In order for a general dental practitioner to give a valid answer to a question asked according to the Problem-Intervention-Comparison-Outcome (PICO)-system, three questions need to be asked regarding validity, relevance and applicability of studies. The validity is determined by the position of the research on the ladder of evidence, and also by the assessment of the methodological quality of the study at stake. In this assessment, the study is rated on the basis of specific criteria.A randomized controlled trial for example can be assessed with regard to the randomisation procedure, blinding of patients, raters and treatment, and the number of patients lost for follow-up. In cohort studies and case-control studies the criteria on the basis of which an article can be assessed are the comparability of groups, the degree of independence among measurements, and the length and thoroughness of the follow-up. Furthermore, in all studies it is important that the quality of the measurement instruments is good. The assessment criteria for systematic reviews are a clear research question, a clearly written and repeatable search action for articles and an independent assessment of the methodological quality of the included articles. Finally, the general dental practitioner in determining applicability needs to pay attention to the sample and the type of patient used in the research.