CYCLIC FATIGUE OF THE SODIUM HYPOCHLORITE TREATED AND /OR STEAM AUTOCLAVED NICKEL-TITANIUM ENDODONTIC FILES

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Restor Dent Endod. 2008;33(1):54-65

Publication date (electronic) : 2008 January 14

doi : https://doi.org/10.5395/JKACD.2008.33.1.54

Hye-Young Cho , Il-Young Jung , Chan-Young Lee , Euiseong Kim ^,

Department of Conservative Dentistry, College of Dentistry, Yonsei University, Seoul, Korea5

^*Corresponding Author: Euiseong Kim, Department of Conservative Dentistry, College of Dentistry, Yonsei University 134 Shinchon-Dong, Seodamun-Ku, Seoul, 120-752, Korea, Tel: 82-2-2228-8700 Fax: 82-2-313-7575, E-mail: andyendo@yuhs.ac

Received 2007 October 17; Revised 2007 December 11; Accepted 2008 January 09.

Abstract

The purpose of this study was to determine the effect of sodium hypochlorite and steam autoclaving on the cyclic fatigue of nickel-titanium endodontic files.

Two types of files with a .06 taper and #30 were used, K3^® (SybronEndo, Glendora, California, USA) and Hero642^®(Micro-Mega, Besançon, France).

The files were divided into 6 experimental groups containing 10 files each group depending the soaking time in 6% sodium hypochlorite solution and number of cycles of steam autoclave. After sterilization, a cyclic fatigue test was performed on each file, and the fracture time was recorded in seconds. The control group underwent the cyclic fatigue test only. After the test, the surface characteristics of the files were observed using scanning electron microscopy (SEM).

All groups containing the Hero 642^® files showed a similar cyclic fatigue fracture time. However, the cyclic fatigue fracture time with the K3^® files was significantly shorter in groups which were treated with sodium hypochlorite than in the control group (P < 0.05). SEM revealed both Hero642^® and K3^® files to have significant corrosion on the file surface in groups treated with sodium hypochlorite, compared with the sharp and regular blades of the control group. K3^® files showed more corrosion than the Hero642^® files. Bluntness of the blades of the K3^® file was observed in groups treated with steam autoclave. Although there was no obvious destruction on the surface of steam autoclaved Hero642^® files, slight bluntness was observed.

Sterilizing with a steam autoclave is much less destructive to K3^® files than sodium hypochlorite. The longer time exposed to sodium hypochlorite, the more destructive pattern was shown on the blades of the files. Therefore, when using sodium hypochlorite solution, the exposure time should be as short as possible in order to prevent corrosion and increase the cyclic fatigue fracture time.

Keywords: Cyclic fatigue fracture; Ni-Ti endodontic files; sodium hypochlorite solution; steam autoclave

Figure 1.

A photograph and a schematic diagram of the machine for cyclic fatigue test.

Figure 2.

Sloped metal block with a guiding path of 2 mm width.

Figure 3.

Cyclic fatigue fracture time of K3^® (sec) (Mean ± SD).

Figure 4.

Cyclic fatigue fracture time of Hero 642^® (sec) (Mean ± SD).

Figure 5.

SEM view of files of the control groups.

Figure 6.

SEM view of files of the N15 groups.

Figure 7.

SEM view of files of the N30 groups.

Figure 8.

SEM view of files of the H5 groups.

Figure 9.

SEM view of files of the H10 groups.

Figure 10.

SEM view of files of the H5N15 groups.

Figure 11.

SEM view of files of the H10N30 groups.

Figure 12.

Files in NaOCl solution.

Figure 13.

Surface of files after 15 minutes of NaOCl treatment.

Figure 14.

Qualitative analysis of Hero 642^®.

Figure 15.

Qualitative analysis of K3^®.

Table 1.

Pretreatment of each groups before cyclic fatigue test

Table 2.

Quantitative analysis of Hero 642^®

Table 3.

Quantitative analysis of K3^®

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