The Journal of the American Dental Association
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

J Am Dent Assoc, Vol 139, No 11, 1496-1505.
© 2008 American Dental Association
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Shenker, B. J.
Right arrow Articles by McKinlay, S.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Shenker, B. J.
Right arrow Articles by McKinlay, S.
Related Collections
Right arrow Restoratives

RESEARCH

JADA Continuing Education

Immune Function Effects of Dental Amalgam in Children

A Randomized Clinical Trial



Bruce J. Shenker, PhD, Nancy N. Maserejian, ScD, Annie Zhang, MS and Sonja McKinlay, PhD


   ABSTRACT
TOP
 ABSTRACT
SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSION
 REFERENCES
 
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.

Key Words: Dental amalgam; mercury; immunotoxicity

Abbreviations: CD: Cluster of differentiation • DHE: Dihydroethidium • Hg: Mercury • H2O2: Hydrogen peroxide • Ig: Immunoglobulin • NECAT: New England Children’s Amalgam Trial • O2–· Superoxide • PHA: Phytohemagglutinin • PMA: Phorbol myristate acetate • PWM: Pokeweed mitogen • Rho: Dihydrorhodamine • U-Hg: Total urinary mercury • WBC: White blood cell

Exposure to mercury compounds is widespread in the U.S. population as well as throughout the world. It is well-known that the toxic effects of mercury are directly related to its chemical form, dose and route of exposure.1–3 Concerns regarding mercury exposures generally have focused on neurodevelopment and nephrotoxicity.4 In addition, there has been significant interest in the potential immunotoxic effects of mercuric compounds, with particular concern focused on the impact of chronic exposure to low levels of mercury.5–18 Such immunotoxic effects could perturb the immune system and lead to immune suppression, a decline in immune competence and possibly autoimmune destruction or immune stimulation contributing to hypersensitivity reactions.

The potential of mercuric compounds to induce immunotoxicity has led to concern that amalgam restorations may have similar adverse effects. Conventional dental amalgam is an alloy that consists of approximately 50 percent mercury; this may be released as mercury vapor or corrosion products such as ionized mercury (Hg++). While the total mercury body burden is derived from multiple sources, dental amalgam restorations are the largest single source of systemic inorganic mercury exposure in the general population,19 and it is estimated that more than 70 million dental amalgam restorations are placed annually in the United States.20 However, the health risks posed by the chronic release of metallic mercury vapor from amalgam restorations remain unclear.

Researchers in most studies involving adult populations in which amalgam restorations were considered the primary source of mercury have not found significant associations between neuropsychological function and various amalgam exposure indexes including urinary mercury level, number of amalgam restorations, total number of amalgam surfaces and number of occlusal amalgam surfaces.21–26 Other studies have suggested associations between dental amalgams and neurodegenerative disorders such as Alzheimer disease and multiple sclerosis.27,28 There also is no clear evidence that amalgam restorations contribute to adverse effects on the immune systems of adults, such as hyperreactivity and cytogenetic alterations.

Amalgam restorations in a child’s mouth are associated with increased exposure to mercury,4 as determined by significantly elevated urinary mercury levels.29–32 Researchers and clinicians are concerned that there is a lack of data regarding the possible immunotoxic effects of mercury released from dental amalgams in children. In 2006, Bellinger and colleagues33 and DeRouen and colleagues34 reported results of two separate randomized clinical trials in which they found no statistically significant differences in adverse neuropsychological or renal effects during a five-to seven-year period in children whose teeth were restored with amalgam or composite materials.

In this article, we report on a substudy of the New England Children’s Amalgam Trial (NECAT) in which we evaluated the immune cells of children in vitro for manifestations of immunotoxic effects of amalgam restorations.


   SUBJECTS AND METHODS
TOP
 ABSTRACT
 SUBJECTS AND METHODS
RESULTS
 DISCUSSION
 CONCLUSION
 REFERENCES
 
Study design and participants. Participants were a subgroup of children in NECAT equally sampled from each treatment group (Figure 1Go). The main trial and the immune function substudy were approved by the institutional review boards of New England Research Institutes in Watertown, Mass.; five dental clinics in the urban Boston area; and one in rural Farmington, Maine. Children were eligible if they were 6 to 10 years of age as of their last birthday; were fluent in English; had no known prior or existing amalgam restorations; had two or more posterior teeth with dental caries requiring that restoration would include the occlusal surfaces; and, by parental report, had no physician-diagnosed psychological, behavioral, neurological, immunological or renal disorders. We screened 5,116 children for eligibility for participation in NECAT; we confirmed 598 of these as being eligible and obtained for 534 of them both parental consent and children’s assent for participation in the main trial. A detailed description of both the main trial and the immune function substudy protocols is provided elsewhere.31,33


Figure 1
View larger version (65K):
[in this window]
[in a new window]

  		Figure 1. Profile of recruitment, randomization and follow-up in the New England Children’s Amalgam Trial (NECAT) immune function substudy. The recruitment period ran from September 1997 through September 1999, with follow-up ending in March 2005. The primary reason for refusal to participate in the substudy was fear of blood draws, mentioned by 75 percent of invited participants, followed by time commitment, mentioned by 40 percent.

