The effect of autoclave sterilization on Cyclic fatigue resistance & Cutting efficiency of two Ni-Ti systems (an In-Vitro study)

Abstract

R oot canal cleaning and shaping are important phases in endodontic therapy. The objectives of instrumentation include; debriding the root canal system, continuously tapering in a conical form and maintain the original shape and position of the apical foramen. However, in curved root canals, ledge formation, transportation of apical foramen and non-tapered hourglass shaped preparation are problems frequently observed after instrumentation. Properties of different instruments are affected by several factors, one of them is the repetitive autoclaving and sterilization of them which may affect their cutting efficiency, cyclic fatigue resistance and their surface roughness and dentinal debris accumulation on them. Cutting efficiency is one of the basic properties of endodontic instruments ‎which defined as the ability to remove dentine from root system. Several ‎parameters such as angle incidence between instrument and root. cross-‎sectional design, rake and helical angles, hardness of the alloy, heat treatments ‎and instrument motion influence the cutting efficiency of endodontic ‎instruments.‎ The ADA/ANSI Specification have both recommended minimum standards for instrument size, taper, tip angle, total length, and various mechanical properties. But there are no agreed guidelines for instrument cutting efficiency nor its assessment. The use of nickel-titanium (NiTi) rotary instruments for root canal system preparation has increased due to their undeniably favourable qualities; however, unexpected fracture is an important disadvantage of these instruments. Controversy remains regarding the contribution of torsional fracture, fatigue fracture and the combination of both to the separation of NiTi rotary instruments. Some have implicated fatigue fracture to be a main reason for the separation of endodontic files in the clinical setting. Fatigue fracture occurs due to repeated compressive and tensile stresses accumulated at the point of maximum flexure of an instrument rotating in a curved canal without the instrument being bind to the root canal.