Effect of surface defects and cross-sectional configuration on the fatigue fracture of NiTi rotary files under cyclic loading

Yu-Mi Shin; Eui-Sung Kim; Kwang-Man Kim; Kee-Yeon Kum

doi:10.5395/JKACD.2004.29.3.267

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Original Article Effect of surface defects and cross-sectional configuration on the fatigue fracture of NiTi rotary files under cyclic loading: Yu-Mi Shin¹, Eui-Sung Kim¹, Kwang-Man Kim², Kee-Yeon Kum¹; 2004;29(3):-272.
DOI: https://doi.org/10.5395/JKACD.2004.29.3.267
Published online: May 31, 2004

¹Department of Conservative Dentistry, Yonsei University, Korea.

²Department of Dental Materials, Yonsei University, Korea.

Corresponding author: Kee-Yeon Kum. Department of Endodontics, Youngdong Severance Hospital, College of Dentistry, Yonsei University, Dokok-Dong, Kangnam-Gu, 146-92, Seoul, 135-270, Korea. Tel: 82-2-3497-3566, Fax: 82-2-3463-0551, kum6139@yumc.yonsei.ac.kr

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Abstract
REFERENCES

Abstract

The purpose of this in vitro study was to evaluate the effect of surface defects and cross-sectional configuration of NiTi rotary files on the fatigue life under cyclic loading. Three NiTi rotary files (K3™, ProFile®, and HERO 642®) with #30/.04 taper were evaluated. Each rotary file was divided into 2 subgroups: control (no surface defects) and experimental group (artificial surface defects). A total of six groups of each 10 were tested. The NiTi rotary files were rotated at 300rpm using the apparatus which simulated curved canal (40 degree of curvature) until they fracture. The number of cycles to fracture was calculated and the fractured surfaces were observed with a scanning electron microscope. The data were analyzed statistically. The results showed that experimental groups with surface defects had lower number of cycles to fracture than control group but there was only a statistical significance between control and experimental group in the K3™ (p<0.05). There was no strong correlation between the cross-sectional configuration area and fracture resistance under experimental conditions. Several of fractured files demonstrated characteristic patterns of brittle fracture consistent with the propagation of pre-existing cracks.

This data indicate that surface defects of NiTi rotary files may significantly decrease fatigue life and it may be one possible factor for early fracture of NiTi rotary files in clinical practice.
Keywords: Surface defect; Cross-sectional configuration; Cyclic fatigue; Brittle fracture; Ductile fracture; NiTi rotary files

Figure 1

Cross-sectional configuration of K3™, ProFile®, and HERO 642®.

Figure 2

The apparatus developed for fracturing NiTi rotary files under cyclic loading (Schneider's curvature: 40°).

Figure 3

A SEM image of surface defect (arrow) of K3™ (experimental group, ×150).

Figure 5

A higher magnification view of the rectangular area shown in Figure 4. Ultimate ductile fracture region that are typically characterized with microvoid formation and dimpling are seen (×1000).

Figure 4

A SEM image of the fractured surface of HERO 642® file after cyclic loading: a control group (×150).

Download Figure

Figure 7

A higher magnification view of brittle fracture (BF) area shown in Figure 6. A region of brittle fracture is shown originating from the pre-existing surface defects (×500).

Figure 6

SEM image of the fractured surface of ProFile® after cyclic loading (experimental group, ×150): The left square area shows a region of brittle fracture (BF) which transit to ultimate ductile failure (DF).

Download Figure

Table 1

Study Design of control and experimental groups.

Table 2

Mean number of cycles to fracture and statistical comparison between control and experimental group of each file system.

S: Statistically significant at p < 0.05 (Wilcoxon Rank Sum Test). NS: Non-significant

Number of cycles to fracture = Time to fracture (sec)×5 (300 rpm = 300 cycles/min)

Table 3

Statistical comparison between the number of cycles to fracture and the cross sectional configuration area at 5 mm level.

^†Statistically significant between cross sectional area (D₅) and number of cycles to fracture (Kruskal-Wallis test, p < 0.05)

REFERENCES

1. Mize SB, Pruett JP, Clement DJ, Carnes DL. Effect to sterilization on cyclic fatigue of rotary nickel-titanium endodontic instruments. J Endod. 1998;24(12):843-847.PubMed
2. Pruett JP, Clement DJ, Carnes DL. Cyclic fatigue testing of nickel-titanium endodontic instruments. J Endod. 1997;23(2):77-85.Article PubMed
3. Haikel Y, Serfaty R, Bateman G, Senger B, Allemann C. Dynamic and cyclic fatigue of engine-driven rotary nickel-titanium endodontic instruments. J Endod. 1999;25(6):434-440.Article PubMed
4. Kuhn G, Tavernier B, Jordan L. Influence of structure on Nickel-Titanium endodontic instrument failure. J Endod. 2001;27(8):516-520.PubMed
5. Karn T. Fractographic analysis of experimentally separated NiTi rotary files. 2003;University of Connecticut; MS Thesis.
6. Li UM, Lee BS, Shih CT, Lan WH, Lin CP. Cyclic fatigue of endodontic nickel-titanium rotary instruments: static and dynamic tests. J Endod. 2002;28(6):448-451.Article PubMed
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(7):414-417.Article PubMed
8. Jeon IS, Spangberg LS, Yoon TC, Kazemi RB, Kum KY. Smear layer production of three NiTi rotary reamers in straight root canals. A SEM study. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2003;96(5):601-607.PubMed

Tables & Figures

Figure 1

Cross-sectional configuration of K3™, ProFile®, and HERO 642®.