 
For the immune function substudy, our goal was to recruit 80 subjects, 40 in each treatment group. Of the 257 children invited to participate in the substudy, 66 (26 percent) provided consent/assent (35 children in the amalgam treatment group and 31 children in the composite group). The primary reason for refusal to participate in the substudy was fear of blood draws, mentioned by 75 percent of invited participants, followed by time commitment, mentioned by 40 percent. Immune function data at both baseline and follow-up, which were required for inclusion in this analysis, were available for 59 children (29 in the amalgam group, 30 in the composite group).

Interventions and follow-up. For children assigned to the amalgam group, study dentists used a dispersed-phase amalgam (Dispersalloy, Denstply Caulk, Milford, Del.) to restore all posterior teeth with caries at baseline and to restore teeth with new caries during the five-year trial period. For children assigned to the composite group, study dentists used a resin-based composite material (Dyract, Dentsply Caulk, in permanent dentition; Z100, 3M ESPE, St. Paul, Minn., in primary dentition) for all restorations. However, for both groups, study dentists used resin-based composite material to restore the front teeth, according to standard clinical practice.

Each child in both groups had semiannual dental examinations and restorative dental visits at one of the six participating dental clinics, at which study dentists documented pertinent dental data. At the annual visits, study staff members collected anthropometric measurements and urine samples. Initially, we attempted to collect timed overnight urine samples but, mid-trial, we switched to spot samples. We collected hair samples biennially. We collected blood samples from all subjects at baseline (pre-randomization), five to seven days after they completed baseline dental treatment and six, 12 and 60 months after they entered the substudy.

Mercury measurements. Details regarding the measurement methods for total urinary mercury (U-Hg), hair mercury and blood lead levels have been published.31,34 We reduced the detection limit for U-Hg, initially 1.5 nanogram per milliliter, to 0.45 ng/mL after Feb. 1, 2000, as a result of the laboratory technicians’ having increased the volume of urine analyzed from each child. This altered detection limit prevents the direct comparison of U-Hg values from samples taken before and after February 2000. For this reason, we considered urine data only from years 3 through 5 in this analysis. We imputed nondetectable concentrations (< 0.45 ng/mL) as having a concentration of 0.45/{surd}2.35 U-Hg is expressed as creatinine-corrected U-Hg (micrograms/gram).36,37

Immunological outcome measures. We sent heparinized blood samples to a central laboratory (University of Pennsylvania, Philadelphia), where trained laboratory technicians performed all assays. To maintain the sample tubes at room temperature, we shipped them overnight in insulated containers with gel packs prewarmed to 30°C. Immune parameters that we assessed fall into four categories:

– white blood cell (WBC) enumeration;
– assessment of T-cell responsiveness;
– assessment of B-cell responsiveness;
– analysis of neutrophil and monocyte responsiveness.

Laboratory technicians optimized and checked assays for reproducibility. They used fluorescent calibration beads to standardize the flow cytometer from day to day; this enabled comparison of absolute results (that is, fluorescence intensity) rather than just percentages of positive cells. They ran test samples to ensure reproducibility, particularly with respect to blood stability under shipping conditions. They coded blood samples to ensure that laboratory technicians were blinded with respect to subject treatment group.

The laboratory technicians performed total WBC enumeration using Wright stain and hemo-cytometer. They determined distribution of neutrophils, monocytes, T cells, B cells and natural killer cells as well as cluster of differentiation (CD) subtypes CD4 and CD8 by means of flow cytometry using the IMK+ Simultest kit (BD Biosciences, San Jose, Calif.). Functional analysis of T cells after mitogenic activation involved two approaches: analysis of activation markers and cell cycle distribution. Technicians incubated T cells with phytohemagglutinin (PHA) (5 µg/mL) for 24 hours to assess expression of activation markers; they determined CD69 and CD25 expression by means of immunofluorescence using flow cytometry as described previously.14 They assessed cell cycle distribution after 72 hours’ incubation in the presence of PHA.38 They monitored B-cell activation by means of analyzing expression of CD69 and increased expression of CD23 after stimulation with pokeweed mitogen (10 µg/mL).

