Abstract
NiTi instruments have a high risk of separation due to torsional or flexural fatigue (cyclic fatigue). Chemomechanical preparation, cleaning procedures, chemical disinfection and sterilization cause the corrosion of endodontic instruments that may weaken the fracture resistance of the instruments. ObjectiveTo assess the effects of NaOCl immersion and autoclave sterilization on the cyclic fatigue resistance of ProFile, FlexMaster, Mtwo and TwistedFiles NiTi instruments (tip size 25, 0.06 taper, n=160).Material and MethodsThe instruments (n=10 for each subgroup) were dynamically immersed in NaOCl; immersed in NaOCl and sterilized in one autoclave cycle; 5 cycles immersed in NaOCl and sterilized in autoclave and not immersed in NaOCl and not sterilized (control group). Dynamic cyclic fatigue resistance was tested. The number of cycles to failure (NCF) were statistically analyzed (P<0.05).ResultsKruskall-Wallis test indicated significant differences among the tested instruments in terms of NCF (P=0.000). The mean NCF of Mtwo (556.75) was higher than that of the Twisted File, Flexmaster and ProFile, 483.1, 376.12, 365.25, respectively. NaOCl immersion and autoclave sterilization have no effect on the NCF values of the tested instruments (P>.05).ConclusionsCyclic fatigue resistance of the tested NiTi instruments cannot be adversely affected by NaOCl immersion and autoclave sterilization. Production process (TwistedFiles) or design (Twisted Files, FlexMaster, Mtwo and ProFile) of the instruments can influence their cyclic fatigue resistance.
Highlights
Nickel-titanium (NiTi) instruments are very popular and provide many advantages during root FDQDO WUHDWPHQW +RZHYHU 1L7L LQVWUXPHQWV KDYH D KLJK ULVN RI VHSDUDWLRQ GXH WR WRUVLRQDO RU ÀH[XUDO fatigue23
Condition31 :KHQ WKH WLS RU VRPH SDUW RI WKH ¿OH binds in the root canal during rotation, torsional failure occurs23
Chemomechanical preparation, cleaning procedures, chemical disinfection, and sterilization cause the corrosion of endodontic instruments17
Summary
Nickel-titanium (NiTi) instruments are very popular and provide many advantages during root FDQDO WUHDWPHQW +RZHYHU 1L7L LQVWUXPHQWV KDYH D KLJK ULVN RI VHSDUDWLRQ GXH WR WRUVLRQDO RU ÀH[XUDO fatigue (cyclic fatigue). Fractures due to cyclic fatigue occur because of metal fatigue and are more prevalent in curved root canals. The instrument URWDWHV IUHHO\ DW WKH FXUYDWXUH ZLWKRXW ELQGLQJ so that the tensile and compressive stresses are FRQFHQWUDWHG DW WKH SRLQW RI PD[LPXP ÀH[XUH Resistance to fracture prior to an actual fracture LV GHWHUPLQHG E\ WKH QXPEHU RI F\FOHV LQ ZKLFK DQ LQVWUXPHQW RSHUDWHV XQGHU D VSHFL¿F ORDGLQJ condition31 :KHQ WKH WLS RU VRPH SDUW RI WKH ¿OH binds in the root canal during rotation, torsional failure occurs. Chemomechanical preparation, cleaning procedures, chemical disinfection, and sterilization cause the corrosion of endodontic instruments. NaOCl selectively removes nickel from the instrument surface and causes micropitting. NaOCl selectively removes nickel from the instrument surface and causes micropitting22 These are the DUHDV ZKHUH VWUHVV JHWV FRQFHQWUDWHG IRUPLQJ cracks and increasing the probability of fatigue
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