Figure 2

The apparatus developed for fracturing NiTi rotary files under cyclic loading (Schneider's curvature: 40°).

Figure 3

A SEM image of surface defect (arrow) of K3™ (experimental group, ×150).

Figure 5

A higher magnification view of the rectangular area shown in Figure 4. Ultimate ductile fracture region that are typically characterized with microvoid formation and dimpling are seen (×1000).

Figure 4

A SEM image of the fractured surface of HERO 642® file after cyclic loading: a control group (×150).

Download Figure

Figure 4

A SEM image of the fractured surface of HERO 642® file after cyclic loading: a control group (×150).

Download Figure

Figure 7

A higher magnification view of brittle fracture (BF) area shown in Figure 6. A region of brittle fracture is shown originating from the pre-existing surface defects (×500).

Figure 6

Download Figure

Figure 6

Download Figure

Table 1

Study Design of control and experimental groups.

Table 2

Mean number of cycles to fracture and statistical comparison between control and experimental group of each file system.

S: Statistically significant at p < 0.05 (Wilcoxon Rank Sum Test). NS: Non-significant

Number of cycles to fracture = Time to fracture (sec)×5 (300 rpm = 300 cycles/min)

Table 3

Statistical comparison between the number of cycles to fracture and the cross sectional configuration area at 5 mm level.

^†Statistically significant between cross sectional area (D₅) and number of cycles to fracture (Kruskal-Wallis test, p < 0.05)

REFERENCES

1. Mize SB, Pruett JP, Clement DJ, Carnes DL. Effect to sterilization on cyclic fatigue of rotary nickel-titanium endodontic instruments. J Endod. 1998;24(12):843-847.PubMed
2. Pruett JP, Clement DJ, Carnes DL. Cyclic fatigue testing of nickel-titanium endodontic instruments. J Endod. 1997;23(2):77-85.Article PubMed
3. Haikel Y, Serfaty R, Bateman G, Senger B, Allemann C. Dynamic and cyclic fatigue of engine-driven rotary nickel-titanium endodontic instruments. J Endod. 1999;25(6):434-440.Article PubMed
4. Kuhn G, Tavernier B, Jordan L. Influence of structure on Nickel-Titanium endodontic instrument failure. J Endod. 2001;27(8):516-520.PubMed
5. Karn T. Fractographic analysis of experimentally separated NiTi rotary files. 2003;University of Connecticut; MS Thesis.
6. Li UM, Lee BS, Shih CT, Lan WH, Lin CP. Cyclic fatigue of endodontic nickel-titanium rotary instruments: static and dynamic tests. J Endod. 2002;28(6):448-451.Article PubMed
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(7):414-417.Article PubMed
8. Jeon IS, Spangberg LS, Yoon TC, Kazemi RB, Kum KY. Smear layer production of three NiTi rotary reamers in straight root canals. A SEM study. Oral Surg Oral Med Oral Pathol Oral Radiol Endod. 2003;96(5):601-607.PubMed

Citations

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Effect of surface defects and cross-sectional configuration on the fatigue fracture of NiTi rotary files under cyclic loading

J Korean Acad Conserv Dent. 2004;29(3):267-272. Published online May 31, 2004

DOI: https://doi.org/10.5395/JKACD.2004.29.3.267

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Figure

Effect of surface defects and cross-sectional configuration on the fatigue fracture of NiTi rotary files under cyclic loading

Figure 1 Cross-sectional configuration of K3™, ProFile®, and HERO 642®.

Figure 2 The apparatus developed for fracturing NiTi rotary files under cyclic loading (Schneider's curvature: 40°).

Figure 3 A SEM image of surface defect (arrow) of K3™ (experimental group, ×150).

Figure 4 A SEM image of the fractured surface of HERO 642® file after cyclic loading: a control group (×150).

Figure 5 A higher magnification view of the rectangular area shown in Figure 4. Ultimate ductile fracture region that are typically characterized with microvoid formation and dimpling are seen (×1000).

Figure 6 SEM image of the fractured surface of ProFile® after cyclic loading (experimental group, ×150): The left square area shows a region of brittle fracture (BF) which transit to ultimate ductile failure (DF).

Figure 7 A higher magnification view of brittle fracture (BF) area shown in Figure 6. A region of brittle fracture is shown originating from the pre-existing surface defects (×500).

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Effect of surface defects and cross-sectional configuration on the fatigue fracture of NiTi rotary files under cyclic loading

Table 1

Study Design of control and experimental groups.

Table 2

Mean number of cycles to fracture and statistical comparison between control and experimental group of each file system.

S: Statistically significant at p < 0.05 (Wilcoxon Rank Sum Test). NS: Non-significant

Number of cycles to fracture = Time to fracture (sec)×5 (300 rpm = 300 cycles/min)

Table 3

Statistical comparison between the number of cycles to fracture and the cross sectional configuration area at 5 mm level.

^†Statistically significant between cross sectional area (D₅) and number of cycles to fracture (Kruskal-Wallis test, p < 0.05)

Table 1 Study Design of control and experimental groups.

Table 2 Mean number of cycles to fracture and statistical comparison between control and experimental group of each file system.

S: Statistically significant at p < 0.05 (Wilcoxon Rank Sum Test). NS: Non-significant

Number of cycles to fracture = Time to fracture (sec)×5 (300 rpm = 300 cycles/min)

Table 3 Statistical comparison between the number of cycles to fracture and the cross sectional configuration area at 5 mm level.

^†Statistically significant between cross sectional area (D₅) and number of cycles to fracture (Kruskal-Wallis test, p < 0.05)