The study technicians determined the functional status of neutrophils and monocytes by means of monitoring the oxidative burst in response to stimulation with phorbol myristate acetate (PMA) (0.5 µg/mL). They used the fluorescent probes dihydroethidium and dihydrorhodamine to assess both superoxide (O2–·) and hydrogen peroxide (H2O2) generation, respectively; they determined fluorescence by means of flow cytometry 30 minutes after cell activation.39

Sample size and power calculations. As this was an exploratory study of immune function, it yielded little information on which to base power calculations. In calculating the effect size, which is a measure of the strength of the relationship between two variables, we found that with the 59 children in the final main analysis, there was approximately 67 percent power to detect an effect size of 0.63, or 80 percent power to detect an effect size of 0.74. (An effect size of 0.2 is considered small, 0.5 medium and 0.8 large.) Considering the limited power and lack of existing knowledge about the subject, our emphasis during interpretation of the results was on the observation of trends rather than on statistical significance.

Statistical analysis. The primary analysis compared each of the immune function markers by treatment assignment. We depicted time trends in means for each outcome graphically by treatment group. We used repeated-measures analysis of covariance (ANCOVA) models to test the difference across time for each outcome. Because the profiles of the means for amalgam and composite groups were similar across time—that is, there was no interaction between time and treatment—models included only main effects, adjusted for baseline corresponding immune function measurement, age, sex, socioeconomic status, hair mercury level and blood lead level. We calculated socioeconomic status by using the method described by Green.40 In secondary analyses, we compared immune outcomes by urinary-mercury excretion at year 5 by using ANCOVA, restricted to participants with both immune function measures and U-Hg measures at year 5 (amalgam group, n = 20; composite group, n = 23). Regardless of children’s treatment assignment, we categorized children as having low (0–0.49 µg/g), medium (0.50–0.99 µg/g) or high (1.0–2.2 µg/g) U-Hg, using categories based on the distribution of U-Hg level among all participants at year 5. All statistical tests were two-sided, performed at an {alpha} level of .05 and conducted using statistical software (SAS version 9.1, SAS Institute, Cary, N.C.).


   RESULTS
TOP
 ABSTRACT
 SUBJECTS AND METHODS
 RESULTS
DISCUSSION
 CONCLUSION
 REFERENCES
 
Baseline characteristics of substudy participants. Substudy participants in the two treatment groups were similar in terms of most baseline characteristics, including age, race/ethnicity, household income, education of primary care-giver, full-scale intelligence quotient and hair and urinary mercury concentrations (Table 1Go). Moreover, the immune function substudy population reflected the baseline characteristics of the larger NECAT population. We noted two differences, however. The sex distribution was less balanced across treatment groups in the substudy, with more boys (65.5 percent) in the amalgam group and more girls (63.3 percent) in the composite group. Also, the mean number of carious surfaces in the substudy was lower in the amalgam group than in the composite group (7.8 versus 10.1 surfaces). These differences were not statistically significant and likely were caused by small numbers.


View this table:
[in this window]
[in a new window]

  		TABLE 1 Baseline characteristics of immune function substudy participants and all NECAT* participants,{dagger} by treatment group.

 
Table 2Go (page 1501) displays four categories of baseline immune status: WBC number/distribution, lymphocyte function, monocyte function and neutrophil function. At baseline, the two treatment groups did not differ in total WBC count or in the distribution of lymphocytes, monocytes and neutrophils. T cells obtained from both treatment groups exhibited similar levels of mitogenic responsiveness at baseline; 83.9 percent and 77 percent of T cells from the amalgam group expressed CD69 and CD25, respectively, 24 hours after activation with PHA, compared with 82.2 percent and 74.7 percent of T cells from the composite group. Baseline values for B cells from the two treatment groups were similar as well. In addition, the percentage of monocytes exhibiting an oxidative burst in response to PMA was similar in both treatment groups with respect to the production of both O2–· (as determined via ethidium fluorescence) and H2O2 (as determined via rhodamine fluorescence); 69.7 percent (O2–·) and 55.7 percent (H2O2) monocytes for the amalgam group compared with 65.6 percent (O2–·) and 54.2 percent (H2O2) for the composite group. Neutrophil oxidative burst at baseline also did not differ significantly between treatment groups; it was 92.2 percent (O2–·) and 87.6 percent (H2O2) for the amalgam group compared with 88.9 percent (O2–·) and 82.4 percent (H2O2) for the composite group. Also, the amount of free radicals produced as measured as a function of the mean channel fluorescence did not vary significantly between the two groups (data not shown).


