Pregnancy outcome in women working as dentists, dental assistants or dental technicians

Mercury exposure and its effects on fertility and pregnancy outcome

Mercury (Hg), a highly toxic environmental pollutant, shows harmfulness which still represents a big concern for human health, including hazards to fertility and pregnancy outcome. Research has shown that Hg could induce impairments in the reproductive function, cellular deformation of the Leydig cells and the seminiferous tubules, and testicular degeneration as well as abnormal menstrual cycles. Some studies investigated spontaneous abortion and complicated fertility outcome due to occupational Hg exposure. Moreover, there is a relation between inhaled Hg vapour and reproductive outcome. This MiniReview evaluates the hypothesis that exposure to Hg may increase the risk of reduced fertility, spontaneous abortion and congenital deficits or abnormalities.

Effects of environmental contaminants on fertility and reproductive health

Recent research indicates that the human infertility rate is increasing. Although various reasons have been hypothesized for the growing infertility rate, environmental contaminants are potentially important causal agents associated with this change. Chemical contaminants are widespread throughout our environment and human exposure is virtually unavoidable. The overall contribution of environmental exposure to infertility is unknown, but studies involving occupational exposure, together with results from animal experiments, suggest that environmental contaminants may adversely affect fertility. We reviewed the adverse effects of environmental exposure on fertility and related reproductive outcomes. Environmental contaminants covered in this review include heavy metals, organic solvents, pesticides and endocrine disrupting chemicals. It is hoped that this review will highlight the need for further research in this area.

Perinatal death and exposure to dental amalgam fillings during pregnancy in the population-based MoBa cohort

OBJECTIVES

The aim was to gain knowledge regarding the risk of perinatal death related to exposure to dental amalgam fillings in the mother.

DESIGN

Population-based observational cohort study.

SETTING

The Norwegian Mother and Child Cohort Study, a Norwegian birth cohort of children born in 1999-2008 conducted by the Norwegian Institute of Public Health.

PARTICIPANTS

72,038 pregnant women with data on the number of teeth filled with dental amalgam.

MAIN OUTCOME MEASURES

Data on perinatal death (stillbirth ≥ 22 weeks plus early neonatal death 0-7 days after birth) were obtained from the Medical Birth Registry of Norway.

RESULTS

The absolute risk of perinatal death ranged from 0.20% in women with no amalgam-filled teeth to 0.67% in women with 13 or more teeth filled with amalgam. Analyses including the number of teeth filled with amalgam as a continuous variable indicated an increased risk of perinatal death by increasing number of teeth filled with dental amalgam (crude OR 1.065, 95% CI 1.034 to 1.098, p<0.001). After adjustment for potential confounders (mothers' age, education, body mass index, parity, smoking during pregnancy, alcohol consumption during pregnancy) included as categorical variables, there was still an increased risk for perinatal death associated with increasing number of teeth filled with amalgam (ORadj 1.041, 95% CI 1.008 to 1.076, p = 0.015). By an increased exposure from 0 to 16 teeth filled with amalgam, the model predicted an almost doubled odds ratio (ORadj 1.915, 95% CI 1.12 to 3.28). In groups with 1 to 12 teeth filled with amalgam the adjusted odds ratios were slightly, but not significantly, increased. The group with the highest exposure (participants with 13 or more teeth filled with amalgam) had an adjusted OR of 2.34 (95% CI 1.27 to 4.32; p = 0.007).

CONCLUSION

The current findings suggest that the risk of perinatal death could increase in a dose-dependent way based on the mother's number of teeth filled with dental amalgam. However, we cannot exclude that the relatively modest odds ratios could be a result of residual confounding. Additional studies on the relationship between exposure to dental amalgam fillings during pregnancy and perinatal death are warranted.

Neurological disease or intellectual disability among sons of female Swedish dental personnel

OBJECTIVE

Prenatal exposure to elemental mercury may be a potential hazard for the offspring of female dental personnel working with dental amalgam. The aim of this study was to investigate whether potential in utero exposure to mercury might have affected the development of nervous system of the sons of Swedish female dental personnel leading to an increased risk of neurological disease or intellectual disability.

MATERIAL AND METHODS

We used national Swedish registers to investigate risks for diseases potentially related to adverse effects on neurodevelopment. Sons of female dentists (n=1690) and dental nurses (n=10,420) were compared with cohorts consisting of sons of other female healthcare personnel. Due to changes in mercury exposure in dentistry during the study period, analyses were stratified by decade of birth. Hazard ratios (HRs) were calculated using Cox proportional hazard models.

