Endodontic instrument fracture: causes and prevention.

Endodontic file fracture has traditionally been considered an uncommon event; however, a recent perception of increased fracture incidence with rotary nickel-titanium (NiTi) instruments has emerged. It is essential for the clinician to understand the likelihood of instrument fracture and the reasons for this unfortunate occurrence. Removal of fractured files is both technically difficult and time consuming and therefore it is of key importance to limit the probability of fracture. Over the last ten years, a range of NiTi alloy modifications have been made by instrument manufacturers, with varying reports of success, in an attempt to reduce the likelihood of file separation. The aim of this review was to investigate the incidence and aetiology of file fracture as well as analysing recommended prevention protocols. Additionally, the effectiveness of alloy modifications in reducing the incidence of file fracture was considered. Analysis demonstrated that the bulk of the literature relating to instrument fracture is in vitro evidence, which limits its clinical relevance. The reported incidence of NiTi instrument fracture is similar to stainless-steel (SS) files; however, inconsistent methodologies hamper accurate comparison. NiTi instruments are reported to fail by torsional overload and/or flexural fatigue, with file fracture occurring principally in the apical third of the canal or with inappropriate use. Finally, operator skill, manufacturer modifications and limiting file reuse have been demonstrated to be significant in reducing fracture incidence indicating the importance of a prevention strategy.