Buckling resistance, bending stiffness, and torsional resistance of various instruments for canal exploration and glide path preparation.
OBJECTIVE
This study compared the mechanical properties of various instruments for canal exploration and glide-path preparations.


METHODS
The buckling resistance, bending stiffness, ultimate torsional strength, and fracture angle under torsional load were compared for C+ file (CP, Dentsply Maillefer), M access K-file (MA, Dentsply Maillefer), Mani K-file (MN, Mani), and NiTiFlex K-file (NT, Dentsply Maillefer). The files of ISO size #15 and a shaft length of 25 mm were selected. For measuring buckling resistance (n = 10), the files were loaded in the axial direction of the shaft, and the maximum load was measured during the files' deflection. The files (n = 10) were fixed at 3-mm from the tip and then bent 45° with respect to their long axis, while the bending force was recorded by a load cell. For measuring the torsional properties, the files (n = 10) were also fixed at 3-mm, and clockwise rotations (2-rpm) were applied to the files in a straight state. The torsional load and the distortion angle were recorded until the files succumbed to the torque.


RESULTS
The CP was shown to require the highest load to buckle and bend the files, and the NT showed the least. While MA and MN showed similar buckling resistances, MN showed higher bending stiffness than MA. The NT had the lowest bending stiffness and ultimate torsional strength (p < 0.05).


CONCLUSIONS
The tested instruments showed different mechanical properties depending on the evaluated parameters. CP and NT files were revealed to be the stiffest and the most flexible instruments, respectively.
Department of Conservative Dentistry, School of Dentistry and Dental Research Institute, Pusan National University, Yangsan, Korea.
Sang-Won
SW
Kwak
Department of Conservative Dentistry, School of Dentistry, Kyungpook National University, Daegu, Korea.
Jung-Hong
JH
Ha
Department of Conservative Dentistry, School of Dentistry and Dental Research Institute, Seoul National University, Seoul, Korea.
WooCheol
W
Lee
Department of Conservative Dentistry, School of Dentistry, Kyungpook National University, Daegu, Korea.
Sung-Kyo
SK
Kim
Department of Conservative Dentistry, School of Dentistry and Dental Research Institute, Pusan National University, Yangsan, Korea.
Hyeon-Cheol
HC
Kim
Bending stiffness; Buckling resistance; Glide path; Nickel-titanium rotary file; Stainless steel file; Torsional resistance