RESULTS

We found no elevated risk for neurological disease, epilepsy or intellectual disability among the sons of dental personnel during any of the decades studied. HRs for neurological disease among the dental nurse cohort were even below 1.00 during the 1970s and 1980s. A low number of events resulted in uncertainty regarding results in the dentist cohort.

CONCLUSIONS

We did not find any support for the hypothesis that mercury exposure in Swedish dentistry during the 1960s, 1970s or 1980s had any effect on the incidence of neurological disease or intellectual disability among the sons of female dental personnel. Our results imply that current use of dental amalgam should not represent an elevated risk for neurological disease or intellectual disability among the offspring of dental personnel.

Maternal occupational exposure to ionizing radiation and major structural birth defects

BACKGROUND

Ionizing radiation (IR) is known to be carcinogenic and mutagenic, but little is known about the association between maternal occupational exposure to IR and birth defects.

METHODS

We studied 38,009 mothers who participated in the National Birth Defects Prevention Study and delivered between 1997 and 2009. We assessed odds ratios [ORs] for the association between maternal occupations with potential exposure to IR and 39 birth defects.

RESULTS

We observed significant odds ratios (ORs) for isolated hydrocephaly (adjusted OR [AOR], 2.1; 95% confidence interval [CI], 1.1-4.2), isolated anotia/microtia (AOR, 2.0; 95% CI, 1.0-4.0), isolated colonic atresia (crude OR, 7.5; 95% CI, 2.5-22.3), isolated omphalocele (AOR, 2.3; 95% CI, 1.1-4.6) and isolated anencephaly (crude OR, 0.23; 95% CI, 0.06-0.94). We also observed a nonsignificant OR for birth defects in aggregate (AOR, 2.0; 95% CI, 0.9-4.6) among mothers with potential occupational exposure to fluoroscopy.

CONCLUSION

We assessed 39 birth defects, observing that maternal occupations with potential exposure to IR were associated with a significantly increased risk for 4 birth defects and a significantly protected risk for 1 birth defect. These results should be interpreted cautiously because our measurement of exposure is qualitative, some of these associations may be due to occupational exposures that are correlated with IR and some may be due to chance. However, these findings serve as the first evaluation of these relationships in a large study and may be useful for generating hypotheses for future studies.

Mortality among sons of female dental personnel--a national cohort study

AIMS

Dental personnel are exposed to mercury when using dental amalgam. This exposure constitutes a potential hazard to offspring of women working in dentistry. The present study examined increased mortality risk in offspring of mothers working in dentistry.

METHODS

Mortality was compared between sons of dental personnel and sons of nondental health-care personnel. Hazard ratios were calculated for three decades (1960s-1980s), when the magnitude of mercury exposure in dentistry was likely to have varied.

RESULTS

During the 1960s, there was a statistically significant increase in the risk of neonatal mortality for sons of dental nurses when compared with sons of assistant nurses: hazard ratio (HR) 1.82 (95% confidence interval, CI: 1.04-3.22). There was no increased risk in the subsequent decades, but a trend test demonstrated a consistent decrease in the risk over the three decades: HR for trend 0.63 (95% CI: 0.44-0.90). The raised mortality risk was limited to neonatal mortality. The comparison between dentists and physicians had insufficient statistical power.

CONCLUSIONS

There is no increased mortality risk among sons of female dentists after the 1960s. Although the results should be interpreted with caution, they suggest a modestly raised risk of neonatal mortality, during the 1960s, when exposure to mercury was thought to be highest.

Differences in prenatal exposure to mercury in South African communities residing along the Indian Ocean

