Effect of internal stress on cyclic fatigue failure in K3

Article information

Restor Dent Endod. 2012;37(2):74-78

Publication date (electronic) : 2012 May 18

doi : https://doi.org/10.5395/rde.2012.37.2.74

Jun-Young Kim, DDS, MSD , Jin-Woo Kim, DDS, PhD , Kyung-Mo Cho, DDS, PhD , Se-Hee Park, DDS, PhD

Department of Conservative Dentistry, Gangneung-Wonju National University School of Dentistry, Gangneung, Korea.

Correspondence to Se-Hee Park, DDS, PhD. Assistant Professor, Department of Conservative Dentistry, Gangneung-Wonju National University School of Dentistry, 120 Daehang-ro, Gangneung, Korea 210-702. TEL, +82-33-640-2760; FAX, +82-33-640-3103; drendo@gwnu.ac.kr

Received 2011 December 22; Revised 2012 February 06; Accepted 2012 February 12.

Abstract

Objectives

This study aimed to evaluate the relationship between the cyclic fatigue of a K3 file and internal stress intentionally induced until the activation of the auto-stop function of the torque-controlled motor.

Materials and Methods

K3 (Sybron Endo) .04 and .06 taper, size 25, 30, 35, 40 and 45 were used in this study. To give the internal stress, the K3 files were put into the .02 taper Endo-Training-Bloc (Dentsply Maillefer) until the activation of the auto-stop function of the torque-controlled motor. The rotation speed was 300 rpm and torque value was 1.0 N·cm. K3 were grouped by the number of induced internal stress and randomly distributed to 4 experimental groups (n = 10, Stress 0 [control], Stress 1, Stress 2 and Stress 3). For measuring the cyclic fatigue failure, the K3 files were worked against a sloped glass block and time for file separation was recorded. Data was statistically analyzed Statistical analyses were performed using two-way ANOVA and Duncan post-hoc test at p < 0.05 level.

Results

Except .04 taper size 30 in Stress 1 group, there were statistically significant differences in time for file separation between control and all experimental groups. K3 with .04 taper showed higher cyclic fatigue resistance than those of .06 taper.

Conclusion

In the limitation of this study, the cyclic fatigue of the K3 file was influenced by the accumulated internal stress from use until the auto-stop function was activated by the torque-controlled motor. Therefore, clinicians should avoid the reuse of the K3 file that has undergone auto-stops.

Keywords: Auto-stop; Cyclic fatigue failure; Internal stress; K3; Separation; Torsional stress

Notes

This study was supported by research funding of 2011 year from Gangneung-Wonju National University Dental Hospital (2011-0089).

No potential conflict of interest relevant to this article was reported.

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This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Figure 1

Representative image of cyclic fatigue test (inclined glass plane).

Figure 2

FE-SEM view of K3. (a) Torsional fracture of K3 .04/#25. Central dimples and circular abrasion mark (white arrow) (×200); (b) Torsional distorsion of K3 .04/#25; (c) Torsional distorsion of K3 .04/#30 (×30); (d) Cyclic fatigue fracture of K3 .04/#45. Radial striations linked at a point on the edge (black arrow) (×120). The surfaces of cyclic fatigue fracture in all experimental groups showed same patterns. FE-SEM, field emission scanning electron microscope.

Table 1

Time for file separation of K3 .04 taper

Same superscripts shows no statistically significant difference in same size.

Stress 0 group was not induced internal stress, Stress 1 group was induced internal stress 1 time, Stress 2 was induced internal stress 2 times, and Stress 3 was induced internal stress 3times by activation of the auto-stop function of the torque-controlled motor.

Table 2

Time for file separation of K3 .06 taper

Same superscripts shows no statistically significant difference in same size.