Neurological symptoms among dental assistants: a cross-sectional study

Mercury air, urine monitoring and health effects on occupationally exposed dental healthcare workers in Delhi, India

BACKGROUND

Mercury (Hg) is a toxic heavy metal with multiple uses in various medical devices. Hg is used in dentistry as a restorative material. Such use creates significant exposure to dental practitioners. Hence, it is important to assess the risk created by Hg use in healthcare.

OBJECTIVE

To quantify airborne Hg vapour exposure and Hg levels in dental healthcare workers, and determine the association of various symptoms and diseases to Hg exposure.

METHODS

Air monitoring of Hg vapours were conducted in dental clinics and amalgam rooms. Urine samples were collected from occupationally exposed dental healthcare workers and urine Hg levels were measured. A cross-sectional health survey was conducted in 23 healthcare units of Delhi to determine an association between Hg exposure and various health effects.

RESULTS

Hg vapour concentration ranged from 0.96μg/m3 to 15μg/m3, the highest concentration was recorded in the amalgam room (15μg/m3). Urine Hg levels in healthcare workers (0.51±0.17μg/L) were higher than the control (0.29±0.05μg/L). A cross-sectional health survey revealed a significant prevalence of confusion, forgetfulness, muscle spasm, and tremors by the respondents.

CONCLUSION

Hg concentration in dental clinics may hover above the prescribed safe levels posing a definitive health risk to healthcare workers. Urinary Hg measurements did not reveal an excess of body burden except in one case. Since Hg bio accumulates, it is probable as these workers grow older, they may end up with a higher body burden of Hg that may lead to a variety of adverse health outcomes.

Adverse Health Effects and Mercury Exposure in a Colombian Artisanal and Small-Scale Gold Mining Community

The aim of this study was, first of all, to associate the mercury (Hg) concentrations and respiratory functions of the gold miners in the artisanal small-scale gold mining (ASGM) environment in San Martín de Loba, Colombia. We carried out a cross-sectional study using a survey whereby we collected basic demographic information, occupational medical history, and applied two validated questionnaires (Q16 and SF36). We measured Hg levels in all volunteers using direct thermal decomposition-atomic absorption spectrometry. Univariate and bivariate statistical analyses were carried out for all variables, performing logistic regression to assess the effect of ASGM on health outcomes. Volunteers enrolled (n = 124) were between the ages of 20 and 84 years (84% miners and 79% males). No changes were found in the systolic blood pressure, diastolic blood pressure, and heart rate from the ASGM miners, in crude and adjusted statistical analyses. ASGM miners increased 8.91 (95% confidence interval, 1.55-95.70) times the risk of having these than of having neurotoxic effects. Concentrations of total whole blood mercury (T-Hg) in all participants ranged from 0.6 to 82.5 with a median of 6.0 μg/L. Miners had higher T-Hg concentrations than non-miners (p-value = 0.011). Normal and abnormal respiratory spirometry patterns showed significant differences with the physical role and physical function of quality-of-life scales (the (p-value was 0.012 and 0.004, respectively). The spirometry test was carried out in 87 male miners, with 25% of these miners reporting abnormalities. Out of these, 73% presented a restrictive spirometry pattern, and 27%, an obstructive spirometry pattern. The ASGM population had higher Hg concentrations and worse neurotoxic symptomatology than non-miners of the same community.

Mercury exposure, neopterin profile, and tryptophan degradation in dental technicians

Amalgam has been widely used as a restorative dental material for over 150 years. Most standard dental amalgam formulations contain approximately 50% elemental mercury in a mixture of copper, tin, silver, and zinc. Mercury is a highly volatile metal, which can easily vaporize to a colorless and odorless gas. It has been demonstrated that mercury is released from dental amalgam, which is increased by chewing, eating, brushing, and drinking hot liquids. Besides this, amalgam is the main occupational exposure source of mercury for dental workers. It is known that mercury exposure causes immune modulation in humans. In this study, it was aimed to evaluate the changes in neopterin levels and tryptophan (Trp) degradation in dental technicians. It was observed that low levels of occupational mercury exposure resulted in decreased neopterin, kynurenine (Kyn), and Kyn/Trp levels. Moreover, mercury and neopterin levels had a significant positive correlation in workers. The lower neopterin levels and Kyn/Trp in dental technicians compared to an unexposed group indicates a possible immune suppression with low level of occupational mercury exposure during amalgam preparation. The relationship between urinary mercury levels as an indicator of occupational mercury exposure and neopterin reminded an effect on T-cell-mediated immune response.