Mercury is a persistent environmental pollutant that has the potential to adversely affect human health, particularly, foetal neurodevelopment. The purpose of the study was to investigate prenatal mercury (Hg) exposure in the population in three sites along the South Africa coast. Study subjects included women (n=350) who were admitted for delivery at the local hospitals. Maternal and cord blood samples were collected to measure total mercury and each participant was required to answer a questionnaire. The 90th percentile of mercury levels in maternal and cord blood of the total population was 1.15 μg/l and 1.67 μg/l, respectively. Site 1 (Manguzi) participants had the highest maternal geometric mean (GM) values of 0.93 μg/l, which was significantly different from Site 2 (Port Shepstone) (0.49 μg/l) and Site 3 (Empangeni) (0.56 μg/l) (ANOVA test, p<0.001). Umbilical cord blood GM Hg level for Site 1 (1.45 μg/l) was more than double the GM Hg level in Site 2 (0.70 μg/l) and Site 3 (0.73 μg/l). Univariate analysis indicated that the following maternal characteristics were positive predictors for elevated umbilical cord Hg levels: maternal blood Hg levels, living with a partner, residing in Site 1, living in informal housing, using wood and gas for cooking, borehole water as a drinking source, and a member of the household being involved in fishing. Maternal dietary predictors of elevated Hg levels in umbilical cord blood included consuming fresh fish, tinned fish, fruit or dairy products, daily. This study provides baseline data and reveals that 2% of the study population were above the EPA's reference value (5.8 μg/l) suggesting low level exposure to mercury in pregnant women and the developing foetus in South Africa. Further research is required to explore the sources of elevated Hg levels in Site 1.

Occupational exposures and adverse pregnancy outcomes among nurses: a systematic review and meta-analysis

BACKGROUND

The nursing profession has been associated with several adverse pregnancy outcomes. However, the associations between occupational exposures and adverse pregnancy outcomes among this group have not been systematically examined. This review collates all epidemiological evidence to examine the strength of associations and consistency among eligible studies.

METHODS

A computer search of EMBASE and PubMed from 1966 through August 2009 was performed, followed by a search of reference lists of relevant studies and narrative reviews

RESULTS

Fourteen studies explored the relation between anesthetic gases and spontaneous abortion, 8 the relation between anesthetic gases and congenital malformations, 7 the relation between chemotherapy agents and congenital malformations, and 4 the relation between shift work and spontaneous abortion. In the random-effects models the summary odds ratio (OR) was moderately elevated for all the relations: OR = 1.27, 95% confidence interval (CI) 0.99-1.63 for anesthetic gases and spontaneous abortion. The summary OR was between 1.05 and 1.09 in high-quality studies, registry-based studies, and cohort studies: OR = 1.33, 95% CI 1.09-1.68 for anesthetic gases and congenital malformation. The summary OR was between 0.97 and 1.22 for high-quality studies, registry-based studies, and cohort studies: OR = 1.35; 95% CI 0.91-2.01 for chemotherapy agent and spontaneous abortion. The summary OR was between 1.34 and 1.69 for high-quality studies, registry-based studies, and cohort studies: OR = 1.44, 95% CI 1.06-1.95 for shift work and spontaneous abortion.

CONCLUSIONS

Nurses were found to be at increased risk of adverse pregnancy outcomes, but the strength of association was weaker in the well-designed studies. The significance of the findings is limited by the number and heterogeneity of the studies.

Mercury levels in maternal and cord blood and attained weight through the 24 months of life

Birth weight is a strong determinant of attained weight at early ages. Until now, many studies have reported that low birth weight corresponds with high mercury levels. However, the relationship between mercury exposure and attained weight of infant has not been well studied. Therefore, the aim of the present study was to assess the degree of prenatal exposure to mercury by measuring the total mercury levels in maternal and cord blood, and examine the relationship between the mercury level during pregnancy and the attained weight of infant during the first 24 months of life. The prospective cohort study of Mothers and Children's Environmental Health (MOCEH) was built up in 2006, and 921 mother-infant pairs were recruited. Information on the socio-demographic characteristics, health behavior and environmental exposure were collected from an interview with trained nurses. After delivery, infants and mothers were followed up at 6, 12 and 24 months and the weights of the infants were measured. The mercury concentrations in the late maternal blood (β=-0.19. p=0.05) and cord blood (β=-0.36. p=0.01) were negatively associated with the infants' attained weight over the first 24 months of age. The infants' attained weight in the small for their gestational age (SGA) group was lower than the normal birth weight group at the highest quartile of the mercury level. Therefore, efforts should be made to reduce the mercury level in the maternal blood at late pregnancy and cord blood. Further research on the possible harmful effects of prenatal mercury exposure on postnatal growth is recommended.

Work as a nurse and a midwife and adverse pregnancy outcomes: a Finnish nationwide population-based study

OBJECTIVE

To assess whether work as a nurse and a midwife during pregnancy increases the risk of adverse pregnancy outcomes.

