Does the ADA need a root canal? (Advice & dissent: letters from our readers).

"Heavy Metal Harm" was well written, clear and concise. However, there is one point that bears closer examination. On page 31, you write, "The American Dental Association (ADA) denies that there are any safety problems with dental amalgam. `Studies have failed to show any link between amalgam restorations and any medical disorder,' the association says."

There is voluminous information on this topic, starting with the well-known dentist Mark A. Breiner, who wrote Whole Body Dentistry. "I had learned in dental school that amalgams ... were perfectly safe and posed no threat whatsoever to human health," he writes. "In 1978, my dental assistant's five-year-old daughter had her first cavity. I placed her first mercury amalgam filling. Two days later she had a seizure. Having faith in the ADA, I was stunned to find an abundance of documented research and scientific data that called into question the safety of amalgam use."

The mercury issue goes back at least to 1850, and no one has conclusively shown that mercury fillings are safe. The ADA gave you the same answer they give everyone else. While we worry about the rising amount of mercury in our waste stream and in fish, the unsafe heavy metal is in our mouths already.

Mercury is, as you write, very cheap. It is easy to mix with other metals and molds easily. Its implantation is fast, convenient and allows the dentist to see more patients. I think these are the real reasons why the ADA says what it says.

Jim Robicsek, M.H., Westford, VT

I'm writing in response to your article on mercury. As its name suggests, dental amalgam contains many different elements, chiefly silver and mercury, that are chemically bound, forming a very stable molecule. (Mercury is not dissolved, as stated in the article.) Unfortunately, not understanding this basic fact, your reporter taints an otherwise fairly well-reasoned report. Condemning dental amalgam, which in modern formulations contains no elemental mercury, is not too dissimilar from raising an alarm about table salt, which contains the dangerous elements sodium and chlorine.

My other concern is that you do a grave disservice to your readers who are not so scientifically inclined and would not be able to discern your error. They come to our offices with all kinds of questions and concerns, and we have to reeducate them to reassure falsely created anxieties. We have many good alternatives to dental amalgam, but there are situations, such as cavities below the gum line, where there are no good substitutes.

James R Weber, DDS, Cincinnati, OH

E responds: Our research indicates this is not such a cut-and-dried situation. While it may be true that mercury is supposed to remain chemically bound in fillings, small amounts of the toxic element actually do get released. The following report from the U.S. Agency for Toxic Substances and Disease Registry, at www.atsdr.cdc.gov/toxprofiles/ phs46.html, explains:

"Once the amalgam is hard, the mercury is bound within [it], but very small amounts are slowly released from the surface of the filling due to corrosion or chewing or grinding motions. Part of the mercury at the surface of the filling may enter the air as mercury vapor or be dissolved in the saliva ...

"Estimates of the amount of mercury released from dental amalgams range from three to 17 micrograms per day. The mercury from dental amalgam may contribute from zero to more than 75 percent of your total daily mercury exposure, depending on the number of amalgam fillings you have, the amount of fish consumed, the levels of mercury in those fish, and exposure from other less-common sources ... Whether the levels of exposure to mercury vapor from dental amalgam are sufficiently high to cause adverse health effects, and exactly what those effects are, continues to be researched and debated by scientists and health officials."

Such mercury release can be a particular problem for pregnant women, children and those with impaired kidney or immune function. Removal of dental amalgams can be quite risky, and should only be undertaken with expert professional guidance.