Mercury vapor volatilization from particulate generated from dental amalgam removal with a high-speed dental drill - a significant source of exposure

Background

The ubiquitous use of dental amalgam for over 180 years has resulted in the exposure of millions of dental workers to mercury. Dental amalgam contains approximately 50% mercury. Dental workers, including dentists, dental assistants, and dental hygienists, have been shown to have increased levels of mercury and suffer more from health issues related to mercury exposure than the general public. Mercury is known to be absorbed via inhalation or through the skin. There are many routine dental procedures that require the removal of dental amalgam by using the dental high-speed drill, which we suspected generates an occupational mercury exposure that is not sufficiently recognized.

Results

We showed that drilling dental amalgam generates particulate that volatilizes significant amounts of mercury vapor generally for more than an hour after removal. The levels of mercury vapor created by this procedure frequently exceed the safety thresholds of several jurisdictions and agencies.

Conclusions

A significant, underrecognized source of localized exposure to mercury vapor was identified in this study. The vapor was created by microgram levels of particulate generated from dental amalgam removal with a high-speed dental drill, even when all feasible engineering controls were used to reduce mercury exposure. This exposure may explain why dental workers incur health effects when safety thresholds are not breached. The dispersion patterns for the particulate are not known, so the use of effective skin barriers and inhalation protection are required during amalgam removal to protect the dental worker from this form of occupational mercury exposure. Standard methodologies for occupational mercury exposure assessment appear to be inadequate when assessing mercury exposure during amalgam removal.

Neurotoxic effects of mercury exposure in dental personnel

Numerous studies have reported neurobehavioural effects in dental personnel occupationally exposed to chronic low levels of mercury (Hg). Hg exposure from dental work may also induce various chronic conditions such as elevation of amyloid protein expression, deterioration of microtubules and increase or inhibition of transmitter release at motor nerve terminal endings. Therefore, clinical studies of Hg toxicity in dentistry may provide new knowledge about disturbed metal homeostasis in neurodegenerative diseases such as Alzheimer's disease, multiple sclerosis and mood disorders. The purpose of this MiniReview is to evaluate the evidence of possible relevance between Hg exposure in dentistry and idiopathic disturbances in motor functions, cognitive skills and affective reactions, as well as dose-response relationships.

Mercury exposure and health impacts in dental personnel

Based on toxicological, clinical, and epidemiological knowledge, the present paper reviews the status regarding possible deleterious health effects from occupational exposure to metallic mercury (Hg) in dental practice. Symptoms from the central nervous system are among the health problems that most often are attributed to Hg exposure in dentists and dental nurses working with amalgam. Uncharacteristic symptoms of chronic low-level Hg vapor exposure including weakness, fatigue, and anorexia have been observed in numerous studies of dental personnel. It is crucial to protect both human health and the environment against negative effects of Hg. In line with this, the use of dental amalgam in industrial countries is about to be phased out. In Norway and Sweden, the use of the filling material is banned.

The risk of occupational exposure to mercury vapor in some public dental clinics of Baghdad city, Iraq

BACKGROUND

Dental workers are exposed to elevated levels of elemental mercury vapor substantially above the occupational exposure standards when placing or removing mercury/silver tooth restorations and disposing of mercury waste. This results in a significant increase in occupational exposure and risk of mercury intoxication.

METHODS

To evaluate the occupational exposure of dental workers to amalgam in four dental clinics in Baghdad city, the concentrations of mercury vapor were measured seasonally from February to November 2016. Samples of blood and urine were collected from 30 dental workers (exposed individuals) and five non-occupationally exposed individuals. Biochemical parameters such as cholesterol, liver enzymes (alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase), renal enzymes (urea and creatinine), total protein and reduced glutathione (GSH) were observed.