METHODS

We identified from the 1990-2006 Finnish Medical Birth Registry all singleton births to nurses (n=109,542), midwives (n=3,009), and teachers (n=23,454) (referents). The main outcomes were sexual differentiation, low and high birth weight, preterm and postterm delivery, small and large for gestational age, and perinatal death.

RESULTS

The prevalence of low birth weight (2.9% vs. 2.5%), preterm delivery (4.4% vs. 4.1%), postterm delivery (4.7% vs. 4.1%), small for gestational age (1.8% vs. 1.4%), perinatal death (0.45% vs. 0.41%) and stillbirth (0.30% vs. 0.25%) was higher among the newborns of nurses than those of teachers. The adjusted odds ratio (OR) from generalized estimating equations was 1.17 (95% confidence interval [CI] 1.07-1.26) for low birth weight, 1.09 (95% CI 1.02-1.16) for preterm delivery, 1.11 (95% CI 1.03-1.18) for postterm delivery, 1.17 (95% CI 1.05-1.30) for small for gestational age, 1.12 (95% CI 0.90-1.35) for perinatal death, and 1.27 (95% CI 0.98-1.56) for stillbirth. For midwives, the risk of small for gestational age (OR=1.25, 95% CI 0.95-1.55) was elevated, but the 95% CI included unity. There was no substantial difference in the sex distribution.

CONCLUSIONS

This study provides evidence that work as a nurse may reduce fetal growth and duration of pregnancy. The inference is based on the newborns of teachers as the reference group. However, the prevalence of most of the outcomes was higher among the newborns of all other working women combined than in the newborns of both nurses and teachers.

A 30-year follow-up of residual effects on New Zealand School Dental Nurses, from occupational mercury exposure

This paper reports possible residual adverse effects from occupational mercury exposure in dentistry, Thirty years ago, the all-women exposed group worked with both silver and copper amalgam filling material without protective gloves or a ventilation system, resulting in chronic mercury exposure. The aim of the study was to test the null hypothesis in a survey of general and reproductive health, and a battery of nine neurobehavioral tests. The population was the 115 graduates of one school for dental nurses from 1968 to 1971. The sample was 43 mercury-exposed women and 32 matched controls. Statistical comparisons revealed that the two groups were equivalent on cognitive tasks and four of the six mood subscales. Significant between-group differences were found in current health symptom experience and reproductive health, especially early hysterectomy experience. Reporting of Occupational Overuse Syndrome was strongly positively correlated with years of work. In general, the study suggests that acute symptoms from mercury exposure may be reversible, while some residual health effects may be becoming more of a concern with the women's increasing age.

Dental amalgam restorations and children's neuropsychological function: the New England Children's Amalgam Trial

BACKGROUND

A concern persists that children's exposure to mercury vapor from dental amalgams produces neurotoxicity.

OBJECTIVE

Our goal was to compare the neuropsychological function of children, without prior exposure to dental amalgam, whose caries were repaired using either dental amalgam or mercury-free composite materials.

METHODS

We conducted a randomized controlled trial involving 534 6- to 10-year-old urban and rural children who were assessed yearly for 5 years using a battery of tests of intelligence, achievement, language, memory, learning, visual-spatial skills, verbal fluency, fine motor function, problem solving, attention, and executive function.

RESULTS

Although the mean urinary mercury concentration was greater among children in the amalgam group than the composite group (0.9 vs. 0.6 microg/g creatinine), few significant differences were found between the test scores of children in the two groups. The differences found were inconsistent in direction. Analyses using two cumulative exposure indices--surface years of amalgam and urinary mercury concentration--produced similar results.

CONCLUSIONS

Exposure to elemental mercury in amalgam at the levels experienced by the children who participated in the trial did not result in significant effects on neuropsychological function within the 5-year follow-up period.

Occupational exposure in dentistry and miscarriage

BACKGROUND

Information on the reproductive effects of chemical exposures in dental work is sparse or inconsistent.

AIM

To investigate whether dental workers exposed to acrylate compounds, mercury amalgam, solvents or disinfectants are at an increased risk of miscarriage.

METHODS

The study was conducted among women dental workers and a comparison group of workers occupationally unexposed to dental restorative materials. Information on pregnancies was obtained from national registers and outpatient units of hospitals. Data on occupational exposure were obtained using postal questionnaires. The final study population included 222 cases of miscarriage and 498 controls (births). An occupational hygienist assessed exposure to acrylate compounds, disinfectants and solvents. Exposure to other agents was assessed on the basis of the questionnaire data. Odds ratios (ORs) and confidence intervals (CIs) were estimated using conditional logistic regression.

