Watertown, MA - The New England Children's Amalgam Trial, one of the first two randomized controlled clinical trials ever done to investigate the safety of silver amalgam used to fill tooth cavities
, has found no adverse health effects in children who received amalgam fillings. Its findings, and parallel findings from a concurrent study at the University of Washington, appear in the April 19th edition of JAMA.
Despite the wide-spread use of dental amalgam for over 150 years, its safety remains controversial. Amalgam is approximately 50% elemental mercury by weight, and mercury is known to be toxic in large doses.
The New England Children's Amalgam Trial, funded by the National Institutes of Health, was led by a team of researchers that included scientists from the New England Research Institutes, the Forsyth Institute, Children's Hospital Boston, and the University of Rochester School of Medicine. Beginning in 1996, 534 children aged 6-10 who had never had an amalgam filling and had at least 2 back molars with unfilled cavities were recruited from the metro Boston area and the rural community of Farmington, Maine. As part of their treatment, half of the children were randomized to receive silver amalgam restorations, while the other half received mercury-free, white composite fillings.
The health of each child was tracked for 5 years. The primary health outcome was IQ. Other neuropsychological tests, kidney function, and urinary mercury levels were measured as well. Health outcomes were monitored annually, and adverse events were reported by parents of the children.
At the start of the study, the children had an average of five teeth with untreated cavities. Additionally, children had, on average, one new cavity each year during the study. New cavities were filled with either amalgam or composite during twice-yearly dental visits.
As expected, children who received amalgam fillings had higher levels of mercury detected in their urine than children who received composite fillings. The main concern of the investigators of this study was not whether urinary mercury levels increased, but whether an increase would have any harmful health effects.
The trial's results showed no significant differences between the two groups in scores for IQ, memory, visual-motor function, renal function or in reporting of adverse health events. Dr. Sonja McKinlay, the Principal Investigator for this study, emphasized that, "Because this was a carefully designed randomized clinical trial, we can be assured of the safety of silver amalgam fillings from the definitive results."
The lead author of the report, Dr. David Bellinger, noted, "Our confidence in the findings is increased by the fact that we evaluated the children yearly, administering a large battery of tests. None of the results provided any indication that the children were being harmed by amalgam."
Dr. Bellinger also noted the importance of results from a different group of investigators at the University of Washington in Seattle, who conducted a similar study at the same time among children living in Portugal. That study, called the Casa Pia Children's Amalgam Trial, followed 507 children for 7 years and found similar results: no differences in health outcomes by type of filling material (amalgam or composite).
Prospective randomized controlled studies such as the Children's Amalgam Trials are the only type that can establish, definitively, if a causal relationship exists. With approximately 100 million amalgam fillings in the mouths of US children, this study provides assurance to dentists and parents that amalgam is safe to use and thus alleviates a large public health concern.