Dental amalgam and psychosocial status: the New England Children's Amalgam Trial

Direct composite resin fillings versus amalgam fillings for permanent posterior teeth

BACKGROUND

Traditionally, amalgam has been used for filling cavities in posterior teeth, and it continues to be the restorative material of choice in some low- and middle-income countries due to its effectiveness and relatively low cost. However, there are concerns over the use of amalgam restorations (fillings) with regard to mercury release in the body and the environmental impact of mercury disposal. Dental composite resin materials are an aesthetic alternative to amalgam, and their mechanical properties have developed sufficiently to make them suitable for restoring posterior teeth. Nevertheless, composite resin materials may have potential for toxicity to human health and the environment. The United Nations Environment Programme has established the Minamata Convention on Mercury, which is an international treaty that aims "to protect the [sic] human health and the environment from anthropogenic emissions and releases of mercury and mercury compounds". It entered into force in August 2017, and as of February 2021 had been ratified by 127 governments. Ratification involves committing to the adoption of at least two of nine proposed measures to phase down the use of mercury, including amalgam in dentistry. In light of this, we have updated a review originally published in 2014, expanding the scope of the review by undertaking an additional search for harms outcomes. Our review synthesises the results of studies that evaluate the long-term effectiveness and safety of amalgam versus composite resin restorations, and evaluates the level of certainty we can have in that evidence.

OBJECTIVES

To examine the effects (i.e. efficacy and safety) of direct composite resin fillings versus amalgam fillings.

SEARCH METHODS

An information specialist searched five bibliographic databases up to 16 February 2021 and used additional search methods to identify published, unpublished and ongoing studies SELECTION CRITERIA: To assess efficacy, we included randomised controlled trials (RCTs) comparing dental composite resin with amalgam restorations in permanent posterior teeth that assessed restoration failure or survival at follow-up of at least three years. To assess safety, we sought non-randomised studies in addition to RCTs that directly compared composite resin and amalgam restorative materials and measured toxicity, sensitivity, allergy, or injury.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane.

MAIN RESULTS

We included a total of eight studies in this updated review, all of which were RCTs. Two studies used a parallel-group design, and six used a split-mouth design. We judged all of the included studies to be at high risk of bias due to lack of blinding and issues related to unit of analysis. We identified one new trial since the previous version of this review (2014), as well as eight additional papers that assessed safety, all of which related to the two parallel-group studies that were already included in the review. For our primary meta-analyses, we combined data from the two parallel-group trials, which involved 1645 composite restorations and 1365 amalgam restorations in 921 children. We found low-certainty evidence that composite resin restorations had almost double the risk of failure compared to amalgam restorations (risk ratio (RR) 1.89, 95% confidence interval (CI) 1.52 to 2.35; P < 0.001), and were at much higher risk of secondary caries (RR 2.14, 95% CI 1.67 to 2.74; P < 0.001). We found low-certainty evidence that composite resin restorations were not more likely to result in restoration fracture (RR 0.87, 95% CI 0.46 to 1.64; P = 0.66). Six trials used a split-mouth design. We considered these studies separately, as their reliability was compromised due to poor reporting, unit of analysis errors, and variability in methods and findings. Subgroup analysis showed that the findings were consistent with the results of the parallel-group studies. Three trials investigated possible harms of dental restorations. Higher urinary mercury levels were reported amongst children with amalgam restorations in two trials, but the levels were lower than what is known to be toxic. Some differences between amalgam and composite resin groups were observed on certain measures of renal, neuropsychological, and psychosocial function, physical development, and postoperative sensitivity; however, no consistent or clinically important harms were found. We considered that the vast number of comparisons made false-positive results likely. There was no evidence of differences between the amalgam and composite resin groups in neurological symptoms, immune function, and urinary porphyrin excretion. The evidence is of very low certainty, with most harms outcomes reported in only one trial.