RESULTS

The ORs adjusted for confounding factors were increased for moderate-exposure and high-exposure categories of mercury amalgam (OR 2.0, 95% CI 1.0 to 4.1 and OR 1.3, 95% CI 0.6 to 2.5, respectively). The risk was slightly increased for the highest-exposure category of 2-hydroxyethylmethacrylate (OR 1.4, 95% CI 0.7 to 2.6) and polymethylmethacrylate dust (OR 1.4, 95% CI 0.8 to 2.4). A slightly increased risk was also detected for likely exposure to organic solvents (OR 1.4, 95% CI 0.8 to 2.3) and disinfectants (OR 1.5, 95% CI 0.9 to 2.7).

CONCLUSIONS

No strong association or consistent dose-response relationship was observed between exposure to chemical agents in dental work and the risk of miscarriage. A slightly increased risk was found for exposure to mercury amalgam, some acrylate compounds, solvents and disinfectants. These findings indicate that the possibility of a weak association between exposure to these agents and an increased risk of miscarriage cannot be excluded.

Elevation of Macrophage Colony-Stimulating Factor in Amniotic Fluid at Late Stage of Normal Pregnancy

PROBLEM

Macrophage colony-stimulating factor (M-CSF) promotes placental growth and maintenance, and regulates trophoblast invasion into the placental bed. We evaluated whether the amniotic fluid M-CSF levels at the late stage of normal pregnancy is altered compared with those at the middle stage.

METHOD OF STUDY

This study enrolled 52 subjects experiencing normotensive pregnancies with single fetuses, of whom 26 were women at the late stage (term gravidas) and 26 were women at the middle stage (controls). The average gestational age at entry was 38 weeks of gestation and 17 weeks, respectively. Amniotic fluid was collected from these subjects. Amniotic fluid M-CSF levels were determined by the enzyme-linked immunosorbent assay method then compared between term gravidas and controls.

RESULTS

Amniotic fluid M-CSF concentrations were 4815 pg/mL (median) in term gravidas and 3795 pg/mL in controls; the concentrations were significantly higher in term gravidas than in controls.

CONCLUSIONS

We demonstrated a significant increase in amniotic fluid M-CSF levels in term gravidas. These results suggest that elevated levels of M-CSF in amniotic fluid have an important immunological function in the maintenance of pregnancy and fetal growth.

Granulocyte-Macrophage Colony-Stimulating Factor Levels in Amniotic Fluid Before the Onset of Labor and During Labor Do Not Differ in Normal Pregnancies

PROBLEM

Granulocyte-macrophage colony-stimulating factor (GM-CSF) at the implantation site may regulate invasion and differentiation of placental trophoblast. We evaluated whether GM-CSF levels in amniotic fluid during labor contributing to subsequent delivery differed from those before the onset of labor in normal pregnancies.

METHOD OF STUDY

This study enrolled 36 Japanese women experiencing normal pregnancies with single fetuses who had no infection. Of these pregnancies, 18 were women during labor that led to subsequent term delivery (labors). The other 18 were women without labor underwent cesarean section (controls). These two groups (18 labors and 18 controls) were compared. The average gestational age at entry was 38-39 weeks of gestation. The women's ages and gestational ages did not differ significantly between the two groups. Amniotic fluid was collected and the GM-CSF levels were compared between two groups. The GM-CSF level was determined by the enzyme-linked immunosorbent assay method.

RESULTS

There was no significant increase in GM-CSF levels in amniotic fluid during labor compared with that before the onset of labor.

CONCLUSIONS

The GM-CSF in amniotic fluid may not promote the onset of labor at term and/or term labor contributing to subsequent delivery may not induce the production and secretion of GM-CSF into amniotic cavity.

The use of national health registers for studying environmental causes of congenital defects

This review summarizes and discusses the use of central health registers in studies of causes of congenital malformations. The review is illustrated using data from the Swedish Medical Birth Register with adjacent registers and gives examples of different methods to identify environmental exposures. The review stresses the usefulness of this approach but also the inherent problems of which the researcher must be fully aware.

Amalgam toxicity--environmental and occupational hazards

OBJECTIVES

To discuss briefly the recent developments in mercury production, consumption and waste handling especially in relation to the use of mercury in dentistry. Furthermore, to discuss the toxicological and reproductive aspects of the mercury body burden of dental personnel.

