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The main aim is to evaluate the cyclic fatigue resistance of blue heat-treated instruments with different kinematics. Twenty-four endodontic instruments of the same brand were used for each of three experimental groups: VB (Vortex Blue 40/0.04), RB (RECIPROC Blue 40/0.06), and XB (X1 Blue 40/0.06). The instruments were randomly distributed and subjected to temperatures of 20°C and 37°C. The fatigue test was performed using a stainless steel device. Data were analysed using the Shapiro–Wilk test, Student's t-test, the F test, and Tukey's and Tamhane tests at significance level P = 0.05. The instruments' cyclic fatigue resistance at both temperatures differed significantly for each instrument type (P < 0.001). The RB instruments displayed greater cyclic fatigue resistance at the tested temperatures compared with the VB and XB instruments (P < 0.001). Reciprocating kinematics positively influenced cyclic fatigue resistance. Blue heat-treated instruments showed decreased cyclic fatigue resistance as the temperature increased (P < 0.001). [ABSTRACT FROM AUTHOR]

Objectives: To compare the remaining root canal filling material, dentin removal, apical transportation, and apical extrusion of debris after the retreatment of canals filled with bioceramic or resin-based sealers using the Reciproc or Reciproc Blue instruments. Materials and methods: Sixty mandibular molars with severely curved mesial roots were selected. The samples were initially instrumented with Reciproc (R25) and then divided into four experimental groups according to the endodontic sealer and retreatment instrument (n = 15): BC Sealer/Reciproc (BCRC), BC Sealer/Reciproc Blue (BCRB), AH Plus/Reciproc (AHRC), and AH Plus/Reciproc Blue (AHRB). The procedure time was measured, and an Eppendorf tube was used in each root canal to store the debris extrusion. The samples were scanned by micro-CT before and after retreatment. The apical transportation, volume of dentin, and filling material were evaluated. Results: There were no significant differences in the reduction of the volume of obturator material or dentin removal between groups (p >.05). There were also no differences in the amount of extruded material or apical transportation (p >.05). The retreatment time for the AHRC group was significantly lower than that for the other groups (p =.004). Conclusions: All tested instruments obtained similar efficacy in filling material removal procedures, although no system completely removed the filling material. Retreatment of canals filled with bioceramic BC Sealer may be more time consuming. Clinical relevance: This study reported that Reciproc and Reciproc Blue can be indicated in retreatment of severely curved root canals filled either with bioceramic or resin-based sealers. [ABSTRACT FROM AUTHOR]