View this table:
[in this window]
[in a new window]

  		TABLE 2 Baseline immune function data, according to restoration type.

 
Exposure to dental amalgam. The cumulative number of surfaces restored during the course of the trial was 16.9 for children in the composite group and 13.5 for children in the amalgam group, with an average of 10.6 amalgam-filled surfaces in the amalgam group and zero in the composite group. Numbers of restored surfaces were greatest shortly after entry into the study. While restorations placed in primary teeth at baseline often were lost during the course of the trial, children had recurrent treatment needs averaging approximately one additional filled surface per year. The mean number of restored surfaces present in each child’s mouth at the end of the five years was 5.9 in the composite group and 5.3 in the amalgam group (of which 4.2 were restored with amalgam).

Urinary mercury excretion. Children assigned to the amalgam group had significantly higher mean urinary mercury excretion levels than did children assigned to the composite group (Figure 2Go). Mean urinary mercury excretion in the amalgam group was 0.89, 0.81 and 0.85 µg/g creatinine at years 3, 4 and 5, respectively. This compares with 0.64, 0.50 and 0.68 µg/g creatinine for the composite group. Urinary mercury was detectable in 65 percent (year 3), 48 percent (year 4) and 61 percent (year 5) of children in the amalgam group and in 24 percent (year 3), 24 percent (year 4) and 42 percent (year 5) of children in the composite group.


Figure 2
View larger version (53K):
[in this window]
[in a new window]

  		Figure 2. Urinary mercury excretion by year and treatment group. Boxes indicate upper and lower quartiles, and error bars indicate 2.5 percent and 97.5 percent values with points for outliers. P = .07 for the difference between amalgam and composite groups at year 3; P = .03 at year 4; and P = .20 at year 5. µg: Microgram. g: Gram.

 
Immunological function. We assessed changes in immunological measurements from baseline at five to seven days, six months, 12 months and 60 months after treatment (Table 3Go). The distribution of lymphocytes, monocytes and neutrophils fluctuated across time, both within and between treatment groups. We observed no consistent or statistically significant differences between the two treatment groups in graphical evaluations of trends or in the ANCOVA models.


View this table:
[in this window]
[in a new window]

  		TABLE 3 Changes in immune status from baseline values.

 
In the amalgam group we found a slight but not statistically significant decline in responsiveness of T cells (as measured via expression of the activation markers CD69 and CD25 in response to PHA) at five to seven days after treatment; however, we consistently observed no differences at six, 12 or 60 months after treatment. We noted no differences between treatment groups for proliferative responses of T cells (data not shown) or B-cell function (measured via expression of CD69 and CD23) across time.

We monitored the functional status of monocytes and neutrophils by measuring the generation of free radicals O2–· (as determined via ethidium fluorescence) and H2O2 (as determined via rhodamine fluorescence) after activation by PMA. Compared with monocytes in the composite group, monocytes in the amalgam population exhibited reduced responsiveness within five to seven days in terms of both O2–· (7.8 percent) and H2O2 (8.4 percent); this trend did not persist beyond this time point. Neutrophil responses exhibited fluctuation within and between the treatment groups; however, none of these was statistically significant.

In secondary analyses considering urinary mercury excretion, we observed no consistent trends or statistically significant differences in immune function measures when comparing children with low, medium or high levels of urinary mercury excretion (data not shown).


   DISCUSSION
TOP
 ABSTRACT
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
CONCLUSION
 REFERENCES
 
The aim of this randomized study was to ascertain whether exposure to low levels of mercury released by amalgam restorations caused adverse effects on host defense systems in children. Specifically, we assessed lymphocytes, monocytes and neutrophils obtained from children who were randomly assigned to receive either amalgam or composite restorations for in vitro manifestations of immunotoxicity. As there was little existing knowledge regarding this subject and limited power, this was an exploratory study; therefore, results and interpretations are based on the observation of trends rather than on statistical significance. In light of these limitations, results should be viewed with caution. The study was strengthened by its eligibility criteria of at least two posterior teeth with caries and no prior amalgam restorations, which ensured equivalence of treatment groups at baseline as well as high restoration rates to study potential adverse effects of dental amalgam. Indeed, the amalgam treatment group exhibited small but persistent statistically significant elevations in urinary mercury levels three to five years after treatment. However, there were no consistent or statistically significant differences between the two treatment groups in terms of lymphocyte (both B and T cell), monocyte and neutrophil blood distribution.

