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

Abstract

The effects of cyclic fatigue on bending properties of NiTi endodontic instruments were investigated. Sixteen Profiles ® were divided into two groups (A, and B). The sequence of cantilever bending test and cyclic fatigue test was alternated repeatedly until file separation occurred. In the cyclic fatigue test, the instrument curvature was 19° in group A and 38° in group B. Fractographic examination was performed to determine fracture patterns. In group A, there were significant differences between the bending load values measured before the cyclic fatigue test and the last cantilever bending test before instrument fracture at each deflection (p<0.05). Fractographic examination showed the specific patterns of cyclic fatigue fracture. The stress required to induce martensitic transformation might be reduced due to the softening behavior caused by the cyclic fatigue under the relaxation condition of the superelasticity range (group A). The SEM images were able to display specific patterns indicating cyclic fatigue fracture.

Effect of sodium hypochlorite and saline on cyclic fatigue resistance of WaveOne Gold and Reciproc reciprocating instruments

“…A dimpled rupture inside the overload zones is the distinctive feature of a ductile fracture. The crack originated at the cutting edge in all instruments (Shen et al 2011, Piao et al 2014. Multiple fatigue crack initiation locations were found in Reciproc fractured fragments (Fig.…”

“…, Piao et al . ). Multiple fatigue crack initiation locations were found in Reciproc fractured fragments (Fig.…”

Cyclic fatigue resistance of OneShape and WaveOne instruments using different angles of curvature

“…The occurrence of dimpled rupture inside the overload zones was characteristic of ductile fracture. The crack origins typically started at the cutting edge in both instruments 2,35,43) . Multiple fatiguecrack initiation sites were found in OS fractured segments (Fig.…”

“…On the other hand, they are prone to unpredictable fractures due to cyclic fatigue, a result of the alternating tension-compression cycles which they are subject to when rotated near the apical third of root canals with a severe curvature [1][2][3][4][5] . Different manufacturing strategies have been employed to enhance the flexibility and fatigue fracture resistance of NiTi rotary endodontic instruments.…”

“…Rotary nickel-titanium (NiTi) endodontic instruments have become popular due to their increased flexibility, better cutting ability, and higher success rates in root canal preparation [1][2][3] . On the other hand, they are prone to unpredictable fractures due to cyclic fatigue, a result of the alternating tension-compression cycles which they are subject to when rotated near the apical third of root canals with a severe curvature [1][2][3][4][5] .…”