RESULTS

The results indicated that mercury vapor levels varied from 84.7 ± 18.67 to 609.3 ± 238.90 µg/m³ and most concentrations were above the occupational exposure standards. The results of the biochemical parameters showed a significant increase in levels of cholesterol, aspartate aminotransferase (AST) and alanine aminotransferase (ALT) and no significant increase in blood urea and creatinine in dental workers in comparison with unexposed persons (control). Although the results showed a significant reduction in the levels of glutathione and total protein, there was no significant decrease in the levels of alkaline phosphatase (ALP) in exposed dental workers when compared with non-occupationally exposed individuals.

CONCLUSIONS

It is concluded that mercury vapor concentrations in the indoor air of some dental clinics in Baghdad city are high and exceed the OSHA STEL(Occupational Safety and Health Administration Short Term Exposure Limit). The present data showed that altered biochemical parameters can be used as efficient bioindicators for mercury toxicity.

Metals and Circadian Rhythms

Circadian rhythms describe the behavioral and physiological changes that occur in living organisms in order to attune to a 24 hour cycle of day and night. The most striking aspect of circadian function is the sleep-wake cycle, however many other physiological processes are regulated in 24 hour oscillations, including blood pressure, body temperature, appetite, urine production, and the transcription and translation of thousands of circadian dependent genes. Circadian disruption and sleep disorders are strongly connected to neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, and Huntington's disease as well as others. Metal exposures have been implicated in neurodegenerative diseases, in some cases involving metals that are essential micronutrients but are toxic at high levels of exposure (such as manganese, copper, and zinc), and in other cases involving metals that have no biological role but are toxic to living systems (such as lead, mercury, and aluminum). In this review, we examine the evidence for circadian and sleep disorders with exposures to these metals and review the literature for possible mechanisms. We suggest that giving the aging population, the prevalence of environmental exposures to metals, and the increasing prevalence of neurodegenerative disease in the aged, more research into the mechanisms of circadian disruption subsequent to metal exposures is warranted.

A Review of Mercury Exposure and Health of Dental Personnel

Considerable effort has been made to address the issue of occupational health and environmental exposure to mercury. This review reports on the current literature of mercury exposure and health impacts on dental personnel. Citations were searched using four comprehensive electronic databases for articles published between 2002 and 2015. All original articles that evaluated an association between the use of dental amalgam and occupational mercury exposure in dental personnel were included. Fifteen publications from nine different countries met the selection criteria. The design and quality of the studies showed significant variation, particularly in the choice of biomarkers as an indicator of mercury exposure. In several countries, dental personnel had higher mercury levels in biological fluids and tissues than in control groups; some work practices increased mercury exposure but the exposure levels remained below recommended guidelines. Dental personnel reported more health conditions, often involving the central nervous system, than the control groups. Clinical symptoms reported by dental professionals may be associated with low-level, long-term exposure to occupational mercury, but may also be due to the effects of aging, occupational overuse, and stress. It is important that dental personnel, researchers, and educators continue to encourage and monitor good work practices by dental professionals.

Low-level mercury in children: associations with sleep duration and cytokines TNF-α and IL-6

There is a sizeable literature suggesting that mercury (Hg) exposure affects cytokine levels in humans. In addition to their signaling role in the immune system, some cytokines are also integrally associated with sleep behavior. In this cross-sectional study of 9-11 year old children (N=100), we measured total blood Hg in whole blood, serum levels of tumor necrosis factor α (TNF-α) and interleukin 6 (IL-6), and objectively measured sleep and activity using actigraphy. Increasing blood Hg was associated with significantly shorter sleep duration and lower levels of TNF-α. IL-6 was not associated with sleep or blood Hg. This study is the first to document an association between total blood Hg and sleep (albeit a small effect), and the first to consider the associations of total blood Hg with cytokines TNF-α and IL-6 in a pediatric sample. Further research using alternative designs (e.g., time-series) is necessary to determine if there is a causal pathway linking low-level Hg exposure to sleep restriction and reduced cytokines.

Mercury vapour exposure during dental student training in amalgam removal

Background

Amalgam that is used for dental fillings contains approximately 50% elemental mercury. During dental student training, amalgam is often removed by drilling without the use of water spray and suction, which are protective measures in preventing mercury aerosol. In this study we measured mercury vapor levels in ambient air during amalgam removal as is typically performed in dental training.

