Dental amalgam exposure and urinary mercury levels in children: the New England Children's Amalgam Trial

The association of auditory function measures with low-level methylmercury from oceanic fish consumption and mercury vapor from amalgam: The Seychelles Child Development Study Nutrition 1 Cohort

BACKGROUND

Some authors have reported that low-level exposure to methylmercury (MeHg) adversely impacts measures of auditory function. These reports, however, are not consistent in their findings. Consequently, we examined auditory function in a population exposed to low-level methylmercury (MeHg) exposure from fish consumption and to mercury vapor (Hg0) from dental amalgams. We analyzed their associations with the participants hearing acuity, absolute and interwave ABR latencies, and otoacoustic emissions (distortion product/DPOAE and click evoked/CEOAE).

DESIGN

We administered an audiometry test battery to 246 participants from the Seychelles Child Development Study (SCDS) Nutrition Cohort 1 (NC1) at 9 years of age. The test battery included standard pure-tone audiometry, tympanometry, Auditory Brainstem Responses (ABR) and Distortion Product and Click Evoked Otoacoustic Emissions (DPOAE and CEOAE) testing. We measured prenatal MeHg exposure in maternal hair and postnatal MeHg in children's hair. We approximated prenatal Hg0 exposure using maternal amalgam surface area and postnatal Hg0 using children amalgam surface area. Complete exposure records and audiometric data were available on 210 participants and in them we analyzed the association of MeHg and Hg0 exposures with auditory outcomes using covariate-adjusted linear regression models adjusted for sex and tympanometric pressure.

RESULTS

Hg exposures were similar for both sexes. Seven of the 210 evaluable participants examined had either a mild (5) or moderate (2) hearing loss. Four had a mild monaural hearing loss and 3 had either a mild (1) or moderate (2) bilateral hearing loss. No participant had greater than a moderate hearing loss in either ear. Hg exposures were higher in participants with either a mild or moderate hearing loss, but these differences were not statistically significant. Among the 210 with complete data, neither prenatal nor postnatal MeHg nor Hg0 exposure was statistically significantly associated with any of the ABR endpoints (p > 0.05 for all 72 associations). Neither prenatal nor postnatal Hg0 exposure was associated with any of the OAE endpoints (p > 0.05). MeHg exposure was statistically associated with 6 of the 56 DPOAE endpoints (p-values between 0.0001 and 0.023), but none of the 40 CEOAE endpoints. Two of the associations occurred with prenatal MeHg exposures and 1 of those would suggest a beneficial effect. Four of the other associations occurred with postnatal MeHg exposures with only 2 found in left ears of both males and females and the other 2 in the left and right ear of females at only one frequency.

CONCLUSION

Overall, these data do not present a clear and consistent pattern to suggest that the auditory system is negatively affected by low-level methylmercury exposure due to dietary consumption of oceanic fish or mercury vapor exposure from dental amalgams.

Prenatal and postnatal mercury exposure and blood pressure in childhood

Elevated blood pressure in childhood is an important risk factor for hypertension in adulthood. Environmental exposures have been associated with elevated blood pressure over the life course and exposure to mercury (Hg) has been linked to cardiovascular effects in adults. As subclinical vascular changes begin early in life, Hg may play a role in altered blood pressure in children. However, the evidence linking early life Hg exposure to altered blood pressure in childhood has been largely inconsistent. In the ongoing New Hampshire Birth Cohort Study, we investigated prenatal and childhood Hg exposure at multiple time points and associations with blood pressure measurements in 395 young children (mean age 5.5 years, SD 0.4). Hg exposure was measured in children's toenail clippings at age 3 and in urine at age 5-6 years, as well as in maternal toenail samples collected at ∼28 weeks gestation and 6 weeks postpartum, the latter two samples reflecting early prenatal and mid-gestation exposures, respectively. Five measurements of systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) were averaged for each child using a standardized technique. In covariate-adjusted linear regression analyses, we observed that a 0.1 μg/g increase in child toenail Hg at age 3 or a 0.1 μg/L urine Hg at age 5-6 were individually associated with greater DBP (toenail β: 0.53 mmHg; 95% CI: -0.02, 1.07; urine β: 0.48 mmHg; 95% CI: 0.10, 0.86) and MAP (toenail β: 0.67 mmHg; 95% CI: 0.002, 1.33; urine β: 0.55 mmHg; 95% CI: 0.10, 1.01). Neither early prenatal nor mid-gestation Hg exposure, as measured by maternal toenails, were related to any changes to child BP. Simultaneous inclusion of both child urine Hg and child toenail Hg in models suggested a potentially stronger relationship of urine Hg at age 5-6 with DBP and MAP, as compared to toenail Hg at age 3. Our findings suggest that Hg exposure during childhood is associated with alterations in BP. Childhood may be an important window of opportunity to reduce the impacts of Hg exposure on children's blood pressure, and in turn, long-term health.

