Cyclic Fatigue and Fracture Characteristics of Ground and Twisted Nickel-Titanium Rotary Files

doi:10.1016/j.joen.2009.09.037

Journal of Endodontics

Volume 36, Issue 1, January 2010, Pages 147-152

https://doi.org/10.1016/j.joen.2009.09.037 Get rights and content

Abstract

Introduction

The purposes of this study were to compare the fatigue resistance of traditional, ground nickel-titanium rotary instruments with the Twisted File and to examine the fracture characteristics of the fatigued fragment.

Methods

Size #25, 0.06 tapered, TF (SybronEndo), RaCe (FKG Dentaire), Helix (DiaDent), and ProTaper F1 (Dentsply Maillefer) were examined with scanning electron microscope for surface characteristics before subjected to a cyclic (rotational bending) fatigue test. The time until fracture was recorded to calculate the number of revolutions for each instrument. The data were compared for differences by using analysis of variance and post hoc Scheffé test. The fragments were examined with scanning electron microscope both in lateral view and fractographically.

Results

TF showed a significantly higher resistance to cyclic fatigue than other nickel-titanium files that were manufactured with a grinding process (P < .05). The path of crack propagation appeared to be different for electropolished (TF and RaCe) versus non-electropolished (Helix and ProTaper) instruments.

Conclusions

Although all specimens showed similar fractographic appearance, which indicated a similar fracture mechanism, instruments with abundant machining grooves seemed to have a higher risk of fatigue.

Section snippets

Material and Methods

Four brands of NiTi instruments with similar cross-sectional geometries were tested. The following instrument of each brand was examined: TF #25/0.06 taper (SybronEndo), RaCe #25/0.06 taper (FKG Dentaire), ProTaper F1 (Dentsply Maillefer, Ballaigues, Switzerland), and Helix #25/0.06 taper (DiaDent, Chongju, Korea). TF and RaCe both have an equilateral triangular cross section, whereas ProTaper and Helix have similar cross section of a convex triangle. The ProTaper F1 (tip size #20 with 7% taper

Results

The surface features of each brand of instrument under the SEM are shown in Fig. 1. Despite having been electropolished by the manufacturer, TF's surface was not perfectly smooth but showed a unique surface texture that seemed to be a kind of machining grooves (or traces from rolling, shaping, or injection molding) running along the length of the file with multiple pits (Fig. 1A). In contrast, obvious machining grooves, which ran almost perpendicular to the long axis of the instrument, were

Discussion

File fracture is a major concern during endodontic treatment. Although multiple factors are responsible for instrument separation in use, cyclic fatigue has been shown to be an important cause because the rotary instrument might be used in curved root canals 7, 8, 9. The shorter the radius of curvature, the greater is the chance of fatigue breakage 7, 13. Cyclic fatigue occurs when a metal is subjected to repeated cycles of tension and compression that cause its structure to break down (as a

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Basic ResearchCyclic Fatigue and Fracture Characteristics of Ground and Twisted Nickel-Titanium Rotary Files

Abstract

Introduction

Methods

Results

Conclusions

Section snippets

Material and Methods

Results

Discussion

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Cyclic Fatigue and Fracture Characteristics of Ground and Twisted Nickel-Titanium Rotary Files