J Korean Acad Conserv Dent.  2009 Sep;34(5):424-429. 10.5395/JKACD.2009.34.5.424.

Effect of cross-sectional area of 6 nickel-titanium rotary instruments on the fatigue fracture under cyclic flexural stress: A fractographic analysis

• Hwang SY
• Oh SR
• Lee Y
• Lim SM
• Kum KY

• KMID: 1986605
• DOI: http://doi.org/10.5395/JKACD.2009.34.5.424

Abstract

This study aimed to assess the influence of different cross-sectional area on the cyclic fatigue fracture of Ni-Ti rotary files using a fatigue tester incorporating cyclical axial movement. Six brands of Ni-Ti rotary files (ISO 30 size with .04 taper) of 10 each were tested: Alpha system (KOMET), HeroShaper (MicroMega), K3 (SybronEndo), Mtwo (VDW), NRT (Mani), and ProFile (Dentsply). A fatigue-tester (Denbotix) was designed to allow cyclic tension and compressive stress on the tip of the instrument. Each file was mounted on a torque controlled motor (Aseptico) using a 1:20 reduction contra-angle and was rotated at 300 rpm with a continuous, 6 mm axial oscillating motion inside an artificial steel canal. The canal had a 60degrees angle and a 5 mm radius of curvature. Instrument fracture was visually detected and the time until fracture was recorded by a digital stop watch. The data were analyzed statistically. Fractographic analysis of all fractured surfaces was performed to determine the fracture modes using a scanning electron microscope. Cross-sectional area at 3 mm from the tip of 3 unused Ni-Ti instruments for each group was calculated using Image-Pro Plus (Imagej 1.34n, NIH). Results showed that NRT and ProFile had significantly longer time to fracture compared to the other groups (p < .05). The cross-sectional area was not significantly associated with fatigue resistance. Fractographycally, all fractured surfaces demonstrated a combination of ductile and brittle fracture. In conclusion, there was no significant relationship between fatigue resistance and the cross-sectional area of Ni-Ti instruments under experimental conditions.

Keyword

artificial steel canal; cross-sectional area; fatigue resistance; fractographic analysis

MeSH Terms

Electrons
Fatigue
Fractures, Stress
Nickel
Radius
Steel
Titanium
Torque
Nickel
Steel
Titanium

Figure

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  Figure 1 Schematic diagrams and pictures of an artificial canal and a fatigue tester (Denbotix).

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  Figure 2 Standard deviation and mean values of time to fracture of 6 Ni-Ti files (second). * Statistically significant (p < .05).

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  Figure 3 SEM views of cross-sectional shapes of 6 Ni-Ti rotary instruments and the calculated cross-sectional area at 3 mm from the tip(×200).

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  Figure 4 A photograph of fractured surface of NRT instrument (A, × 200) and the magnified view (round circle) showing the presence of micro-crack at lateral surface (C, white arrow, ×500) near the separated tip region. A photograph of fractured K3 instrument showing dimples at central area (B, white arrow, ×500). Evidence of brittle fracture is present as reflected by the multiple linear striations of on the peripheral fractured surface of K3 instrument (D, white arrow, ×1000).

Reference

1. Esposito PT, Cunningham CJ. A comparison of canal preparation with nickel-titanium and stainless steel instruments. J Endod. 1995. 21:173–176.

2. Peters OA. Current challenges and concepts in the preparation of root canal systems: a review. J Endod. 2004. 30:559–567.

3. Kosa DA, Marshall G, Baumgartner JC. An analysis of canal centering using mechanical instrumentation techniques. J Endod. 1999. 25:441–445.

4. Bahia MGA, Melo MCC, Buono VTL. Influence of simulated clinical use on the torsional behavior of nickeltitanium rotary endodontic instruments. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2006. 101:675–680.

5. Pruett JP, Clement DJ, Carnes DL. Cyclic fatigue testing of nickel-titanium endodontic instruments. J Endod. 1997. 23:77–85.

6. Sattapan B, Nervo GJ, Palamara JEA, Messer HH. Defects in rotary nickel-titanium files after clinical use. J Endod. 2000. 26:161–165.

7. Turpin YL, Chagneau F, Vulcain JM. Impact of two theoretical cross-sections on torsional and bending stresses of nickel-titanium root canal instrument models. J Endod. 2000. 26:414–417.

8. Xu X, Zheng Y, Eng D. Comparative study of torsional and bending properties for six models of nickel-titanium root canal instruments with different cross-sections. J Endod. 2006. 32:372–375.

9. Berutti E, Chiandussi G, Gaviglio I, Ibba A. Comparative analysis of torsional and bending stresses in two mathematical models of nickel-titanium rotary instruments: ProTaper versus ProFile. J Endod. 2003. 29:15–19.

10. Cheung GS, Darvell BW. Low-cycle fatigue of Ni-Ti rotary instruments of various cross-sectional shapes. Int Endod J. 2007. 40:626–632.

11. Shin YM, Kim ES, Kim KM, Kum KY. Effect of surface defects and cross-sectional configurations on the fatigue fracture of Ni-Ti rotary files in a dynamic model. J Korean Acad Conserv Dent. 2004. 29:267–272.

12. Kim JK, Kum KY, Kim ES. Comparative study on morphology of cross-section and cyclic fatigue test with different rotary Ni-Ti files and handling methods. J Korean Acad Conserv Dent. 2006. 31:96–102.

13. Haikel Y, Serfaty R, Bateman G, Senger B, Alleman C. Dynamic and cyclic fatigue of engine-driven rotary nickel-titanium endodontic instruments. J Endod. 1999. 25:434–440.

14. Li UM, Lee BS, Shih CT, Lan WH, Lin CP. Dynamic and cyclic fatigue of engine-driven rotary nickel-titanium endodontic instruments. J Endod. 2002. 28:448–451.

15. Dederich DN, Zakariasen KL. The effects of cyclical axial motion on rotary endodontic instrument fatigue. Oral Surg Oral Med Oral Pathol. 1986. 61:192–196.

16. Dieter GE. Mechanical metallurgy. 1986. 3rd ed. New York: McGraw-Hill;119138185–188. 382–387. 394

17. Schäfer E, Dzepina A, Danesh G. Bending properties of rotary nickel-titanium instruments. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2003. 96:757–763.

18. Ruddle CL. Nickel-titanium rotary systems: review of existing instruments and geometries. Dent Today. 2000. 19:86–95.

19. Yao JH, Schwartz SA, Beeson TJ. Cyclic fatigue of three types of rotary nickel-titanium files in a dynamic model. J Endod. 2006. 32:55–65.

20. Tripi TR, Bonaccorso A, Condorelli GG. Cyclic fatigue of different nickel-titanium endodontic rotary instruments. Oral Surg Oral Med Oral Pathol Oral radiol Endod. 2006. 102:e106–e114.

21. Hayashi Y, Yoneyama T, Yahata Y, Suda K. Phase transformation behavior and bending properties of hybrid nickel-titanium rotary endodontic instruments. Int Endod J. 2007. 40:247–253.

22. Ku JH, Chang HS, Jang SW, Min KS. The instrument-centering ability of four nickel-titanium instruments in simulated curved root canals. J Korean Acad Conserv Dent. 2006. 31:113–118.