Background: During the course of a non-surgical orthograde endodontic retreatment, supplementary instrumentation is usually required for better removal of root canal filling material. Aim: The aim of this study was to assess the effectiveness of XP-Endo Finisher R in endodontic retreatment of oval root canals. Materials and Methods: The study was performed on extracted mandibular incisors preliminary cut at the cementoenamel junction. The root canals of 12 extracted lower central incisors were initially shaped with the rotary nickel–titanium system XP-Endo Shaper (30/.04) and filled with continuous waves of condensation. Root canal retreatment was performed with the МTwo Retreatment – R1 (15/.05) and R2 (25/.05) files, followed by the XP-Endo Finisher R (30/.00). Three micro-computed tomography scans were performed during the course of the experiment: 1) after the filling of the root canals, 2) after the first retreatment procedures, and 3) after the supplementary shaping. Kolmogorov–Smirnov test for normality and Friedman and Kruskal–Wallis tests for comparison of several independent samples. Results: There were no statistically significant differences in the percentage of removed obturation material in the different parts of the root canal after the use of Mtwo-R ( P = 0.649) and XP-Endo Finisher R ( P = 0.934). The additional instrumentation with XP-FR reduced the percentage of the remaining root canal filling insignificantly ( P = 0.190). Conclusions: The combined action of Mtwo-R retreatment files and XP-Endo Finisher R resulted in significant reduction of the amount of root canal filling material. Nevertheless, none of the examined rotary systems guaranteed its complete removal.

Purpose: The aim of this in vitro study was to evaluate the effect of different irrigation regimens of root dentin microhardness. Materials and methods: Twenty extracted, single-rooted, non-endodontically treated upper incisors were decoronated and further sectioned longitudinally in buccolingual direction. The surfaces of all forty samples were polished, evenly distributed into four groups (n=10) and then immersed in the following solutions: group 1: 2% sodium hypochlorite for 2 minutes followed by 17% EDTA for 2 minutes; group 2: 2% sodium hypochlorite for 2 minutes followed by 17% EDTA for 2 minutes, both ultrasonically activated; group 3: 5.25% sodium hypochlorite for 2 minutes followed by 17% EDTA for 2 minutes; group 4: distilled water (control group). Afterwards, the samples were dried and subjected to microhardness testing by using 300g load with a dwell time of 20 seconds. The averaged values of each sample’s Vicker’s hardness numbers were calculated and statistically analyzed. Results: All irrigation regimens significantly decreased the mean hardness of dentin when compared to the control group 4 (p0.05) regardless of the concentration and the ultrasonic activation of the solutions. Conclusions: The dentin microhardness was decreased regardless of the irrigation protocols used. Additional studies should clarify the clinical relevance of the compromised mechanical properties of dentin tissue and their relationship with the overall treatment success.