Safety of Dental Amalgam

Based on the best available evidence IADR:

• Affirms the safety of dental amalgam for the general population without allergies to amalgam components or severe renal diseases.
• Supports maintaining its availability as the best restorative option when alternatives are less than optimal based on clinical, economic or practical reasons.
• Supports the phase-down strategy described in the Minamata Convention on Mercury.
• Emphasizes the need for increased oral disease prevention efforts to reduce the need for any kind of restorative material,
• Emphasizes the need for further research on new biocompatible and environmentally-friendly restorative materials and approaches that are proven to have equal or improved long term clinical longevity and cost effectiveness when compared to amalgam restorations.

Low levels of mercury released from dental amalgam

While it is true that those with dental amalgam fillings generally have higher levels of blood and urine mercury levels, it is important to note that slight increases in mercury exposure due to dental amalgam do not rise to a level of concern and are not expected to lead to adverse health effects. The expected exposure to mercury from dental amalgam is well below the EU safety limits established for those occupationally exposed to mercury.⁹ The U.S. Agency for Toxic Substances and Disease Registry (ATSDR) established a minimum risk level (MRL) for chronic inhalation of mercury vapor of approximately 4 micrograms inhaled mercury per day, which is less than people in the U.S. and Canada are exposed to from their amalgam fillings. The MRL is the level of mercury that can be inhaled without the expectation of suffering adverse health effects. Exposure to a higher level of mercury vapor does not necessarily mean the exposed would suffer adverse health effects but that at the MRL, no adverse effect is expected. This value takes into account infants, older people and people with poor health.¹⁰ The U.S. Environmental Protection Agency (EPA) derived a similar risk estimate of 6 micrograms per day.^{11, 2}

The amount of mercury released from amalgam restorations is likely dependent on a number of factors including the number of restorations, the surface area of the restorations, chewing and brushing habits and the ages of the restorations.^{8, 10} Urine levels of mercury increase by approximately 1-2 units in adults for every 10 amalgam fillings placed.¹² Furthermore, the amount of mercury released from amalgam fillings decreases over time.^13-15

²The MRL derived by ATSDR is for noncancer health effects as is the risk estimate by the U.S. EPA. The EPA assessed potential cancer-causing effects of inhalation of elemental mercury – the type of mercury released by dental amalgam – and did not find enough evidence to draw a conclusion.

Amalgam removal

Some patients have had their amalgam fillings removed out of unfounded health concerns. However, amalgam fillings should not be removed except in the case of an allergic reaction.^{9, 10} Patients who had their amalgam fillings removed did not experience a meaningful decrease in blood mercury levels even years after the removal.⁸ Most studies showed patients did not receive symptomatic relief after removal. In some studies, symptoms did not correlate with the number of amalgam fillings or exposure to mercury, meaning that their symptoms were likely not due to their fillings in the first place. Furthermore, the experience of negative life events made it difficult to attribute symptoms to their amalgam fillings.^{9, 16}

Vulnerable populations

There is particular concern around the use of dental amalgam in vulnerable populations, particularly in children and pregnant and breastfeeding women. The systematic reviews performed by the FDA and SCENIHR included studies on these populations. Both the FDA and SCENIHR reviews found that fetal exposure to mercury from dental amalgam correlated with the number of maternal fillings but that exposure decreases after birth even with breastfeeding. Fetal exposure to mercury from maternal dental amalgam restorations is below the “level considered to be hazardous for neurodevelopmental effects in children exposed to [mercury] in utero;¹³ the more times since the mother’s last filling, the less mercury to which the fetus is exposed; and most importantly, has not been linked to adverse health effects in children exposed to mercury from dental amalgam in the womb.^{8, 9}

Two studies are particularly notable. The National Institute of Dental and Craniofacial Research funded two studies in Portugal and the U.S. to determine if there were any adverse health effects in children whose teeth were restored with dental amalgam. Both studies were randomized clinical trials and were conducted over seven and five years, respectively. In each study, over 500 children were randomly assigned to group receiving either amalgam or composite resin fillings. As expected, both studies showed that children with amalgam restorations had higher levels of mercury in their urine compared to children treated with composite resin.^{15, 17} In the Portugal study, urinary mercury levels plateaued by the second year of the study and declined throughout the rest of the study. Furthermore, there was no statistical difference between children in the amalgam or composite resin groups in behavioral tests, including memory and attention, at any point during this study. Children whose teeth were restored with composite resin in this study also experienced more failure of their tooth restorations, congruent with previous observations.^{5, 6, 15} In the study conducted in the U.S., there was also no statistical difference between children treated with dental amalgam and composite resin in neurological tests, including for IQ and memory, or kidney function.¹⁷ Since 2014, studies on pregnant women and children showed increased mercury in urine and blood of children and pregnant women with dental amalgam fillings, as expected;^{18, 19} no statistically significant association between maternal amalgam restorations and stillbirth after accounting for maternal parameters such as age and smoking, among others;²⁰ higher maternal and cord blood in mothers with amalgam restorations but no difference in birth weight, length or head circumference;²¹ and no increased risk of child mortality or neurological disorders of the sons of female dental staff.^{22, 23}

