Torsional behaviour of rotary NiTi ProTaper Universal instruments after multiple clinical use

By Viera E, Nakagawa R, Buono V, Bahia M

Date: 01/2009
Journal: IEJ

Purpose:

To evaluate torsional resistance & angular deflection of ProTaper after multiple uses. N=88 total files (S1, S2, F1, F2), Control: 10 sets of new instruments

Materials/Methods:

  • Files used by 1 endodontist in 5 molars. (50 total molars)
  • Instruments cleaned by ultrasonic & steam autoclave after each use
  • Radiographs taken to determine canal radius & angle at max curvature within canals
  • Microscopic evaluation by microscope & SEM (3 sets for each) for presence of distortion, unwinding, deformation
  • Torsion testing to determine max torque and angular deflection @ fracture

Results:

  1. No instrument fracture or permanent deformation during clinical procedures.
  2. Pre-op: mean radius = 4mm, angle of curvature = 33.1°
  3. ↑ file diameter = ↑ torsional resistance (ss when comparing control group files to each other)
  4. Multiple use = ↓ torsional resistance (ss for S2/F1/F2) ↓ angular deflection @ fracture (ss for S2/F1) ( this is not clinically significant because a locked tip will fracture in 1/5 of a second) ↑ Flexural fatigue (i.e., a decrease in max measured torque) = S1 (6%), S2 (19%), F1 (12%), F2 (13%)
  1. All used instruments had microcracks transverse & longitudinal to cutting edge, widening of machined grooves, blunting of cutting edges

Clinical Significance:

More curved canals and narrow canals will decrease the lifespan of a file

Files used previously are more likely to fracture than new ProTaper files