AUTHORS' CONCLUSIONS

Low-certainty evidence suggests that composite resin restorations may have almost double the failure rate of amalgam restorations. The risk of restoration fracture does not seem to be higher with composite resin restorations, but there is a much higher risk of developing secondary caries. Very low-certainty evidence suggests that there may be no clinically important differences in the safety profile of amalgam compared with composite resin dental restorations. This review supports the utility of amalgam restorations, and the results may be particularly useful in parts of the world where amalgam is still the material of choice to restore posterior teeth with proximal caries. Of note, however, is that composite resin materials have undergone important improvements in the years since the trials informing the primary analyses for this review were conducted. The global phase-down of dental amalgam via the Minamata Convention on Mercury is an important consideration when deciding between amalgam and composite resin dental materials. The choice of which dental material to use will depend on shared decision-making between dental providers and patients in the clinic setting, and local directives and protocols.

Is Dental Amalgam a Higher Risk Factor rather than Resin-Based Restorations for Systemic Conditions? A Systematic Review

Objective: The aim of this study was to confirm the hypothesis that patients with one or more amalgam restorations have an increased risk for systemic diseases rather than patients with resin-based restorations. Data: The data search produced an initial 3568 total number of records. All titles and abstract were reviewed by five independent examiners, and only 36 records were selected for full text in depth examination. Out of these, only nine publications matched the inclusion criteria and were included in this systematic review. Sources: Electronic databases (MEDLINE, Scopus, Embase, and Web of Knowledge) were searched up to June 2019. In addition, a manual search was carried out on journals related to this topic. Study selection: All selected human clinical studies compared patients with dental amalgam restorations to patients with non-amalgam restorations on restorative material related diseases/health conditions with at least 50 patients and a reasonable follow up. The systemic effects of dental restorations were analyzed. As for any systemic effects, there was no difference between amalgam and composite restoration. Conclusions: With the limitations of the few available randomized controlled trials (RCTs) on the matter, amalgam restorations, similarly to other modern resin-based materials, were not related to an increased risk of systemic diseases or conditions. Clinical significance: On the basis of the available RCTs, amalgam restorations, if compared with resin-based fillings, do not show an increased risk for systemic diseases. There is still insufficient evidence to exclude or demonstrate any direct influence on general health. The removal of old amalgam restorations and their substitution with more modern adhesive restorations should be performed only when clinically necessary and not just for material concerns. In order to better evaluate the safety of dental amalgam compared to other more modern restorative materials, further RCTs that consider important parameters such as long and uniform follow up periods, number of restorations per patient, and sample populations representative of chronic or degenerative diseases are needed.

Clinical Effects of Mercury in Conservative Dentistry: A Systematic Review, Meta-Analysis, and Trial Sequential Analysis of Randomized Controlled Trials

Methods

A systematic literature search was conducted in four electronic databases (Ovid via PubMed, Web of Science, Scopus, and CENTRAL) including all available randomised controlled trials published in the last 15 years comparing the use of dental amalgam with composite resins in humans with a follow-up period of at least one year. The primary outcome was the Hg concentration in biological fluids (urine, hair, blood, and saliva) with the aim of assessing their reliability as biomarkers of Hg exposure. The risk of bias was assessed through the Cochrane Collaboration tool and the overall quality of evidence through the Grading of Recommendations, Assessment, Development and Evaluations (GRADE) system. The results of the meta-analysis were expressed using a random-effects model, and their power was assessed through the trial sequential analysis (TSA).

Results

From the initial 2555 results, only 6 publications were included in the review: five were considered as having high risk of bias, whereas one as having moderate risk. Only two articles were eligible for quantitative analysis. The meta-analysis gathered data from 859 patients but was nevertheless not significant (p = 0.12). The TSA confirmed this evidence revealing that it was due to a lack of statistical power since the required information size (RIS) threshold is not reached.

Conclusions

The existing evidence revealed that there are not enough data to support the hypothesis that restorations with dental amalgam can cause nephrotoxicity when compared with composite resins restorations.

Knowledge, Attitude, and Behavior of Restorative, Orthodontic, and Pediatric Departments' Members toward Bisphenol A Dental Exposures

AIM AND OBJECTIVES

The aim of this study is to evaluate the knowledge, attitude, and behavior of Restorative, Orthodontic, and Pediatric Dentistry Departments' members at King Abdulaziz University (KAU), Jeddah, Saudi Arabia, toward bisphenol A (BPA) dental exposure.

MATERIALS AND METHODS

A survey was pretested for face and content validity. It included ten knowledge-, four attitude-, and five behavior-based items. The collected data were analyzed using Windows SPSS software version 22 (IBM Corp., Armonk, NY, USA). Significant levels were set at 0.05.

