No inclusion criteria regarding participants were reported.
Studies that examined single crowns and/or direct restorations (such as resin composites, amalgam, cements) on root canal-treated teeth were selected for inclusion. Eligible studies had to report the success of crowns and restorations (or rather, the absence of failure). Failure of root canal-treated teeth restorations was defined as fracture of the tooth, fracture of the restoration, post fracture, post de-cementation, dislodgement of the restoration, marginal leakage of the restoration and tooth loss.
Clinical studies with sufficient data on individual teeth to calculate life table curves were eligible for inclusion in the review. Descriptive studies, reviews, and case reports were excluded. Studies with a follow-up period less than two years were also excluded from the review.
Two reviewers performed the selection.