Which represents the highest level of evidence in the evidence-based dentistry hierarchy?

In the hierarchy of evidence-based dentistry from lowest to highest: (1) In vitro/animal studies, (2) Expert opinion, (3) Case reports and case series, (4) Case-control studies, (5) Cohort studies (prospective > retrospective), (6) Randomized controlled trials (RCTs), (7) Systematic reviews, (8) Meta-analyses. Meta-analysis (especially of multiple systematic reviews/RCTs) sits at the apex of the evidence hierarchy because it pools results from multiple independent studies, producing the most statistically powerful and reliable estimates of effect. The Cochrane database represents the gold standard for systematic reviews in healthcare.