Introduction: The purpose of this retrospective study was to evaluate and compare the outcome of endodontic micro-resurgery with that of primary endodontic microsurgery and determine prognostic factors affecting the outcome of micro-resurgery. Methods: A clinical database was searched for endodontic microsurgery cases between 2001 and 2016. Nearest neighbor 2:1 propensity score matching for the following 5 variables was performed for cases of primary microsurgery and those of micro-resurgery: age, sex, tooth type, lesion type, and postoperative restoration. For the matched cases, the outcome was categorized as success or failure according to clinical and radiographic evaluations performed at least 1 year after surgery. Kaplan-Meier survival analysis and log-rank tests were performed to compare the outcome of primary microsurgery with that of micro-resurgery over time. For the micro-resurgery group, multivariate Cox proportional hazard regression analysis was performed to identify prognostic factors and estimate their effects. Results: In total, 571 cases of endodontic microsurgery (498 primary microsurgery and 73 micro-resurgery cases) were identified, and 146 cases of primary microsurgery were matched to 73 cases of micro-resurgery through 2:1 propensity score matching. After matching, all covariates demonstrated an absolute standardized difference of <0.1. The estimated 5-year success rates were 91.6% and 87.6% for primary microsurgery and micro-resurgery, respectively (P =.594). The tooth type was found to be the only contributing factor for the outcome of micro-resurgery, with molars showing a higher probability of failure than anterior teeth (hazard ratio, 8.53; P =.002). Conclusions: Within the limitations, the findings of this study suggest that the outcome of endodontic micro-resurgery is comparable with that of primary endodontic microsurgery.
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