to systematically assess the 4- to 6-year outcome of orthograde retreatment in Phases 3 and 4 of the Toronto Study and (2) to examine outcome predictors for orthograde retreatment in the pooled samples of Phases 1– 4.
•N= 126 teeth. Excluded: teeth with root fracture
•Graduate Endodontics students performed the treatments under supervision of qualified endodontists.
•The previous root filling quality was described as adequate (no voids and adequate length) or inadequate (either voids present, or inadequate length) •Gutta-percha was removed with hand files or rotary nickel-titanium instruments, with or without the use of chloroform.
•perforations if present were sealed with GIC in phases 1&2 and MTA in phases 3&4.
•Cleaning and shaping were performed in a crown-down manner with hand files and rotary instruments of different designs. Canals of teeth treated in more than 1 session were medicated with CaOH2.
•The canals were filled with GP with different techniques (lateral, vertical, single cone or injectable GP).
•Subjects were recalled 4–6 years after treatment. teeth were examined and classified as healed (periapical index score ≤2; no signs or symptoms) or diseased.
•Most highlighted Results:
•When pooled with Phases 1 and 2, 82% of the teeth were healed.
•Logistic regression identified significant outcome predictors: root filling quality (healed: inadequate, 88%; adequate, 66%), perforation (healed: absent, 87%; present, 56%), and radiolucency (healed: absent, 93%; present, 80%).
•In teeth with radiolucency, outcome predictors were number of treatment sessions (healed: one, 100%; ≥2, 77%) and previous root filling quality (healed: inadequate, 86%; adequate, 50%).
the findings of the study could help to predict the retreatment outcomes based on the significant predictive factors. the number of treatment sessions in teeth with preoperative AP requires confirmation from randomized controlled trials.