The Toronto Study: Outcome of Endodontic Orthograde Re-treatment (1993-1997)

Objective: This prospective cohort study assessed the 4-6 year outcome of orthograde retreatment performed by graduate endodontics students during Phases I (1993-1995) and II (1996-1997) of the modular "Toronto Study". Methods: 524 teeth in 444 patients were subjected to orthograde retreatment, using either vertically or laterally condensed gutta-percha. All pre- and intra-operative data were entered by each treatment provider in "real time", into a computerized database developed before commencing the study. Results: Of the total population, 144 teeth were excluded (discontinuers), 251 lost to follow-up (dropouts), 25 extracted, and 104 (34% recall) examined clinically and radiographically by one independent calibrated examiner for each phase. Outcome was dichotomized as "healed" (no apical periodontitis [AP], signs and symptoms), or "diseased" (either AP, signs or symptoms). Analysis was performed on the pooled samples of both phases, using chi-square and Fisher's exact test (p<0.05), and logistic regression. The "healed" rate (81%) was significantly associated with the following variables: Pre-operative AP (absent - 97%; present - 75%), pre-operative root filling length (adequate - 70%; inadequate - 88%), pre-operative perforation (absent - 87%; present - 42%), intra-operative filling length in teeth with AP (adequate - 82%; inadequate - 50%) and restoration at follow-up (permanent - 85%; temporary - 40%). Logistic regression revealed an increased risk of persistent disease for: Pre-operative presence of AP (odds ratio [OR]=12.1), inadequate intra-operative filling length (OR=3.4) and less than 1 year elapsed since initial treatment (OR=3.9). Conclusions: This study confirmed AP as the dominant prognostic factor in orthograde retreatment, and indicated that prognosis could be influenced by additional pre-, intra- and post-operative factors. Further insight into the prognostic significance of those factors is expected as additional phases of the Toronto Study are completed. This study was supported in part by a grant form the Canadian Academy of Endodontics Endowment.