Restor Dent Endod.  2017 Aug;42(3):216-223. 10.5395/rde.2017.42.3.216.

Effect of surface treatment on the mechanical properties of nickel-titanium files with a similar cross-section

• Kwak SW
• Lee JY
• Goo HJ
• Kim HC

• KMID: 2386775
• DOI: http://doi.org/10.5395/rde.2017.42.3.216

Abstract

OBJECTIVES
The aim of this study was to compare the mechanical properties of various nickel-titanium (NiTi) files with similar tapers and cross-sectional areas depending on whether they were surface-treated.
MATERIALS AND METHODS
Three NiTi file systems with a similar convex triangular cross-section and the same ISO #25 tip size were selected for this study: G6 (G6), ProTaper Universal (PTU), and Dia-PT (DPT). To test torsional resistance, 5 mm of the straightened file's tip was fixed between polycarbonate blocks (n = 15/group) and continuous clockwise rotation until fracture was conducted using a customized device. To evaluate cyclic fatigue resistance, files were rotated in an artificial curved canal until fracture in a dynamic mode (n = 15/group). The torsional data were analyzed using 1-way analysis of variance and the Tukey post-hoc comparison test, while the cyclic fatigue data were analyzed using the Mann-Whitney U test at a significance level of 95%.
RESULTS
PTU showed significantly greater toughness, followed by DPT and G6 (p < 0.05). G6 showed the lowest resistance in ultimate torsional strength, while it showed a higher fracture angle than the other files (p < 0.05). In the cyclic fatigue test, DPT showed a significantly higher number of cycles to failure than PTU or G6 (p < 0.05).
CONCLUSIONS
Within the limitations of this study, it can be concluded that the torsional resistance of NiTi files was affected by the cross-sectional area, while the cyclic fatigue resistance of NiTi files was influenced by the surface treatment.

Keyword

Cross-section; Cyclic fatigue; Nickel-titanium file; Surface treatment; Torsional strength

MeSH Terms

Fatigue

Figure

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  Figure 1 Customized test devices used in this study. (A) A test device for the torsional test (AEndoS, DMJ system, Busan, Korea); (B) A test device for the cyclic fatigue test (EndoC, DMJ system).

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  Figure 2 Scanning electron micrographs of the fractured surface after the torsional fracture test. (A) Dia-PT nickel-titanium file system (DPT; Dia-Dent, Cheongwon, Korea); (B) ProTaper Universal nickel-titanium file system (PTU; Dentsply Maillefer, Ballaigues, Switzerland); (C) G6 nickel-titanium file system (G6; Global Top Inc., Goyang, Korea). Cross-sectional aspects of all groups revealed the typical features of torsional fractures, such as concentric abrasion marks (circular arrow) and fibrous dimples (asterisk) from the torsional center. In the lateral aspects, the DPT and G6 groups showed a smooth surface, while PTU showed many machining grooves. The arrows on the lateral aspects indicate unwound distortion areas with a reverse helix.

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  Figure 3 Scanning electron micrographs of the fractured specimens after the cyclic fatigue test. (A) Dia-PT nickel-titanium file system (DPT; Dia-Dent, Cheongwon, Korea); (B) ProTaper Universal nickel-titanium PTU (Dentsply Maillefer, Ballaigues, Switzerland); (C) G6 nickel-titanium file system (G6; Global Top Inc., Goyang, Korea). Cross-sectional aspects of all groups revealed the typical features of cyclic fatigue fracture such as crack initiation area and fibrous fast fracture zone (dotted area). In the lateral aspects, the PTU group showed multiple machining grooves (white triangle), while the other groups showed smooth surfaces. Micro-cracks were shown (asterisk) near the fracture area from the group G6.

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