Torsional Fatigue Resistance of Blue-treated Reciprocating Instruments

Introduction: The aim of the present study was to evaluate the influence of blue thermal treatment on the torsional resistance behavior of M-Wire Reciproc files (VDW, Munich, Germany). Methods: Ten M-Wire Reciproc R25 (25/0.08v) and 10 Reciproc Blue R25 (25/0.08v, VDW) instruments were used. The torque and angle of rotation at failure of new instruments (n = 10) were measured according to ISO 3630-1. Three millimeters of each instrument tip was clamped to a small load cell by a lever arm linked to the torsion axis. The fracture surface of all fragments was examined with a scanning electron microscope. Results were statistically analyzed using the Student t test at a significance level of P < .05. Results: The maximum torsional strength of M-Wire Reciproc was higher than Reciproc Blue instruments (P < .05). Reciproc Blue instruments showed significantly higher angular rotation to fracture than M-Wire Reciproc instruments (P < .05). Scanning electron microscopy of the fracture surface showed similar and typical features of torsional failure for the 2 types of instruments, including concentric abrasion marks and the fibrous dimple marks at the center of rotation. Conclusions: Reciproc Blue instruments showed a higher angle of rotation to fracture but a lower torque to failure than M-Wire Reciproc instruments.