Factors Influencing Defects of Rotary Nickel-Titanium Endodontic Instruments After Clinical Use

Abstract

This study examined used, discarded rotary nickel-titanium instruments obtained from 14 endodontists in four countries, and identified factors that may influence defects produced during clinical use. A total of 7,159 instruments were examined for the presence of defects. Unwinding occurred in 12% of instruments and fractures in 5% (1.5% torsional, 3.5% flexural). The defect rates varied significantly among endodontists. Instrument design factors also influenced defect rate, but to a lesser extent. The mean number of uses of instruments with and without defects was 3.3 +/- 1.8 (range: 1-10), and 4.5 +/- 2.0 (range: 1-16), respectively. The most important influence on defect rates was the operator, which may be related to clinical skill or a conscious decision to use instruments a specified number of times or until defects were evident.

A study on the influence of Ni–Ti M-Wire in the flexural fatigue life of endodontic rotary files by using Finite Element Analysis

“…When the applied torque exceeds the elastic limit of the metal, fracture is inevitable [8]. Some motors already bring safety mechanisms that will prevent fracture by torsion, with automatic stop-reverse functions in the case of twist lock.…”

Correlation between cyclic fatigue and the bending properties of nickel titanium endodontic instruments

“…However, cyclic fatigue failures of NiTi files are known to occur unexpectedly and without any sign of previous permanent deformation [1][2][3][4] . Conversely, instrument distortion in stainless steel files serves as a warning of impending separation [5][6][7] . There are two mechanisms that govern the separation of NiTi instruments, namely that of cyclic fatigue and torsional failure 8,9) .…”

Obturation Over an S1 ProTaper Instrument Fragment in a Mandibular Molar with Three Years of Follow-up

“…The continuous cycle of tensile, shear and compressive forces, as well as torsional load transferred onto the file during instrumentation, can fracture the brittle and ductile NiTi files (4)(5)(6)(7). Thus, adequate straight-line access and preparation of a glide path with passive use of NiTi rotary files into the canal are essential steps to prevent the occurrence of fracture (4,8).…”

“…Thus, adequate straight-line access and preparation of a glide path with passive use of NiTi rotary files into the canal are essential steps to prevent the occurrence of fracture (4,8). Furthermore, monitoring of reused files is important to identify signals of fatigue (3)(4)(5). If the operator fails to observe these factors, the chance of NiTi file fracture during clinical use increases (4).…”