Prenatal exposure to mercury in relation to infant infections and respiratory symptoms in the New Hampshire Birth Cohort Study

BACKGROUND

Mechanistic studies support the potential for mercury (Hg) to alter immunity, including via in utero exposure. As yet, there are few prospective studies of in utero Hg exposure and subsequent immune-related outcomes, especially in infancy.

OBJECTIVES

We investigated the association of biomarkers of prenatal Hg exposure and maternal silver-mercury dental amalgams with the occurrence of infant allergy, respiratory infection, and respiratory symptoms in the first year of life.

METHODS

The New Hampshire Birth Cohort Study (NHBCS) ascertained information on infant allergies, infections and symptoms through telephone interviews at 4, 8 and 12 months postpartum and measured total Hg in maternal toenails collected at ~28-30 weeks gestation. Information on maternal fish consumption and presence of dental amalgams was obtained from a questionnaire administered at study enrollment at 24-28 weeks. A total of 1321 NHBCS mother-infant pairs had at least one Hg exposure measure (toenail Hg or information on dental amalgams) and information on dietary fish intake. Generalized linear models and generalized estimating equation models with Poisson regression adjusted for potential confounders (maternal age, level of education, parity, smoking, alternative Healthy Eating Index-2010, infant sex, gestational age, feeding mode, and day care attendance) were used to assess the association between infant outcomes and prenatal toenail Hg levels. We subsetted this analysis on mothers who consumed fish (n = 706) as a measure of in utero methylmercury (MeHg) exposure. Associations between infant outcomes and dental amalgams as a measure of in utero inorganic Hg exposure were assessed among mothers who did not consume fish (n = 218).

RESULTS

Among women who ate fish during pregnancy, higher maternal toenail Hg concentrations were associated with an increased risk of lower respiratory infections and respiratory symptoms requiring a doctor visit among infants age 9-12 months (relative risk (RR) 1.4 (95% CI: 1.1, 1.9) and 1.2 (95% CI: 1.0, 1.4) respectively), whereas a reduced risk of lower respiratory infections was observed among infants 0-4 months of age (RR = 0.7 (95% CI: 0.5, 1.0). We found little to no evidence of associations of toenail Hg with upper respiratory infections, allergy or eczema at any age to one year. Among infants of mothers who did not consume fish, we found an elevated risk of upper respiratory infections requiring a doctor visit in relation to having dental amalgams during pregnancy (RR = 1.5 (95% CI: 1.1, 2.1)). Overall, weaker associations were observed with lower respiratory infections, respiratory symptoms, and medically confirmed allergies, and there was no association with eczema.

CONCLUSIONS

Our analyses of a US birth cohort, along with prior mechanistic work, raise the possibility that gestational Hg exposure through fish/seafood consumption and dental amalgams may alter respiratory infections and respiratory symptoms in infants.

