Cyclic fatigue test
All instruments used were analyzed, and resistance to cyclic fatigue
(ten for each group of instrument [n=5 for continuous mode and n=5 for
reciprocating mode]) was tested at controlled room temperature (37º ±
1ºC) 12,13. The instruments were connected to a VDW
Silver engine (VDW GmbH, Munich, Germany), which was connected to the
cyclic fatigue device. The predefined programs were selected according
to the manufacturers for the continuous motion. ProDesign Logic2 25.03
and 25.05 instruments were used in continuous motion at 950 rpm with 2
N/cm and 4N/cm of torque, respectively. Flat File instruments were used
in continuous motion at 500 rpm with 2 N/cm of torque. When the
reciprocating motion was tested, the instruments were coupled to an
Eighteeth E-connect Pro motor (Eighteeth, Changzhou City, China)
connected to the cyclic fatigue device. The ProDesign Logic 25.03,
25.05, and Flat File 25.04 were used in reciprocating motion at 350rpm
with an angle of rotation of 150º forward and 30º reverse.
The instruments were positioned in a device simulating an artificial
canal made of stainless steel, with a curvature of 60º and a radius of
curvature of 5 mm located 5 mm from the instrument’s tip. The device has
an outer arch with a 1 mm deep groove that served as a guide for the
instruments’ path, keeping them in the curvature and allowing them to
rotate freely during the tests. This device allowed a precise and
reproducible position of the curvature that was established for all
instruments used.
A digital stopwatch recorded the time to fracture, and a digital camera
captured data to ensure fracture time accuracy in seconds.