DATA, SOURCES AND STUDY SELECTION

The data discussed are primarily based on published scientific studies and on publications and reviews from governmental and other official authorities which have been published within the last 10 years, References have been traced manually or by MEDLINE.

CONCLUSIONS

Global production and consumption of mercury is decreasing, as is the production of amalgam fillings in some countries. By proper measures it is possible to further reduce the environmental burden of mercury from dental clinics. In general, the mercury body burden of the dental personnel can be kept below the normally accepted toxicological limits and reproductive effects have not been proven provided a proper mercury hygiene regimen is adopted.

Maternal occupational exposure to chemical substances and the risk of infants small-for-gestational-age

BACKGROUND

The association between maternal occupational exposure to specific chemical substances (organic solvents, carbon tetrachloride, herbicides, chlorophenols, polychlorinated biphenyls, aromatic amines, lead and lead compounds, mercury and mercury compounds) and birth of small-for-gestational-age (SGA) infants was evaluated using data from a prospective cohort study of 3,946 pregnant women in West Germany from 1987 to 1988.

METHODS

Occupational, medical, and psychosocial information was gathered through a questionnaire from pregnant women who were recruited between 15 and 28 gestational weeks. Exposure to chemical substances at the current workplace was assessed by a job-exposure matrix constructed by Pannett in 1985 and weighted for the number of working hours per week. Women not working at the time of the interview, women with multiple births, and women with stillbirths were excluded from analysis. Data were analyzed using dichotomous and polytomous logistic regression to control for age, smoking status, alcohol consumption, body mass index, and number of former births.

RESULTS

The results of the dichotomous logistic regression analysis suggest that leather work might be associated with the birth of infants small-for-gestational-age through exposure to chlorophenols (P = 0.02) and aromatic amines (P = 0.05). In the polytomous logistic regression analysis, only the association between exposure to mercury and growth retardation reached statistical significance (P = 0.02); however, the power of the study is limited. Further adjustment for income, shift work, and heavy physical work had no substantial effect on the results.

CONCLUSIONS

These findings suggest that maternal exposure to specific chemicals at work may be a risk factor for the birth of SGA infants.

Reproductive toxicity of occupational mercury. A review of the literature

OBJECTIVES

This paper aims to give the dental practitioner insight into the potential reproductive effects of handling dental silver amalgam, c.q. mercury.

DATA SOURCES

Experimental studies on animals, case reports and epidemiologic studies.

STUDY SELECTION

Experimental animal studies show high doses/concentrations of mercury to increase the risk of reproductive disorders, e.g. infertility, spontaneous abortion, stillbirth and congenital malformations. Some case reports suggest an association between the disorders in humans and high levels of mercury. Therefore, the present article reviews epidemiological studies on the relationship between occupational exposure to mercury, mainly as vapour in the dental practice, and females' procreative ability. Studies concerning the reproductive effects of males' occupational mercury body burden are scarce. The reproductive risk of patients' mercury uptake from silver amalgam fillings is assessed.

CONCLUSIONS

It seems warranted to conclude that negative reproductive effects from exposure to mercury in the dental office are unproven, but safe levels have not been established. Seemingly problems are unlikely to occur, unless a poor hygiene causes the mercury concentration in the air to exceed females' time-weighted long-term Threshold Limit Value (TLV). Consequently, in view of the in general low amounts of mercury stemming from dental amalgam fillings, the population at large is at even less risk than dental staff. The effects of occupational elemental mercury concentrations lower than the TLV on the menstrual cycle, conception, male fertility and children's behaviour need, however, more research.

Environmental toxicants and female reproduction

OBJECTIVE

To review current knowledge on the potential effects of environmental toxicants on female reproduction in laboratory animals, wildlife, and humans.

DESIGN

Published literature about the effects of endocrine disruptors, heavy metals, solvents, pesticides, plastics, industrial chemicals, and cigarette smoke on female reproduction.