Mercury in Children: Current State on Exposure through Human Biomonitoring Studies

Mercury (Hg) in children has multiple exposure sources and the toxicity of Hg compounds depends on exposure routes, dose, timing of exposure, and developmental stage (be it prenatal or postnatal). Over the last decades, Hg was widely recognized as a threat to the children’s health and there have been acknowledgements at the international level of the need of a global policy intervention—like the Minamata treaty—aimed at reducing or preventing Hg exposure and protecting the child health. National human biomonitoring (HBM) data has demonstrated that low levels of exposure of Hg are still an important health concern for children, which no one country can solve alone. Although independent HBM surveys have provided the basis for the achievements of exposure mitigation in specific contexts, a new paradigm for a coordinated global monitoring of children’s exposure, aimed at a reliable decision-making tool at global level is yet a great challenge for the next future. The objective of the present review is to describe current HBM studies on Hg exposure in children, taking into account the potential pathways of Hg exposure and the actual Hg exposure levels assessed by different biomarkers.

Exposure to mercury in susceptible population groups living in the former mercury mining town of Idrija, Slovenia

500 years of mercury (Hg) mining in the town of Idrija has caused severe pollution in Idrija and its surroundings. Following the closure of the mine in 1995, the environment remains contaminated with Hg. Sources of elemental-, inorganic- and methyl Hg exposure were identified, potential environmental level of exposure to Hg was evaluated and actual internal exposure to Hg was assessed in selected susceptible population groups comprising school-age children and pregnant women living in Idrija and in control groups from rural and urban environments. The study of pregnant women (n=31) was conducted between 2003 and 2008, and the study of school-age children (n=176) in 2008. Potential interaction of Hg with selenium (Se) in plasma was assessed in both study populations, while in pregnant women antioxidative enzyme activity (glutathione peroxidase, superoxide dismutase and catalase) in erythrocytes of maternal and cord blood was also assessed. Actual exposure to Hg as indicated by levels of Hg in children's blood (geometric mean (GM) 0.92µg/L), mother's blood (GM 1.86µg/L), children's urine (GM 1.08µg/g crea.), mother's urine (GM 2.51µg/L), children's hair (GM 241ng/g) and mother's hair (GM 251ng/g) was higher in the two study groups from Idrija than in the control groups from rural areas, but was still at the level of a "normal" population and reflects mainly exposure to elemental Hg (Hg°) from dental amalgam and, to a certain extent atmospheric Hg°. Furthermore, the internal doses of Hg received during pregnancy did not decrease the bioavailability of Se. Based on observation in children, the increase in Se protein expression is suggested to be a consequence of moderately elevated exposure to Hg°. The observed changes in activity of antioxidative enzymes, as biomarkers of oxidative stress, appear to be mainly associated with pregnancy per se and not with an increased exposure to Hg. In view of the continuing increased potential for Hg exposure and the low number of pregnant women studied, the results warrant a further longitudinal study of a larger group of pregnant women residing in the area of the former mercury mine.

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.

Dental amalgam exposure can elevate urinary mercury concentrations in children

OBJECTIVES

Owing to its cost-effectiveness and operative convenience, dental amalgam remains in use as a restorative material for tooth caries in children in many countries. The aim of this study was to evaluate the relationship between dental amalgam exposure and urinary mercury (U-Hg) concentrations in children.

METHODS

In this longitudinal study, 463, 367 and 348 children, 8-11 years of age, were evaluated at baseline, and at the first and second follow-up visits, respectively. The interval between each survey was 6 months. For the oral examination and urine sample, the amalgam-filled tooth surface (TS), and U-Hg and creatinine concentrations of participants were determined, and the cumulative amalgam-filled TS and cumulative creatinine-adjusted U-Hg were calculated. To assess potential covariates, socio-demographic factors, oral health behaviour and dietary factors were surveyed by questionnaire. Data were analysed by the t-test, correlation analysis and mixed-model analysis. The statistical analyses were performed using SPSS 18.0.

RESULTS

Children with more than one amalgam-filled TS exhibited significantly higher creatinine-adjusted U-Hg concentrations than those without, in all three survey periods (P < 0.001). The results for the current and cumulative amalgam-filled TS significantly correlated with those for the current and cumulative creatinine-adjusted U-Hg concentration, respectively, in all surveys (P < 0.001). In the repeated-measures mixed model analysis, current and cumulative amalgam-filled TS was significantly related to current and cumulative creatinine-adjusted U-Hg concentration, respectively (P < 0.001).

