Objective: This study was undertaken to determine if any current materials can prevent coronal leakage in the restoration of endodontic access openings in permanently fixed crowns following nonsurgical root canal therapy. Method and materials: Sixty mandibular first molars and 36 maxillary central incisors were assigned into 1 of 8 complete-coverage crown groups. Endodontic access openings were made through the restorations and randomly placed in 1 of 5 access restorative modalities. A culture of Proteus vulgaris was placed into the coronal reservoir of each assembly of a leakage assessment apparatus for 30 days. Specimens were examined weekly, and turbidity was recorded. Results: Chi-square tests and Fisher's exact test were used for statistical evaluation. A total of 51% of specimens (41/80) demonstrated turbidity. The findings did not indicate a statistically significant association between the materials used and the presence of bacterial leakage. All-metal noble crowns demonstrated the lowest rate of turbidity (20%), and all-porcelain crowns exhibited the highest rate of turbidity (70%) among posterior teeth. Anterior teeth were more than 3.5 times as likely to exhibit bacterial leakage as posterior teeth. Conclusion: When challenged with bacteria, all materials allowed significant leakage. All-porcelain crowns demonstrated more leakage than the other types of crowns. Anterior crowns leaked the most, regardless of crown or restoration type.