Which study design provides the HIGHEST level of evidence-based dentistry?

Meta-analysis / Systematic Review (A) provides the highest level of evidence. Evidence hierarchy:
1. Systematic Review + Meta-analysis ← HIGHEST
2. Randomized Controlled Trial (RCT)
3. Cohort Study (prospective observational)
4. Case-Control Study (retrospective observational)
5. Cross-sectional Study / Survey
6. Case Series / Case Report
7. Expert Opinion / Animal Studies ← LOWEST

• Meta-analysis: statistically combines results of multiple RCTs, increasing statistical power and generalizability.
• Systematic review: comprehensively reviews all available evidence on a topic using pre-defined criteria.
• The Cochrane Collaboration produces the gold standard systematic reviews in dentistry and medicine.
• Key for board exams: 'most evidence' questions → meta-analysis/systematic review.