CONCLUSIONS

Amalgam-filled TS was significantly correlated with U-Hg concentrations in children. Therefore, dental amalgam exposure can affect the systemic mercury concentration in children.

Vasorelaxant effects of mercury on rat thoracic aorta: the nitric oxide signaling mechanism

Mercury, a heavy metal, is widespread and persistent in the environment and has been elucidated as a possible risk factor in cardiovascular diseases. Mercury has been reported to selectively impair the nitric oxide (NO) pathway in the vascular endothelium as a consequence of oxidative stress. Conversely, mercury per se causes endothelium-dependent vasorelaxation at lower concentration via the NO pathway. Little is known about the effects of mercury per se on other endothelial mediators. To elucidate possible mechanisms involved in this action, isometric tension was measured in aortic rings precontracted with phenylephrine (10 µM) from Wistar rats. Responses to increasing concentrations of inorganic mercuric chloride (10(-12)-10(-5) M) were obtained in the presence and absence of endothelium. Inorganic mercury produced a biphasic response in endothelium-intact aortic rings and produced only vasoconstriction in endothelium-denuded aortic rings. To study the possible underlying mechanisms for the biphasic response of mercury, increasing concentrations of mercuric chloride (10(-12)-10(-5) M) were used before and after N(G)-nitro-L-arginine methyl ester (L-NAME (10(-4) M)), glybenclamide (10(-5) M), superoxide dismutase (10 U/ml) + catalase (100 U/ml), and nifedipine (10(-4) M) treatment. Results suggest that mercury produces endothelium-dependent relaxation at low concentration mediated by endothelial-generated NO and endothelium-derived hyperpolarizing factor and endothelium-independent contraction resulting from the blockade of L-type Ca(2+) channels by generation of free radicals.

Neurodevelopmental outcomes at 5 years in children exposed prenatally to maternal dental amalgam: the Seychelles Child Development Nutrition Study

Limited human data are available to assess the association between prenatal mercury vapor (Hg⁰)) exposure from maternal dental amalgam restorations and neurodevelopment of children. We evaluated the association between maternal dental amalgam status during gestation and children's neurodevelopmental outcomes at 5 years in the Seychelles Child Development Nutrition Study (SCDNS). Maternal amalgam status was determined prospectively in a longitudinal cohort study examining the associations of prenatal exposure to nutrients and methylmercury (MeHg) with neurodevelopment. A total of 236 mother-child pairs initially enrolled in the SCDNS in 2001 were eligible to participate. Maternal amalgam status was measured as number of amalgam surfaces (the primary metric) and number of occlusal points. The neurodevelopmental assessment battery was comprised of age-appropriate tests of cognitive, language, and perceptual functions, and scholastic achievement. Linear regression analysis controlled for MeHg exposure, maternal fatty acid status, and other covariates relevant to child development. Maternal amalgam status evaluation yielded an average of 7.0 surfaces (range 0-28) and 11.0 occlusal points (range 0-40) during pregnancy. Neither the number of maternal amalgam surfaces nor occlusal points were associated with any outcome. Our findings do not provide evidence to support a relationship between prenatal exposure to Hg⁰ from maternal dental amalgam and neurodevelopmental outcomes in children at 5 years of age.

Health effects in the Flemish population in relation to low levels of mercury exposure: from organ to transcriptome level

Due to possible health risks, quantification of mercury accumulation in humans was included in the Flemish biomonitoring programmes FLEHS I (2002-2006) and FLEHS II (2007-2011). The general objective of FLEHS I was to assess regional exposure levels in order to link possible differences in these internal exposure levels to different types of local environmental pressure. Therefore, Hg and MMHg (methylmercury) were only measured in pooled blood samples per region and per age class. In FLEHS II, mercury concentrations were measured in hair of each participant. About 200 adolescents and 250 mothers (reference group) and two times 200 adolescents (2 hotspots) were screened. The main objectives of the FLEHS II study were: (1) to determine reference levels of mercury in hair for Flanders; (2) to assess relations between mercury exposure and possible sources like fish consumption; (3) to assess dose-effect relations between mercury exposure and health effect markers. The results showed that mercury concentrations in the Flemish population were rather low compared to other studies. Mercury levels in the Flemish populations were strongly related to the age of the participants and consumption of fish. Significant negative associations were observed between mercury in hair and asthma, having received breast feeding as a newborn, age at menarche in girls, allergy for animals and free testosterone levels. Significant correlations were also observed between mercury in hair and genes JAK2, ARID4A, Hist1HA4L (boys) and HLAdrb5, PIAS2, MANN1B1, GIT and ABCA1 (girls).

