Abstract
The use of motorized nickel titanium instruments is an essential component in contemporaneous clinical endodontics. The mechanical properties of nickel titanium are optimal for the cleaning and shaping of root canal systems. However, instrumentation carries risks, particularly instrument fracture, which may become an obstacle to achieving adequate disinfection of the canal system. Although the biomechanics of instrument fracture have been extensively investigated previously, certain facets remain unexplored, specifically torsional fatigue. This review presents a comprehensive overview of the modern understanding of the biomechanics involved in nickel titanium instrument fracture. Importantly, while research has tended to describe fatigue fracture and torsional failure as distinct and separate entities, clinical conditions are likely a combination of the two. Moreover, intracanal instrument fractures may also occur following a different mechanism, torsional fatigue. This should be taken into consideration for further research and clinical guidance.