Evaluation of torsional strength and bending stiffness of Edge Endo file systems using different heat treatments

Introduction
Ideal endodontic instruments should exhibit high fracture resistance and flexibility, which facili­tate endodontic therapy and result in no complications.

Objectives
This study aimed to evaluate and compare the torsional strength and bending stiffness of three diffe­rent Edge Endo file systems.

Material and methods
Ninety NiTi rotary files of EdgeFile X7 (EX7), Edge X7 Utopia (EX7 Utopia), and EdgeOne Blaze Utopia (EOB Utopia) of 25 mm length and #25 tip size were used. Torsional strength was evaluated at BT (n 15/file) by repetitive torsional load method, using endomotor with auto-stop property at 300 rpm and 2 Ncm maximum speed and torque. Fractured files were examined under SEM to identify topographic charac­teristics of fracture surface. Cantilever bending test was employed to assess bending stiffness at BT (n 15/file) by applying a load at 3 mm from the tip, and bending stress resistance was recorded. Data were analyzed by one-way ANOVA and Tukey HSD tests at p < 0.05 significance level.

Results
The EX7 file demonstrated the highest torsional resistance and the lowest bending resistance (p < 0.05), while the EOB Utopia file showed the lowest torsional resistance. The EX7 Utopia file displayed the highest bending resistance.

Conclusions
Torsional and bending resistance of the tested rotary NiTi file systems significantly decreased with the FireWire Blaze new heat treatment.