RESULTS

A total of 109 members participated in this study. Most of them (80 [73.4]) had never attended a lecture or read an article on BPA dental exposure previously. The restorative department members showed the highest (mean ± standard deviation score) in knowledge-based questions (3.32 ± 3.323), and those who reported that they had heard of BPA previously, read an article, or attended a lecture on BPA received significantly higher mean knowledge scores (P < 0.0001). The pediatric dentistry departments' members showed significantly higher agreements to attitude questions. Only ten participants (9.2%) followed the recommended guidelines to reduce patients' exposure to BPA during the application of BPA-containing dental materials.

CONCLUSIONS

Reading an article or attending a lecture on BPA significantly improves the knowledge scores. Therefore, there is a need to increase the awareness on BPA dental exposure among different departments' members in KAU to ensure that BPA exposure to patients is minimized and to ensure the spread of this knowledge to the dental students.

Determination of Highly Sensitive Biological Cell Model Systems to Screen BPA-Related Health Hazards Using Pathway Studio

Bisphenol-A (BPA) is a ubiquitous endocrine-disrupting chemical. Recently, many issues have arisen surrounding the disease pathogenesis of BPA. Therefore, several studies have been conducted to investigate the proteomic biomarkers of BPA that are associated with disease processes. However, studies on identifying highly sensitive biological cell model systems in determining BPA health risk are lacking. Here, we determined suitable cell model systems and potential biomarkers for predicting BPA-mediated disease using the bioinformatics tool Pathway Studio. We compiled known BPA-mediated diseases in humans, which were categorized into five major types. Subsequently, we investigated the differentially expressed proteins following BPA exposure in several cell types, and analyzed the efficacy of altered proteins to investigate their associations with BPA-mediated diseases. Our results demonstrated that colon cancer cells (SW480), mammary gland, and Sertoli cells were highly sensitive biological model systems, because of the efficacy of predicting the majority of BPA-mediated diseases. We selected glucose-6-phosphate dehydrogenase (G6PD), cytochrome b-c1 complex subunit 1 (UQCRC1), and voltage-dependent anion-selective channel protein 2 (VDAC2) as highly sensitive biomarkers to predict BPA-mediated diseases. Furthermore, we summarized proteomic studies in spermatozoa following BPA exposure, which have recently been considered as another suitable cell type for predicting BPA-mediated diseases.

Risk of subsequent attention-deficit/hyperactivity disorder among children and adolescents with amalgam restorations: A nationwide longitudinal study

OBJECTIVES

Dental amalgam has been used as a common restorative material since the 1800s, but concerns have been raised regarding its purported neuropsychological effects due to the neurotoxicity of mercury. In this study, a nationwide population-based database was employed to investigate the association of dental amalgam restoration with the risk of attention-deficit/hyperactivity disorder (ADHD).

METHODS

After matching, 88 068 young people with at least one tooth restoration during 2002-2010 and no ADHD history before 2001 were selected and then collected the further information until the end of 2011. Cox proportional hazard models were employed to estimate the possible effect of amalgam restorations on the risk of ADHD during the period of 2002-2011. Subgroup analyses were performed according to age, sex and number of amalgam restorations.

RESULTS

In total, 2073 people (2.4%) received an ADHD diagnosis during the study period, yielding an incidence rate of 32.4 per 100 000 person-years. Those who had 6 or more amalgam restorations had a higher risk of future ADHD in the unadjusted Cox proportional hazard regression model (hazard ratio=1.20, 95% confidence interval [CI]=1.04-1.38, P=.015) than those who had received composite resin or glass ionomer restorations. However, after adjustment for potential confounding factors, the result was found to be confounded by age.

CONCLUSIONS

The univariate analysis results showed that those who had 6 or more amalgam restorations had a 20% higher risk of future ADHD; however, the association disappeared after the model was adjusted for age. Despite this study analysing a larger sample than those analysed in previous studies, no association was observed between young patients' having received amalgam restorations and a future ADHD diagnosis. Further research aimed at evaluating the association between dental amalgam and other subsequent neuropsychological effects is warranted, especially for people who are vulnerable to mercury exposure.

