Is the reciprocating movement per se able to improve the cyclic fatigue resistance of instruments?

By Keifner P, Ban M, De-Deus G

Date: 01/2014
Journal: IEJ

Summary:

  • Purpose: To compare cyclic fatigue resistance of two geometrically similar NiTi instruments used in reciprocating and continuous rotary motion.
  • N= 144 Mtwo & Reciproc instruments were used. 

Materials/Methods:

  • 8 experimental groups (n = 18)
    • G1) Reciproc” R25 in reciprocation movement
    • G2) Reciproc” R40 in reciprocation movement
    • G3) Reciproc” R25 in rotary movement
    • G4) Reciproc” R40 in rotary movement
    • G5) Mtwo” M25 in reciprocation movement
    • G6) Mtwo” M40 in reciprocation movement
    • G7) Mtwo” M25 in rotary movement
    • G8) Mtwo” M40 in rotary movement

  • dimensions of the simulated root canal were as follows: 1.4 mm diameter, angle of curvature 60 ° and a curvature radius of 5.0 mm. 

  • To simulate clinical conditions, instead of rotating the file in static position, the set-up was designed to produce a continuous up-and-down pecking motion along the vertical axis of the instrument.  

  • The time to fracture was recorded with a digital chronometer. The parameter push–pull cycles (PPC) denotes the number of cycles in vertical push–pull direction (pecking movement).

  • The fractured fragment surfaces were examined with SEM.

Most highlighted Results:

1.The highest resistance to failure was observed with Reciproc” files in reciprocal movement, followed by Mtwo” files in reciprocal movement and Reciproc” files in continuous rotary motion. 

2.Mtwo” files used in continuous rotary movement had the least resistance. 

3.Reciproc” files in reciprocating movement had a significantly higher NCF than Mtwo” files, when used in continuous rotation. 

4.SEM analysis of the fracture surface confirmed typical features of cyclic fatigue failure. 

Conclusion: 

  • The time to fracture was three times higher for Reciproc” instruments in reciprocating movement compared with Mtwo” instruments, which have the same instrument tip size, when used in continuous rotary motion. 
  • Reciprocating movement increased the cyclic fatigue resistance of NiTi instruments.