Is "biological dentistry" an ethical science? Could it be harmful?

Is this considered a real discipline by the ADA or any other peer organization? Why does the American Cancer Society say this about "biological dentistry" on their website?

"...clinical studies that have been published in peer-reviewed medical journals found no link between mercury-containing fillings and the development of cancer and other diseases. The amount of mercury absorbed by the body from amalgams is so small it is considered harmless. A study of US dentists found that dentists themselves have higher mercury levels in their bodies than patients with mercury-containing fillings, because of daily exposure at work. However, the dentists showed the same disease patterns as everyone else, and actually outlived non-dentists by about 3 years."

Additional Details

Link to American Cancer Society
http://www.cancer.org/docroot/eto/conten...