Systematic review

A systematic review searches the literature comprehensively and explicitly for every study that meets a defined set of criteria on a specific clinical question, then evaluates and summarizes them together, rather than relying on the results of any single trial in isolation. Because it pools evidence across many studies and many patients, a well-done systematic review generally carries more weight than any one study it includes, which is why it sits near the top of most evidence hierarchies used in dentistry and medicine.

Some systematic reviews go a step further and perform a meta-analysis, statistically combining the numerical results across studies into one pooled estimate, for example, an overall 5-year survival percentage for a type of crown, calculated from thousands of individual crowns across dozens of separate studies rather than from any one of them alone.

The quality of a systematic review still depends entirely on the quality of the studies it includes; a review built from a pool of weak trials produces a more confident-sounding number than the underlying evidence actually supports, which is part of why evidence grade is assessed as its own separate question.