To our knowledge, this is the first study to report on the immune status of children after treatment with dental amalgam. These findings are strengthened by the randomized trial design, which ensures that differences between the treatment groups do not result from possible confounding factors. The range of cell functions that could be assessed was limited by the size and frequency of blood samples and limited knowledge of potential in vivo effects of both dental amalgams and mercury on the immune status of children. In vitro studies suggest that mercury exposure can lead to immunotoxicity, culminating in lymphocyte and monocyte death.14,15,41,42 Thus, it was important that we assess both the number and distribution of WBCs; any reduction in cell number could be interpreted as evidence of chronic exposure to high levels of mercury. Our results indicate that amalgam restorations, compared with composite restorations, failed to alter either the absolute number or distribution of B and T cells (and their subsets), monocytes or neutrophils in the blood of the treated children. This is not surprising, inasmuch as amalgam-treated children had levels of urinary mercury excretion that were low relative to established background population levels.4 Similarly, Herrström and colleagues43 did not detect any evidence of amalgam mercury–induced cytogenetic damage to lymphocytes in adolescents; it is noteworthy that they did observe cytogenetic damage in cells from people treated with composite restorations.

Several investigators have demonstrated that low levels of both inorganic and organic mercury can lead to altered immune function. Indeed, we and others have shown that in vitro exposure of lymphocytes and monocytes to 10 to 500 ng/mL of mercury impairs cell responsiveness.14,42,44–48 Furthermore, Petruccioli and Turillazzi49 demonstrated that monkeys exposed to mercuric chloride for periods as long as 120 days manifested reduced levels of serum immunoglobulin (Ig) G and IgM. Consistent with these observations, we did observe a small, transient but not statistically significant decline in lymphocyte and monocyte responsiveness during the five- to seven-day period after amalgam treatment. Henderson and colleagues50 also observed decreased lymphocyte responsiveness in some people treated with dental amalgam. Moreover, Osorio and colleagues51 observed transient effects of amalgam exposure on the distribution of subsets of T cells.

The slight decline in T-cell responsiveness that we observed was reflected in activation marker expression after in vitro mitogenic stimulation. Furthermore, the reductions were transient and no longer present at six, 12 or 60 months after treatment. There was a similar transient decline in monocyte responsiveness measured in terms of the cells’ ability to mount an oxidative burst in response to PMA in vitro. We noted no differences between treatment groups in terms of neutrophils. The magnitude and duration of these fluctuations led us to conclude that they were unlikely to be of clinical significance and might have been attributable to sampling variation, because the sample size was small and statistical significance was lacking. Nonetheless, the effects of dental amalgam on host defense are worthy of further investigation.

Researchers have suggested that certain people, owing to genetic abnormalities, may exhibit heightened sensitivity to toxic substances such as mercury. Yoshida and colleagues52,53 recently demonstrated that metallothionein-null mice were more sensitive to mercury toxicity than were wild-type mice. The NECAT study was not designed to evaluate the role of genetic polymorphism in the safety of amalgam restorations. For this reason, our analysis is unable to provide information about the role of metallothionein deficiency or other genetic polymorphisms in amalgam safety.


   CONCLUSION
TOP
 ABSTRACT
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSION
REFERENCES
 
Our randomized study confirms that treatment of children with amalgam restorations leads to increased, albeit low-level, exposure to mercury. Within our small sample size, this exposure did not cause overt immune deficits, although we did observe a transient decline in certain aspects of both lymphocyte and monocyte activation that warrants further investigation. Given the exclusion criteria and exploratory nature of this analysis, these results do not support a move at this time to discontinue the use of mercury-based amalgam as the standard of care for restoration of teeth with caries.

This is especially important because the safety of many mercury-free alternatives has not been tested thoroughly. For example, Herrström and colleagues43 reported evidence of immunotoxicity associated with the use of acrylate-containing tooth fillings and none associated with mercury-containing amalgam fillings. Indeed, the lack of evidence regarding immunotoxic, neuropsychological or renal effects of dental amalgam and factors such as low cost, improved longevity and practitioners’ expertise in handling support the continued use of amalgam materials for restorative dentistry.33,34,54,55


   FOOTNOTES
 

Dr. Shenker is the associate dean for research, a professor and the chair, Department of Pathology, School of Dental Medicine, University of Pennsylvania, 240 S. 40th St., Philadelphia, Pa. 19104, e-mail "shenker{at}upenn.edu". Address reprint requests to Dr. Shenker.