Risk aspects of dental restoratives: From amalgam to tooth-colored materials

Dental materials’ choice of patients has considerably changed. Whereas cast gold and amalgam have been the predominant biomaterials for decades, today tooth-colored materials like resin-based composites and ceramics are more and more successful. However, are we going to replace a good but biologically questionable material (amalgam) with an equal material (resin composite) being more esthetic but also biologically questionable For amalgam, long-term clinical studies reported some significant hints that in single cases amalgam may be a health hazard for patients, finally Norway banned amalgam completely. The main advantage of a resin-based composite over amalgam is its tooth-like appearance and more or less absence of extensive preparation rules. For many years it was believed that resin-based composites may cause pulpal injury. However, pulpal injury associated with the use of resin-based composites is not correlated with their cytotoxic properties. Nevertheless, resin-based composites and other dental materials require rigorous safety evaluation and continuous monitoring to prevent adverse events similar like with amalgam. Because of non-biocompatible pulp responses to resin-based composites and amalgam, they should not be placed in direct contact with the dental pulp. The less dentin remaining in the floor of preparations between resin-based composites or other dental materials is more likely to cause pulpitis. Percentage of patients and dental practitioners who display allergic reactions is between 0.7% and 2%. The release of cytotoxic monomers from resin-based materials is highest after polymerization and much lower after 1 wk. Substances released from resin-based composites have been shown to be toxic in cytotoxicity tests. Nevertheless, in vitro cytotoxicity assays have shown that amalgam has greater toxic effects than resin-based composites, sometime 100-700-fold higher. Altogether, the risk of side-effects is low, but not zero, especially for dental personnel.

Prenatal exposure to dental amalgam in the Seychelles Child Development Nutrition Study: associations with neurodevelopmental outcomes at 9 and 30 months

BACKGROUND

Dental amalgam is approximately 50% metallic mercury and releases mercury vapor into the oral cavity, where it is inhaled and absorbed. Maternal amalgams expose the developing fetus to mercury vapor. Mercury vapor can be toxic, but uncertainty remains whether prenatal amalgam exposure is associated with neurodevelopmental consequences in offspring.

OBJECTIVE

To determine if prenatal mercury vapor exposure from maternal dental amalgam is associated with adverse effects to cognition and development in children.

METHODS

We prospectively determined dental amalgam status in a cohort of 300 pregnant women recruited in 2001 in the Republic of Seychelles to study the risks and benefits of fish consumption. The primary exposure measure was maternal amalgam surfaces present during gestation. Maternal occlusal points were a secondary measure. Outcomes were the child's mental (MDI) and psychomotor (PDI) developmental indices of the Bayley Scales of Infant Development-II (BSID-II) administered at 9 and 30 months. Complete exposure, outcome, and covariate data were available on a subset of 242 mother-child pairs.

RESULTS

The number of amalgam surfaces was not significantly (p>0.05) associated with either PDI or MDI scores. Similarly, secondary analysis with occlusal points showed no effect on the PDI or MDI scores for boys and girls combined. However, secondary analysis of the 9-month MDI was suggestive of an adverse association present only in girls.

CONCLUSION

We found no evidence of an association between our primary exposure metric, amalgam surfaces, and neurodevelopmental endpoints. Secondary analyses using occlusal points supported these findings, but suggested the possibility of an adverse association with the MDI for girls at 9 months. Given the continued widespread use of dental amalgam, we believe additional prospective studies to clarify this issue are a priority.