Domain specific effects of postnatal toenail methylmercury exposure on child behaviour

OBJECTIVE

Very little is known about the relationship between postnatal methylmercury concentrations (via toenails as bioindicator) and behavioural characteristics of Pacific Island children living in New Zealand. The aim of this study was to explore the association between total mercury exposure and different domains of behavioural problems in Pacific children.

MATERIALS AND METHODS

A sample of nine-year-old Pacific Island children resident in Auckland, New Zealand participated in this study. Total mercury was determined in biological samples (toenail clippings) on behavioural problems as identified by mothers (using the child behaviour checklist). Specific behavioural domains, particularly aggression, rule breaking, attention and social problems were studied in relation to mercury exposure using toenails. The determination of mercury concentration in toenail clippings, after acid digestion was carried out using inductively coupled plasma mass spectrometry.

RESULTS

The observational study was conducted between July 2010 and July 2011 in which 278 eligible nine-year-old Pacific Island children were enrolled (Girls n=58%; boys n=42%).

FINDINGS

showed that 21% of the children had total toenail mercury concentrations (1.5μg/g to 6μg/g) higher than the United State Environmental Protection Agency recommended levels (RfD; 1μg/g Hg) for optimal health in children. Aggressive behaviour was associated with total toenail mercury exposure after adjusting for gender, ethnicity and income levels (OR: 2.15 95% CI 1.45, 3.18 p-value <0.05; OR 1.38 95% CI 0.83, 1.2 p value <0.05, respectively).

CONCLUSIONS

Overall, this research contributes to the understanding of total toenail mercury concentrations for Pacific people in New Zealand using toenail clippings as biomarkers in terms of associations with child behavioural problems. Mercury in toenails demonstrated a moderate association with a specific behavioural domain - aggressive behaviour.

Bisphenol A Release: Survey of the Composition of Dental Composite Resins

BACKGROUND

Bisphenol A (BPA) is an endocrine disruptor with potential toxicity. Composite resins may not contain pure BPA, but its derivatives are widely used. Several studies found doses of BPA or its derivatives in saliva or urine of patients after composite resin placement.

OBJECTIVE

The aims of this study were to establish an exhaustive list of composite resins marketed in Europe and their composition, and to assess the extent of BPA derivatives used.

METHODS

A research on manufacturers' websites was performed to reference all composite resins marketed in Europe, then their composition was determined from both material safety data sheets and a standardized questionnaire sent to manufacturers. Manufacturers had to indicate whether their product contained the monomers listed, add other monomers if necessary, or indicate "not disclosed".

RESULTS

160 composite resins were identified from 31 manufacturers and 23 manufacturers (74.2%) responded to the survey. From the survey and websites, the composition of 130 composite resins (81.2%) was: 112 (86.2%) based on BPA derivatives, 97 (74.7%) on bis-GMA, 17 (13.1%) without monomer derived from BPA (UDMA, sometimes with TEGDMA) and 6 (4.6%) with UDMA (only); 1 (0.8%) did not contain a BPA derivative or UDMA or TEGDMA. Pure BPA was never reported.

CONCLUSION

This work has established a list of 18 composite resins that contain no BPA derivative. Manufacturers should be required to report the exact composition of their products as it often remains unclear or incomplete.

Changes in urinary bisphenol A concentrations associated with placement of dental composite restorations in children and adolescents

BACKGROUND

Bisphenol A-glycidyl methacrylate (bis-GMA)-based dental composite restorations may release bisphenol A (BPA). The authors assessed changes in urinary BPA concentrations over a 6-month follow-up period in children and adolescents who received bis-GMA-based restorations.

METHODS

The authors collected data from 91 study participants aged 3 to 17 years who needed composite restorations. Participants provided urine samples and information on BPA-related exposures before and at approximately 1 day, 14 days, and 6 months after treatment. The authors used multivariable linear regression models to test associations between the number of surface restorations placed and the changes in urinary BPA concentrations.

