During the past decades, major methodological developments have taken place with regard to the clinical domains of etiology, diagnosis, prognosis and therapy. As a result scientific journals set increasingly high standards for publications and the research designs on which they are based. The development of evidence based guidelines for clinical practice in oral health care has increased as well. An evidence based programme for clinical practice consists of a number of steps, the first of which is a search strategy which will lead to the identification of relevant publications, based on an answerable clinical question. After a critical evaluation of such publications according to their validity, reliability and applicability, the evidence can be judged. This evidence is subsequently incorporated in the formulation of an answer to the clinical question and its application to the individual patient. As a result of social developments, the increasing assertiveness of the patient as a clinical consumer and economizing in recent years on the part of (the Dutch) overnment and insurance companies, the impact of evidence derived from medical and oral health literature on clinical practice has increased enormously. It is, nevertheless, the clinician who makes the judgements, takes the decisions and accepts responsibility for them, on the basis of the available evidence and the quality of that evidence, the preferences and values of the patient, the specific clinical situation and social developments.

In the process of evidence-based dentistry the value of each article located by means of a search action has to be determined. This is done based on the research design used. The internal validity of these designs indicates the degree to which alternative explanations might be responsible for the found results. On the basis of internal validity, research designs can be placed on the so-called ladder of ‘evidence’. Clinical experimental studies (randomised controlled trials, cross-over design and split-mouth design), studies in which the researcher introduces changes or intervenes and keeps the other factors constant, have the highest level of internal validity. Observational studies (cohort study, case-control study, cross-sectional study, patient series and case study), in which groups are described and compared in their natural habit, can introduce bias, leading to a lower level of evidence. In order to assess the value of research, it is necessary to have some understanding of what these research designs are concerned with.

The application of evidence-based dentistry to diagnosis should result in a reduction in errors in decision making. The frequency of errors is dependent not only on the accuracy of a diagnostic test for pathology but also on the prior chance of disease being present. If this chance is low and below a certain threshold then, for example, applying a diagnostic test can result in more decision errors and therefore inappropriate treatment than omitting to use the test. In deciding on the usefulness of a diagnostic test an additional factor to take into account is the relative value of the possible health states resulting from diagnosis and subsequent therapy. These can be determined by eliciting from the patient the numerical values of the appropriate dental health conditions using a visual analogue scale technique. Although clinical decision analysis is starting to influence the development of guidelines for the diagnostic use of radiographs, its application in dentistry needs further refinement and development.