Dental composites and amalgam and physical development in children

Resin-based composite dental restoration materials may release bisphenol-A, an endocrine-disrupting chemical. Using secondary analysis of a randomized clinical safety trial of amalgam vs. composites, we tested the hypothesis that dental restoration materials affect children's growth. Children (N = 218 boys, N = 256 girls) aged 6 to 10 yrs at baseline with ≥ 2 decayed posterior teeth were randomized to amalgam or composites (bisphenol-A-diglycidyl-dimethacrylate composite for permanent teeth, urethane-dimethacrylate compomer for primary teeth) for treatment of posterior caries throughout follow-up. Primary outcomes for this analysis were 5-year changes in BMI-for-age z-scores, body fat percentage (BF%), and height velocity; exploratory analyses (n = 113) examined age at menarche. Results showed no significant differences between treatment assignment and changes in physical development in boys [(composites vs. amalgam) BF%, 4.9 vs. 5.7, p = 0.49; (BMI-z-score) 0.13 vs. 0.25, p = 0.36] or girls (8.8 vs. 7.7, p = 0.95; 0.36 vs. 0.21, p = 0.49). Children with more treatment on primary teeth had greater increases in BF% regardless of material type. Girls assigned to composites had lower risk of menarche during follow-up (hazard ratio = 0.57, 95% CI 0.35-0.95). Overall, there were no significant differences in physical development over 5 years in children treated with composites or amalgam. Additional studies examining these restoration materials in relation to age at menarche are warranted (clinicaltrials.gov number NCT00065988).

Dental composite restorations and neuropsychological development in children: treatment level analysis from a randomized clinical trial

BACKGROUND

Resin-based dental restorations may intra-orally release their components and bisphenol A. Gestational bisphenol A exposure has been associated with poorer executive functioning in children.

OBJECTIVES

To examine whether exposure to resin-based composite restorations is associated with neuropsychological development in children.

METHODS

Secondary analysis of treatment level data from the New England Children's Amalgam Trial, a 2-group randomized safety trial conducted from 1997 to 2006. Children (N=534) aged 6-10 y with ≥2 posterior tooth caries were randomized to treatment with amalgam or resin-based composites (bisphenol-A-diglycidyl-dimethacrylate-composite for permanent teeth; urethane dimethacrylate-based polyacid-modified compomer for primary teeth). Neuropsychological function at 4- and 5-year follow-up (N=444) was measured by a battery of tests of executive function, intelligence, memory, visual-spatial skills, verbal fluency, and problem-solving. Multivariable generalized linear regression models were used to examine the association between composite exposure levels and changes in neuropsychological test scores from baseline to follow-up. For comparison, data on children randomized to amalgam treatment were similarly analyzed.

RESULTS

With greater exposure to either dental composite material, results were generally consistent in the direction of slightly poorer changes in tests of intelligence, achievement or memory, but there were no statistically significant associations. For the four primary measures of executive function, scores were slightly worse with greater total composite exposure, but statistically significant only for the test of Letter Fluency (10-surface-years β=-0.8, SE=0.4, P=0.035), and the subtest of color naming (β=-1.5, SE=0.5, P=0.004) in the Stroop Color-Word Interference Test. Multivariate analysis of variance confirmed that the negative associations between composite level and executive function were not statistically significant (MANOVA, P=0.18). Results for greater amalgam exposure were mostly nonsignificant in the opposite direction of slightly improved scores over follow-up.

CONCLUSIONS

Dental composite restorations had statistically insignificant associations of small magnitude with impairments in neuropsychological test change scores over 4- or 5-years of follow-up in this trial.

Dental composite restorations and psychosocial function in children

BACKGROUND AND OBJECTIVE

Resin-based dental materials may intraorally release their chemical components and bisphenol A. The New England Children's Amalgam Trial found that children randomized to amalgam had better psychosocial outcomes than those assigned to composites for posterior tooth restorations. The objective of this study was to examine whether greater exposure to dental composites is associated with psychosocial problems in children.

METHODS

Analysis of treatment-level data from the New England Children's Amalgam Trial, a 2-group randomized safety trial comparing amalgam with the treatment plan of bisphenol A-glycidyl methacrylate (bisGMA)-based composite and urethane dimethacrylate-based polyacid-modified composite (compomer), among 534 children aged 6 to 10 years at baseline. Psychosocial function at follow-up (n = 434) was measured by using the self-reported Behavior Assessment System for Children (BASC-SR) and parent-reported Child Behavior Checklist (CBCL).

