Children with such fillings were no more likely than other youngsters to suffer such problems, the researchers found.
Some experts found the findings powerfully reassuring. But the studies are unlikely to end the fierce debate over the long-term effects of what are known as amalgam fillings, and some advocates bitterly accused the researchers of conducting unethical experiments on children.
Amalgam fillings, also called silver fillings, are made of mercury and other metals and have been used by dentists for 150 years. But their use has dropped in recent years as more and more doctors switch to resin composite fillings, which are considered more appealing because they are white.
Some advocacy groups and dentists have long contended that the mercury in fillings can leach into the body and cause harmful neurological effects, including autism.
"Mercury is a known neuron-toxin in high doses. We know that," The Early Show medical correspondent Dr. Emily Senay said to co-anchor Harry Smith Wednesday. "And there's a concern (over whether we're) exposing our children, even in small amounts, to something that could harm them developmentally, affect their IQ or their memory. So, that's been at the heart of this (overall) controversy and concern over mercury."
The latest studies were published in Wednesday's Journal of the American Medical Association.
"We didn't see any indications of harm to these kids," said Dr. Timothy DeRouen, a University of Washington professor of biostatistics and dental public health sciences, who led a study of 507 children, ages 8 to 10, in Portugal, to determine if mercury fillings had any neurological effects. "And we tested them repeatedly over seven years."
The other study, led by Dr. Sonja McKinlay of the New England Research Institutes, looked at the effect on intelligence, memory and other mental functions, and kidney function. It involved 534 children in New England, ages 6 to 10.
McKinlay said she is confident that such fillings are safe for children in this age group, in large part because the youngsters were given far more amalgam than the average American child gets.
"If there was no sign of any health problems from this study in these kids with all this amalgam in their mouths ... you know it is going to be safe for kids in the same age group in the rest of the country because they are getting much less exposure," she said.
McKinlay also said that, while the study revealed children with the mercury fillings had higher mercury levels in their urine, there was no evidence they had a higher incidence of kidney damage.
"They really didn't find any problem with the mercury fillings (in either study)," Senay summarized. "… There was no decline in IQ, no decline in memory functioning. So, these researchers are pretty confident that parents should be reassured that mercury is safe."
Still, she says these studies likely won't be the last word. "I don't think (the prevailing controversy) is over, but these studies were pretty persuasive."
Senay points out that you have a choice in the dentist's office, and can ask that you not get silver fillings, adding, "Talking to your dentist about it is a good idea."