RESULTS

Participants had a mean (standard deviation [SD]) of 1.4 (1.0) for surfaces restored with composite at the first treatment visit and 2.3 (1.6) for surfaces restored during the entire study period. Mean (SD) change in urinary BPA concentrations between pretreatment and day 1 was 1.71 (9.94) nanograms per milliliter overall and 0.87 (5.98) after excluding 1 participant who had 8 surfaces restored at the visit. Overall, the authors observed an association between a greater number of composite surface restorations placed and higher urinary BPA concentrations in the 1-day sample (posterior-occlusal exponentiated coefficients [e(β)] = 1.47; 95% confidence interval [CI], 1.18-1.83; P < .001), but the association was attenuated after the authors restricted the sample to the 88 participants who had up to 4 restorations (e(β) = 1.19; 95% CI, 0.86-1.64), and they did not observe any association using 14-day (e(β) = 0.94; 95% CI, 0.75-1.18) or 6-month (e(β) = 0.88; 95% CI, 0.74-1.04) samples.

CONCLUSIONS

Placement of bis-GMA-based restorations in children and adolescents may produce transient increases in urinary BPA concentrations that are no longer detectable in urine samples taken approximately 14 days or 6 months after treatment. After placement of a few restorations, increases in urinary BPA concentrations may not be detectable, owing to a high level of variation in background BPA exposure.

PRACTICAL IMPLICATIONS

These results suggest that leaching of BPA from newly placed composite restorations ceases to be detectable in urine within 2 weeks after restoration placement. The potential human health impact of such short-term exposure remains uncertain.

The decision to repair or replace a defective restoration is affected by who placed the original restoration: findings from the National Dental PBRN

OBJECTIVES

To evaluate how restoration characteristics are associated with the decision to repair or replace an existing restoration. The following hypotheses were studied: dentists who placed the original restoration are more likely to repair instead of replace restorations (H1) that are in molar teeth; (H2) that are in the upper arch; (H3) that have amalgam restorative material; (H4) if a fracture is not the primary reason for the defect; and (H5) when the restoration comprises more than one surface.

METHODS

This cross-sectional study used a consecutive patient/restoration recruitment design. 194 dentists members of a dental practice-based research network recorded data on restorations in permanent teeth that needed repair or replacement.

RESULTS

For 6623 of the 8770 defective restorations in 6643 patients, the treatment was provided by the dentist who had not placed the original restoration (75%). The 2-way interaction revealed that dentists who had placed the original restoration often chose to repair when the defective restoration was in a molar, relative to premolar or anterior teeth (OR=2.2, p<.001); and chose to replace when the restoration had amalgam (OR=0.5, p<.001), and when it was a fracture compared to another reason (OR=0.8, p=001).

CONCLUSION

Most dentists are not conservative when they revisit a restoration that they originally placed regardless of type of failure, number of surfaces or material used. However, dentists who had placed the original restoration were significantly more likely to repair it when the defective restoration was in a molar tooth.

CLINICAL SIGNIFICANCE

Most dentists who placed the original restoration were prone to replace it, however if the defective restoration was located in a molar tooth they would consider repairing it.

Mercury exposure levels in children with dental amalgam fillings

OBJECTIVES

Mercury combined with other metals to form solid amalgams has long been used in reconstructive dentistry but its use has been controversial since at least the middle of the 19th century. The exposure and body burden of mercury reviews have consistently stated that there is a deficiency of adequate epidemiological studies addressing this issue. Fish and dental amalgam are two major sources of human exposure to organic (MeHg) and inorganic Hg respectively.

MATERIALS AND METHODS

A total of 150 subjects aged between 9 and 14 years were divided into two groups of 75 subjects each depending on their diet, i.e. seafood or nonseafood consuming. Each category was subdivided into three groups based on number of restorations. Scalp hair and urine samples were collected at baseline and 3 months later to assess the organic and inorganic levels of mercury respectively by atomic absorption spectrophotometer (AAS).

RESULTS

The mean values of urinary mercury (inorganic mercury) in the group of children with restorations were 1.5915 μg/l as compared to 0.0130 μg/l in the groups with no amalgam restorations (p < 0.001) (Wilcoxon sign rank test and paired t-test). The hair mercury levels (organic mercury) varied signi-ficantly between the fsh-eating group and nonfsh-eating group, the average values being 1.03 μg/l and 0.84 μg/l respectively (p < 0.001) (Mann-Whitney U-test and paired t-test).