RESULTS

Children with higher cumulative exposure to bisGMA-based composite had poorer follow-up scores on 3 of 4 BASC-SR global scales: Emotional Symptoms (β = 0.8, SE = 0.3, P = .003), Clinical Maladjustment (β = 0.7, SE = 0.3, P = .02), and Personal Adjustment (β = -0.8, SE = 0.2, P = .002). Associations were stronger with posterior-occlusal (chewing) surfaces, where degradation of composite was more likely. For CBCL change, associations were not statistically significant. At-risk or clinically significant scores were more common among children with greater exposure for CBCL Total Problem Behaviors (16.3% vs 11.2%, P-trend = .01) and numerous BASC-SR syndromes (eg, ≥ 13 vs 0 surface-years, Interpersonal Relations 13.7% vs 4.8%, P-trend = .01). No associations were found with compomer, nor with amalgam exposure levels among children randomized to amalgam.

CONCLUSIONS

Greater exposure to bisGMA-based dental composite restorations was associated with impaired psychosocial function in children, whereas no adverse psychosocial outcomes were observed with greater urethane dimethacrylate-based compomer or amalgam treatment levels.

Effect of mercury (Hg) dental amalgam fillings on renal and oxidative stress biomarkers in children

We examined the effect of mercury (Hg) associated with dental amalgam fillings on biomarkers of renal and oxidative stress in children between the ages of 5-15.5 years. Urine samples were analyzed for N-acetyl-β-D-glucosaminidase (NAG), α(1)-microglobulin (α(1)-MG), β(2)-microglobulin (β(2)-MG), retinol binding protein (RBP), albumin (ALB), 8-hydroxy-2-deoxyguanosine (8-OHdG) and malondialdehyde (MDA). The level of urinary Hg (UHg-C) was calculated as μg/g creatinine. Multiple regression analyses revealed that the excretion of urinary NAG was significantly associated with the presence of dental amalgam fillings (β=0.149, P=0.03) and the levels of UHg-C (β=0.531, P=0), with an interaction between the two (P=0). The increase in urinary NAG in relation to UHg-C levels had a dose-effect pattern. The lowest observed effect was seen at UHg-C levels above 1.452 μg/g creatinine, which is lower than previously reported. In contrast, α(1)-MG was negatively associated with the presence of dental amalgam fillings (β=-0.270, P=0), but positively with UHg-C levels (β=0.393, P=0). There were 7 children without, and one child with, dental amalgam fillings with urinary α(1)-MG levels above the reference limit of >7 mg/g creatinine. Even though α(1)-MG seems to be a reliable biomarker for early changes in renal functions, it might exert its effect only at a higher level of exposure. An inverse relationship was also observed between urinary 8-OHdG levels and the presence of dental amalgam fillings. This might suggest that the dental amalgam does not increase DNA damage but reduces the capacity to repair DNA, leading to lower urinary excretion of 8-OHdG. On the other hand, we found that Hg affected the excretion of urinary 8-OHdG in a dose-related pattern that was mostly associated with long-term exposure to low Hg levels. Urinary NAG levels were positively associated with urinary MDA levels (β=0.516, P=0) but not with 8-OHdG (β=0.134, P=0.078) after adjustment for potential confounders. Both UHg-C and the presence of dental amalgam fillings remained predictors of the NAG model. Our data provide evidence that low exposure to Hg from dental amalgam fillings exerts an effect on kidney tubular functions in children. Oxidative stress may have played a role in this mechanism. The results of this study would also suggest that urinary NAG is the most sensitive of all the investigated renal biomarkers. These results should be confirmed with further investigation.

Improper waste disposal of silver-mercury amalgam

The objective of this work was to estimate the quantity of mercury residue present in dental amalgam that is generated and discarded in the city of Manaus (Amazon-Brazil). For this purpose, the locations of amalgam usage (10 public and 31 private dental clinics), the method by which the residue is discarded (14 clinics improper disposal), and the analysis of total mercury in the sediment of the controlled landfill (2.68-3 μgHg/g), were described. It was concluded that: there are dental clinics in the city that discard mercury residue into the common waste disposal system, which contravenes health safety standards.

