Jun 2010 —
Recent Trends in the Safety of Dental Amalgam
Hari Parkash, BDS, MDS, MICD, FIMFT, FACD, FDSRCPS; Utkal K. Mohanty, MDS; Anil Kohli, BDS, MDS, FDS, RCS, DNB, FACD, D. Litt; and Sunil Chaudhary, BDS, MDS, PGDMLS
ABSTRACTDental amalgam material has been controversial for years because of the health hazards of mercury. Therefore, it is necessary to review the safety and performance of dental amalgam as a restorative material and its potentially harmful effects to patients and the dental care personnel. Various claims have been made about systemic conditions, particularly neurologic and psychologic effects, with amalgam as the suspected causal agent. However, the scientific evidence for risks of adverse systemic effects is inconclusive and the current use of dental amalgam does not pose a risk of systemic disease.
As dentistry evolves, various attempts have been made to improve the profession, with the challenge of providing quality and affordable healthcare. Mercury is an element that has been used in the healthcare sectors for centuries in different forms. Dental amalgam, widely used for restorations, is one form. Much controversy surrounds the safety of dental amalgam as a restorative material.
In developing nations such as India, dental amalgam is an important restorative material in the dentist’s armory. It is inexpensive for patients and user friendly for dentists working in peripheral setups. Eliminating or banning the use of dental amalgam may be a significant financial burden for many patients seeking restorative care. Therefore, amidst the hue and cry for or against the use of dental amalgam, uniform agreement and specified guidelines are needed . This article reviews several contradictory studies regarding dental amalgam.
Worldwide, approximately 3439 metric tons of mercury are needed annually for anthropogenic use. About 8% (270 tons) is used in dentistry.1 In Europe, dental amalgam is the second largest use of mercury, and in the United States, the dental field is the third largest user of mercury (44 metric tons).2 According to the World Health Organization (WHO), mercury in dental amalgam material (as well as in laboratory and medical devices) is the source of approximately 53% of all mercury emissions.3 According to the Canadian Global Emissions Interpretation Centre, Southeast Asia is one of the world’s worst regions, releasing mercury into the air at a constant rate of 0.1 tons to 0.5 tons annually.4
Toxic Effects of Dental Amalgam
The third National Health and Nutrition Examination Survey (NHANES III) in the United States (1988 to 1994) demonstated that the number of dental fillings was significantly associated with cancer, along with diseases of the eye, circulatory, nervous, and respiratory systems. At that time, most dental fillings were silver amalgam.5 According to the World Health Organization, mercury in dental amalgam materials was the highest source of mercury vapor in nonindustrialized regions in 1991. Populations in these areas were exposed to mercury levels significantly above recommended levels.6 Many additional studies have reported similar findings.7,8
Mercury toxicity occurs through either elemental, inorganic, and organic forms, which vary in absorption and excretion rates. The chemical form determines the toxicologic profile: these are classified in order of toxicity:9 1) methyl and ethyl mercury compounds (organomercury); 2) mercury vapors (elemental mercury); and 3) inorganic salts and additional organic forms.
Mercury vapor, or elemental mercury, is the most significant form for the dentist’s and patient’s healthcare concerns. Inorganic mercury vapor, inhaled through the lungs, is absorbed at an estimated rate of 75%.10 However, gastrointestinal absorption is lower (0.01% to 10%).11 Elemental mercury builds in the kidneys and brain. Chronic mercury toxicity (resulting in erethism, hydrargaria, or mercurialism) causes symptoms such as memory loss, tremors, irritability, depression, and insomnia.12
There are many factors impacting the release of mercury from amalgam restorations including number of teeth restored, diet, oral hygiene regimens, and breathing and swallowing patterns. A consensus average estimate of mercury released from amalgam is 10 μg per day of amalgam-derived mercury (3 μg/day to 17 μg/day), according to WHO.13
Risk to Dental Healthcare Workers
Inadequate management of dental amalgam that results in chronic exposure is a health hazard for dental professionals. The risk of exposure is mainly associated with improper handling (during preparation, placement, removal, and polishing); spillage; and skin contact. Dental personnel generally have a higher mercury body burden than is found in the broad population. Their average urine mercury levels has been reported to be 3 μg/L to 22 μg/L (the range for other groups is 1μg/L to 5 μg/L).14 Among dentists, urinary mercury levels appear to correspond significantly with the number of hours in the operatory (r = 0.22, P = .006) and the weekly number of amalgam restorations placed (r = 0.38, P < .001) and removed (r = 0.29, P < .001). Urinary mercury levels in dentists range from 0.02 to 20.90 (mean 2.58) nmol mercury per nmol creatinine.15 Slight neurotoxicity may occur in dental healthcare providers who may have shown urine concentrations of mercury within the accepted threshold limit.14
However, because of improvements in amalgam capsule design, better awareness and practice of appropriate mercury hygiene measures, and growing use of alternative, nonmercury-containing materials, mercury exposure levels among dental professionals have been steadily decreasing.
