Table 1. Level of evidence for research questions9.
| Type | Level | Description |
|---|---|---|
| Published human studies | I | Randomized controlled trial (RCT) |
| Split-mouth study | ||
| II | Prospective cohort1 | |
| Systematic review with level II studies | ||
| Poor-quality RCT (e.g., <80% follow-up) | ||
| III | Case-control study2 | |
| Retrospective cohort study3 | ||
| Systematic review with under level III studies | ||
| IV | Case series or case report no/or historical, control group and poor designed human studies | |
| Animal studies | ||
| In vivo studies (cell culture) | ||
| In vitro studies |
1Patients were compared with a control group of patients treated at the same time and same institution.
2Patients with a particular outcome (‘cases’) were compared with those who did not have the outcome (‘controls’).
3The study was initiated after treatment was performed.