), while Hg concentrations were found lower in the hair and nails on third day of fillings (1.53 μg/g for hair and 2.35 μg/g for nails) as compared to the 12th day (2.95 μg/g for hair and 3.5 μg/g for nails). The correlations were found significant (p ˂ 0.05) between Hg concentrations in the biological samples of MDA and biological variables (the number of restoration, fish consumption, number, and surface area of fillings), while no significant (p ˃ 0.05) correlations were observed for Hg concentrations in the biological samples with age and weight of MDA. These observations unveil the fact that the use of Hg-based dental filling is the undesirable exposure to Hg which should be replaced by composite (a safer filling material).

Alterations in biochemical markers due to mercury (Hg) exposure and its influence on infant's neurodevelopment

This study examined the role of oxidative stress due to mercury (Hg) exposure on infant's neurodevelopmental performance. A total of 944 healthy Saudi mothers and their respective infants (aged 3-12 months) were recruited from 57 Primary Health Care Centers in Riyadh City. Total mercury (Hg) was measured in mothers and infants urine and hair samples, as well as mother's blood and breast milk. Methylmercury (MeHg) was determined in the mothers and infants' hair and mother's blood. Urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), malondialdehyde (MDA), and porphyrins were used to assess oxidative stress. The infant's neurodevelopment was evaluated using Denver Developmental Screening Test II (DDST-II) and Parents' Evaluation of Developmental Status. The median total Hg levels in mother's urine, infant's urine, mother's hair, infant's hair, and mother's blood and breast milk were 0.995μg/l, 0.716μg/l, 0.118μg/g dw, 0.101μg/g dw, 0.635μg/l, and 0.884μg/l respectively. The median MeHg levels in mother's hair, infant's hair, and mother's blood were 0.132μg/g dw, 0.091μg/g dw, and 2.341μg/l respectively. A significant interrelationship between mothers and infants Hg measures in various matrices was noted. This suggests that mother's exposure to different forms of Hg (total and/or MeHg) from various sources contributed significantly to the metal body burden of their respective infants. Even though Hg exposure was low, it induced high oxidative stress in mothers and infants. The influence of multiplicative interaction terms between Hg measures and oxidative stress biomarkers was tested using multiple regression analysis. Significant interactions between the urinary Hg levels in mothers and infants and oxidative stress biomarkers (8-OHdG and MDA) were noted. The MeHg levels in mother-infant hair revealed similar interaction patterns. The p-values for both were below 0.001. These observations suggest that the exposure of our infants to Hg via mothers either during pregnancy and/or neonatal life, promoted oxidative stress that might have played a role in infant neurodevelopmental delays that we reported previously. The results confirmed that the interaction between infant's MeHg in hair and 8-OHdG and MDA levels was significantly associated with a delay in DDST-II performance (ß=-0.188, p=0.028). This finding provides an insight into the potential consequences of Hg-induced oxidative stress to infant's cognitive neurodevelopment for the first time. This observation still needs future studies to be validated. Given the low MeHg levels in our population, these findings are of particular importance.

Genome-Wide Association Study to Identify Genes Related to Renal Mercury Concentrations in Mice

BACKGROUND

Following human mercury (Hg) exposure, the metal accumulates in considerable concentrations in kidney, liver, and brain. Although the toxicokinetics of Hg have been studied extensively, factors responsible for interindividual variation in humans are largely unknown. Differences in accumulation of renal Hg between inbred mouse strains suggest a genetic interstrain variation regulating retention or/and excretion of Hg. A.SW, DBA/2 and BALB/C mouse strains accumulate higher amounts of Hg than B10.S.

OBJECTIVES

We aimed to find candidate genes associated with regulation of renal Hg concentrations.

METHODS

A.SW, B10.S and their F1 and F2 offspring were exposed for 6 weeks to 2.0 mg Hg/L drinking water. Genotyping with microsatellites was conducted on 84 F2 mice for genome-wide scanning with ion pair reverse-phase high-performance liquid chromatography (IP RP HPLC). Quantitative trait loci (QTL) were established. Denaturing HPLC was used to detect single nucleotide polymorphisms for haplotyping and fine mapping in 184 and 32 F2 mice, respectively. Candidate genes (Pprc1, Btrc and Nfkb2) verified by fine mapping and QTL were further investigated by real-time polymerase chain reaction. Genes enhanced by Pprc1 (Nrf1 and Nrf2) were included for gene expression analysis.

RESULTS

Renal Hg concentrations differed significantly between A.SW and B10.S mice and between males and females within each strain. QTL analysis showed a peak logarithm of odds ratio score 5.78 on chromosome 19 (p = 0.002). Haplotype and fine mapping associated the Hg accumulation with Pprc1, which encodes PGC-1-related coactivator (PRC), a coactivator for proteins involved in detoxification. Pprc1 and two genes coactivated by Pprc1 (Nrf1 and Nrf2) had significantly lower gene expression in the A.SW strain than in the B10.S strain.

