Controlled trials of dental amalgam are needed

EDITOR, - The response of almost every writer from the dental profession to the suggestion that dental amalgam is hazardous to health is that adopted by Ivar A Mjor: to sit back and challenge the opponents of amalgam to produce proof of harm.1 Not only is this notoriously difficult to do, as in all cases of chronic low level toxicity, but it is fundamentally the wrong approach. The initial question is not a scientific one at all but a question of the burden of proof.

With any procedure that may be hazardous the onus of proof must shift. It is up to the advocates of that procedure to show its safety, not for its opponents to prove damage. The charge against the dental profession is that this has never satisfactorily been done. It is not enough to rely on comparisons with staff who handle mercury, but who absorb it in different ways from dental patients; on theoretical considerations of dose; or on a hundred or more years of use (what about smoking?). Contact hypersensitivity is not the issue here. Nothing less than long term population studies with proper controls, in the best traditions of rigorous research, will suffice in a case of such potential seriousness. These have not been done.

The dental profession should get its house in order with regard to research; above all, attention should be paid to the key question of the burden of proof in medical as well as environmental matters of this kind.