Author's replyBMJ 1995; 310 doi: https://doi.org/10.1136/bmj.310.6971.58a (Published 07 January 1995) Cite this as: BMJ 1995;310:58
EDITOR,—A large number of patients are needed to determine whether a side effect is significant. At an incidence of 1 in 1000 about 4000 patients receiving the same treatment have to be examined to confirm any reaction if 95% confidence intervals are used.1 Objectively diagnosed side effects to dental restorative materials are rare. Thus controlled clinical studies to establish their incidence are difficult and costly. Clinical experience showing the safety and efficacy of dental restorations is, however, overwhelming and does not call for the incidence to be established; an estimate, as indicated in my editorial, is considered adequate. If the media focus on a cause and effect relation this undoubtedly affects the incidence of reports by patients, especially if vague, general symptoms are involved. This is a likely explanation for the report referred to by Harald J Hamre, that 4% of Swedes believed they had or had had health problems caused by dental amalgam.
The importance of self diagnosis of disease is difficult to assess. Undoubtedly, something is wrong, but differential diagnosis would require extensive investigations. So far as mercury from amalgam restorations is concerned, the comprehensive reviews that I referred to in the editorial excluded this source as a likely aetiological factor of systemic diseases. Another review, from an expert group appointed by the Swedish National Board of Health and Welfare, was published after my editorial.2 It concluded that results from scientific studies since 1991 “have not shown that mercury from amalgam has an adverse effect on health, with the exception of isolated cases of allergic reactions.”
The latest Swedish report pointed to the heterogeneity of patients with alleged adverse effect from amalgam fillings and identified “a considerable proportion of psychic disturbances and psychosomatic overtones.”2 Thus many types of specialists are required to provide adequate treatment for these patients. How easy it would be to help these patients if all it took was the removal of their amalgam fillings.