CONCLUSIONS

This study supports Pprc1 as a key regulator for renal Hg excretion.

CITATION

Alkaissi H, Ekstrand J, Jawad A, Nielsen JB, Havarinasab S, Soderkvist P, Hultman P. 2016. Genome-wide association study to identify genes related to renal mercury concentrations in mice. Environ Health Perspect 124:920-926; http://dx.doi.org/10.1289/ehp.1409284.

The extent of mercury (Hg) exposure among Saudi mothers and their respective infants

A total of 1016 healthy Saudi mothers and their respective infants (aged 3-12 months) were recruited from 57 Primary Health Care Centers (PHCCs) in Riyadh, Saudi Arabia, to evaluate the extent of mercury (Hg) exposure and predict its sources in the healthy Saudi population. Total Hg levels were measured in maternal urine, breast milk, blood, and hair and in the infants' urine and hair. Only 1.9% of the mothers had urinary Hg (UHg)>10 μg/l, the limit for asymptomatic adults recommended by the World Health Organization, but the median (0.99 μg/l) was higher than in other countries. Also, 49.3% of the mothers had UHg>1 μg/l, the German reference value for adults. Median infant UHg was 0.729 μg/l, and 77 and 93 % of the infants had levels higher than 0.4 and 0.1 μg/l, the reference values of the Centers for Disease Control and Prevention and for Germany, respectively. The median Hg level in breast milk was 0.884 μg/l. Even though 43.2% of the milk samples were above the background level for Hg in human milk (1 μg/l), our results were lower than those reported from other countries. Median maternal total Hg in blood was 0.637 μg/l, and only 0.4 and 6.9% of samples were higher than the Hg reference levels of 5.8 μg/l of the Environmental Protection Agency (EPA) and of 2 μg/l for Germany, respectively. Total Hg levels in hair (HHg) varied widely among mothers and infants, but only 3.9% of the mothers and 2.8% of the infants had HHg>1 μg/g (the EPA reference level). Median HHg values were 0.117 μg/g dry weight in mothers and 0.1 μg/g dry weight in infants; both were lower than in other countries. The Hg levels in mothers and their respective infants were relatively low, but our results were consistent with other studies indicating that dental amalgam fillings and fish consumption were the main predictors of maternal Hg exposure. Among the several biomarkers of Hg exposure, Hg levels in maternal hair and urine were the strongest predictors of infant exposure. The lack of an association between Hg in breast milk and Hg in infant urine and hair suggested that the infants were exposed to Hg predominately during pregnancy rather than during breastfeeding. We expect that our data can serve as a baseline for further biomonitoring and follow-up studies, particularly of the long-term impact of Hg on childhood neurodevelopment.

Longitudinal analysis of the association between removal of dental amalgam, urine mercury and 14 self-reported health symptoms

BACKGROUND

Mercury vapor poses a known health risk with no clearly established safe level of exposure. Consequently there is debate over whether the level of prolonged exposure to mercury vapor from dental amalgam fillings, combining approximately 50% mercury with other metals, is sufficiently high to represent a risk to health. The objective of our study is to determine if mercury exposure from amalgam fillings is associated with risk of adverse health effects.

METHODS

In a large longitudinal non-blind sample of participants from a preventative health program in Calgary, Canada we compared number of amalgam fillings, urine mercury measures and changes in 14 self-reported health symptoms, proposed to be mercury dependent sub-clinical measures of mental and physical health. The likelihood of change over one year in a sample of persons who had their fillings removed was compared to a sample of persons who had not had their fillings removed. We use non-parametric statistical tests to determine if differences in urine mercury were statistically significant between sample groups. Logistic regression models were used to estimate the likelihood of observing symptom improvement or worsening in the sample groups.

RESULTS

At baseline, individuals with dental amalgam fillings have double the measured urine mercury compared to a control group of persons who have never had amalgam fillings. Removal of amalgam fillings decreases measured urine mercury to levels in persons without amalgam fillings. Although urine mercury levels in our sample are considered by Health Canada to be too low to pose health risks, removal of amalgam fillings reduced the likelihood of self-reported symptom deterioration and increased the likelihood of symptom improvement in comparison to people who retained their amalgam fillings.

CONCLUSIONS

Our findings suggest that mercury exposure from amalgam fillings adversely impact health and therefore are a health risk. The use of safer alternative materials for dental fillings should be encouraged to avoid the increased risk of health deterioration associated with unnecessary exposure to mercury.