CONCLUSION AND SIGNIFICANCE

The notion about the mercury being released from the amalgam restorations as a sole exposure source needs to be put to a rest, as environmental factors collectively overpower the exposure levels from restorations alone. How to cite this article: Varkey IM, Shetty R, Hegde A. Mercury Exposure Levels in Children with Dental Amalgam Fillings. Int J Clin Pediatr Dent 2014;7(3):180-185.

Dental sealants and flowable composite restorations and psychosocial, neuropsychological, and physical development in children

PURPOSE

Dental sealant materials may intraorally release their components, including bisphenol-A (BPA), but long-term health effects are uncertain. The New England Children's Amalgam Trial (NECAT) found that composite restorations were associated with psychosocial, but not neuropsychological or physical, outcomes. The previous analysis did not consider sealants and preventive resin restorations (PRRs), which were routinely placed. The purpose of this analysis was to examine sealant/PRR exposure in association with psychosocial and other health outcomes.

METHODS

NECAT recruited 534 six- to 10-year-olds and provided dental care during a five-year follow-up. Annually, examiners conducted psychosocial and neuropsychological tests and measured body mass index (BMI) and fat percentage (BF%). Associations between surface years (SY) of sealants/PRRs and outcomes were tested using multivariable models.

RESULTS

Cumulative exposure level to sealants and/or PRRs was not associated with psychosocial assessments (eg, total problems: Child Behavior Checklist, 10-SY β=-0.2 ± 0.3, P=.60) or neuropsychological tests (eg, full-scale IQ, 10-SY β=0.1 ± 0.2, P=.60). There were no associations for changes in BMI-for-age z-score (P=.40), BF% (girls 10-SY β=-0.2 ± 0.3; boys 10-SY β=-0.1 ± 0.3), or menarche (10-SY hazard ratio=0.91, 95% confidence interval=0.83-1.01, P=.08).

CONCLUSIONS

This study showed no associations between exposure level of dental sealants or PRRs and behavioral, neuropsychological, or physical development in children over 5-years.

Critical appraisal: dental amalgam update--part II: biological effects

Dental amalgam restorations have been controversial for over 150 years. In Part I of this Critical Appraisal, the clinical efficacy of dental amalgam was updated. Here in Part II, the biological effects of dental amalgam are addressed.

Bisphenol A and human health: a review of the literature

There is growing evidence that bisphenol A (BPA) may adversely affect humans. BPA is an endocrine disruptor that has been shown to be harmful in laboratory animal studies. Until recently, there were relatively few epidemiological studies examining the relationship between BPA and health effects in humans. However, in the last year, the number of these studies has more than doubled. A comprehensive literature search found 91 studies linking BPA to human health; 53 published within the last year. This review outlines this body of literature, showing associations between BPA exposure and adverse perinatal, childhood, and adult health outcomes, including reproductive and developmental effects, metabolic disease, and other health effects. These studies encompass both prenatal and postnatal exposures, and include several study designs and population types. While it is difficult to make causal links with epidemiological studies, the growing human literature correlating environmental BPA exposure to adverse effects in humans, along with laboratory studies in many species including primates, provides increasing support that environmental BPA exposure can be harmful to humans, especially in regards to behavioral and other effects in children.

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.

Human exposure and health effects of inorganic and elemental mercury

Mercury is a toxic and non-essential metal in the human body. Mercury is ubiquitously distributed in the environment, present in natural products, and exists extensively in items encountered in daily life. There are three forms of mercury, i.e., elemental (or metallic) mercury, inorganic mercury compounds, and organic mercury compounds. This review examines the toxicity of elemental mercury and inorganic mercury compounds. Inorganic mercury compounds are water soluble with a bioavailability of 7% to 15% after ingestion; they are also irritants and cause gastrointestinal symptoms. Upon entering the body, inorganic mercury compounds are accumulated mainly in the kidneys and produce kidney damage. In contrast, human exposure to elemental mercury is mainly by inhalation, followed by rapid absorption and distribution in all major organs. Elemental mercury from ingestion is poorly absorbed with a bioavailability of less than 0.01%. The primary target organs of elemental mercury are the brain and kidney. Elemental mercury is lipid soluble and can cross the blood-brain barrier, while inorganic mercury compounds are not lipid soluble, rendering them unable to cross the blood-brain barrier. Elemental mercury may also enter the brain from the nasal cavity through the olfactory pathway. The blood mercury is a useful biomarker after short-term and high-level exposure, whereas the urine mercury is the ideal biomarker for long-term exposure to both elemental and inorganic mercury, and also as a good indicator of body burden. This review discusses the common sources of mercury exposure, skin lightening products containing mercury and mercury release from dental amalgam filling, two issues that happen in daily life, bear significant public health importance, and yet undergo extensive debate on their safety.