RESULT(S)

Published data indicate that chemical exposures may cause alterations in reproductive behavior and contribute to subfecundity, infertility, pregnancy loss, growth retardation, intrauterine fetal demise, birth defect, and ovarian failure in laboratory animals and wildlife. Data on the association of chemical exposures and adverse reproductive outcomes in humans are equivocal and often controversial. Some studies indicate that chemical exposures are associated with infertility, spontaneous abortion, or reproductive cancer in women. In contrast, other studies indicate that there is no association between chemical exposures and adverse reproductive outcomes. The reasons for ambiguous findings in human studies are unknown but likely include the fact that many studies are limited by multiple confounders, inadequate methodology, inappropriate endpoints, and small sample size. The mechanism by which chemicals alter reproductive function in all species is complex and may involve hormonal and/or immune disruption, DNA adduct formation, altered cellular proliferation, or inappropriate cellular death.

CONCLUSION(S)

Studies are needed to clarify which toxicants affect human reproduction and by which mechanisms of action. Furthermore, methods should be developed to minimize exposure to known reproductive toxicants such as dioxins and cigarette smoke.

[Illnesses caused by amalgam?]

BACKGROUND

As side effects of dental amalgam have been mentioned allergy, oral lichen, electro-galvanism, amalgam tattoos of gingiva or oral mucosa, and undesirable esthetics. Patients with amalgam restorations show increased mercury levels in different body fluids compared to amalgam-free controls. An intoxication due to dental amalgam fillings, however, is not to be expected-despite equivocal statements in the literature.

SCIENTIFIC RESULTS

In contrast, recent studies revealed that dental amalgam contributes to mercury exposure less than assumed few years ago. Therefore, amalgam will stay an option as a restorative material in future. The removal of intact amalgam fillings in the intention of "detoxification" is not science-based.

CONCLUSION

Successful caries prevention (e.g. due to the widespread use of fluoride) and the further development of esthetic restorative materials based on composite resins will limit the utilisation of amalgam. Thus, alternative materials have not been shown to have a lower rate of side effects (e.g. allergy) compared to amalgam.

Paternal work in the power industry: effects on children at delivery

Although reports on reproductive disturbances among occupational groups of electrical workers have been discussed, few studies have focused explicitly on the children of workers employed in the power industry. Birth outcome and cancer in the offspring of fathers who were exposed to electric and magnetic fields at time of sperm production were studied in two cohorts. In Study 1, male occupation in the power industry was identified in censuses. Study 2 is a prospective cohort study of newly employed power industry workers. Birth data were obtained by record linkage between censuses and several available health registers in Sweden. Multiple births, birth weight, sex, survival, congenital malformations, and cancer have been analyzed with relation to the father's exposure to electric and magnetic fields one year before the child was born. There were six cancer cases among infants in the exposed group (2.4 expected) and six in the unexposed group (3.2 expected) in Study 1. Jointly, the 12 cancer cases found among the infants were more than expected (P = 0.02). However, this total excess may be random. No cancer cases were observed in the prospective study. For chromosomal abnormalities, such as Down's syndrome, one case was observed among infants of exposed fathers and three cases among unexposed fathers in Study 1. In Study 2, no cases were observed. There was a slightly higher proportion of malformation diagnoses among infants of exposed fathers than among infants of unexposed fathers in Study 2, but this could be random (odds ratio = 1.59; 95% Confidence interval 0.43-1.48). No clear-cut effects on infants fathered by men who were exposed to electric and magnetic fields around the time of sperm production could be seen in these two studies.

Birthweight of term infants and maternal occupation in a prospective cohort of pregnant women. The ALSPAC Study Team

OBJECTIVE

To study the relation between birthweight of term infants and maternal occupation.

METHODS

Information on job titles since the age of 16, and sociodemographic and other lifestyle factors were obtained by means of questionnaires as part of the Avon longitudinal study of pregnancy and childhood (ALSPAC), from a cohort of 14,000 pregnant women. The British 1990 standard occupational classification was used to code jobs within nine major job groups.

RESULTS

For 9282 women who delivered term infants and reported a job for the relevant period, there was a significant difference in mean birthweight among the nine major job groups. A 148 g difference was found between the mean birthweight of infants born to women with professional occupations and those with plant and machine operative jobs. Multiple regression analysis adjusted for sex of infant, parity, maternal height, smoking, caffeine consumption, and race. After adjustment the maternal job was no longer significantly associated with birthweight.

CONCLUSION

Despite the absence of a significant association between birthweight and job after adjustment, there were several findings which agreed with publications on maternal occupation and pregnancy outcome. The major job groups with the lowest birthweights included the following jobs; metal forming or welding, electric or electronic work, jobs in the textile trade, and assembling and working with equipment (mobile and stationary). The lack of an association may indicate that the study was of insufficient power to detect a small difference; it may indicate the presence of confounding variables that were not adjusted for or it may indicate that no association exists.