Methods

Mercury vapor levels in ambient air were measured in a dental school laboratory during removal of amalgam fillings from artificial teeth set into a dental jaw simulator. Mercury vapor was measured under three conditions (25 measurements each): with the simultaneous use of water spray and suction, with the use of suction only, and with the use of neither suction nor water spray. These three conditions are all used during dental student training. Results were compared to Alberta occupational exposure limits for mercury vapor in order to assess potential occupational risk to students. Analysis of variance testing was used to compare data obtained under the three conditions.

Results

When water spray and suction were used, mercury vapor levels ranged from 4.0 to 19.0 μg/m³ (arithmetic mean = 8.0 μg/m³); when suction only was used, mercury vapor levels ranged from 14.0 to 999.0 (999.0 μg/m³ represents the high limit detection of the Jerome analyzer) (arithmetic mean = 141.0 μg/m³); when neither suction nor water was used, the vapor levels ranged from 34.0 to 796.0 μg/m³ (arithmetic mean = 214.0 μg/m³).

Conclusions

The Alberta Occupational Health and Safety threshold limit value for mercury vapor over an eight-hour time-weighted period is 25.0 μg/m³. The absolute ceiling for mercury vapor, not to be exceeded at any time, is 125.0 μg/m³. When both water spray and suction were used, mercury vapor levels were consistently below this threshold. When suction without water spray was used, mercury vapor levels exceeded the safety threshold 8% of the time. When neither water spray nor suction was used, 36% of the mercury vapor readings exceeded the absolute ceiling value. To maximize safety, dental schools should train students to remove amalgam only while using water spray and high volume suction. Alternatively, students should use appropriate occupational hygiene personal protective equipment during amalgam removals.

The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances

Whilst facing a worldwide fast increase of food and environmental allergies, the medical community is also confronted with another inhomogeneous group of environment-associated disabling conditions, including multiple chemical sensitivity (MCS), fibromyalgia, chronic fatigue syndrome, electric hypersensitivity, amalgam disease and others. These share the features of poly-symptomatic multi-organ cutaneous and systemic manifestations, with postulated inherited/acquired impaired metabolism of chemical/physical/nutritional xenobiotics, triggering adverse reactions at exposure levels far below toxicologically-relevant values, often in the absence of clear-cut allergologic and/or immunologic involvement. Due to the lack of proven pathogenic mechanisms generating measurable disease biomarkers, these environmental hypersensitivities are generally ignored by sanitary and social systems, as psychogenic or "medically unexplained symptoms". The uncontrolled application of diagnostic and treatment protocols not corresponding to acceptable levels of validation, safety, and clinical efficacy, to a steadily increasing number of patients demanding assistance, occurs in many countries in the absence of evidence-based guidelines. Here we revise available information supporting the organic nature of these clinical conditions. Following intense research on gene polymorphisms of phase I/II detoxification enzyme genes, so far statistically inconclusive, epigenetic and metabolic factors are under investigation, in particular free radical/antioxidant homeostasis disturbances. The finding of relevant alterations of catalase, glutathione-transferase and peroxidase detoxifying activities significantly correlating with clinical manifestations of MCS, has recently registered some progress towards the identification of reliable biomarkers of disease onset, progression, and treatment outcomes.

Occurrence of cognitive and neurological symptoms in norwegian dentists

Objectives

Previous investigations have presented some evidence of late cognitive effects in dental personnel exposed to metallic mercury. We wanted to examine if Norwegian dentists have an increased prevalence of symptoms consistent with neurological and/or cognitive malfunction.

Methods

The study group consisted of 406 dentists from central Norway and 217 controls from the general population, all under the age of 70. They had responded to a standardised postal questionnaire (Euroquest) inquiring about seven symptoms in regard to neurology, psychosomatics, memory, concentration, mood, sleep disturbances, and fatigue. A score was calculated for each symptom based on 4 to 15 single questions scored on a scale from 1 (seldom or never) to 4 (very often).

Results

The dentists and controls had a participation rate of 57.2% and 42.9% respectively. The dentists reported no more cognitive symptoms than the controls, with low average symptom scores from 1.16 for neurological symptoms in males to 1.73 for fatigue in females. Corresponding figures for the controls were 1.22 and 1.77. There were a total of 1.2% of the dentists and 1.8% of the controls who reported having three or more of the seven symptoms "often" or more frequently.