The SCENIHR review did recommend alternative restorative materials for the primary teeth of children and the teeth of pregnant women, but this recommendation was made to comply with the provisions of the Minamata Convention on Mercury to address environmental concerns (see section, “Mercury and the Environment – the Minamata Convention”).⁹

It is, however, well recognized that amalgam should not been used in patients with a verified contact allergy to amalgam or its components.²⁴ Furthermore, the SCENIHR reports draws attention to the fact that amalgams should not be the restoration of choice for patients with severe renal diseases as mercury excretion is impaired in this cohort.

Occupational safety issues and dental amalgams

Another concern is the occupational safety of using dental amalgam. Dental professionals who place dental amalgam are exposed to more mercury than the general population, although exposure should be decreasing due to the use of encapsulated dental amalgam and increased awareness and precautions when handling dental amalgam.^{8, 9} In addition there is a preference for placing tooth-colored materials over dental amalgam.²⁵ Indeed, studies of U.S. dentists since 2014 found a substantial decline in mercury exposure from 1976 when the average level exceeded 20 micrograms per liter urine to 2012 when the average was less than 2 micrograms per liter for the reasons described above. On average, dentists were still exposed to more mercury than the general population but only by about 1 microgram per liter.^{26, 27}

The FDA found too many confounding variables and significant weaknesses in the studies reviewed to draw a conclusion about the neurobehavioral effects of mercury exposure on dental professionals, including the presence of other chemicals used in dental clinics.⁸ A 2015 study found an association between tremor and urinary mercury levels and cumulative mercury exposure. The study is based on a convenience sample of dentists, so there may be selection bias in that some dentists were perhaps more motivated to participate than others or less able to participate based on health status. Furthermore, the authors did not have access to data on fish consumption of the participants and other possible confounding variables.

Occupational safety studies have uncovered poor adherence to safety guidelines. The SCENIHR review noted one study that found violations of environmental and personal safety standards in 67% and 45%, respectively, of clinics visited.²⁸ Some recent studies also revealed violations of occupational safety regulations and indicated the need for more training on the safe use of dental amalgam, properly ventilated dental clinics and oversight.^{29, 30} The study by Khwaja and colleagues also highlighted the fact that there is still a high level of dental amalgam use among dentists in Pakistan, even in children and pregnant women and use can vary dramatically by location.²⁹ The FDI and WHO recommend using proper personal protective equipment and techniques and monitoring of mercury vapor levels in dental clinics to minimize exposure of dental personnel to mercury vapor,⁷ which is especially important for dentists who will continue to place high amounts of amalgam fillings. These data also reiterate the need for prevention to reduce the need for amalgam in the first place.

Since 2014, two studies in Taiwan using national insurance claims data on the neurological effects of dental amalgam warrant further investigation. The first study found that women with dental amalgam fillings had a higher overall risk of having Alzheimer’s Disease than women without dental amalgam fillings after adjusting for age, location and income, ³¹ and the second found that people with dental amalgam fillings had a greater risk of having Parkinson’s Disease.³² Neither study include a “pure” control group as the analysis was conducted from claims data, so the authors could not examine patients to ensure control group members had not received fillings before the beginning of the study date. Furthermore, the authors did not account for fish consumption (a source of methyl mercury). It is possible that once these factors are accounted for, the difference between the study and control groups would disappear. In particular, Hsu and colleagues’ study on Parkinson’s Disease noted that most patients were diagnosed two years after receiving dental treatment and that “it is unlikely that mercury would induce [Parkinson’s Disease] in such a short time.” The authors concluded that the study was unable to establish a causal association.³²

These recent studies on associations between neurological health effects on dentists and the general population provide important contributions and directions for future studies that should address these limitations and provide more conclusive results but are not on their own sufficient to establish a causal relationship between dental amalgam fillings and Alzheimer’s or Parkinson’s Disease.

Mercury and the Environment – the Minamata Convention

Over 100 countries have ratified the Minamata Convention on Mercury and agreed to provisions to protect the environment from mercury emission to land, air and water, including phasing down the use of dental amalgam. IADR agreed to promote research into alternative restorative materials and has been active in this regard. IADR calls on parties to the Convention to invest in research and development to accelerate the clinical use of new restorative dental materials. IADR especially supports the provision for countries to increase oral disease prevention efforts to reduce the need for any kind of restorative material in the first place, as the global pervasiveness of oral diseases will continue to slow the phase-down. According to the treaty, new measures that include the phase-down of amalgam restorations shall be regularly reassessed during the Conference of the Parties to the Convention.

(Adopted June 2019)