Objective: This study was undertaken to determine if any materials in clinical use can prevent coronal leakage when used to restore endodontic access openings in permanently fixed crown restorations. Method and materials: Ninety-six teeth were allocated to 1 of 8 complete-coverage crown groups. Endodontic access openings were made through the crowns and restored with 1 of 5 restorative modalities. Methylene blue dye was placed in the coronal reservoir of each assembly of a leakage assessment apparatus for 30 days. Teeth were embedded in methylmethacrylate, sectioned, and computer scanned. Three calibrated, independent examiners assessed computer-projected views with a predetermined scoring system. Results: The overall difference between the material-crown margin and the crown-tooth margin indicated more leakage on the latter, but the difference was not statistically significant. Porcelain-covered crowns showed greater leakage, but no statistically significant difference was found among crown types. Glass-ionomer restorations had higher leakage values, but there was no statistically significant difference among materials. Conclusion: Coronal leakage at the material-crown margin is substantial when endodontic access openings are restored in complete-crown restorations that have undergone nonsurgical root canal therapy.