Current materials and techniques for direct restorations in posterior teeth. Part 1: Silver amalgam

This paper, the first of two reviewing materials and techniques for direct intracoronal restorations in posterior teeth, deals with the use of silver amalgam. Based on a consensus view on appropriate applications and contraindications for silver amalgam, the toxicity of amalgam and competing materials, financial implications and international legislation, consideration is given to the continued use of this material. It is concluded that silver amalgam still has a place in everyday practice, albeit restricted in comparison to its former use. Amalgam should only be used where it offers clear advantages over other materials. This requirement for use of silver amalgam will continue until true substitutes are developed and evaluated, alternative materials are optimised and dentists are fully trained in the use of adhesive techniques.

The dissemination of false data through inadequate citation

OBJECTIVES

That occupational exposure to mercury causes reproductive failure in dental personnel has been propagated by repeated reference to a single epidemiological study in Poland, published in 1987. The present paper scrutinizes the results of this study, and monitors its subsequent citation in the literature.

METHOD

Articles referring to the study were located in the Science Citation Index. From references in these papers and through other references, further articles were found. These papers were reviewed, and their content organized in relation to the way in which the Polish study was cited.

RESULT

Most authors referred to the findings in the Polish study without critical evaluation of the data presented.

CONCLUSIONS

Citation of irrelevant or misleading scientific data in the literature raises unfounded concerns in nonscientific circles and may lead to unwarranted regulations. It is therefore essential that editors and reviewers of scientific articles also scrutinize the literature quoted.

Behavioural effects of prenatal metallic mercury inhalation exposure in rats

The effects of administration by inhalation of metallic mercury vapour (Hg0) to pregnant rats, approximately corresponding to doses of 0.2 mg Hg0/kg/day (high dose) or 0.07 mg Hg0/kg/day (low dose), on the developmental and behavioural repertoire of the offspring were studied. Exposure occurred during days 11-14 plus 17-20 of gestation. The dose levels were selected so as not to induce maternal toxicity. Maturation variables such as surface righting, negative geotaxis, pinna unfolding, and tooth eruption revealed no differences between Hg0-treated offspring and controls. Tests of spontaneous motor activity showed that the Hg0-treated offspring were hypoactive at 3 months of age but hyperactive at 14 months. In spatial learning tasks the prenatally exposed offspring showed retarded acquisition in the radial arm maze but no differences in circular swim maze. A simple test of learning, habituation to a novel environment (activity chambers), indicated a reduced ability to adapt. These data suggest that prenatal exposure to Hg0 vapour results in similar behaviour changes in the offspring as reported for methylmercury.

Teratological aspects of dental amalgam

The teratogenic effect is determined by four factors: (1) the agent, (2) the dose, (3) the stage of embryonic development, and (4) the genetic constitution of the embryo. The first two factors are of particular interest and warrant further comment. It should be emphasized that the mercury released from dental amalgam is mainly metallic mercury vapor. The dose of mercury vapor from dental amalgam fillings in the order of 5 micrograms/day is very low compared with the doses in a teratological study and is not likely to exceed the threshold necessary for a teratogenic effect to occur. The concentration of the teratogen at the target tissue is determined not only by the degree of placental transfer but also by other factors, such as the distribution within the maternal organism, the affinity to the fetal liver and blood, the hematocrit value, and the passage through the ductus venosus. These factors might help to explain toxicological mechanisms and species differences and have to be considered if the results of animal experiments are to be extrapolated to human conditions. Neither epidemiological data nor animal experimental data indicate that the release of metallic mercury vapor from dental amalgam therapy should cause teratogenic effects. A comparison with the incorporation of the fetotoxic methyl mercury might be justified.

Amalgam--fact and fiction

A brief history of amalgam is given, stressing the role of G. V. Black. The background and the progress of the two Amalgam Wars are sketched. Aspects are presented of the drawbacks of amalgam with respect to toxic effects of, especially, mercury vapor and corrosion products. An account is given of some frequent fallacies concerning the health hazards of dental amalgam fillings and the role of psychosocial factors in the development of illness attributed to amalgam is emphasized.

Oral galvanism in Sweden

Although a questionnaire response showed that many Swedes are concerned about oral galvanism, it seems that the symptoms changed as each theory was challenged. The symptoms changed with additional knowledge of the patient and the environment.