Engle et al have quantified the amount of mercury vapor released during dental procedures, which ranges from 1 µg to 2 µg for trituration to 44 µg for dry polishing.16 For occupational mercury exposure, WHO has designated the lower limit of 25 μg/m3 as the threshold limit value (TLV). Assuming a respiration rate of 22 μg/m3 per day, a safe amount for mercury vapor absorption through respiration is believed to be 20 μg/m3 a day for the average person. The clinical mercury threshold is 100 µg/m3 (lowest-observed-adverse-effect level) and the nephrotoxicity level is 50 µg/m3.6,17,18
Neurotoxic effects. Kingman et al examined 1663 dentate veterans for neurologic signs, vibrotactile thresholds, and levels of peripheral neuropathy, and observed no significant associations between amalgam exposure and clinical neurologic signs.19 In a randomized 7-year clinical trial examining dental amalgam and composite restorations, children were studied for any effects on memory and attention, vasomotor function, and nerve conduction velocities. The authors concluded that those with dental restorative treatment with amalgam did not show statistically significant differences in neurobehavioral assessments or nerve conduction velocities compared with children who had composite fillings.20 In similar studies, no statistically significant differences were found in neuropsychologic or renal effects observed in children with amalgam fillings compared with those with composite fillings.21-25
Pregnancy. It has been reported that the number of amalgam fillings positively influenced the mercury concentrations in amniotic fluid; however, as this was not statistically significant, it is believed that there are no adverse outcomes at this level.26 In a study of low birth weight related to number of amalgam fillings, the researchers concluded there was no statistically significant risk.27 There appears to be no evidence of a connection between dental healthcare workers’ occupational exposure to mercury and pregnancy outcomes.28
Kidney disease. Ritchie et al reported that, compared to control groups, dentists were found to have four times the level of urinary mercury. However, while dentists were more likely to report having kidney disorders, this did not correspond significantly with urinary mercury levels. In addition, no significant correlation between urinary mercury levels and self-reported memory problems were noted.29
Situation in India and Other SEAR Countries
For the past few years, India has produced the most dental surgeons (78,096); and currently there are 291 dental colleges established in the nation. However, awareness of the adverse health effects of dental amalgam is lacking among dental surgeons and assistants. Therefore, educating dentists, dental students, and assistants about the hazards of inappropriate use of dental amalgam is essential. Proper training, adequate equipment, and sufficient resource allocation is necessary for safe dental mercury management. Therefore, regulating bodies such as the Dental Council of India and the Indian Dental Association should take steps to establish guidelines for mercury disposal, making it mandatory to register all the dental clinics and colleges, as well as hospitals, for a centralized amalgam waste collection system. The initial cost should be capped to elicit greater response from dental healthcare practices.
Click here to view "Recommended Management of Dental Amalgam".
Precautions During Preparation and Placement of Amalgam
Instead of manual manipulation, only precapsulated amalgam alloys should be used. If possible, the capsules should be recapped after use and stored in closed containers for recycling. Avoid skin contact with mercury or freshly mixed amalgam. High-volume evacuation systems must be employed during finishing or removing amalgam restorations. After condensation, the scrap should be collected and stored in water, glycerine, or an x-ray fixer in a tightly capped jar (almost filled with liquid to reduce the space where mercury can collect). Rubber dams, high-volume evacuation, and water cooling should be used to reduce the vapor released during removal of old amalgam restorations. Instruments employed for dental amalgam restoration procedures retain some amalgam material on the surface and may release mercury vapors during sterilization. Thus, venting the air or proper isolation of sterilization areas is essential. Capsules and mercury-contaminated cotton or paper should not be disposed with general trash; instead they should be retained in separate plastic containers.30
Amalgam Storage and Handling
Dental assistants handling dental amalgam should be educated about the hazards of mercury vapor. Work areas should be well ventilated, with fresh air exchanges and exhaust. Air conditioning filters should be replaced periodically, and floor coverings should be nonabsorbent. Carpeting should not be used where an accidental mercury spill might occur, because chemical decontamination may be ineffective as mercury droplets can permeate the carpet. The mercury vapor level should be monitored periodically by dosimeter badges to maintain the OSHA limit for mercury vapor, which is 50 µg/m3 in a 8-hour work shift for a 40-hour work week.28
Safe Disposal of Amalgam
Waste amalgam particles are created during the placement and removal of amalgam restorations, and some are found in the dental setup wastewater. Amalgam separators are one way of reducing the amount of amalgam that dental practices discard into sewers. Amalgam separators use sedimentation, filtration, and centrifugation and ion exchange techniques. While there are various amalgam separators available, considering the economic factors that may be present in a typical office, this technology will be hard to implement universally.
In April 2006, the Journal of the American Medical Association published two large clinical studies indicating that dental amalgam is a safe and effective cavity-filling material. The ADA Council of Scientific Affairs reviewed the literature on amalgam and concluded that amalgam is a “valuable, viable, and safe choice” for dental fillings.30 The US Food and Drug Administration issued a press release on July 21, 2009, stating that mercury-containing fillings are safe for use in dental treatment, thus changing an earlier caution against their use in certain patients.
Dental amalgam remains an effective restorative material. From the multiple perspectives of performance and economics, it may be deemed the material of choice for some restorations in posterior teeth.
However, the use of dental amalgam should be done with required precaution to minimize as much as possible the exposure to elemental mercury, which is suspected to be the main cause of amalgam toxicity for the patient and dentist. In India and other developing nations, uniformity is lacking for disposing the waste generated from discarded amalgam. In India, dentists should follow all possible precautions at their clinical setups to minimize the adverse effect of elemental mercury exposure as much as realizable.
The overwhelming scientific evidence supports the usefulness of dental amalgam as a safe and effective restorative dental material. It remains an important and inexpensive option; however, dental healthcare workers must be aware that mercury should be handled cautiously.
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|About the Authors
Hari Parkash is Director-General, I.T.S. Centre for Dental Studies and Research, Ghaziabad, India.
Utkal K Mohanty is Former Senior Lecturer, I.T.S. Centre for Dental Studies and Research, Ghaziabad, India.
Anil Kohli is President, Dental Council of India, New Delhi, India.
Sunil Chaudhary is Associate Professor, Department of Oral Medicine and Radiology, I.T.S Centre for Dental Studies and Research, Ghaziabad, India.