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.

Mercury (Hg) burden in children: the impact of dental amalgam

The risks and benefits of using mercury (Hg) in dental amalgam have long been debated. This study was designed to estimate Hg body burden and its association with dental amalgam fillings in 182 children (ages: 5-15 years) living in Taif City. Hg was measured in urine (UHg), hair (HHg) and toenails (NHg) by the Atomic Absorption Spectrophotometer with Vapor Generator Accessory system. Urinary Hg levels were calculated as both micrograms per gram creatinine (μg/g creatinine) and micrograms per liter (μg/L). We found that children with amalgam fillings (N=106) had significantly higher UHg-C levels than children without (N=76), with means of 3.763 μg/g creatinine versus 3.457 μg/g creatinine, respectively (P=0.019). The results were similar for UHg (P=0.01). A similar pattern was also seen for HHg, with means of 0.614 μg/g (N=97) for children with amalgam versus 0.242 μg/g (N=74) for those without amalgam fillings (P=0). Although the mean NHg was higher in children without amalgam (0.222 μg/g, N=61) versus those with (0.163 μg/g, N=101), the relationship was not significant (P=0.069). After adjusting for many confounders, the multiple logistic regression model revealed that the levels of UHg-C and HHg were 2.047 and 5.396 times higher, respectively, in children with dental amalgam compared to those without (P<0.01). In contrast, a significant inverse relationship was seen between NHg levels and dental amalgam fillings (P=0.003). Despite the controversy surrounding the health impact of dental amalgam, this study showed some evidence that amalgam-associated Hg exposure might be related with symptoms of oral health, such as aphthous ulcer, white patches, and a burning-mouth sensation. Further studies are needed to reproduce these findings. The present study showed that significant numbers of children with or without amalgam had Hg levels exceeding the acceptable reference limits. The detrimental neurobehavioral and/or nephrotoxic effects of such an increased Hg on children should be a cause of concern, and further investigation is warranted. Our results are alarming and indicate an urgent need for biomonitoring and assessment of exposure. Changes in dental practices involving amalgam, especially for children, are highly recommended in order to avoid unnecessary exposure to Hg.

Immune function effects of dental amalgam in children: a randomized clinical trial

BACKGROUND

Dental amalgam is a widely used restorative material containing 50 percent elemental mercury that emits mercury vapor. No randomized clinical trials have determined whether there are adverse immunological effects associated with this low-level mercury exposure in children. The objective of this study was to evaluate a subpopulation of the participants in the New England Children's Amalgam Trial for in vitro manifestations of immunotoxic effects of dental amalgam.

METHODS

The authors conducted a randomized clinical trial in which children requiring dental restorative treatment were randomly assigned to receive either amalgam for posterior restorations or resin-based composite restorations. They assessed 66 children, aged 6 to 10 years, for total white blood cell counts, specific lymphocyte (T-cell and B-cell) counts and lymphocyte, neutrophil and monocyte responsiveness across a five-year period. Because of the small number of participants, the authors acknowledge that the study is exploratory in nature and has limited statistical power.

RESULTS

The mean number of tooth surfaces restored during the five-year period was 7.8 for the amalgam group and 10.1 for the composite group. In the amalgam group, there was a slight, but not statistically significant, decline in responsiveness of T cells and monocytes at five to seven days after treatment; the authors consistently observed no differences at six, 12 or 60 months.

CONCLUSIONS

The findings of this study confirm that treatment of children with amalgam restorations leads to increased, albeit low-level, exposure to mercury. In this exploratory analysis of immune function, amalgam exposure did not cause overt immune deficits, although small transient effects were observed five to seven days after restoration placement.

CLINICAL IMPLICATIONS

These findings suggest that immunotoxic effects of amalgam restorations are minimal and transient in children and most likely do not need to be of concern to practitioners considering the use of this restorative dental material.