Basic Study for Preventing Endodontic Instrument from fatigue breadking

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In endodontic treatment, it is a serious problem that accidentally breaking often results from metal fatigue of the endodontic instrument. The purpose of this study was to investigate the preventing endodontic instrument from accidentally braking.The fatigue breaking test machine was made and determined breaking torque, breaking angular deflection of three stainless steel reamers and a nickel-titanium file in conformity with the ISO standars (3630-1 : 1992). Fractographic observation was used the scanning electron microscope and the composition was analyzed with the electron probe X-ray microanalyzer.The results of the study are as follows :1. Fatigue breaking test machine worked fully for ISO standards. This machine had the aluminum chuck did not make the fracture and the transformation of endodontic instrument.2. The composition of nickel-titanium file was 49.7 atom.% nickel and 50.3atom.% titanium. The nickel-titanium file had lower hardness, bending torque and breaking torque than the stainless steel reamers.These results were reported to the dental society of iwate medical university in 1994 and the japan endodontic association, the international asscoiation for dental research and the japanese society of conservative dentistry in 1995.We would go on studying for the mechanism of fatigue breaking and preventing endodontic instrument from accidentally breaking.