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.

The dental amalgam toxicity fear: a myth or actuality

Amalgam has been used in dentistry since about 150 years and is still being used due to its low cost, ease of application, strength, durability, and bacteriostatic effect. When aesthetics is not a concern it can be used in individuals of all ages, in stress bearing areas, foundation for cast-metal and ceramic restorations and poor oral hygiene conditions. Besides all, it has other advantages like if placed under ideal conditions, it is more durable and long lasting and least technique sensitive of all restorative materials, but, concern has been raised that amalgam causes mercury toxicity. Mercury is found in the earth's crust and is ubiquitous in the environment, so even without amalgam restorations everyone is exposed to small but measurable amount of mercury in blood and urine. Dental amalgam restorations may raise these levels slightly, but this has no practical or clinical significance. The main exposure to mercury from dental amalgam occurs during placement or removal of restoration in the tooth. Once the reaction is complete less amount of mercury is released, and that is far below the current health standard. Though amalgam is capable of producing delayed hypersensitivity reactions in some individuals, if the recommended mercury hygiene procedures are followed the risks of adverse health effects could be minimized. For this review the electronic databases and PubMed were used as data sources and have been evaluated to produce the facts regarding amalgam's safety and toxicity.

Restorative material and other tooth-specific variables associated with the decision to repair or replace defective restorations: findings from The Dental PBRN

OBJECTIVES

Using data from dentists participating in The Dental Practice-Based Research Network (DPBRN), the study had 2 main objectives: (1) to identify and quantify the types of restorative materials in the existing failed restorations; and (2) to identify and quantify the materials used to repair or replace those failed restorations.

METHODS

This cross-sectional study used a consecutive patient/restoration recruitment design. Practitioner-investigators recorded data on consecutive restorations in permanent teeth that needed repair or replacement. Data included the primary reason for repair or replacement, tooth surface(s) involved, restorative materials used, and patient demographics.

RESULTS

Data for 9875 restorations were collected from 7502 patients in 197 practices for which 75% of restorations were replaced and 25% repaired. Most of the restorations that were either repaired or replaced were amalgam (56%) for which most (56%) of the material used was direct tooth-coloured. The restorative material was 5 times more likely to be changed when the original restoration was amalgam (OR=5.2, p<.001). The likelihood of changing an amalgam restoration differed as a function of the tooth type (OR=3.0, p<.001), arch (OR=6.6, p<.001); and number of surfaces in the original restoration (OR=12.2, p<.001).

CONCLUSION

The probability of changing from amalgam to another restorative material differed with several characteristics of the original restoration. The change was most likely to take place when (1) the treatment was a replacement; (2) the tooth was not a molar; (3) the tooth was in the maxillary arch; and (4) the original restoration involved a single surface.

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.

Bisphenol A and related compounds in dental materials

CONTEXT

Dental sealants and composite filling materials containing bisphenol A (BPA) derivatives are increasingly used in childhood dentistry. Evidence is accumulating that BPA and some BPA derivatives can pose health risks attributable to their endocrine-disrupting, estrogenic properties.

OBJECTIVES

To systematically compile and critically evaluate the literature characterizing BPA content of dental materials; to assess BPA exposures from dental materials and potential health risks; and to develop evidence-based guidance for reducing BPA exposures while promoting oral health.

METHODS

The extant toxicological literature and material safety data sheets were used as data sources.

RESULTS

BPA is released from dental resins through salivary enzymatic hydrolysis of BPA derivatives, and BPA is detectable in saliva for up to 3 hours after resin placement. The quantity and duration of systemic BPA absorption is not clear from the available data. Dental products containing the bisphenol A derivative glycidyl dimethacrylate (bis-GMA) are less likely to be hydrolyzed to BPA and have less estrogenicity than those containing bisphenol A dimethacrylate (bis-DMA). Most other BPA derivatives used in dental materials have not been evaluated for estrogenicity. BPA exposure can be reduced by cleaning and rinsing surfaces of sealants and composites immediately after placement.

CONCLUSIONS

On the basis of the proven benefits of resin-based dental materials and the brevity of BPA exposure, we recommend continued use with strict adherence to precautionary application techniques. Use of these materials should be minimized during pregnancy whenever possible. Manufacturers should be required to report complete information on the chemical composition of dental products and encouraged to develop materials with less estrogenic potential.

Randomized controlled trial demonstrates that exposure to mercury from dental amalgam does not adversely affect neurological development in children

SUBJECTS

The study subjects were 507 children (228 females and 279 males) from the Casa Pia school system in Lisbon, Portugal; the same cohort of children used in a previous study. The children were 8 to 12 years old at the time of enrollment in the study, which began in January of 1997. To be included in the study, a child must have had at baseline at least one carious lesion in a permanent tooth, no previous exposure to amalgam treatments, urinary mercury level less than 10 mg/L, blood lead level less than 15 mg/dL, IQ greater than or equal to 67 as obtained with the Comprehensive Test of Nonverbal Intelligence, and no interfering health condition.

KEY EXPOSURE/STUDY FACTOR

Study subjects were randomly assigned to receive dental treatment with either amalgam or resin-based composite for posterior restorations (and composite for all anterior restorations). By the end of year 1, the participants had a mean of 8.3 surfaces restored with amalgam, and the mean number of surfaces restored varied between 7.7 and 10.7 during the 7 years of follow-up.

MAIN OUTCOME MEASURE

The primary outcome measures for the study were the presence of neurological hard signs (NHSs), such as tremor, and the presence and severity of neurological soft signs (NSSs), such as synkinesias. NHSs were scored as present or absent. Tremor was reported separately from other NHSs because of its relationship to mercury toxicity. Observation of NSSs did not begin until follow-up year 2, so there were no baseline data for NSSs. NSSs were evaluated using the examination described by Peters et al, and each item was scored from 0 (absent) to 3 (maximum deviation).

MAIN RESULTS

Over the 7-year duration of the study, there were slight differences in the percentages of subjects exhibiting any NHSs (including tremor, which was reported separately) between the 2 treatment groups, but the directions of the differences were not consistent from year to year, and the differences were not statistically significant in any year. No statistically significant difference in NSSs--either percentage of subjects exhibiting NSSs or NSS severity scores--was observed between the 2 groups in any year.

CONCLUSIONS

The results of this study demonstrate that exposure to mercury from dental amalgam does not adversely affect neurological development in children.

The Release of Mercury from Amalgam Restorations and Its Health Effects: A Review

Amalgam remains an important restorative material in dentistry. Because of continuing controversy concerning the material's safety and environmental friendliness, dentists should remain current in their knowledge of the effect of mercury and its release from amalgam. This will enable dentists to provide accurate, evidence-based information to their patients.

Nephrotoxicity, neurotoxicity, and mercury exposure among children with and without dental amalgam fillings

PURPOSE

A scientific review panel for the US Food and Drug Administration (FDA) recently identified the need for more data on the health risk of mercury exposure from dental amalgam among susceptible populations. We evaluated impacts of low-level mercury exposure on renal function and neurobehavioral and neuropsychological performance among children.

METHODS

Dental histories for 403 children aged 7-11 years in five schools from Xuhui, Shanghai were checked by dentists. Of them, 198 with confirmed amalgam fillings were recruited (exposure group). Reference children (N=205) were those who never had dental amalgam treatment. In May 2004, each child provided a urine sample for measurements of total mercury, N-acetyl-beta-D-glucosaminidase activity, microalbumin, and creatinine (Cr). The Child Behavior Checklist, Eysenck Personality Questionnaire, and an intelligence screening test were administered.

RESULTS

The geometric mean urinary mercury concentration was 1.6 microg/g Cr for children with and 1.4 microg/g Cr for children without amalgam fillings. No differences were found between children with and without fillings for either renal function biomarker, or on neurobehavioral, neuropsychological, or intelligence tests.

CONCLUSIONS

Although urinary mercury concentration was slightly elevated among children with amalgam fillings, we found no evidence of adverse effects on the outcomes evaluated. These results agree with those from recent trials in developed countries.