Conclusion

Norwegian dentists do not report more cognitive and neurological symptoms than controls from the general population.

Is dental amalgam safe for humans? The opinion of the scientific committee of the European Commission

It was claimed by the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR)) in a report to the EU-Commission that "....no risks of adverse systemic effects exist and the current use of dental amalgam does not pose a risk of systemic disease..." [1, available from: http://ec.europa.eu/health/ph_risk/committees/04_scenihr/docs/scenihr_o_016.pdf].SCENIHR disregarded the toxicology of mercury and did not include most important scientific studies in their review. But the real scientific data show that:(a) Dental amalgam is by far the main source of human total mercury body burden. This is proven by autopsy studies which found 2-12 times more mercury in body tissues of individuals with dental amalgam. Autopsy studies are the most valuable and most important studies for examining the amalgam-caused mercury body burden.(b) These autopsy studies have shown consistently that many individuals with amalgam have toxic levels of mercury in their brains or kidneys.(c) There is no correlation between mercury levels in blood or urine, and the levels in body tissues or the severity of clinical symptoms. SCENIHR only relied on levels in urine or blood.(d) The half-life of mercury in the brain can last from several years to decades, thus mercury accumulates over time of amalgam exposure in body tissues to toxic levels. However, SCENIHR state that the half-life of mercury in the body is only "20-90 days".(e) Mercury vapor is about ten times more toxic than lead on human neurons and with synergistic toxicity to other metals.(f) Most studies cited by SCENIHR which conclude that amalgam fillings are safe have severe methodical flaws.

Symptoms of intoxication in dentists associated with exposure to low levels of mercury

The present study examined the effects of occupational exposure of a group of dentists to low levels of mercury. The study population consisted of 106 dentists and 94 general practitioners (referent group), from private and public clinics in Shiraz city. Subjects were requested to complete a questionnaire on demographic variables, suspicious symptoms of intoxication and work practices. Additionally, atmospheric and urinary concentrations of mercury were measured by Atomic Absorption Spectroscopy technique. The data were analysed by χ(2) test, independent sample t-test and multivariate logistic regression analysis, where applicable. Both groups were similar as far as most demographic and socioeconomic variables, but age and number of personal amalgam fillings, were concerned. Median of atmospheric concentration of mercury was found to be 3.35 μg/m(3). Likewise, the urinary concentration of mercury in dentists was estimated to be 3.16 μg/g creatinine. This value was significantly higher than that of the referent group. Similarly, analysis of the data revealed that neuropsychological, muscular, respiratory, cardiovascular and dermal symptoms were more prevalent in dentists. Our findings indicate that occupational exposure of dentists to mercury, even at low levels, is associated with a significant increase in the prevalence of symptoms of intoxication.

Sensitivity-related illness: the escalating pandemic of allergy, food intolerance and chemical sensitivity

The prevalence of allergic-related diseases, food intolerance, and chemical sensitivities in both the pediatric and adult population has increased dramatically over the last two decades, with escalating rates of associated morbidity. Conditions of acquired allergy, food intolerance and chemical hypersensitivity are frequently the direct sequelae of a toxicant induced loss of tolerance (TILT) in response to a significant initiating toxic exposure. Following the primary toxicant insult, the individuals become sensitive to low levels of diverse and unrelated triggers in their environment such as commonly encountered chemical, inhalant or food antigens. Among sensitized individuals, exposure to assorted inciting stimuli may precipitate diverse clinical and/or immune sequelae as may be evidenced by clinical symptoms as well as varied lymphocyte, antibody, or cytokine responses in some cases. Recently recognized as a mechanism of disease development, TILT and resultant sensitivity-related illness (SRI) may involve various organ systems and evoke wide-ranging physical or neuropsychological manifestations. With escalating rates of toxicant exposure and bioaccumulation in the population-at-large, an increasing proportion of contemporary illness is the direct result of TILT and ensuing SRI. Avoidance of triggers will preclude symptoms, and desensitization immunotherapy or immune suppression may ameliorate symptomatology in some cases. Resolution of SRI generally occurs on a gradual basis following the elimination of bioaccumulated toxicity and avoidance of further initiating adverse environmental exposures. As has usually been the case throughout medical history whenever new evidence regarding disease mechanisms emerges, resistance to the translation of knowledge abounds.