Movement kinematics and cyclic fatigue of NiTi rotary instruments: a systematic review

Abstract

The aim of this review was to provide a detailed analysis of the literature concerning the correlation between different movement kinematics and the cyclic fatigue resistance of NiTi rotary endodontic instruments. From June 2014 to August 2015, four independent reviewers comprehensively and systematically searched the Medline (PubMed), EMBASE, Web of Science, Scopus and Google Scholar databases for works published since January 2005, using the following search terms: endodontics; nickel-titanium rotary files; continuous rotation; reciprocating motion; cyclic fatigue. In addition to the electronic searches, manual searches were performed to include articles listed in the reference sections of high-impact published articles that were not indexed in the databases. Laboratory studies in English language were considered for this review. The electronic and manual searches resulted in identification of 75 articles. Based on the inclusion criteria, 32 articles were selected for analysis of full-text copies. Specific analysis was then made of 20 articles that described the effects of reciprocating and continuous movements on cyclic fatigue of the instruments. A wide range of testing conditions and methodologies have been used to compare the cyclic fatigue resistance of rotary endodontic instruments. Most studies report that reciprocating motion improves the fatigue resistance of endodontic instruments, compared to continuous rotation, independent of other variables such as the speed of rotation, the angle or radius of curvature of simulated canals, geometry and taper, or the surface characteristics of the NiTi instruments.

NiTi loss on the dentinal walls and instrument deformation during root canal preparation

“…Although the results showed no statistical difference regarding Ni and Ti loss, which confirmed the null hypothesis, an extended lifespan was recorded for instruments used in reciprocating motion (Ferreira et al, 2017;Karataş, Arslan, B€ uker, Seçkin, & Çapar, 2016). The Conversely, corrosion of the instruments may also have been generated by the presence of NaOCl in the root canal and contact of the instruments with the dentin walls.…”

“…Although the results showed no statistical difference regarding Ni and Ti loss, which confirmed the null hypothesis, an extended lifespan was recorded for instruments used in reciprocating motion (Ferreira et al, ; Karataş, Arslan, Büker, Seçkin, & Çapar, ). The increased fatigue resistance and the reduction of torsional stress of NiTi instruments have been postulated to be due to the release of reaction stresses built up in the material by reversing the rotational direction (De‐Deus, Moreira, Lopes, & Elias, ; Ferreira et al, ; Karatas et al, 2016; Yared, ). A recent systematic review confirmed this finding.…”

“…A recent systematic review confirmed this finding. Ferreira et al () evaluated 20 papers that described the effects of reciprocating and continuous movements on cyclic fatigue of the instruments. The authors found that the majority of the studies reported that reciprocating motion improves the fatigue resistance of endodontic instruments when compared to continuous rotation, independent of other variables such as the angle or radius of curvature of simulated canals, the surface characteristics of the NiTi instruments, the speed of rotation, or geometry and taper of the instruments.…”

“…increased fatigue resistance and the reduction of torsional stress of NiTi instruments have been postulated to be due to the release of reaction stresses built up in the material by reversing the rotational direction (De-Deus,Moreira, Lopes, & Elias, 2010;Ferreira et al, 2017; Karatas et al, 2016;Yared, 2008). A recent systematic review confirmed this finding Ferreira et al (2017).…”

A critical appraisal of studies on cyclic fatigue resistance of engine‐driven endodontic instruments

“…The prevalence of NiTi instrument fracture has been described as to 0.4%–5% of root canal treatments (McGuigan et al ) or 5% of instruments used (Parashos et al , Zinelis ). The proposed reasons for such fractures amongst others include operator experience (Mandel et al , Yared et al ), rotational speed (Zelada et al , Martín et al ), number of uses (Parashos et al ), number of rotations (Ferreira et al ), pre‐flaring (Roland et al ), glide path (Patiño et al ), angle and radius of a curvature (Li et al , Zelada et al ), and sterilization of the instruments (Hilfer et al, ). In some studies, up to 93% of instrument fractures have been classified as result of flexural fatigue (Cheung et al , Peng et al ).…”