Effect of cyclic torsional preloading on cyclic fatigue resistance of ProTaper Next and Mtwo nickel–titanium instruments

Abstract

Aim: To evaluate the influence of different torsional preloads on cyclic fatigue resistance of endodontic rotary instruments made by conventional nickel-titanium (NiTi) or M-Wire. Methods: Eighty new Mtwo (#25/0.06) (Sweden & Martina, Due Carrare, Padova, Italy) and ProTaper Next X2 (Dentsply Maillefer, Ballaigues, Switzerland) were used. The Torque and distortion angles at failure of new instruments (n = 10) were measured and 0% (n = 10), 25%, 50%, and 75% (n = 20) of the mean ultimate torsional strength as preloading condition were applied according to ISO 3630-1 for each brand. The twenty files tested for every extent of preload were subjected to 25 or 50 torsional cycles (n = 10). After torsional preloading, the number of cycles to failure was evaluated in a simulated canal with 608 angle of curvature and 5 mm of radius of curvature. Data were analyzed using 2-way analysis of variance. Scanning electron microscope (SEM) was performed to evaluate the fracture surface of each fragment.Peer review under responsibility of Società Italiana di Endodonzia.

Influence of Access Cavity Design on Fatigue Resistance of Reciproc Blue: Conservative vs. Truss Access

“…The scanning electron microscopic analysis showed typical fractographic appearances of cyclic fatigue fractures [2,22] for instruments used in teeth with both kind of endodontic access designs tested. This confirms that fractographic findings correspond to those ones due to the last stress applied (cyclic fatigue test in this study) [33].…”

Analysis of cyclic fatigue resistance of ProTaper Universal and ProTaper Next rotary instruments

“…In addition to alloy differences, instrument cross-sectional differences are a significant contributing factor to the greater fatigue resistance of NiTi rotary instruments. The larger contact area of the rotating NiTi instrument in the canal leads to less flexibility and less resistance to cyclic fatigue [20]. ProTaper Universal instruments have a triangular cross-section and are manufactured using the cutting technology that is standard for conventional instruments.…”

“…The ProTaper Next has a rectangular cross-section with an off-center position that reduces the area of contact with the root canal walls during instrumentation providing greater resistance to cyclic fatigue [20,22]. Asymmetric movements during the rotation of the ProTaper Next instrument ensure efficiency in canal instrumentation, while the rectangular section ensures superior mechanical properties [18].…”

“…Pored razlika u leguri, razlike u poprečnom preseku instrumenata predstavljaju značajan faktor koji doprinosi većoj otpornosti na zamor kod NiTi rotirajućih instrumenta. Veća kontaktna površina rotirajućeg NiTi instrumenta u kanalu dovodi do manje fleksibilnosti i manje otpornosti na ciklični zamor [20]. Instrumenti ProTaper Universal imaju trougaoni poprečni presek i proizvode se tehnologijom klasičnog rezanja, koja je standardna za konvencionalne instrumente.…”

Influence of Heat Treatment of Nickel–Titanium Instruments on Cyclic Fatigue Resistance in Simulated Curved Canals

“…Fracture can be caused by torsion, when the tip of the instrument is locked in a canal while the shaft continues to rotate, or by fatigue, when the instrument is subjected to several tension-compression cyclic fatigue at the same point. [8][9][10][11][12][13][14][15] Bassi Logic (Bassi Endo, Belo Horizonte, Brazil) is a rotary file system with files available in tip sizes ranging from #15 to #50 and constant tapers of 0.01, 0.03, 0.04, 0.05, and 0.06. The cross-section depends on the taper of the instrument: the 0.01 taper instruments have four cutting edges; the 0.03, 0.05 and 0.06 taper instruments have a double helix; the 0.04 taper instruments have a triple helix; and the 15.03 and 15.05 instruments have a quadrangular section.…”