Dr. Maserejian is a research scientist, New England Research Institutes, Watertown, Mass.


When this article was written, Ms. Zhang was an associate research scientist, New England Research Institutes, Watertown, Mass. She now is a senior biostatistician, Parexel International, Lowell, Mass.


Dr. McKinlay is the president, New England Research Institutes, Watertown, Mass.


Disclosure. None of the authors reported any disclosures.


This study was supported by U.S. Public Health Service grant N01 DE 72622.


The authors would like to acknowledge Ali Zekavat, BS, Rose Espiritu and the staff of SDM Flow Cytometry, Philadelphia, for their technical expertise and contribution to the execution of this study.


   REFERENCES
TOP
 ABSTRACT
 SUBJECTS AND METHODS
 RESULTS
 DISCUSSION
 CONCLUSION
 REFERENCES
 

  1. Atchison WD, Hare MF. Mechanisms of methylmercury-induced neurotoxicity. FASEB J 1994;8(9):622–629.[Abstract]

  2. Clarkson TW. The toxicology of mercury. Crit Rev Clin Lab Sci 1997;34(4):369–403.[Medline]

  3. Harada M. Minamata disease: methylmercury poisoning in Japan caused by environmental pollution. Crit Rev Toxicol 1995;25(1):1–24.[Medline]

  4. World Health Organization. Concise International Chemical Assessment Document 50: Elemental Mercury and Inorganic Mercury Compounds: Human Health Aspects. Geneva: World Health Organization; 2003.

  5. Dantas DC, Queiroz ML. Immunoglobulin E and autoantibodies in mercury-exposed workers. Immunopharmacol Immunotoxicol 1997; 19(3):383–392.[Medline]

  6. Dieter MP, Luster MI, Boorman GA, Jameson CW, Dean JH, Cox JW. Immunological and biochemical responses in mice treated with mercuric chloride. Toxicol Appl Pharmacol 1983;68(2):218–228.[Medline]

  7. Lawrence DA. Heavy metal modulation of lymphocyte activation, 1: in vitro effects of heavy metals on primary humoral immune responses. Toxicol Appl Pharmacol 1981;57(3):439–451.[Medline]

  8. Stejskal VD, Cederbrant K, Lindvall A, Forsbeck M. Melisa: an in vitro tool for the study of metal allergy. Toxic in Vitro 1994;8(5): 991–1000.

  9. Stejskal VD, Forsbeck M, Cederbrant KE, Asteman O. Mercury-specific lymphocytes: an indication of mercury allergy in man. J Clin Immunol 1996;16(1):31–40.[Medline]

  10. Warfvinge G, Larsson Å. Contact stomatitis to mercury associated with spontaneous mononuclear cell infiltrates in brown Norway (BN) rats with HgCl2-induced autoimmunity. J Oral Pathol Med 1994; 23(10):441–445.[Medline]

  11. Gopinath C. Pathology of toxic effects on the immune system. Inflamm Res 1996;45(suppl 2):S74–S78.[Medline]

  12. Koropatnick J, Zalups RK. Effect of non-toxic mercury, zinc or cadmium pretreatment on the capacity of human monocytes to undergo lipopolysaccharide-induced activation. Br J Pharmacol 1997;120(5):797–806.[Medline]

  13. Pollard KM, Hultman P. Effects of mercury on the immune system. In: Sigel A, Sigel H, eds. Mercury and Its Effects on Environment and Biology. New York City: Marcel Dekker; 1997:421–440. Metal Ions in Biological Systems; vol. 34.

  14. Shenker BJ, Rooney C, Vitale L, Shapiro IM. Immunotoxic effects of mercuric compounds on human lymphocytes and monocytes, I: suppression of T-cell activation. Immunopharmacol Immunotoxicol 1992;14(3):539–553.[Medline]

  15. Shenker BJ, Datar S, Mansfield K, Shapiro IM. Induction of apoptosis in human T-cells by organomercuric compounds: a flow cytometric analysis. Toxicol Appl Pharmacol 1997;143(2):397–406.[Medline]

  16. Shenker BJ, Guo TL, Shapiro IM. Low-level metylmercury exposure causes human T-cells to undergo apoptosis: evidence of mitochondrial dysfunction. Environ Res 1998;77(2):149–159.[Medline]

  17. Shenker BJ, Guo TL, O I, Shapiro IM. Induction of apoptosis in human T-cells by methyl mercury: temporal relationship between mitochondrial dysfunction and loss of reductive reserve. Toxicol Appl Pharmacol 1999;157(1):23–35.[Medline]

