A review of cyclic fatigue testing of nickel-titanium rotary instruments

By Plotino G, Grande N, Cordaro M. Testarelli L and Gambarini G.

Date: 01/2009
Journal: JOE

Summary:

Purpose:  to summarize and analyze devices used for cyclic fatigue testing, and to explain the differences between them.

Materials/Methods:

Not mentioned

Most highlighted Results: 

•Radius and angle of curvature of artificial canals followed either Schneider’s technique or Pruett’s technique Fig.1,2 radius of curvature is the most influencing factor of cyclic fatigue (i.e Pruett’s technique is more accurate)

•Artificial canals were made of  glass or metal tube, SS needles (16-18 G), sloped metal block, 3-SS pins, grooved block-and-rod assembly Fig.3

•The drawbacks of testing in cylindrical tubes:

1- The larger inner diameter of the tube compared to the instruments. Thus not constricting the shaft to the designed curve (i.e the file rotates in trajectory of greater radius and reduced angle (unpredictable)) comparing files with variable trajectories would be difficult and inconsistent.

2- The space in the tube allows the file to vibrate within the space ( stress)

•The drawback of testing in a sloped metal block:

The maximum curvature of the file is variable depending on the physical and geometric properties of the instrument

•The drawback of testing in a 3-SS pins:

  NiTi files differ in taper and cross section between files and within the same file

•The drawback of testing in a grooved block-and-rod assembly:

  Trajectory is given to the external surface of the file rather its axis (variation in files with different tapers (might be loose or tight+ radius and angle of curvature might not be repeatable+ cant control depth)

•A copper duplicate of the files to manufacture artificial canals has allowed a specific trajectory of each file.

Conclusion:

•An International standard for cyclic fatigue testing of NiTi rotary instruments is required to ensure uniformity of methodology and comparable results.