Sir, Dr Ahearne raises an important point regarding the problem of evaluating contradictory literature1. Clinical trials are limited by both the nature and size of the study or sample population.

The most important evidence that the results of such studies provides can often only be applied to a more general population than the subjects in the study represent. Thus, the conclusions from Moore et al2 can only be related to a population that has the same characteristics as those recruited: in this case, a South London group of subjects with a prevalence of disease representative of most UK populations.

As stated in the paper, these results are not consistent with those previously published regarding populations studied in the USA which were drawn from groups with a much higher prevalence of severe disease. Differences in the study populations may also explain the conflicting results between Moore et al2 and Radnai et al3.

A second potential reason for differences arises from the numbers of subjects and type of study. In the studies referred to by Dr Ahearne, the contrast was between a large prospective study2 and a small case-control study described as a pilot study3. Evidence-based public health and clinical dentistry must be based on well-conducted research, but no single clinical trial can produce conclusions related to all people in all places all of the time. This can only be approached through systematic review of a number of published clinical trials. Unfortunately, for many clinical questions, no such conclusive evidence exists, and practitioners must weigh carefully the evidence that is available (be it research papers, reviews or clinical experience) and judge its relevance to their own clinical situation. No one said evidence-based dentistry was easy!