  18. Via CS, Nguyen P, Niculescu F, Papadimitriou J, Hoover D, Silbergeld EK. Low-dose exposure 17 to iorganic mercury accelerates disease and mortality in acquired murine lupus. Environ Health Perspect 2003;111(10):1273–1277.[Medline]

  19. Cederbrant K, Gunnarsson LG, Hultman P, Norda R, Tibbling-Grahn L. In vitro lymphoproliferative assays with HgCl2 cannot identify patients with systemic symptoms attributed to dental amalgam. J Dent Res 1999;78(8):1450–1458.[Abstract/Free Full Text]

  20. American Dental Association Survey Center. The 1999 Survey of Dental Services Rendered. Chicago: American Dental Association; 2002.

  21. Kingman A, Albers JW, Arezzo JC, Garabrant DH, Michalek JE. Amalgam exposure and neurological function. Neurotoxicology 2005; 26(2):241–255.[Medline]

  22. Factor-Litvak P, Hasselgren G, Jacobs D, et al. Mercury derived from dental amalgams and neuropsychologic function. Environ Health Perspect 2003;111(5):719–723.[Medline]

  23. Dalen K, Lygre GB, Køve H, Gjerdet NR, Askevold E. Memory functions in persons with dental amalgam. J Dent 2003;31(7):487–492.[Medline]

  24. Nitschke I, Müller F, Smith J, Hopfenmüller W. Amalgam fillings and cognitive abilities in a representative sample of the elderly population. Gerontology 2000;17(1):39–44.

  25. Björkman L, Pedersen NL, Lichtenstein P. Physical and mental health related to dental amalgam fillings in Swedish twins. Community Dent Oral Epidemiol 1966;24(4):260–267.

  26. Saxe SR, Snowdon DA, Wekstein MW, et al. Dental amalgam and cognitive function in older women: findings from the Nun Study. JADA 1995;126(11):1495–1501.[Abstract/Free Full Text]

  27. Mutter J, Naumann J, Sadaghiani C, Schneider R, Walach H. Alzheimer disease: mercury as pathogenetic factor and apolipoprotein E as a moderator. Neuro Endocrinol Lett 2004;25(5):331–339.[Medline]

  28. Bates MN, Fawcett J, Garrett N, Cutress T, Kjellstrom T. Health effects of dental amalgam exposure: a retrospective cohort study. Int J Epidemiol 2004;33(4):894–902.[Abstract/Free Full Text]

  29. Trepka MJ, Heinrich J, Krause C, et al. Factors affecting internal mercury burdens among eastern German children. Arch Environ Health 1997;52(2):134–138.[Medline]

  30. Gabrio T, Benedikt T, Broser G, et al. 10 years of obsevation by public health offices in Baden-Wurttemberg—assessment of human biomonitoring for mercury due to dental amalgam fillings and other sources [in German]. Gesundheitswesen 2003;65(5):327–335.[Medline]

  31. Maserejian N, Trachtenberg F, Assmann S, Barregard L. Dental amalgam exposure measures and urinary mercury levels in children: The New England Children’s Amalgam Trial. Environ Health Perspect 2008;116(2):256–262.[Medline]

  32. Levy M, Schwartz S, Dijak M, Weber JP, Tardif R, Rouah F. Childhood urine mercury excretion: dental amalgam and fish consumption as exposure factors. Environ Res 2004;94(3):283–290.[Medline]

  33. Bellinger DC, Daniel D, Trachtenberg F, Tavares M, McKinlay S. Dental amalgam restorations and children’s neurosychological function: the New England Children’s Amalgam Trial. Environ Health Perspect 2006;115(3):440–446.[Medline]

  34. DeRouen TA, Martin MD, Leroux BG, et al. Neurobehavioral effects of dental amalgam in children: a randomized clinical trial. JAMA 2006;295(15):1784–1792.[Abstract/Free Full Text]

  35. Hornung R, Reed L. Estimation of average concentration in the presence of nondetectable values. Appl Occup Environ Hyg 1990;51(1):46–51.

  36. Barber TE, Wallis G. Correction of urinary mercury concentraton by specific gravity, osmolality and creatinine. J Occup Med 1986;28(5):354–359.[Medline]

  37. Barregard L. Mercury from dental amalgam: looking beyond the average. Occup Environ Med 2005;62(6):352–353.[Free Full Text]

  38. Shenker BJ, Besack D, McKay TL, Pankoski L, Zekavat A, Demuth DR. Induction of cell cycle arrest in lymphocytes by Actinobacillus actinomycetemcomitans cytolethal distending toxin requires three subunits for maximum activity. J Immunol 2005;174(4): 2228–2234.[Abstract/Free Full Text]

  39. In Sug O, Datar S, Koch CJ, Shapiro IM, Shenker BJ. Mercuric compounds inhibit human monocyte function by inducing apoptosis: evidence for formation of reactive oxygen species, development of mitochondrial membrane permeability transition and loss of reductive reserve. Toxicol 1997;124(3):211–224.[Medline]

  40. Green LW. Manual for scoring socioeconomic status for research on health behavior. Public Health Rep 1970;85(9):815–827.[Medline]

  41. Shenker BJ, Berthold P, Decker S, et al. Immunotoxic effects of mercuric compounds on human lymphocytes and monocytes, II: alterations in cell viability. Immunopharmacol Immunotoxicol 1992;14(3): 555–577.[Medline]

  42. Shenker BJ, Berthold P, Rooney C, Vitale LA, DeBolt K, Shapiro IM. Immunotoxic effects of mercuric compounds on human lymphocytes and monocytes, III: alterations in B-cell function and viability. Immunopharmacol Immunotoxicol 1993;15(1):87–112.[Medline]

  43. Herrström P, Bratt I, Holmén A, Högstedt B. Micronuclei in lymphocyte subsets in relation to plasma mercury, dental amalgam and acrylate-containing tooth fillings. Sci Total Environ 2003;309(1–3): 253–255.[Medline]

  44. Shenker BJ, Mayro JS, Rooney C, Vitale LA, Shapiro IM. Immunotoxic effects of mercuric compounds on human lymphocytes and monocytes, IV: alterations in cellular glutathione content. Immunopharmacol Immunotoxicol 1993;15(2–3):273–290.[Medline]

  45. Nakatsuru S, Oohashi J, Nozaki H, Nakada S, Imura N. Effect of mercurials on lymphocyte functions. Toxicol 1985;36(4):297–305.[Medline]

  46. Nordlind K. Inhibition of lymphoid cell DNA synthesis by metal allergens at various concentrations. Int Archs Allergy Appl Immunol 1983;70(2):191–192.[Medline]

  47. Castranova V, Bowman L, Reasor MJ, Miles PR. Effects of heavy metal ions on selected oxidative metabolic processes in rat alveolar macrophages. Toxicol Appl Pharmacol 1980;53(1):14–23.[Medline]

  48. Malamud D, Dietrich SA, Shapiro IM. Low levels of mercury inhibit the respiratory burst in human polymorphonuclear leukocytes. Biochem Biophys Res Commun 1985;128(3):1145–1151.[Medline]

  49. Petruccioli L, Turillazzi P. Serum immunoglobulin levels in monkeys treated with methylmercury. Drug Chem Toxicol 1990;13(4): 297–307.[Medline]

  50. Henderson DC, Clifford R, Young DM. Mercury-reactive lymphocytes in peripheral blood are not a marker for dental amalgam associated disease. J Dent 2001;29(7):469–474.[Medline]

  51. Osorio E, Toledano M, Bravo M, Osorio R. Short-term changes in lymphocytes after placement of silver amalgam restorations in healthy subjects. Dent Mater 1995;11(5):323–326.[Medline]

  52. Yoshida M, Watanabe C, Horie K, Satoh M, Sawada M, Shimada A. Neurobehavioral changes in metallothionein-null mice prenatally exposed to mercury vapor. Toxicol Lett 2005;155(3):361–368.[Medline]

  53. Yoshida M, Watanabe C, Kishimoto M, et al. Behavioral changes in metallothionein-null mice after the cessation of long-term, low-level exposure to mercury vapor. Toxicol Lett 2006;161(3):210–218.[Medline]

  54. Soncini JA, Maserejian NN, Trachtenberg F, Tavares M, Hayes C. The longevity of amalgam versus compomer/composite restorations in posterior primary and permanent teeth: findings from the New England Children’s Amalgam Trial. JADA 2007;138(6):763–772.[Abstract/Free Full Text]

  55. Bernardo M, Luis H, Martin MD, et al. Survival and reasons for failure of amalgam versus composite posterior restorations placed in a randomized clinical trial. JADA 2007;138(6):775–783.[Abstract/Free Full Text]





This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Shenker, B. J.
Right arrow Articles by McKinlay, S.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Shenker, B. J.
Right arrow Articles by McKinlay, S.
Related Collections
Right arrow Restoratives

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS