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Effect of fatigue on torsional failure of nickel-titanium controlled memory instruments Campbell, Les 2013

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	 ?	 ?EFFECT	 ?OF	 ?FATIGUE	 ?ON	 ?TORSIONAL	 ?FAILURE	 ?OF	 ?NICKEL-?TITANIUM	 ?CONTROLLED	 ?MEMORY	 ?INTRUMENTS	 ?	 ?by	 ?Les	 ?Campbell	 ?	 ?DDS,	 ?University	 ?of	 ?Alberta	 ?1991	 ?	 ?A	 ?THESIS	 ?SUBMITTED	 ?IN	 ?PARTIAL	 ?FULFILLMENT	 ?OF	 ?	 ?THE	 ?REQUIREMENTS	 ?FOR	 ?THE	 ?DEGREE	 ?OF	 ?	 ?	 ?	 ?MASTER	 ?OF	 ?SCIENCE	 ?	 ?in	 ?	 ?THE	 ?FACULTY	 ?OF	 ?GRADUATE	 ?AND	 ?POSTDOCTORAL	 ?STUDIES	 ?	 ?(Craniofacial	 ?Science)	 ?	 ?	 ?THE	 ?UNIVERSITY	 ?OF	 ?BRITISH	 ?COLUMBIA	 ?	 ?(Vancouver)	 ?	 ?	 ?August	 ?2013	 ?	 ?	 ??	 ?Les	 ?Campbell,	 ?2013	 ?	 ?	 ? ii	 ?	 ?Abstract	 ?	 ?Introduction:	 ? This	 ? study	 ? was	 ? undertaken	 ? to	 ? understand	 ? how	 ? fatigue	 ? affects	 ? the	 ?torsional	 ? properties	 ? of	 ? both	 ? traditional	 ? nickel-??titanium	 ? (NiTi)	 ? and	 ? nickel-??titanium	 ?controlled	 ? memory	 ? (CM)	 ? files.	 ?Methods:	 ? Typhoon	 ? (TYP)	 ? 25.04	 ? and	 ? 40.04	 ? rotary	 ?files,	 ? in	 ? both	 ? NiTi	 ? and	 ? CM,	 ? were	 ? tested	 ? using	 ? a	 ? three-??point	 ? bending	 ? apparatus	 ? to	 ?obtain	 ? the	 ?mean	 ?number	 ?of	 ? cycles	 ? to	 ? failure	 ? (mNCF).	 ?New	 ? files	 ?were	 ?precycled	 ? to	 ?four	 ? conditions	 ? (i.e.,	 ? 0%,	 ? 25%,	 ? 50%,	 ? and	 ? 75%	 ? of	 ? the	 ? mNCF)	 ? before	 ? torsional	 ?resistance	 ? tests	 ? were	 ? performed.	 ? Each	 ? file	 ? was	 ? exposed	 ? to	 ? torsional	 ? stress	 ? until	 ?failure,	 ? and	 ? at	 ? that	 ? point	 ? the	 ? torque	 ? and	 ? distortion	 ? angles	 ? were	 ? measured.	 ? The	 ?fracture	 ? surface	 ? of	 ? each	 ? fragment	 ? was	 ? examined	 ? with	 ? a	 ? scanning	 ? electron	 ?microscope.	 ?Results:	 ?The	 ?TYP	 ?CM	 ?files	 ?yielded	 ?a	 ?seven-??fold	 ?improvement	 ?in	 ?mNCF	 ?over	 ?the	 ?TYP	 ?NiTi	 ?files	 ?(P	 ??	 ?0.05).	 ?In	 ?both	 ?file	 ?sizes	 ?there	 ?was	 ?no	 ?difference	 ?in	 ?torque	 ?between	 ?the	 ?CM	 ?files	 ?and	 ?the	 ?conventional	 ?Ni-??Ti	 ? files	 ?(P	 ?>	 ?0.05).	 ?The	 ?torque	 ?of	 ?the	 ?size	 ?40.04	 ?files	 ?was	 ?significantly	 ?higher	 ?than	 ?the	 ?torque	 ?of	 ?the	 ?size	 ?25/.04	 ?files	 ?(P	 ??	 ?0.05).	 ? In	 ? the	 ? 40.04	 ? TYP	 ? files	 ? group,	 ? the	 ? 75%	 ? precycling	 ? group	 ? had	 ? a	 ? significantly	 ?lower	 ?torque	 ?to	 ?failure	 ?than	 ?the	 ?no	 ?precycling	 ?group	 ?(P	 ??	 ?0.05).	 ?The	 ?CM	 ?files	 ?of	 ?both	 ?sizes	 ?had	 ?significantly	 ?higher	 ?distortion	 ?angles	 ?than	 ?the	 ?Ni-??Ti	 ?files	 ?of	 ?both	 ?sizes	 ?(P	 ??	 ?0.05).	 ?	 ?The	 ?40.04	 ?TYP	 ?CM	 ?files	 ?that	 ?were	 ?not	 ?precycled	 ?showed	 ?a	 ?significantly	 ?higher	 ?distortion	 ? angle	 ? than	 ? the	 ? precycled	 ? groups.	 ? 	 ? The	 ? fractured	 ? files	 ? in	 ? the	 ? precycling	 ?groups	 ?showed	 ? the	 ? typical	 ?pattern	 ?of	 ? torsional	 ? failure.	 ?Conclusions:	 ?Cyclic	 ? fatigue	 ?has	 ?an	 ?effect	 ?on	 ?torsional	 ?fracture	 ?resistance	 ?of	 ?TYP	 ?and	 ?TYP	 ?CM	 ?files	 ?on	 ?size	 ?40.04.	 ?	 ?	 ? iii	 ?TYP	 ?CM	 ?files	 ?displayed	 ?a	 ?similar	 ?torque	 ?value	 ?to	 ?TYP	 ?files	 ?but	 ?rotated	 ?a	 ?greater	 ?angle	 ?before	 ?fracture	 ?in	 ?both	 ?preloading	 ?and	 ?no	 ?preloading	 ?groups.	 ?	 ?	 ?	 ? iv	 ?	 ?Preface	 ?	 ?	 ? This	 ?thesis	 ?is	 ?an	 ?original,	 ?unpublished,	 ?and	 ?independent	 ?work	 ?by	 ?the	 ?author,	 ?L.	 ?Campbell.	 ? 	 ? None	 ? of	 ? the	 ? text	 ? of	 ? the	 ? dissertation	 ? is	 ? taken	 ? directly	 ? from	 ? previously	 ?published	 ?or	 ?collaborative	 ?articles.	 ?	 ? The	 ?author	 ?was	 ?responsible	 ?for	 ?all	 ?parts	 ?of	 ?the	 ?research,	 ?including	 ?the	 ?fatigue	 ?testing,	 ? the	 ?torque	 ?testing	 ?and	 ?the	 ?data	 ?gathered	 ?from	 ?such	 ?tests.	 ? 	 ?Dr.	 ?Ya	 ?Shen	 ?and	 ?Dr.	 ? Markus	 ? Haapasalo	 ? provided	 ? the	 ? three-??point	 ? bending	 ? apparatus	 ? used	 ? for	 ? the	 ?cyclic	 ? fatigue	 ? testing	 ? portion	 ? of	 ? this	 ? experimentation.	 ? Both	 ? Dr.	 ? Haapasalo	 ? and	 ? Dr.	 ?Shen	 ?provided	 ?invaluable	 ?guidance	 ?throughout	 ?the	 ?process.	 ?	 ?The	 ?torsion	 ?tests	 ?were	 ?conducted	 ?by	 ?myself	 ?at	 ?the	 ?calibration	 ?department	 ?of	 ?D&S	 ?Dental	 ?in	 ?Tennessee.	 ?	 ?	 ?	 ?	 ?	 ?	 ? Dr.	 ?Ya	 ?Shen	 ?and	 ?Zhejun Wang performed	 ?statistical	 ?analysis	 ?of	 ?the	 ?research.	 ?Dr.	 ?Markus	 ? Haapasalo	 ? made	 ? significant	 ? contributions	 ? to	 ? the	 ? manuscript	 ? and	 ? was	 ? a	 ?reviewer	 ? of	 ? the	 ? final	 ? draft.	 ?Overall,	 ? Dr.	 ? Shen	 ? and	 ?Dr.	 ?Haapasalo	 ? each	 ?made	 ? a	 ? 20%	 ?contribution	 ?to	 ?the	 ?work.	 ?	 ? 	 ?	 ?	 ?	 ? 	 ?	 ?	 ?	 ?	 ?	 ?	 ? v	 ?	 ?Table	 ?of	 ?Contents	 ?	 ?Abstract......................................................................................................................................................... ii	 ?Preface.......................................................................................................................................................... iv	 ?Table	 ?of	 ?Contents .................................................................................................................................... v	 ?List	 ?of	 ?Tables ............................................................................................................................................vii	 ?List	 ?of	 ?Figures ........................................................................................................................................ viii	 ?List	 ?of	 ?Abbreviations ............................................................................................................................. x	 ?Acknowledgements............................................................................................................................... xi	 ?Dedication ............................................................................................................................................... xiii	 ?Chapter	 ?1.	 ?Introduction ....................................................................................................................... 1	 ?Chapter	 ?2.	 ?Review	 ?of	 ?the	 ?Literature ............................................................................................. 6	 ?2.1.	 ?Properties	 ?of	 ?Nickel-??Titanium................................................................................................................ 6	 ?2.2.	 ?Instrument	 ?Fracture ................................................................................................................................ 13	 ?2.2.1.	 ?Cyclic	 ?Fatigue	 ?Failure ..................................................................................................................... 15	 ?2.2.2.	 ?Torsional	 ?Failure.............................................................................................................................. 30	 ?2.3.	 ?Fractographic	 ?Examination .................................................................................................................. 32	 ?2.4.	 ?Overview	 ?of	 ?Thermo-??mechanical	 ?Modified	 ?Wire........................................................................ 34	 ?2.5.	 ?Aim .................................................................................................................................................................. 35	 ?Chapter	 ?3.	 ?Hypothesis ....................................................................................................................... 36	 ?Chapter	 ?4.	 ?Material	 ?and	 ?Methods................................................................................................ 37	 ?	 ?	 ? vi	 ?4.1.	 ?Specimen	 ?Section ...................................................................................................................................... 37	 ?4.2.	 ?Method	 ?to	 ?Cyclically	 ?Fatigue	 ?Files ..................................................................................................... 37	 ?4.3.	 ?Method	 ?to	 ?determine	 ?angle	 ?of	 ?deflection	 ?and	 ?radius ................................................................ 41	 ?4.4.	 ?Torsion	 ?Testing.......................................................................................................................................... 43	 ?4.5.	 ?Fractographic	 ?Examination .................................................................................................................. 44	 ?4.6.	 ?Statistical	 ?Analysis.................................................................................................................................... 45	 ?Chapter	 ?5.	 ?	 ?Results ............................................................................................................................... 46	 ?Chapter	 ?6.	 ?Discussion ........................................................................................................................ 56	 ?Chapter	 ?7.	 ?Conclusions...................................................................................................................... 61	 ?References................................................................................................................................................ 63	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 	 ? 	 ? 	 ?	 ?	 ?	 ?	 ?	 ? vii	 ?	 ?List	 ?of	 ?Tables	 ?	 ?Table	 ?5.1	 ?	 ?The	 ?number	 ?of	 ?revolutions	 ?until	 ?fracture	 ?of	 ?Typhoon	 ?NiTi	 ?and	 ?CM	 ?files	 ?at	 ?a	 ?46?	 ?curvature	 ?with	 ?a	 ?9.5mm	 ?radius	 ?in	 ?water	 ?conditions????..????47	 ?	 ?Table	 ?5.2	 ?(a)	 ?	 ?Resistance	 ?to	 ?torque	 ?of	 ?Typhoon	 ?NiTi	 ?and	 ?CM	 ?files	 ?after	 ?cyclic	 ?precycling	 ?of	 ?the	 ?mNCF???????.....??????????.???.?????48	 ?	 ?Table	 ?5.2	 ?(b)	 ?	 ?Resistance	 ?to	 ?torque	 ?of	 ?	 ?40.04	 ?Typhoon	 ?NiTi	 ?and	 ?CM	 ?files	 ?after	 ?cyclic	 ?precycling	 ?of	 ?the	 ?mNCF??????????......???????????????.49	 ?	 ?Table	 ?5.3	 ?Mean	 ?cyclic	 ?fatigue	 ?life???????...?????.?????..????????.....50	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? viii	 ?	 ?List	 ?of	 ?Figures	 ?	 ?Figure	 ?2.1.	 ?Cuboidal	 ?nature	 ?of	 ?the	 ?austenite	 ?phase..................................................................... 7	 ?Figure	 ?2.2.	 ?Example	 ?of	 ?crystal	 ?structure	 ?of	 ?the	 ?deformed,	 ?detwinned	 ?martensite	 ?phase. .................................................................................................................................................... 8	 ?Figure	 ?2.3.	 ?Differential	 ?scanning	 ?calorimetry	 ?for	 ?TYP	 ?and	 ?TYP-??CM	 ?rotary	 ?endodontic	 ?files. ..................................................................................................................................................... 12	 ?Figure	 ?2.4.	 ?Diagrammatic	 ?representation	 ?of	 ?typical	 ?failure	 ?zones	 ?found	 ?in	 ?cyclical	 ?fatigue	 ?failure.................................................................................................................................. 17	 ?Figure	 ?2.5.	 ?Demonstration	 ?of	 ?the	 ?angle	 ?of	 ?root	 ?curvature	 ?and	 ?the	 ?radius	 ?of	 ?root	 ?curvature. ......................................................................................................................................... 19	 ?Figure	 ?2.6.	 ?Example	 ?of	 ?curved	 ?tube	 ?method	 ?of	 ?testing	 ?cyclical	 ?fatigue. .......................... 20	 ?Figure	 ?2.7.	 ?Example	 ?of	 ?grooved	 ?block	 ?and	 ?rod........................................................................... 22	 ?Figure	 ?2.8.	 ?Example	 ?of	 ?the	 ??V?	 ?cut	 ?into	 ?the	 ?block	 ?to	 ?limit	 ?random	 ?movement	 ?of	 ?the	 ?file	 ?as	 ?it	 ?rotates............................................................................................................................... 23	 ?Figure	 ?2.9.	 ?Example	 ?of	 ?inclined	 ?plane	 ?method	 ?of	 ?testing	 ?cyclical	 ?fatigue....................... 25	 ?Figure	 ?2.10.	 ?Example	 ?of	 ?the	 ?trajectory	 ?of	 ?a	 ?file	 ?while	 ?engaging	 ?an	 ?inclined	 ?plane. .... 26	 ?Figure	 ?2.11.	 ?Example	 ?of	 ?3-??point	 ?bending	 ?apparatus. .............................................................. 29	 ?Figure	 ?2.12.	 ?Typical	 ?examples	 ?fractographic	 ?images	 ?from	 ?fractured	 ?files.	 ?Torsional	 ?failure	 ?and	 ?cyclical	 ?fatigue	 ?failure.......................................................................................... 33	 ?Figure	 ?4.1.	 ?Demonstration	 ?of	 ?a	 ?three-??point	 ?bending	 ?apparatus......................................... 38	 ?Figure	 ?4.2.	 ?Demonstration	 ?of	 ?a	 ?CM	 ?file	 ?in	 ?the	 ?three-??point	 ?bending	 ?apparatus. ........... 39	 ?Figure	 ?4.3.	 ?CM	 ?file	 ?being	 ?exposed	 ?to	 ?cyclic	 ?fatigue	 ?in	 ?a	 ?water	 ?environment. ................ 40	 ?	 ?	 ? ix	 ?Figure	 ?4.4.	 ?	 ?Drawing	 ?the	 ?arc	 ?prior	 ?to	 ?measurement. ............................................................... 41	 ?Figure	 ?4.5.	 ?Calculation	 ?of	 ?radius	 ?and	 ?curvature	 ?angle. ........................................................... 42	 ?Figure	 ?4.6.	 ?Removal	 ?of	 ?a	 ?file	 ?handle	 ?prior	 ?to	 ?a	 ?torsion	 ?test. ................................................. 43	 ?Figure	 ?5.1.	 ?	 ?A	 ?photomicrograph	 ?of	 ?a	 ?fracture	 ?surface ............................................................. 52	 ?Figure	 ?5.2.	 ?Demonstration	 ?of	 ?conventional	 ?NiTi	 ?before	 ?and	 ?after	 ?outlining	 ?of	 ?dimpled	 ?area...................................................................................................................................................... 53	 ?Figure	 ?5.3.	 ?	 ?40.04	 ?NiTi	 ?dimpled	 ?area	 ?demonstration .............................................................. 54	 ?Figure	 ?5.4.	 ?Demonstration	 ?of	 ?40.04	 ?CM	 ?dimpled	 ?area............................................................ 55	 ?	 ?	 ?	 ?	 ? x	 ?	 ?List	 ?of	 ?Abbreviations	 ?	 ?	 ?Af-??	 ?Austenite	 ?finish	 ?temperature	 ?As-??	 ?Austenite	 ?start	 ?temperature	 ?CM-??	 ?Controlled	 ?Memory	 ?Wire	 ?ISO-??	 ?International	 ?Organization	 ?for	 ?Standardization	 ?Mf-??	 ?Martensite	 ?finish	 ?temperature	 ?mNCF-??	 ?Mean	 ?number	 ?of	 ?cycles	 ?to	 ?failure	 ?Ms-??	 ?Martensite	 ?start	 ?temperature	 ?NiTi-??	 ?Nickel-??titanium	 ?SE-??	 ?Super-??elasticity	 ?TYP-??	 ?Typhoon	 ?rotary	 ?endodontic	 ?files	 ?TYP	 ?CM-??	 ?Typhoon	 ?controlled-??memory	 ?rotary	 ?endodontic	 ?files	 ?	 ?	 ?	 ? xi	 ?	 ?Acknowledgements	 ?	 ?	 ? I	 ?would	 ?like	 ?to	 ?express	 ?that	 ?without	 ?Dr.	 ?Ya	 ?Shen,	 ?this	 ?project	 ?could	 ?not	 ?have	 ?been	 ?completed.	 ? 	 ?To	 ?her	 ?I	 ?have	 ?the	 ?deepest	 ?appreciation,	 ?and	 ?I	 ?have	 ?often	 ?thought	 ?that	 ?her	 ?words	 ?were	 ?few	 ?yet	 ?her	 ?influence	 ?was	 ?tremendous.	 ?	 ?It	 ?would	 ?be	 ?difficult	 ?to	 ?overstate	 ?her	 ?impact	 ?on	 ?the	 ?endodontic	 ?program	 ?and	 ?its	 ?students.	 ?	 ?I	 ?would	 ?also	 ?like	 ?to	 ?express	 ?my	 ?deepest	 ?appreciation	 ?for	 ?Dr.	 ?Markus	 ?Haapasalo,	 ?who	 ?with	 ?his	 ?support	 ?and	 ?guidance	 ?has	 ?broadened	 ?my	 ?understanding	 ?of	 ?endodontics.	 ?	 ?I	 ?feel	 ?very	 ?fortunate	 ?to	 ?have	 ?Drs.	 ?Shen	 ?and	 ?Haapasalo	 ?at	 ?UBC	 ?during	 ?my	 ?residency,	 ?and	 ?for	 ?involving	 ?me	 ?in	 ?research	 ?activities	 ?since	 ?my	 ?first	 ?year	 ?in	 ?the	 ?program.	 ? I would like to thank Dr. Jeff Coil for not only his work on my committee, but also as a mentor and program director.  Clinically your guidance was very significant, and I learned much from your patience and your clear direction in patient treatment. Your questions in the classroom caused me much to ponder over, and thus a better understanding of this wonderful discipline.  Contributions in the clinic by Luciana Nakayama, Francisco Briseno, Lois Bermudez and Shauna Catalano improved patient care and brightened each day.   I would also like to thank Dr. Jolanta Aleksejuniene for being on my committee and the input she had into making this successful.    My appreciation goes out to Zhejun Wang and Dr. Ya Shen for their insight and contribution to the statistics in this study.    My gratitude is given to my friends and peers in the SJC community, Anna 	 ?	 ? xii	 ?Belogurova, Ilksen Icen and his sense of humor, Amber Perreca, Stefan Honisch and Dawood Al-Masslawi, who each helped me to complete this work in ways they are not aware of.  My appreciation is given to Anna who changed and shaped my thoughts in many ways and was a role model for hard work.     This research was generously supported by the donation of materials by Clinician?s Choice Dental.  Contributions made by the Canadian Academy of Endodontics, the American Association of Endodontics and the S. Wah Leung endowment were greatly appreciated and facilitated the completion of this research. 	 ?	 ? xiii	 ? Dedication	 ?	 ?	 ?To	 ?my	 ?family	 ?that	 ?supported	 ?me	 ?on	 ?this	 ?adventure	 ???	 ?	 ? 1	 ?	 ?Chapter	 ?1.	 ?Introduction	 ?	 ?To	 ? prepare	 ? endodontic	 ? canals	 ? for	 ? irrigation	 ? delivery	 ? and	 ? eventually	 ?obturation,	 ?they	 ?must	 ?be	 ?properly	 ?cleaned	 ?and	 ?shaped.	 ?	 ?While	 ?cleaning	 ?refers	 ?to	 ?the	 ?removal	 ? of	 ? all	 ? organic	 ? debris,	 ? shaping	 ? implies	 ? the	 ? creation	 ? of	 ? a	 ? unique	 ? shape	 ? for	 ?every	 ?root	 ?canal,	 ?directly	 ?related	 ?not	 ?only	 ?to	 ?the	 ?length	 ?but	 ?also	 ?to	 ?the	 ?position	 ?and	 ?curvature	 ? of	 ? each	 ? individual	 ? root	 ? and	 ? root	 ? canal	 ? (Schilder,	 ? 1974;	 ? Testarelli	 ? et	 ? al.,	 ?2011).	 ? 	 ?While	 ? shaping	 ?has	 ? traditionally	 ? been	 ?done	 ?with	 ? stainless	 ? steel	 ? files,	 ? it	 ? has	 ?been	 ? recognized	 ? that	 ? stainless	 ? steel	 ? has	 ? limitations	 ? in	 ? root	 ? canal	 ? instrumentation,	 ?primarily	 ?because	 ?this	 ?material	 ?is	 ?stiff	 ?and	 ?tends	 ?to	 ?cause	 ?procedural	 ?errors	 ?such	 ?as	 ?zips	 ?and	 ?ledges	 ?in	 ?curved	 ?canals	 ?(Bishop	 ?&	 ?Dummer,	 ?1997;	 ?Kim	 ?et	 ?al.,	 ?2012).	 ?	 ?It	 ?was	 ?evident	 ? that	 ? a	 ? suitable	 ? alternative	 ? for	 ? use	 ? in	 ? endodontics	 ?was	 ? needed	 ? to	 ? stainless	 ?steel.	 ? 	 ?Walia	 ?(1988)	 ?introduced	 ?nickel-??titanium	 ?(NiTi)	 ?to	 ?endodontics,	 ?which	 ?has	 ?led	 ?to	 ? a	 ? completely	 ? new	 ? way	 ? of	 ? thinking	 ? about	 ? and	 ? performing	 ? canal	 ? preparation.	 ?	 ?Nickel-??titanium	 ? has	 ? distinct	 ? advantages;	 ? most	 ? importantly,	 ? it	 ? is	 ? far	 ? more	 ? flexible	 ?than	 ? stainless	 ? steel	 ? as	 ? it	 ? demonstrates	 ? the	 ? property	 ? of	 ? super-??elasticity	 ? (SE).	 ? 	 ? This	 ?allows	 ?files	 ?made	 ?from	 ?NiTi	 ?to	 ?flex	 ?more	 ?before	 ?exceeding	 ?the	 ?material's	 ?elastic	 ?limit	 ?than	 ?files	 ?made	 ?from	 ?stainless-??steel	 ?(Walia	 ?et	 ?al.,	 ?1988),	 ?particularly	 ?as	 ?increased	 ?file	 ?sizes	 ?are	 ?used.	 ? 	 ?More	 ?specifically,	 ?super-??elasticity	 ?allows	 ?for	 ?up	 ?to	 ?8%	 ?deformation	 ?due	 ?to	 ?strain	 ?and	 ?will	 ?still	 ?revert	 ?to	 ?its	 ?original	 ?shape,	 ?whereas	 ?for	 ?stainless-??steel	 ?the	 ?value	 ?is	 ?less	 ?than	 ?1%.	 ? 	 ?Esposito	 ?described	 ?nickel-??titanium	 ?files	 ?as	 ?more	 ?effective	 ?in	 ?	 ?	 ? 2	 ?maintaining	 ? the	 ? original	 ? canal	 ? path	 ? of	 ? curved	 ? root	 ? canals,	 ? particularly	 ? when	 ? the	 ?apical	 ? preparation	 ?was	 ? enlarged	 ? beyond	 ? size	 ? 30	 ? (Esposito	 ? &	 ? Cunningham,	 ? 1995).	 ?	 ?Furthermore,	 ? NiTi	 ? files	 ? seem	 ? to	 ? be	 ? safer	 ? because	 ? of	 ? the	 ? reduced	 ? amount	 ? of	 ?transportation	 ?towards	 ?danger	 ?areas	 ?as	 ?compared	 ?to	 ?stainless	 ?steel	 ?instruments	 ?due	 ?to	 ? their	 ? flexibility	 ? (Chan	 ?&	 ? Cheung,	 ? 1996).	 ? 	 ?Moreover,	 ? the	 ? importance	 ? of	 ?NiTi	 ? has	 ?been	 ?underlined	 ?by	 ?clinically	 ?applicable	 ?research.	 ?	 ?For	 ?example,	 ?endodontic	 ?therapy	 ?performed	 ? with	 ? nickel?titanium	 ? hand	 ? instruments	 ? led	 ? to	 ? a	 ? better	 ? prognosis	 ?(Pettiette	 ? et	 ? al.,	 ? 2001)	 ? and	 ? lower	 ? procedural	 ? errors	 ?with	 ? a	 ? higher	 ? success	 ? rate	 ? as	 ?measured	 ?one-??year	 ?after	 ?treatment	 ?(Cheung	 ?&	 ?Liu,	 ?2009)	 ?when	 ?compared	 ?to	 ?teeth	 ?treated	 ?with	 ?stainless-??steel	 ?instruments.	 ?	 ?However,	 ?nickel-??titanium	 ?and	 ?stainless	 ?steel	 ?both	 ?share	 ?the	 ?unfortunate	 ?trait	 ?of	 ? the	 ?possibility	 ?of	 ? fracture,	 ?which	 ?can	 ?be	 ?sudden	 ?and	 ?without	 ?warning.	 ? 	 ?This	 ?can	 ?occur	 ? with	 ? brand-??new	 ? instruments	 ? or	 ? in	 ? the	 ? hands	 ? of	 ? a	 ? seasoned	 ? practitioner	 ?(Pruett	 ?et	 ?al.,	 ?1997;	 ?Zuolo	 ?&	 ?Walton,	 ?1997;	 ?Arens	 ?et	 ?al.,	 ?2003).	 ?	 ?Factors	 ?contributing	 ?to	 ? instrument	 ? failure	 ? have	 ? being	 ? attributed	 ? to	 ? operator	 ? error,	 ? instrumentation	 ?techniques,	 ? instrument	 ? design,	 ? instrument	 ? size,	 ? radius	 ? of	 ? curvature,	 ? surface	 ?condition	 ?and	 ?rotation	 ?rate.	 ?(Pruett	 ?et	 ?al.,	 ?1997;	 ?Parashos	 ?et	 ?al.,	 ?2004;	 ?Cheung	 ?et	 ?al.,	 ?2005;	 ?Shen	 ?et	 ?al.,	 ?2009b;	 ?Gao	 ?et	 ?al.,	 ?2010).	 ?	 ?However,	 ?Sattapan	 ?(2000a)	 ?was	 ?the	 ?first	 ?to	 ?describe	 ?the	 ?fracture	 ?mechanisms	 ?of	 ?NiTi	 ?rotary	 ?endodontic	 ?files	 ?and	 ?by	 ?doing	 ?so	 ?he	 ?deepened	 ?our	 ?initial	 ?understanding	 ?of	 ?the	 ?types	 ?of	 ?failure	 ?these	 ?files	 ?may	 ?exhibit.	 ?	 ?Sattapan	 ? reported	 ? that	 ? file	 ? failure	 ? occurring	 ? during	 ? routine	 ? clinical	 ? use	 ? could	 ? be	 ?attributed	 ? to	 ? either	 ? torsional	 ? fracture	 ? or	 ? flexural	 ? fatigue.	 ? 	 ? He	 ? identified	 ? torsional	 ?	 ?	 ? 3	 ?fracture	 ?as	 ?the	 ?cause	 ?of	 ?slightly	 ?over	 ?half	 ?of	 ?the	 ?separated	 ?files	 ?he	 ?studied	 ?(Sattapan	 ?et	 ?al.,	 ?2000a).	 ?However,	 ?other	 ?authors	 ?have	 ?attributed	 ?the	 ?majority	 ?of	 ?file	 ?failures	 ?to	 ?cyclical	 ? fatigue	 ? (Ha?kel	 ? et	 ? al.,	 ? 1999;	 ? Shen	 ? et	 ? al.,	 ? 2006).	 ? 	 ? Torsional	 ? fracture	 ? can	 ? be	 ?described	 ? as	 ? what	 ? happens	 ? when	 ? the	 ? tip	 ? of	 ? the	 ? file	 ? binds	 ? in	 ? the	 ? canal,	 ? while	 ? the	 ?remainder	 ? of	 ? the	 ? file	 ? continues	 ? to	 ? rotate.	 ? 	 ? Fatigue	 ? failure,	 ? also	 ? known	 ? as	 ? cyclical	 ?fatigue,	 ? occurs	 ? in	 ? curved	 ? canals	 ? where	 ? one	 ? side	 ? of	 ? the	 ? instrument	 ? undergoes	 ?compression	 ?and	 ?the	 ?other	 ?side	 ?tension	 ?(Kramkowski	 ?&	 ?Bahcall,	 ?2009).	 ?	 ?For	 ?a	 ?better	 ?understanding	 ? of	 ? the	 ? fracture	 ? mechanism,	 ? several	 ? factors	 ? must	 ? be	 ? considered;	 ?however	 ?simulation	 ?of	 ?all	 ?these	 ?factors	 ?in	 ?laboratory	 ?conditions	 ?is	 ?difficult	 ?(Pruett	 ?et	 ?al.,	 ?1997;	 ?Sattapan	 ?et	 ?al.,	 ?2000a;	 ?Gao	 ?et	 ?al.,	 ?2010;	 ?Wycoff	 ?and	 ?Berzins,	 ?2012;	 ?Lopes	 ?et	 ?al.,	 ? 2013).	 ? Thus,	 ? factors	 ? contributing	 ? to	 ? file	 ? fracture	 ? are	 ? frequently	 ? considered	 ?separately.	 ?	 ?Manufacturers	 ?have	 ?attempted	 ?to	 ?improve	 ?the	 ?safety	 ?and	 ?reliability	 ?of	 ?rotary	 ?endodontic	 ? files	 ?by	 ?developing	 ?new	 ?manufacturing	 ?processes,	 ? (Larsen	 ?et	 ?al.,	 ?2009;	 ?Alapati	 ?et	 ?al.,	 ?2009a;	 ?Gambarini	 ?et	 ?al.,	 ?2011;	 ?Ye	 ?&	 ?Gao,	 ?2012)	 ?or	 ?by	 ?introducing	 ?new	 ?alloys	 ?with	 ?superior	 ?mechanical	 ?properties	 ?(Testarelli	 ?et	 ?al.,	 ?2011).	 ? 	 ?An	 ?example	 ?of	 ?this	 ? is	 ? M-??wire	 ? (Sportswire	 ? LLC,	 ? Langley,	 ? OK)	 ? which	 ? has	 ? been	 ? introduced	 ? with	 ? a	 ?proprietary	 ?thermomechanical	 ?manufacturing	 ?process	 ?(Alapati	 ?et	 ?al.,	 ?2009a).	 ?Efforts	 ?to	 ?improve	 ?the	 ?performance	 ?of	 ?files	 ?have	 ?generally	 ?focused	 ?on	 ?the	 ?metallurgical	 ?and	 ?mechanical	 ? properties	 ? of	 ? the	 ? file	 ? itself.	 ? 	 ? However,	 ? factors	 ? that	 ? the	 ? operator	 ? may	 ?introduce,	 ? such	 ? as	 ? cyclical	 ? fatigue	 ? and	 ? torsional	 ? stresses	 ? and	 ? their	 ? effects	 ? on	 ? each	 ?other,	 ?have	 ?received	 ?only	 ?limited	 ?attention	 ?in	 ?the	 ?literature	 ?(Kim	 ?et	 ?al.,	 ?2012).	 ?	 ?	 ?	 ? 4	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?Recently,	 ? a	 ?modification	 ? of	 ? nickel-??titanium	 ?wire	 ? through	 ? a	 ? propriety	 ? thermo-??mechanical	 ? treatment	 ? has	 ? been	 ? introduced	 ? to	 ? the	 ? market	 ? and	 ? is	 ? known	 ? as	 ?controlled-??memory	 ? wire	 ? (Typhoon	 ? CM;	 ? Clinician?s	 ? Choice	 ? Dental	 ? Products,	 ? New	 ?Milford,	 ? CT).	 ? The	 ? manufacturer	 ? claims	 ? that	 ? files	 ? made	 ? from	 ? CM	 ?wire	 ? have	 ? 300%	 ?greater	 ? fatigue	 ? and	 ? more	 ? than	 ? double	 ? the	 ? torsional	 ? resistance	 ? than	 ? conventional	 ?files	 ?made	 ?from	 ?nickel-??titanium	 ?(2010).	 ?Heat	 ?treatment	 ?(thermal	 ?processing)	 ?is	 ?one	 ?of	 ? the	 ?most	 ? fundamental	 ? approaches	 ? for	 ? adjusting	 ? the	 ? transition	 ? temperatures	 ? of	 ?NiTi	 ?alloys	 ?and	 ?affecting	 ?the	 ?fatigue	 ?resistance	 ?of	 ?NiTi	 ?endodontic	 ?files	 ?(Gambarini	 ?et	 ?al.,	 ?2011;	 ?Shen	 ?et	 ?al.,	 ?2011b;	 ?Gutmann	 ?and	 ?Gao,	 ?2012;	 ?Zhou	 ?et	 ?al.,	 ?2012;	 ?Lopes	 ?et	 ?al.,	 ?2013;	 ? Shen	 ? et	 ? al.,	 ? 2013b).	 ? Several	 ? novel	 ? thermomechanical	 ? processing	 ? and	 ?manufacturing	 ?technologies	 ?have	 ?been	 ?developed	 ?to	 ?optimize	 ?the	 ?microstructure	 ?of	 ?NiTi	 ? alloys.	 ? However,	 ? details	 ? of	 ? the	 ? methods	 ? used	 ? are	 ? proprietary.	 ? Introduced	 ?recently,	 ? NiTi	 ? rotary	 ? instruments	 ? made	 ? from	 ? a	 ? NiTi	 ? wire	 ? subjected	 ? to	 ?thermomechanical	 ? processing	 ? (CM	 ? wire)	 ? have	 ? been	 ? introduced	 ? into	 ? the	 ? market	 ?(Typhoon	 ? CM;	 ? Clinician?s	 ? Choice	 ? Dental	 ? Products,	 ? New	 ?Milford,	 ? CT).	 ? The	 ? CM	 ?wire	 ?technology	 ? has	 ? made	 ? the	 ? NiTi	 ? instruments	 ? more	 ? resistant	 ? to	 ? cyclic	 ? fatigue	 ? than	 ?conventional	 ?super-??elastic	 ?NiTi	 ?instruments	 ?(Bishop	 ?and	 ?Dummer,	 ?1997;	 ?Shen	 ?et	 ?al.,	 ?2011a;	 ? 2012).	 ? It	 ? is	 ? expected	 ? that	 ? thermomechanically	 ? treated	 ? NiTi	 ? instruments	 ?maintain	 ? the	 ? same	 ? torsional	 ? properties	 ? as	 ? conventional	 ? SE	 ?NiTi	 ? instruments.	 ? It	 ? is	 ?likely	 ? that	 ? torsional	 ? and	 ? fatigue	 ? forces	 ? happen	 ? simultaneously	 ? during	 ? root	 ? canal	 ?preparation,	 ? but	 ? little	 ? information	 ? is	 ? available	 ? on	 ? the	 ? subject.	 ? 	 ? Furthermore,	 ? it	 ? is	 ?unknown	 ?how	 ?a	 ?previous	 ?exposure	 ?to	 ?fatigue	 ?may	 ?affect	 ?the	 ?properties	 ?of	 ?a	 ?thermo-??mechanically	 ?treated	 ?wire	 ?such	 ?as	 ?CM	 ?files.	 ?	 ?Therefore,	 ?the	 ?aim	 ?of	 ?this	 ?study	 ?was	 ?to	 ?	 ?	 ? 5	 ?evaluate	 ? the	 ? effect	 ? of	 ? cyclic	 ? fatigue	 ? on	 ? torsional	 ? failure	 ? of	 ? Typhoon	 ? Ni-??Ti	 ? and	 ? CM	 ?instruments.	 ?	 ?	 ?	 ? 6	 ?	 ?Chapter	 ?2.	 ?Review	 ?of	 ?the	 ?Literature	 ?	 ?2.1.	 ?Properties	 ?of	 ?Nickel-??Titanium	 ?	 ? The	 ?endodontic	 ?community	 ?has	 ?increasingly	 ?embraced	 ?nickel-??titanium	 ?(NiTi)	 ?files	 ?since	 ?they	 ?were	 ?first	 ?introduced	 ?to	 ?the	 ?discipline	 ?(Walia	 ?et	 ?al.,	 ?1988).	 ?However,	 ?it	 ?is	 ?well-??recognized	 ?in	 ?the	 ?community	 ?that	 ?these	 ?files	 ?can	 ?separate	 ?during	 ?use	 ?with	 ?little	 ?or	 ?no	 ?warning	 ?(Walia	 ?et	 ?al.,	 ?1988;	 ?Sattapan	 ?et	 ?al.,	 ?2000a;	 ?Arens	 ?et	 ?al.,	 ?2003).	 ?	 ?A	 ?better	 ? understanding	 ? of	 ? this	 ? exotic	 ? metal	 ? may	 ? shed	 ? some	 ? light	 ? on	 ? its	 ? failure	 ?mechanisms.	 ?	 ?Nickel-??titanium	 ? does	 ? not	 ? conform	 ? to	 ? normal	 ? behavior	 ? as	 ? described	 ? in	 ?metallurgy,	 ?and	 ?is	 ?therefore	 ?described	 ?as	 ?an	 ?exotic	 ?metal.	 ?	 ?	 ?Endodontic	 ?NiTi	 ?files	 ?are	 ?largely	 ?made	 ?from	 ?nearly	 ?equal	 ?atomic	 ?ratios	 ?of	 ?nickel	 ?and	 ?titanium,	 ?being	 ?described	 ?as	 ? 54-??57.5%	 ? wt	 ? %	 ? nickel	 ? (Walia	 ? et	 ? al.,	 ? 1988;	 ? Esposito	 ? and	 ? Cunningham,	 ? 1995;	 ?Zinelis	 ?et	 ?al.,	 ?2010).	 ?	 ?This	 ?alloy	 ?can	 ?exist	 ?in	 ?various	 ?forms,	 ?differentiated	 ?by	 ?the	 ?shape	 ?of	 ?the	 ?crystal	 ?structures	 ?or	 ?phases.	 ?The	 ?phases	 ?are	 ?generally	 ?known	 ?as	 ?the	 ?austenite	 ?(Figure	 ?2.1),	 ?martensite	 ?(Figure	 ?2.2)	 ?and	 ?the	 ?R-??phase.	 ?The	 ?R-??phase	 ?is	 ?a	 ?short-??lasting	 ?transition	 ?phase	 ?occurring	 ?between	 ? the	 ? austenitic	 ? and	 ?martensitic	 ?phases;	 ? the	 ? ?R?	 ?represents	 ? the	 ? so-??called	 ? rhomboidal	 ? shape	 ? the	 ? lattice	 ? assumes	 ? during	 ? this	 ? brief	 ?period.	 ? 	 ?Both	 ?stress	 ?and	 ?temperature	 ?are	 ? influencing	 ? factors	 ? that	 ?determine	 ?which	 ?phase	 ?the	 ?metal	 ?will	 ?exist	 ?in	 ?at	 ?any	 ?one	 ?time.	 ?	 ?	 ?	 ? 7	 ?	 ?	 ?	 ?	 ?Figure	 ?2.1.	 ?Cuboidal	 ?nature	 ?of	 ?the	 ?austenite	 ?phase.	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 8	 ?	 ?	 ?	 ?Figure	 ?2.2.	 ?Example	 ?of	 ?crystal	 ?structure	 ?of	 ?the	 ?deformed,	 ?detwinned	 ?martensite	 ?phase.	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 9	 ?	 ?	 ?The	 ? special	 ? features	 ? of	 ? NiTi	 ? are	 ? superelasticity	 ? (SE)	 ? and	 ? shape	 ? memory,	 ?exhibited	 ?by	 ? the	 ?changing	 ?dimensions	 ?of	 ? these	 ?crystal	 ?phases	 ?within	 ? the	 ?metal.	 ?SE	 ?occurs	 ?upon	 ?loading,	 ?but	 ?before	 ?deformation;	 ?if	 ?the	 ?stress	 ?introduced	 ?to	 ?the	 ?metal	 ?is	 ?released,	 ? the	 ?metal	 ?will	 ? return	 ? to	 ? its	 ?original	 ?shape.	 ? 	 ?Other	 ?metals	 ?such	 ?as	 ?copper-??aluminum,	 ? nickel-??niobium	 ? and	 ? gold-??cadmium	 ? have	 ? also	 ? shown	 ? SE	 ? behavior;	 ?however	 ?nickel-??titanium	 ? is	 ? considered	 ? to	 ?be	 ? the	 ?most	 ?biocompatible	 ? (Buehler	 ?and	 ?Wang,	 ?1968;	 ?Thompson,	 ?2001).	 ? 	 ? In	 ?1963,	 ?W.F.	 ?Buehler,	 ?while	 ?working	 ?with	 ?metals	 ?for	 ? the	 ? Naval	 ? Ordinance	 ? Laboratory,	 ? described	 ? the	 ? shape-??memory	 ? effect	 ? of	 ??titanium-??nickel?	 ? (Buehler	 ? et	 ? al.,	 ? 1963).	 ? He	 ? demonstrated	 ? that	 ? when	 ? heat	 ? was	 ?applied	 ? to	 ? deformed	 ?metal,	 ? sudden	 ? dimensional	 ? changes	 ?would	 ? occur	 ? so	 ? that	 ? the	 ?metal	 ?would	 ?regain	 ? its	 ?original	 ?shape.	 ? 	 ?This	 ?metal	 ?was	 ?called	 ?Nitinol?	 ? from	 ??ni?	 ? for	 ?nickel,	 ??ti?	 ?for	 ?titanium	 ?and	 ??nol?	 ?for	 ?the	 ?Naval	 ?Ordinance	 ?Laboratory.	 ?	 ?The	 ?phenomena	 ?of	 ?SE	 ?and	 ?shape	 ?memory	 ?can	 ?be	 ?attributed	 ?to	 ?the	 ?particular	 ?phase	 ? present	 ? within	 ? the	 ? metal.	 ? 	 ? Austenite,	 ? also	 ? known	 ? as	 ? the	 ? B2	 ? cubic	 ? crystal	 ?structure	 ?or	 ?the	 ?parent-??phase,	 ?is	 ?a	 ?body-??centered	 ?cuboidal	 ?crystal	 ?that	 ?is	 ?apparent	 ?in	 ?Ni-??Ti	 ?wire	 ?at	 ?higher	 ?temperatures.	 ?	 ?It	 ?is	 ?hard,	 ?stable	 ?at	 ?room	 ?temperature	 ?and	 ?is	 ?the	 ?usual	 ?phase	 ?seen	 ?in	 ?conventional	 ?Ni-??Ti	 ?rotary	 ?instruments	 ?prior	 ?to	 ?clinical	 ?use.	 ?	 ?(See	 ?Figure	 ? 2.1).	 ? 	 ? As	 ? the	 ? temperature	 ? of	 ? the	 ? metal	 ? rises	 ? there	 ? is	 ? a	 ? phase	 ? shift	 ? within	 ?nickel-??titanium	 ?toward	 ?austenite.	 ? 	 ?Should	 ?the	 ?metal	 ?cool	 ?or	 ?when	 ?strain	 ?is	 ?applied,	 ?the	 ?nickel-??titanium	 ?will	 ?enter	 ?the	 ?martensitic	 ?phase.	 ? 	 ?This	 ??daughter	 ?phase?	 ? is	 ?also	 ?	 ?	 ? 10	 ?described	 ?as	 ?having	 ?a	 ?monoclinic	 ?B19?	 ? structure.	 ? (See	 ?Figure	 ?2.2).	 ? 	 ? It	 ? is	 ?present	 ? in	 ?trace	 ? amounts	 ? at	 ? room	 ? temperature	 ? in	 ? most	 ? rotary	 ? nickel-??titanium	 ? instruments.	 ?	 ?Martensite	 ?has	 ?two	 ?phases	 ?attributed	 ?to	 ?it,	 ?namely	 ?twinned	 ?and	 ?detwinned.	 ?	 ?As	 ?the	 ?temperature	 ? cools,	 ? martensite	 ? enters	 ? a	 ? twinned	 ? crystal	 ? structure.	 ? 	 ? Once	 ? stress	 ? is	 ?placed	 ?upon	 ?the	 ?twinned	 ?martensite,	 ?it	 ?will	 ?become	 ?detwinned.	 ?	 ?As	 ?mentioned,	 ?it	 ?is	 ?the	 ? relationship	 ? between	 ? austenite,	 ? and	 ? twinned	 ? and	 ? detwinned	 ? martensite	 ? that	 ?gives	 ?rise	 ?to	 ?the	 ?phenomenon	 ?known	 ?as	 ?shape	 ?memory	 ?(Thompson,	 ?2001).	 ?	 ?When	 ? heat	 ? is	 ? applied	 ? during	 ? the	 ? martensitic	 ? phase,	 ? or	 ? when	 ? a	 ? stress	 ? is	 ?released	 ? before	 ? the	 ? plastic	 ? deformation	 ? limit	 ? is	 ? reached,	 ? the	 ? martensitic	 ? nickel-??titanium	 ? will	 ? enter	 ? a	 ? transformation	 ? period	 ? and	 ? eventually	 ? assume	 ? an	 ? austenitic	 ?structure.	 ?	 ?When	 ?this	 ?happens	 ?the	 ?lattice	 ?will	 ?reassume	 ?a	 ?body-??centered	 ?cube	 ?lattice	 ?and	 ? the	 ?metal	 ?will	 ? exhibit	 ? shape	 ?memory.	 ? 	 ?The	 ? temperature	 ?at	 ?which	 ? this	 ?process	 ?begins	 ? is	 ? the	 ? austenite	 ? transformation	 ? start	 ? temperature	 ? (As).	 ? 	 ? Once	 ? the	 ? heat	 ? has	 ?completed	 ? the	 ? transformation	 ? of	 ? the	 ? metal,	 ? the	 ? austenite	 ? transformation	 ? finish	 ?temperature	 ?(Af)	 ?will	 ?have	 ?been	 ?reached.	 ? 	 ?The	 ?converse	 ?is	 ?also	 ?true.	 ? 	 ?When	 ?nickel-??titanium	 ?is	 ?in	 ?the	 ?austenite	 ?phase	 ?and	 ?is	 ?cooled,	 ? it	 ?will	 ?begin	 ?the	 ?transformation	 ?to	 ?martensite.	 ?	 ?This	 ?is	 ?known	 ?as	 ?the	 ?martensite	 ?transformation	 ?start	 ?temperature	 ?(Ms).	 ?	 ?Once	 ?a	 ?sufficient	 ?cooling	 ?temperature	 ?has	 ?been	 ?reached	 ?the	 ?metal	 ?will	 ?revert	 ?back	 ?to	 ?martensite,	 ?known	 ?as	 ?the	 ?martensite	 ?transformation	 ?finish	 ?temperature	 ?(Mf).	 ?	 ?In	 ?its	 ?martensitic	 ?form,	 ?the	 ?metal	 ?is	 ?soft,	 ?elastic	 ?and	 ?ductile.	 ?	 ?	 ?	 ? 11	 ?Brantley	 ? showed	 ? that	 ? he	 ? could	 ? measure	 ? the	 ? transformation	 ? temperatures	 ?using	 ? a	 ? process	 ? called	 ? Differential	 ? Scanning	 ? Calorimetry	 ? (DSC)	 ? (Brantley	 ? et	 ? al.,	 ?2002).	 ? 	 ? This	 ?was	 ? important	 ? because	 ? he	 ? showed	 ? that	 ? Profile	 ? and	 ? Lightspeed	 ?Ni-??Ti	 ?rotary	 ?instruments	 ?were	 ?in	 ?the	 ?austenite	 ?phase	 ?at	 ?room	 ?temperature	 ?and	 ?therefore	 ?demonstrated	 ?super-??elastic	 ?behavior	 ?during	 ?clinical	 ?use.	 ?	 ?Conventional	 ?Typhoon	 ?Ni-??Ti	 ? also	 ? rests	 ? primarily	 ? in	 ? the	 ? austenite	 ? phase	 ? at	 ? room	 ? temperatures,	 ? however	 ? the	 ?controlled-??memory	 ? variant	 ? does	 ? not	 ? (Shen	 ? et	 ? al.,	 ? 2011b).	 ? 	 ? DSC	 ? curves	 ? of	 ? TYP-??CM	 ?have	 ? shown	 ? transition	 ? temperatures	 ? to	 ? be	 ? well	 ? above	 ? room	 ? temperatures,	 ?prompting	 ?the	 ?metal	 ?to	 ?reside	 ?in	 ?the	 ?martensitic	 ?phase.	 ?	 ?This	 ?ductile	 ?phase	 ?is	 ?largely	 ?responsible	 ? for	 ? the	 ? lack	 ? of	 ? memory,	 ? or	 ? more	 ? specifically	 ? the	 ? reduction	 ? in	 ?superelasticity	 ?(Figure	 ?2.3).	 ? 	 ?The	 ?upper	 ?line	 ?in	 ?Figure	 ?2.3	 ?represents	 ?heating	 ?of	 ?the	 ?metal,	 ?whilst	 ? the	 ? lower	 ? line	 ? represents	 ? the	 ? cooling	 ? curve.	 ? 	 ?Generally	 ? speaking,	 ? the	 ?austenite	 ?phase	 ?lies	 ?to	 ?the	 ?right	 ?of	 ?the	 ??bumps?	 ?on	 ?the	 ?curve	 ?and	 ?martensite	 ?to	 ?the	 ?left.	 ? In	 ? Figure	 ? 2.3	 ? it	 ? is	 ? apparent	 ? that	 ? the	 ? transition	 ? temperatures	 ? for	 ? TYP-??CM	 ? are	 ?higher	 ?than	 ?TYP,	 ?which	 ?explains	 ?the	 ?different	 ?phase	 ?states	 ?of	 ?these	 ?two	 ?rotary	 ?files,	 ?and	 ?that	 ?at	 ?room	 ?temperatures	 ?a	 ?significant	 ?portion	 ?of	 ?the	 ?TYP-??CM	 ?file	 ?will	 ?reside	 ?in	 ?the	 ?martensitic	 ?form	 ?(Shen	 ?et	 ?al.,	 ?2011b).	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 12	 ?	 ?	 ?Figure	 ?2.3.	 ?Differential	 ?scanning	 ?calorimetry	 ?for	 ?TYP	 ?and	 ?TYP-??CM	 ?rotary	 ?endodontic	 ?files.	 ?Reprinted	 ?from	 ?Journal	 ?of	 ?Endodontics:	 ?Shen	 ?et	 ?al,	 ??Metallurgical	 ?Characterization	 ?of	 ?Controlled	 ?Memory	 ?Wire	 ?Nickel-?Titanium	 ?Rotary	 ?Instruments?,	 ?2011,	 ?37:1566-?1571,	 ?Copyright,	 ?with	 ?permission	 ?from	 ?Elsevier.	 ?	 ?	 ?Nickel-??titanium	 ? is	 ? an	 ? exotic	 ? metal,	 ? which	 ? does	 ? not	 ? conform	 ? to	 ? normal	 ?metallurgical	 ? properties.	 ? 	 ? There	 ? is	 ? a	 ? complex	 ? interaction	 ? between	 ? the	 ? different	 ?phases	 ? of	 ? the	 ? material	 ? that	 ? make	 ? it	 ? useful	 ? to	 ? industry.	 ? 	 ? Stress-??induced	 ? or	 ?temperature-??induced	 ? transformations	 ? between	 ? austenite	 ? and	 ? martensite	 ? are	 ?responsible	 ? for	 ? shape	 ? memory	 ? and	 ? super-??elasticity,	 ? and	 ? provide	 ? the	 ? unique	 ?properties	 ?for	 ?this	 ?interesting	 ?metal.	 ?	 ?	 ?	 ? 13	 ?2.2.	 ?Instrument	 ?Fracture	 ?	 ?	 ? The	 ? separation	 ? of	 ? a	 ? portion	 ? of	 ? an	 ? endodontic	 ? rotary	 ? file	 ? during	 ?instrumentation	 ?can	 ?be	 ?an	 ?unexpected	 ?and	 ?unpleasant	 ?situation.	 ? 	 ?It	 ?is	 ?possible	 ?that	 ?the	 ? separated	 ? fragment	 ? could	 ? prevent	 ? proper	 ? chemomechanical	 ? debridement	 ?beyond	 ?its	 ?location	 ?in	 ?the	 ?canal	 ?if	 ?it	 ?not	 ?able	 ?to	 ?be	 ?bypassed	 ?or	 ?removed.	 ?	 ?Depending	 ?on	 ? the	 ? pre-??operative	 ? diagnosis,	 ? the	 ? canal	 ? beyond	 ? the	 ? fractured	 ? instrument	 ? may	 ?contain	 ? a	 ? thriving	 ? biofilm	 ? community,	 ? which	 ? may	 ? decrease	 ? the	 ? likelihood	 ? of	 ? a	 ?successful	 ?endodontic	 ?treatment.	 ?	 ?Fortunately,	 ?the	 ?incidence	 ?of	 ?Ni-??Ti	 ?file	 ?separation	 ?is	 ? low,	 ? generally	 ? less	 ? than	 ?5%	 ?of	 ? all	 ? treatments	 ? (Al-??Fouzan,	 ? 2003;	 ? Parashos	 ? et	 ? al.,	 ?2004;	 ? Spili	 ? et	 ? al.,	 ? 2005).	 ? Parashos	 ? attributed	 ? 1.5%	 ? of	 ? file	 ? separations	 ? to	 ? torsional	 ?failure	 ?and	 ?3.5%	 ?to	 ?cyclical	 ?fatigue.	 ?Most	 ?of	 ?the	 ?time,	 ?the	 ?fragment	 ?will	 ?lodge	 ?itself	 ?in	 ?the	 ? apical	 ? portion	 ? of	 ? the	 ? canal	 ? (Parashos	 ? and	 ?Messer,	 ? 2004),	 ? which	 ?may	 ? prevent	 ?adequate	 ?debridement	 ?of	 ?this	 ?important	 ?area	 ?of	 ?the	 ?canal.	 ?	 ? The	 ?impact	 ?a	 ?separated	 ?instrument	 ?has	 ?on	 ?the	 ?prognosis	 ?of	 ?a	 ?case	 ?seems	 ?to	 ?be	 ? limited.	 ?A	 ?threshold	 ?quality	 ?and	 ?quantity	 ?of	 ?bacteria	 ?cause	 ?endodontic	 ?diseases,	 ?not	 ? a	 ? separated	 ? instrument	 ? in	 ? and	 ? of	 ? itself.	 ? 	 ? Similarly,	 ? in	 ? both	 ? stainless-??steel	 ? and	 ?nickel-??titanium	 ? endodontic	 ? files,	 ? a	 ? separated	 ? fragment	 ? does	 ? not	 ? appear	 ? to	 ?significantly	 ?decrease	 ?the	 ?outcome	 ?of	 ?the	 ?case	 ?(Crump	 ?and	 ?Natkin,	 ?1970;	 ?Spili	 ?et	 ?al.,	 ?2005).	 ? Spili,	 ?who	 ? looked	 ? at	 ? over	 ? 8000	 ? cases	 ? of	 ? instrument	 ? fracture,	 ? determined	 ? a	 ?prevalence	 ? of	 ? 3.3%,	 ? with	 ? the	 ? majority	 ? of	 ? those	 ? separations	 ? being	 ? attributed	 ? to	 ?nickel-??titanium	 ? rather	 ? than	 ? stainless	 ? steel.	 ? 	 ? He	 ? examined	 ? several	 ? variables	 ? to	 ?	 ?	 ? 14	 ?determine	 ?prognosticating	 ?factors	 ?in	 ?cases	 ?involving	 ?a	 ?broken	 ?instrument.	 ?	 ?He	 ?found	 ?the	 ?largest	 ?influence	 ?on	 ?outcome	 ?was	 ?not	 ?whether	 ?a	 ?fractured	 ?instrument	 ?remained	 ?in	 ? the	 ? canal,	 ? but	 ? rather	 ? if	 ? a	 ? case	 ? involving	 ? a	 ? separated	 ? instrument	 ?was	 ? associated	 ?with	 ? a	 ? periapical	 ? lesion.	 ? 	 ? Regardless,	 ? any	 ? potential	 ? loss	 ? of	 ? tooth	 ? structure	 ? whilst	 ?trying	 ?to	 ?remove	 ?the	 ?fractured	 ?fragment	 ?must	 ?be	 ?weighed	 ?into	 ?the	 ?decision	 ?to	 ?try	 ?to	 ?remove	 ?it	 ?or	 ?not	 ?(Souter	 ?and	 ?Messer,	 ?2005).	 ?	 ?File	 ? separation	 ? has	 ? been	 ? considered	 ? as	 ? occurring	 ? from	 ? either	 ? of	 ? two	 ?ways:	 ?fatigue	 ? failure	 ? or	 ? torsional	 ? (shear	 ? stress)	 ? failure.	 ? 	 ? Nickel-??titanium	 ? rotary	 ? files	 ? are	 ?associated	 ?with	 ?fatigue-??failure,	 ?while	 ?hand	 ?files	 ?made	 ?from	 ?stainless	 ?steel	 ?are	 ?more	 ?associated	 ? with	 ? torsional	 ? failure	 ? (Shen	 ? et	 ? al.,	 ? 2009a).	 ? 	 ? However,	 ? a	 ? more	 ? likely	 ?scenario	 ?is	 ?that	 ?a	 ?complex	 ?interaction	 ?exists	 ?between	 ?these	 ?two	 ?types	 ?of	 ?failure,	 ?and	 ?that	 ?they	 ?occur	 ?simultaneously	 ?to	 ?cause	 ?file	 ?separation.	 ?The	 ?details	 ?of	 ?each	 ?mode	 ?of	 ?separation	 ?and	 ?their	 ?laboratory	 ?tests	 ?are	 ?explored	 ?in	 ?the	 ?next	 ?two	 ?sections.	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 15	 ?	 ?	 ?	 ?2.2.1.	 ?Cyclic	 ?Fatigue	 ?Failure	 ?	 ?	 ?	 ?	 ? As	 ?a	 ?file	 ?rotates	 ?in	 ?a	 ?curved	 ?canal,	 ?it	 ?will	 ?experience	 ?tension	 ?and	 ?compression	 ?within	 ?a	 ?single	 ?rotation.	 ?	 ?If	 ?the	 ?file	 ?is	 ?held	 ?in	 ?this	 ?position	 ?for	 ?a	 ?threshold	 ?amount	 ?of	 ?time,	 ? separation	 ?will	 ? occur	 ? due	 ? to	 ? crack	 ?propagation	 ?within	 ? the	 ?metal.	 ? 	 ? There	 ? are	 ?several	 ?laboratory	 ?tests	 ?used	 ?to	 ?measure	 ?cyclic	 ?fatigue;	 ?however	 ?there	 ?is	 ?no	 ?current	 ?International	 ?Organization	 ?for	 ?Standardization	 ?(ISO)	 ?standard	 ?used	 ?to	 ?measure	 ?the	 ?fatigue	 ? life	 ? of	 ? rotary	 ? endodontic	 ? files.	 ? 	 ? This	 ? presents	 ? a	 ? problem	 ? to	 ? the	 ? endodontic	 ?profession,	 ?as	 ?comparing	 ?one	 ?fatigue	 ?study	 ?to	 ?another	 ?is	 ?invalid	 ?due	 ?to	 ?the	 ?different	 ?parameters	 ?of	 ?each	 ?test.	 ?Currently,	 ?the	 ?most	 ?important	 ?result	 ?within	 ?any	 ?particular	 ?fatigue	 ?test	 ?is	 ?how	 ?the	 ?files	 ?rank	 ?when	 ?compared	 ?to	 ?each	 ?other	 ?within	 ?the	 ?same	 ?test.	 ?	 ?Thus,	 ? less	 ? emphasis	 ? should	 ? be	 ? placed	 ? on	 ? comparing	 ? results	 ? between	 ? studies.	 ?	 ?Additionally,	 ?caution	 ?should	 ?be	 ?exercised	 ?in	 ?the	 ?interpretation	 ?of	 ?the	 ?actual	 ?value	 ?in	 ?revolutions	 ?per	 ?minute	 ?or	 ?time	 ?lapsed	 ?before	 ?fracture,	 ?as	 ?the	 ?testing	 ?methods	 ?do	 ?not	 ?accurately	 ? reproduce	 ? clinical	 ? conditions	 ? and	 ? the	 ? results	 ? found	 ? clinically	 ? may	 ? be	 ?quite	 ?different.	 ?	 ?	 ?	 ?	 ? Most	 ? of	 ? the	 ? techniques	 ? used	 ? to	 ? measure	 ? fatigue	 ? in	 ? endodontic	 ? files	 ? use	 ? a	 ?static	 ? handpiece	 ? with	 ? a	 ? second	 ? device	 ? that	 ? introduces	 ? a	 ? curve	 ? into	 ? the	 ? rotary	 ?endodontic	 ?file.	 ?	 ?Once	 ?rotation	 ?begins,	 ?the	 ?time	 ?it	 ?takes	 ?for	 ?the	 ?file	 ?to	 ?fracture	 ?is	 ?then	 ?recorded.	 ? 	 ? However,	 ? one	 ? does	 ? not	 ? keep	 ? the	 ? handpiece	 ? in	 ? a	 ? single	 ? place	 ? during	 ?	 ?	 ? 16	 ?instrumentation	 ? in	 ? a	 ? clinical	 ? setting.	 ? 	 ? The	 ? fatigue	 ? life	 ? of	 ? a	 ? file	 ? can	 ?be	 ? considerably	 ?extended	 ? if	 ? the	 ? file	 ? is	 ?moving	 ? up	 ? and	 ? down	 ?during	 ? instrumentation.	 ? 	 ? It	 ? should	 ? be	 ?noted	 ?that	 ?this	 ?motion	 ?has	 ?been	 ?shown	 ?to	 ?extend	 ?fatigue	 ?life	 ?to	 ?a	 ?greater	 ?extent	 ? in	 ?smaller	 ?diameter	 ?files	 ?compared	 ?to	 ?larger	 ?diameter	 ?files.	 ? 	 ? 	 ?(Dederich	 ?&	 ?Zakariasen,	 ?1986).	 ?	 ?	 ?	 ? In	 ? cyclic	 ? fatigue,	 ? failure	 ? of	 ? the	 ? file	 ? will	 ? occur	 ? through	 ? several	 ? stages.	 ? 	 ? The	 ?failure	 ?will	 ?begin	 ?with	 ?crack	 ?initiation.	 ?	 ?Potential	 ?sites	 ?for	 ?crack	 ?initiation	 ?are	 ?surface	 ?defects	 ?such	 ?as	 ?milling	 ?grooves	 ?created	 ?during	 ?the	 ?manufacturing	 ?of	 ?the	 ?file	 ?(Peng	 ?et	 ?al.,	 ?2005).	 ? 	 ?Inclusions,	 ?which	 ?are	 ?defects	 ?in	 ?the	 ?metal	 ?commonly	 ?containing	 ?carbon,	 ?can	 ?also	 ?contribute	 ?to	 ?a	 ?site	 ?of	 ?crack	 ?initiation.	 ?	 ?The	 ?proximity	 ?of	 ?the	 ?inclusion	 ?to	 ?the	 ?surface	 ?of	 ?the	 ?file	 ?is	 ?important	 ?to	 ?crack	 ?initiation,	 ?as	 ?inclusions	 ?that	 ?are	 ?further	 ?away	 ?from	 ? the	 ?surface	 ?of	 ? the	 ? file	 ?are	 ? less	 ?of	 ?a	 ? threat	 ? to	 ? crack	 ? initiation	 ? (Atkinson	 ?&	 ?Shi,	 ?2003).	 ? 	 ? Subsequently,	 ? the	 ? crack	 ? will	 ? continue	 ? into	 ? the	 ? next	 ? phase,	 ? called	 ? crack	 ?propagation.	 ?	 ?During	 ?the	 ?crack	 ?propagation	 ?phase,	 ?the	 ?file	 ?continues	 ?to	 ?rotate.	 ?	 ?As	 ?it	 ?rotates,	 ? the	 ? file	 ?microscopically	 ? opens	 ? and	 ? closes	 ? at	 ? the	 ? crack	 ? initiation	 ? site.	 ? 	 ? This	 ?can	 ? lead	 ? to	 ?a	 ?particular	 ?pattern	 ?within	 ? the	 ? file	 ? called	 ? ?fatigue	 ?striations?	 ?or	 ? ?beach	 ?marks?	 ? created	 ? by	 ? the	 ? rapid	 ? opening	 ? and	 ? closing	 ? of	 ? the	 ? crack	 ? site	 ? (Cheung	 ? et	 ? al.,	 ?2005).	 ?Once	 ? this	 ?progression	 ?of	 ? successive	 ?micro-??fractures	 ?makes	 ? its	 ?way	 ? through	 ?the	 ? file,	 ? the	 ? pieces	 ?will	 ? suddenly	 ? separate.	 ? 	 ? This	 ? is	 ? known	 ? as	 ? the	 ? ?overload	 ? zone?	 ?(Ounsi	 ? et	 ? al.,	 ? 2007)	 ? and	 ? is	 ? typically	 ? identified	 ?by	 ? a	 ?dimpled	 ?area	 ? at	 ? some	 ?distance	 ?away	 ?from	 ?the	 ?crack	 ?initiation	 ?site	 ?seen	 ?when	 ?the	 ?end	 ?of	 ?the	 ?file	 ?is	 ?examined	 ?under	 ?a	 ?scanning	 ?electron	 ?microscope	 ?(see	 ?Figure	 ?2.4).	 ?	 ?	 ?	 ?	 ? 17	 ?	 ? 	 ?	 ?Figure	 ?2.4.	 ?Diagrammatic	 ?representation	 ?of	 ?typical	 ?failure	 ?zones	 ?found	 ?in	 ?	 ?cyclical	 ?fatigue	 ?failure.	 ?Reprinted	 ?from	 ?Journal	 ?of	 ?Endodontics:	 ?Ounsi	 ?et	 ?al,	 ??Effect	 ?of	 ?Clinical	 ?Use	 ?on	 ?the	 ?Cyclic	 ?Fatigue	 ? Resistance	 ? of	 ? ProTaper	 ?Nickel-?Titanium	 ?Rotary	 ? Instruments?,	 ? 2007,	 ? 33:737-?741,	 ?Copyright,	 ?with	 ?permission	 ?from	 ?Elsevier.	 ?	 ?	 ? 	 ? 	 ?	 ?	 ? 18	 ?	 ? The	 ?angle	 ?at	 ?which	 ?the	 ?file	 ?engages	 ?the	 ?curve	 ?has	 ?an	 ?important	 ?impact	 ?on	 ?the	 ?fatigue	 ?life	 ?of	 ?the	 ?file.	 ?The	 ?greater	 ?the	 ?angle,	 ?the	 ?quicker	 ?the	 ?file	 ?will	 ?fail	 ?(Pruett	 ?et	 ?al.,	 ?1997).	 ? 	 ? 	 ? The	 ?measurement	 ? of	 ? this	 ? angle	 ?was	 ? introduced	 ? by	 ? Schneider	 ? (Schneider,	 ?1971).	 ? 	 ? However,	 ? the	 ? degree	 ? of	 ? curvature	 ? in	 ? the	 ? root	 ? is	 ? only	 ? one	 ? factor	 ? when	 ?considering	 ?the	 ?fatigue	 ?life	 ?of	 ?an	 ?instrument.	 ? 	 ?When	 ?testing	 ?Lightspeed	 ?files,	 ?Pruett	 ?found	 ? that	 ? angles	 ? greater	 ? than	 ?30?	 ? led	 ? to	 ? a	 ? significant	 ?decrease	 ? in	 ? fatigue	 ? life,	 ? but	 ?moreover	 ? Pruett	 ? found	 ? that	 ? the	 ? radius	 ? this	 ? angle	 ? passed	 ? through	 ? also	 ? had	 ? a	 ?significant	 ? effect	 ? on	 ? fatigue	 ? life.	 ? 	 ? As	 ? the	 ? radius	 ? decreased,	 ? the	 ? fatigue	 ? life	 ? of	 ? the	 ?instrument	 ?also	 ?decreased.	 ?	 ?His	 ?conclusions	 ?were	 ?that	 ?the	 ?angle	 ?of	 ?the	 ?root	 ?and	 ?the	 ?radius	 ?of	 ?the	 ?curvature	 ?of	 ?the	 ?root	 ?had	 ?more	 ?effect	 ?on	 ?file	 ?failure	 ?than	 ?the	 ?rotational	 ?speed	 ?of	 ?the	 ?instrument	 ?(Pruett	 ?et	 ?al.,	 ?1997).	 ?	 ?In	 ?other	 ?words,	 ?regardless	 ?if	 ?the	 ?angles	 ?of	 ?root	 ?curvature	 ?are	 ?the	 ?same,	 ?the	 ?radius	 ?of	 ?the	 ?curvature	 ?has	 ?a	 ?significant	 ?effect	 ?on	 ?the	 ?cyclical	 ?fatigue	 ?of	 ?rotary	 ?instruments	 ?(see	 ?Figure	 ?2.5).	 ?	 ?Methods	 ? to	 ? measure	 ? cyclic	 ? fatigue	 ? in	 ? the	 ? laboratory	 ? are	 ? numerous.	 ? 	 ? Each	 ?device	 ?is	 ?designed	 ?to	 ?allow	 ?rotation	 ?of	 ?the	 ?file	 ?while	 ? introducing	 ?minimal	 ?torsional	 ?effects.	 ?	 ?The	 ?cylindrical	 ?curved	 ?tube	 ?has	 ?been	 ?used	 ?to	 ?introduce	 ?an	 ?angle	 ?into	 ?rotary	 ?files.	 ?	 ?They	 ?have	 ?been	 ?made	 ?from	 ?metal	 ?(Pruett	 ?et	 ?al.,	 ?1997;	 ?Mize	 ?et	 ?al.,	 ?1998;	 ?Yared	 ?et	 ? al.,	 ? 1999)	 ? or	 ? from	 ?glass	 ? (Anderson	 ? et	 ? al.,	 ? 2007;	 ?Barbosa	 ? et	 ? al.,	 ? 2008),	 ? and	 ?have	 ?been	 ? made	 ? with	 ? a	 ? variety	 ? of	 ? angles	 ? of	 ? curvature	 ? and	 ? radii.	 ? Ostensibly,	 ? the	 ? glass	 ?offers	 ? the	 ? benefit	 ? of	 ? the	 ? researcher	 ? being	 ? able	 ? to	 ? see	 ? the	 ? file	 ? as	 ? it	 ? rotates.	 ? 	 ? A	 ?diagrammatic	 ?representation	 ?of	 ?the	 ?curved	 ?tube	 ?is	 ?offered	 ?in	 ?Figure	 ?2.6.	 ?	 ?	 ? 19	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?Figure	 ?2.5.	 ?Demonstration	 ?of	 ?the	 ?angle	 ?of	 ?(A)	 ?root	 ?curvature	 ?and	 ?(B)	 ?the	 ?radius	 ?of	 ?root	 ?curvature.	 ?	 ?Reprinted	 ?from	 ?Journal	 ?of	 ?Endodontics:	 ?Pruett	 ?et	 ?al,	 ??Cyclic	 ?Fatigue	 ?Testing	 ?of	 ?Nickel-?Titanium	 ?Endodontic	 ? Instruments?,	 ? 1997,	 ? 23:77-?85,	 ? Copyright,	 ?with	 ? permission	 ? from	 ?Elsevier.	 ?	 ?	 ?	 ? 20	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 	 ?Figure	 ?2.6.	 ?Example	 ?of	 ?curved	 ?tube	 ?method	 ?of	 ?testing	 ?cyclical	 ?fatigue.	 ?	 ?Reprinted	 ? from	 ? Endodontic	 ? Topics,	 ? Cheung,	 ? G.,	 ? ?Instrument	 ? Fracture:	 ? mechanisms,	 ?removal	 ? of	 ? fragments	 ? and	 ? clinical	 ? outcomes?,	 ? 2009,	 ? 16:1-?26,	 ? Copyright,	 ? with	 ?permission	 ?from	 ?Elsevier.	 ?	 ?	 ?	 ? 21	 ?	 ?	 ? The	 ? method	 ? of	 ? using	 ? curved	 ? tubes	 ? to	 ? measure	 ? cyclic	 ? fatigue	 ? has	 ? some	 ?significant	 ? design	 ? problems.	 ? 	 ? Chiefly,	 ? the	 ? angle	 ? of	 ? curvature	 ? and	 ? the	 ? radius	 ? of	 ? the	 ?tube	 ?will	 ?be	 ?slightly	 ?different	 ? from	 ?the	 ?file	 ?depending	 ?on	 ?how	 ?well	 ? the	 ?file	 ? fits	 ? into	 ?the	 ? tube	 ?(Plotino	 ?et	 ?al.,	 ?2009).	 ? 	 ? If	 ? the	 ? tube	 ? is	 ? too	 ?wide	 ? in	 ?diameter	 ? the	 ? files	 ?will	 ? fit	 ?loosely	 ? within	 ? it.	 ? 	 ? This	 ? is	 ? a	 ? problem,	 ? as	 ? superelasticity	 ? will	 ? cause	 ? the	 ? files	 ? to	 ?straighten,	 ? pushing	 ? the	 ? file	 ? to	 ? the	 ? outer	 ? edges	 ? of	 ? the	 ? tube	 ? as	 ? the	 ? file	 ? engages	 ? the	 ?curve.	 ? The	 ? result	 ? is	 ? that	 ? smaller	 ? tapers	 ?will	 ? have	 ? a	 ? different	 ? trajectory	 ?within	 ? the	 ?tube	 ? when	 ? compared	 ? to	 ? files	 ? with	 ? larger	 ? tapers,	 ? and	 ? smaller	 ? files	 ? would	 ? be	 ?overrepresented	 ?in	 ?their	 ?fatigue	 ?life	 ?(Cheung,	 ?2009).	 ?	 ?In	 ?other	 ?words,	 ?the	 ?deformed	 ?angle	 ?and	 ?radius	 ?of	 ?a	 ?smaller	 ?file	 ?will	 ?be	 ?slightly	 ?larger	 ?than	 ?the	 ?larger	 ?file	 ?within	 ?the	 ?same	 ? tube.	 ? 	 ?This	 ?would	 ? lead	 ? to	 ?a	 ? type	 ? I	 ? error	 ?within	 ? the	 ? test.	 ? 	 ?Alternatively,	 ? if	 ? the	 ?tube	 ? is	 ? too	 ? narrow	 ? then	 ? undesirable	 ? torsional	 ? forces	 ? will	 ? be	 ? introduced	 ? into	 ? the	 ?cyclical	 ? test,	 ? as	 ? the	 ? sides	 ?of	 ? the	 ? file	 ?will	 ? bind	 ? into	 ? the	 ? tube.	 ? 	 ?A	 ? theoretical	 ? solution	 ?would	 ? be	 ? to	 ? have	 ? a	 ? series	 ? of	 ? tapered	 ? curved	 ? tubes	 ? that	 ?more	 ? closely	 ?matches	 ? the	 ?geometry	 ?of	 ?the	 ?files	 ?that	 ?are	 ?being	 ?tested,	 ?but	 ?with	 ?adequate	 ?diameter	 ?not	 ?to	 ?cause	 ?binding.	 ?	 ?An	 ? alternate	 ?method	 ?of	 ? cyclically	 ? testing	 ? files	 ? is	 ? the	 ? grooved	 ?block	 ? and	 ? rod	 ?(Figures	 ?2.7	 ?and	 ?2.8).	 ?	 ?It	 ?was	 ?first	 ?suggested	 ?for	 ?use	 ?by	 ?Ha?kel	 ?who	 ?put	 ?a	 ??V?	 ?shape	 ?in	 ?the	 ? block	 ? end	 ? to	 ? keep	 ? the	 ? file	 ? engaged	 ? in	 ? a	 ? single	 ? location	 ? within	 ? the	 ? testing	 ?apparatus	 ?(Ha?kel	 ?et	 ?al.,	 ?1999).	 ?	 ?	 ? 	 ?	 ?	 ?	 ?	 ? 22	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 	 ?Figure	 ?2.7.	 ?Example	 ?of	 ?grooved	 ?block	 ?and	 ?rod.	 ?	 ?	 ?Reprinted	 ? from	 ? Journal	 ? of	 ? Endodontics,	 ?Ha?kel	 ? et	 ? al,	 ? ?Dynamic	 ?and	 ?Cyclic	 ? Fatigue	 ? of	 ?Engine-?Driven	 ? Rotary	 ? Nickel-?Titanium	 ? Endodontic	 ? Instruments?,	 ? 1999,	 ? 25:434-?440,	 ?Copyright,	 ?with	 ?permission	 ?from	 ?Elsevier.	 ?	 ? 	 ?	 ?	 ?	 ?	 ? 23	 ?	 ?	 ?	 ? 	 ?	 ?	 ?	 ?	 ?	 ? 	 ?	 ?Figure	 ?2.8.	 ?Example	 ?of	 ?the	 ??V?	 ?cut	 ?into	 ?the	 ?block	 ?to	 ?limit	 ?random	 ?movement	 ?of	 ?the	 ?file	 ?as	 ?it	 ?rotates	 ?(Indicated	 ?by	 ?the	 ?letter	 ??A?).	 ?	 ?	 ?Reprinted	 ? from	 ? Journal	 ? of	 ? Endodontics,	 ?Ha?kel	 ? et	 ? al,	 ? ?Dynamic	 ?and	 ?Cyclic	 ? Fatigue	 ? of	 ?Engine-?Driven	 ? Rotary	 ? Nickel-?Titanium	 ? Endodontic	 ? Instruments?,	 ? 1999,	 ? 25:434-?440,	 ?Copyright,	 ?with	 ?permission	 ?from	 ?Elsevier.	 ?	 ?	 ?	 ?	 ?	 ? 24	 ?	 ? Notice	 ?that	 ?in	 ?the	 ?block	 ?the	 ??V?	 ?groove	 ?is	 ?tapered.	 ?	 ?This	 ?addresses	 ?some	 ?of	 ?the	 ?problems	 ? encountered	 ? in	 ? the	 ? curved	 ? tube	 ?model;	 ? however	 ? unless	 ? the	 ? file	 ? is	 ? fully	 ?engaged	 ?in	 ?the	 ?apparatus,	 ?it	 ?could	 ?still	 ?suffer	 ?from	 ?different	 ?angles	 ?and	 ?radii	 ?within	 ?the	 ?same	 ?test.	 ?In	 ?this	 ?apparatus,	 ?the	 ?file	 ?is	 ?engaged	 ?throughout	 ?its	 ?length	 ?against	 ?the	 ?rod	 ? or	 ? the	 ? block.	 ? 	 ? Thus,	 ? unless	 ? lubricated,	 ? slight	 ? torsional	 ? resistance	 ? along	 ? with	 ?frictional	 ? heat	 ? could	 ? lead	 ? to	 ? confounding	 ? variables	 ? within	 ? the	 ? test.	 ? 	 ? The	 ? authors	 ?recognized	 ?this	 ?and	 ?addressed	 ?it	 ?by	 ?streaming	 ?cold	 ?air	 ?over	 ?the	 ?rod	 ?and	 ?block.	 ?	 ?It	 ?is	 ?unknown	 ?how	 ?frictional	 ?heat	 ?would	 ?affect	 ?the	 ?phase	 ?transformation	 ?during	 ?this	 ?test,	 ?as	 ?the	 ?possibility	 ?of	 ?a	 ?phase	 ?transformation	 ?toward	 ?austenite	 ?could	 ?occur	 ?along	 ?with	 ?a	 ?loss	 ?of	 ?ductility	 ?of	 ?the	 ?file	 ?during	 ?the	 ?test.	 ?	 ? A	 ?third	 ?way	 ?of	 ?introducing	 ?a	 ?curvature	 ?to	 ?a	 ?file	 ?during	 ?a	 ?cyclic	 ?fatigue	 ?test	 ?is	 ?the	 ? inclined	 ?plane	 ? (Figure	 ?2.9),	 ? or	 ? an	 ? inclined	 ?metal	 ?block	 ? to	 ?which	 ? the	 ? file	 ?would	 ?engage,	 ? introduced	 ?by	 ?Li	 ?(Li	 ?et	 ?al.,	 ?2002).	 ? 	 ?With	 ?a	 ?smooth	 ?inclined	 ?plane,	 ? it	 ?may	 ?be	 ?difficult	 ?to	 ?prevent	 ?the	 ?file	 ?from	 ??walking	 ?off?	 ?the	 ?incline	 ?once	 ?rotation	 ?begins,	 ?or	 ?in	 ?other	 ?words	 ?it	 ?is	 ?difficult	 ?to	 ?keep	 ?the	 ?file	 ?within	 ?its	 ?long	 ?axis.	 ?In	 ?the	 ?following	 ?study	 ?a	 ?groove	 ?was	 ?placed	 ? into	 ? the	 ? inclined	 ?plane	 ? to	 ?keep	 ?the	 ? file	 ? in	 ?place	 ?(Kitchens	 ?et	 ?al.,	 ?2007).	 ?	 ?Plotino	 ?points	 ?out	 ?that	 ?in	 ?both	 ?studies	 ?only	 ?Schneider?s	 ?method	 ?of	 ?calculating	 ?angulation	 ?was	 ? taken	 ? into	 ?account,	 ?without	 ? considering	 ? the	 ? larger	 ? impact	 ? that	 ? the	 ?radius	 ? of	 ? the	 ? curvature	 ? has	 ? on	 ? fatigue	 ? (Plotino	 ? et	 ? al.,	 ? 2009).	 ? Additionally,	 ? this	 ?method,	 ? similarly	 ? as	 ? the	 ?previously	 ? two	 ?described	 ?methods,	 ? is	 ? subject	 ? to	 ? variance	 ?within	 ? the	 ? test	 ?due	 ? to	 ? the	 ?bending	 ?properties	 ?of	 ? the	 ? files	 ? that	 ?are	 ?used	 ? in	 ? the	 ? test.	 ?	 ?The	 ? angulation	 ? and	 ? radius	 ? are	 ? very	 ? challenging	 ? to	 ? consistently	 ? achieve	 ? with	 ? the	 ?inclined	 ?plane	 ?while	 ?using	 ?instruments	 ?of	 ?various	 ?tip	 ?sizes	 ?and	 ?taper.	 ?	 ?	 ? 25	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 	 ?	 ? Figure	 ?2.9.	 ?Example	 ?of	 ?inclined	 ?plane	 ?method	 ?of	 ?testing	 ?cyclical	 ?fatigue.	 ?	 ?	 ?Reprinted	 ? from	 ? Journal	 ?of	 ?Endodontics,	 ?Li	 ? et	 ?al,	 ? ?Cyclic	 ?Fatigue	 ?of	 ?Endodontic	 ?Nickel	 ?Titanium	 ? Rotary	 ? Instruments:	 ? Static	 ? and	 ? Dynamic	 ? Tests?,	 ? 2002,	 ? 	 ? 28:448-?451,	 ?Copyright,	 ?with	 ?permission	 ?from	 ?Elsevier.	 ?	 ?	 ? 26	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 	 ?Figure	 ?2.10.	 ?Example	 ?of	 ?the	 ?trajectory	 ?of	 ?a	 ?file	 ?while	 ?engaging	 ?an	 ?inclined	 ?plane.	 ?	 ?Reprinted	 ? from	 ? Journal	 ?of	 ?Endodontics,	 ?Li	 ? et	 ?al,	 ? ?Cyclic	 ?Fatigue	 ?of	 ?Endodontic	 ?Nickel	 ?Titanium	 ? Rotary	 ? Instruments:	 ? Static	 ? and	 ? Dynamic	 ? Tests?,	 ? 2002,	 ? 	 ? 28:448-?451,	 ?Copyright,	 ?with	 ?permission	 ?from	 ?Elsevier.	 ?	 ?	 ?	 ?	 ? 27	 ?In	 ? the	 ?previous	 ?cyclic	 ? fatigue	 ?devices	 ?discussed,	 ? the	 ?concept	 ?of	 ?how	 ?well	 ?an	 ?instrument	 ? fits	 ? into	 ? the	 ? apparatus	 ? has	 ? not	 ? yet	 ? been	 ? elucidated	 ? in	 ? the	 ? literature.	 ?	 ?Cheung	 ? attempted	 ? to	 ? improve	 ? some	 ? of	 ? these	 ? apparatus	 ? and	 ? the	 ? problems	 ? they	 ?presented	 ?by	 ?introducing	 ?a	 ?three-??point	 ?pin	 ?bending	 ?apparatus	 ?(Cheung	 ?and	 ?Darvell,	 ?2007).	 ? 	 ? The	 ? apparatus	 ? consisted	 ? of	 ? three	 ? hardened	 ? pins	 ? emanating	 ? from	 ? three	 ?vertically	 ? stacked	 ? small	 ? flat	 ? steel	 ? plates	 ? that	 ? could	 ? slide	 ? over	 ? each	 ? other	 ? in	 ? a	 ?horizontal	 ? direction.	 ? 	 ? This	 ? allowed	 ? for	 ? an	 ? adjustment	 ? of	 ? the	 ? curvature	 ? of	 ? the	 ?instrument	 ?that	 ?could	 ?be	 ?customized	 ?for	 ?each	 ?test.	 ?	 ?Another	 ?benefit	 ?of	 ?this	 ?apparatus	 ?is	 ?that	 ?for	 ?testing	 ?it	 ?could	 ?be	 ?immersed	 ?in	 ? liquid.	 ?From	 ?a	 ?metallurgical	 ?engineering	 ?standpoint,	 ?Cheung	 ?claims	 ?that	 ?the	 ?three-??point	 ?bending	 ?apparatus	 ?more	 ?accurately	 ?represents	 ?a	 ?circular	 ?curvature	 ? introduced	 ?into	 ?the	 ?file,	 ?and	 ?this	 ?allows	 ?for	 ?a	 ?more	 ?accurate	 ?mathematical	 ? calculation	 ? of	 ? fatigue	 ? life	 ? (determination	 ? of	 ? the	 ? fatigue	 ? life	 ?when	 ? compared	 ? to	 ? the	 ? strain	 ? amplitude)	 ? (Cheung,	 ? 2009).	 ? However,	 ? as	 ? the	 ? file	 ? is	 ?rotating	 ?the	 ?longitudinal	 ?axis	 ?must	 ?be	 ?kept	 ?constant	 ?and	 ?not	 ?allowed	 ?to	 ?wander	 ?from	 ?its	 ?concentric	 ?rotation.	 ?	 ?In	 ?this	 ?model,	 ?concentricity	 ?along	 ?the	 ?long	 ?axis	 ?of	 ?the	 ?file	 ?is	 ?still	 ?subject	 ?to	 ?variability,	 ?and	 ?any	 ?deviation	 ?in	 ?the	 ?file	 ?from	 ?its	 ?long	 ?axis	 ?will	 ?affect	 ?the	 ?accuracy	 ?of	 ?such	 ?mathematical	 ?calculations.	 ?Similarly	 ?to	 ?other	 ?models,	 ?a	 ?groove	 ?is	 ?cut	 ?into	 ?the	 ?apparatus	 ?to	 ?prevent	 ?deviation	 ?from	 ?the	 ?long	 ?axis	 ?of	 ?the	 ?rotating	 ?file;	 ?in	 ?this	 ?case	 ?it	 ?is	 ?placed	 ?where	 ?the	 ?file	 ?is	 ?in	 ?contact	 ?with	 ?the	 ?lowest	 ?pin.	 ?	 ?Bhagabati	 ?recently	 ?introduced	 ?a	 ?custom-??made	 ?cyclic	 ?fatigue	 ?device,	 ?which	 ?he	 ?claims	 ?is	 ?able	 ?to	 ?precisely	 ?reproduce	 ?a	 ?radius	 ?and	 ?curvature	 ?angle	 ?of	 ? interest.	 ? 	 ?The	 ?	 ?	 ? 28	 ?settings	 ?are	 ?accomplished	 ?through	 ?the	 ?use	 ?of	 ?a	 ?computer-??aided	 ?milling	 ?device.	 ?	 ?The	 ?apparatus	 ?needs	 ?closer	 ?scrutiny;	 ?however	 ?the	 ?idea	 ?of	 ?using	 ?computers	 ?to	 ?calculate	 ?a	 ?	 ?more	 ? precise	 ? angle	 ? and	 ? radius	 ? introduced	 ? to	 ? a	 ? file	 ? is	 ? intriguing	 ? (Bhagabati	 ? et	 ? al.,	 ?2012).	 ?	 ?	 ? As	 ?one	 ?can	 ?see	 ?from	 ?the	 ?previous	 ?descriptions,	 ?there	 ?are	 ?potential	 ?problems	 ?with	 ?each	 ?type	 ?of	 ?cyclic	 ?fatigue	 ?test.	 ?	 ?This	 ?is	 ?likely	 ?the	 ?reason	 ?for	 ?such	 ?a	 ?delay	 ?in	 ?an	 ?ISO	 ? standard	 ? for	 ? the	 ? fatigue	 ? testing	 ?of	 ? rotary	 ? endodontic	 ? files.	 ? 	 ? It	 ?would	 ?be	 ? to	 ? the	 ?enhancement	 ?of	 ?the	 ?scientific	 ?literature	 ?if	 ?cyclic	 ?fatigue	 ?tests	 ?were	 ?to	 ?a	 ?standard,	 ?and	 ?therefore	 ?could	 ?be	 ?comparable	 ?to	 ?each	 ?other.	 ?	 ?	 ? 29	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 	 ?Figure	 ?2.11.	 ?Example	 ?of	 ?3-??point	 ?bending	 ?apparatus.	 ?	 ?Reprinted	 ? from	 ? Journal	 ? of	 ? Endodontics,	 ? Plotino	 ? et	 ? al,	 ? ?A	 ? Review	 ? of	 ? Cyclic	 ? Fatigue	 ?Testing	 ?of	 ?Nickel-?Titanium	 ?Rotary	 ?Instruments?,	 ?2009,	 ?35:1469-?1476,	 ?Copyright,	 ?with	 ?permission	 ?from	 ?Elsevier.	 ?	 ?	 ?	 ?	 ?	 ? 30	 ?2.2.2.	 ?Torsional	 ?Failure	 ?	 ?	 ? While	 ?cyclic	 ? fatigue	 ?will	 ?happen	 ? in	 ?a	 ?curved	 ?canal,	 ? file	 ? failure	 ?due	 ?to	 ? torque	 ?can	 ?happen	 ?in	 ?both	 ?a	 ?curved	 ?or	 ?straight	 ?canal.	 ?	 ?Torsional	 ?failure	 ?occurs	 ?when	 ?the	 ?tip	 ?binds	 ?within	 ?the	 ?canal	 ?and	 ?the	 ?shaft	 ?of	 ?the	 ?file	 ?continues	 ?to	 ?rotate.	 ?	 ?A	 ?stress	 ?is	 ?then	 ?placed	 ?within	 ? the	 ?metal	 ?and	 ? the	 ? file	 ?can	 ?separate.	 ? 	 ?A	 ?stress-??strain	 ?curve	 ?applies	 ? to	 ?the	 ? examination	 ? of	 ? torsional	 ? failure	 ? with	 ? endodontic	 ? rotary	 ? files.	 ? 	 ? As	 ? stress	 ? is	 ?continuously	 ?applied	 ?until	 ?the	 ?elastic	 ?limit	 ?of	 ?the	 ?metal	 ?is	 ?reached,	 ?the	 ?material	 ?will	 ?then	 ?arrive	 ?at	 ? its	 ?yield	 ?point.	 ? 	 ? If	 ?stress	 ? is	 ?continued	 ?to	 ?be	 ?applied	 ?beyond	 ?the	 ?yield	 ?point,	 ? deformation	 ? of	 ? the	 ? metal	 ? will	 ? begin	 ? to	 ? occur.	 ? 	 ? During	 ? this	 ? phase,	 ? plastic	 ?hardening	 ?occurs	 ?until	 ?the	 ?ultimate	 ?strength	 ?of	 ?the	 ?metal	 ?is	 ?reached	 ?and	 ?separation	 ?will	 ?occur	 ?shortly	 ?afterwards,	 ?albeit	 ?typically	 ?at	 ?a	 ?lower	 ?stress	 ?than	 ?that	 ?which	 ?was	 ?needed	 ?to	 ?reach	 ?the	 ?ultimate	 ?strength	 ?of	 ?the	 ?material	 ?(Yum	 ?et	 ?al.,	 ?2011).	 ?	 ?	 ?	 ? To	 ? the	 ? benefit	 ? of	 ? the	 ? discipline,	 ? there	 ? is	 ? a	 ? standard	 ? for	 ? torque	 ? testing	 ? of	 ?endodontic	 ?rotary	 ?files	 ?(ISO3630-??1,	 ?2008).	 ?	 ?This	 ?test	 ?is	 ?performed	 ?with	 ?an	 ?apparatus	 ?called	 ?a	 ?torsiometer.	 ?	 ?The	 ?last	 ?3mm	 ?of	 ?a	 ?file	 ?is	 ?clamped	 ?within	 ?the	 ?soft	 ?brass	 ?jaws	 ?of	 ?a	 ?torsiometer,	 ?from	 ?D0	 ?to	 ?D3.	 ?	 ?A	 ?motor	 ?rotates	 ?the	 ?file	 ?at	 ?a	 ?standard	 ?of	 ?two	 ?cycles	 ?per	 ?minute	 ?until	 ? failure.	 ? 	 ?A	 ?sensor	 ?records	 ? the	 ? torque	 ?applied	 ?and	 ? the	 ?rotational	 ?angle	 ?the	 ?file	 ?passed	 ?through	 ?until	 ?separation.	 ?	 ?	 ?	 ?The	 ?features	 ?of	 ?endodontic	 ?rotary	 ?files	 ?that	 ?contribute	 ?to	 ?their	 ?resistance	 ?to	 ?torsional	 ? failure	 ? are	 ? varied.	 ? 	 ? 	 ? Taper,	 ? tip	 ? size,	 ? and	 ? diameter	 ? of	 ? canal	 ? have	 ? been	 ?implicated	 ?in	 ?torsional	 ?failure,	 ?with	 ?the	 ?bigger	 ?tip	 ?sizes	 ?and	 ?larger	 ?tapers	 ?being	 ?able	 ?	 ?	 ? 31	 ?to	 ?withstand	 ?higher	 ?torque	 ?values	 ?(Sattapan	 ?et	 ?al.,	 ?2000b;	 ?Yared,	 ?2004).	 ? 	 ?However,	 ?other	 ?authors	 ?have	 ?identified	 ?features	 ?other	 ?than	 ?size	 ?of	 ?the	 ?file.	 ?	 ?Reducing	 ?the	 ?pitch	 ?of	 ?the	 ?file	 ?or	 ?in	 ?other	 ?words	 ?increasing	 ?the	 ?amount	 ?of	 ?cutting	 ?edges	 ?per	 ?unit	 ?length	 ?and	 ? also	 ? increasing	 ? the	 ? cross	 ? sectional	 ? area	 ? but	 ? not	 ? the	 ? core	 ? area	 ? of	 ? the	 ? file	 ? are	 ?suggested	 ?to	 ?increase	 ?torque	 ?values	 ?(Baek	 ?et	 ?al.,	 ?2011).	 ?	 ?The	 ?authors	 ?also	 ?suggested	 ?that	 ?rectangular	 ?cross	 ?sections	 ?are	 ?more	 ?resistant	 ?to	 ?torque	 ?than	 ?triangular	 ?sections.	 ?Moreover,	 ? other	 ? authors	 ? suggest	 ? the	 ? cross	 ? sectional	 ? dimensions	 ? of	 ? the	 ? file	 ? are	 ?significantly	 ? more	 ? important	 ? than	 ? tip	 ? size	 ? or	 ? taper	 ? with	 ? regard	 ? to	 ? withstanding	 ?torsional	 ?forces	 ?(Zhang	 ?et	 ?al.,	 ?2010).	 ?	 ?	 ? An	 ? interesting	 ? study	 ? discussed	 ? how	 ? the	 ? viscosity	 ? of	 ? lubricants	 ? affected	 ?torsion	 ? of	 ? files	 ? that	 ? were	 ? used	 ? in	 ? canals	 ? that	 ? contained	 ? mixtures	 ? of	 ? peroxide,	 ?surfactant	 ? and	 ? polyethylene	 ? glycol,	 ? with	 ? distilled	 ?water	 ? and	 ? sodium	 ? hypochlorite.	 ?	 ?They	 ?found	 ?that	 ?regardless	 ?of	 ?the	 ?lubricant	 ?used,	 ?no	 ?significant	 ?difference	 ?in	 ?torque	 ?values	 ?were	 ?measured	 ?after	 ?12	 ?times	 ?of	 ?repeated	 ?use	 ?(Siqueira	 ?et	 ?al.,	 ?2012).	 ?	 ?	 ?	 ? An	 ? interesting	 ? variation	 ? on	 ? measuring	 ? torque	 ? is	 ? called	 ? dynamic	 ? torque	 ? or	 ?torsional	 ? fatigue.	 ? 	 ? The	 ? latter	 ? name	 ? found	 ? in	 ? the	 ? literature	 ? may	 ? be	 ? confused	 ? with	 ?cyclical	 ? fatigue,	 ? which	 ? as	 ? explained	 ? has	 ? an	 ? entirely	 ? different	 ? failure	 ? mechanism.	 ?	 ?Dynamic	 ? torque	 ? is	 ? the	 ? repetitious	 ? rotation	 ?of	 ? the	 ? file	 ? to	 ? a	 ?predetermined	 ?angle	 ?or	 ?torque	 ?to	 ?a	 ?sub-??threshold	 ?failure	 ?level;	 ?a	 ?single	 ?rotation	 ?to	 ?failure,	 ?as	 ?specified	 ?in	 ?the	 ?ISO,	 ?is	 ?not	 ?a	 ?sufficient	 ?means	 ?to	 ?replicate	 ?clinical	 ?conditions	 ?(Cheung,	 ?2009;	 ?Park	 ?et	 ?al.,	 ?2010).	 ? 	 ?One	 ?study	 ?found	 ?that	 ?larger	 ?defection	 ?angles	 ?led	 ?to	 ?significantly	 ?greater	 ?	 ?	 ? 32	 ?failures	 ?in	 ?a	 ?dynamic	 ?torque	 ?model	 ?(Best	 ?et	 ?al.,	 ?2004),	 ?and	 ?another	 ?found	 ?that	 ?files	 ?with	 ? the	 ? same	 ?cross	 ? sectional	 ? shape	 ?had	 ?different	 ? results	 ?when	 ? tested	 ? in	 ?dynamic	 ?torque.	 ? 	 ? They	 ? proposed	 ? this	 ? difference	 ? was	 ? due	 ? to	 ? the	 ? differences	 ? of	 ? the	 ?manufacturing	 ?processes	 ?of	 ?the	 ?different	 ?files	 ?tested	 ?(Park	 ?et	 ?al.,	 ?2010).	 ?	 ?Ostensibly,	 ?when	 ?one	 ?deviates	 ?from	 ?a	 ?uniform	 ?method	 ?of	 ?testing	 ?such	 ?as	 ?the	 ?ISO	 ?torque	 ?test,	 ?the	 ?results	 ?become	 ?impossible	 ?to	 ?compare	 ?between	 ?tests.	 ?	 ?	 ?2.3.	 ?Fractographic	 ?Examination	 ?	 ?	 ?	 ? Fractographic	 ? examination	 ? is	 ? the	 ? viewing	 ? and	 ? description	 ? of	 ? the	 ? broken	 ?endodontic	 ?file	 ?from	 ?end	 ?of	 ?the	 ?file	 ?in	 ?the	 ?longitudinal	 ?axis	 ?(Cheung	 ?et	 ?al.,	 ?2005).	 ?	 ?It	 ?is	 ?accomplished	 ? with	 ? the	 ? aid	 ? of	 ? the	 ? scanning	 ? electron	 ? microscope	 ? (Figure	 ? 2.12).	 ?	 ?Features	 ?of	 ?fractography	 ?with	 ?regard	 ?to	 ?cyclic	 ?fatigue	 ?have	 ?been	 ?described	 ?in	 ?section	 ?2.2.1.	 ?	 ?Fractographic	 ?features	 ?with	 ?cyclic	 ?fatigue	 ?may	 ?involve	 ?more	 ?than	 ?one	 ?location	 ?of	 ? crack	 ? origin	 ? and	 ? progress	 ? along	 ? the	 ? file	 ? with	 ? small	 ? striations	 ? as	 ? the	 ? fatigue	 ?process	 ? continues.	 ? 	 ? Torsional	 ? failures	 ? have	 ? a	 ? markedly	 ? different	 ? pattern,	 ?characterized	 ? by	 ? swirl	 ? marks	 ? on	 ? the	 ? end	 ? of	 ? the	 ? file	 ? with	 ? the	 ? dimpled	 ? area	 ?characteristically	 ?located	 ?toward	 ?the	 ?center	 ?of	 ?the	 ?file.	 ?	 ?	 ? Sattapan	 ? described	 ? some	 ? of	 ? the	 ? differences	 ? between	 ? cyclic	 ? fatigue	 ? and	 ?torsional	 ?failures	 ?as	 ?being	 ?identified	 ?by	 ?the	 ?lateral	 ?appearance	 ?of	 ?the	 ?file	 ?(Sattapan	 ?et	 ?al.,	 ?2000a).	 ?	 ?He	 ?described	 ?torsional	 ?failures	 ?as	 ?being	 ?identified	 ?by	 ?file	 ?unwinding,	 ?and	 ?fatigue	 ?failures	 ?as	 ?having	 ?the	 ?absence	 ?of	 ?this	 ?identifier;	 ?however	 ?Cheung	 ?and	 ?others	 ?	 ?	 ? 33	 ?have	 ? shown	 ? that	 ? unwinding	 ? of	 ? the	 ? file	 ? may	 ? not	 ? occur	 ? yet	 ? the	 ? fractographic	 ?appearance	 ? of	 ? the	 ? file	 ? still	 ? suggests	 ? a	 ? torsional	 ? failure	 ? (Cheung	 ? et	 ? al.,	 ? 2005).	 ?Furthermore,	 ? Cheung	 ? described	 ? the	 ?majority	 ? of	 ? failures	 ? occur	 ? as	 ? a	 ? fatigue	 ? failure	 ?rather	 ?than	 ?a	 ?torsional	 ?failure.	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 	 ?	 ?Figure	 ?2.12.	 ?Typical	 ?examples	 ?fractographic	 ?images	 ?from	 ?fractured	 ?files.	 ?Torsional	 ?failure	 ?(above)	 ?and	 ?cyclical	 ?fatigue	 ?failure	 ?(below)	 ?are	 ?demonstrated.	 ?	 ?	 ? 34	 ?	 ?2.4.	 ?Overview	 ?of	 ?Thermo-??mechanical	 ?Modified	 ?Wire	 ?	 ?	 ? 	 ? Manufacturers	 ?of	 ?earlier	 ?generations	 ?of	 ?rotary	 ?Ni-??Ti	 ?files	 ?concentrated	 ?on	 ?the	 ?geometry	 ?of	 ?the	 ?file,	 ?either	 ?laterally	 ?such	 ?as	 ?the	 ?pitch	 ?and	 ?helical	 ?angle,	 ?or	 ?the	 ?geometry	 ? in	 ? cross	 ? section.	 ? 	 ? The	 ? current	 ? trend	 ? of	 ? attempts	 ? to	 ? improve	 ? the	 ?performance	 ?of	 ?these	 ?instruments	 ?is	 ?to	 ?manipulate	 ?the	 ?metallurgy,	 ?particularly	 ?with	 ?heat	 ? treatments,	 ? the	 ? details	 ? of	 ? which	 ? are	 ? proprietary.	 ? Interestingly,	 ? the	 ? crystal	 ?structure	 ?of	 ?martensite	 ? is	 ?better	 ? able	 ? to	 ?delay	 ? the	 ?onset	 ?of	 ? fatigue,	 ? as	 ? this	 ?may	 ?be	 ?attributed	 ? to	 ? its	 ? twinned	 ?atomic	 ? state	 ? (Shen	 ?et	 ? al.,	 ? 2011a;	 ?2011b).	 ? If	 ? a	 ? file	 ?has	 ? the	 ?simultaneous	 ? phases	 ? of	 ? austenite	 ? and	 ? martensite,	 ? it	 ? will	 ? have	 ? a	 ? better	 ? fatigue	 ?resistance	 ?than	 ?a	 ?file	 ?that	 ?exists	 ?in	 ?an	 ?austenite	 ?phase,	 ?as	 ?crack	 ?propagation	 ?occurs	 ?more	 ? rapidly	 ? in	 ? austenite	 ? than	 ?martensite	 ? (McKelvey	 ? and	 ? Ritchie,	 ? 1999).	 ? 	 ? Indeed	 ?this	 ?has	 ?been	 ?shown	 ?in	 ?newly	 ?introduced	 ?thermo-??mechanically	 ?modified	 ?rotary	 ?files	 ?(Alapati	 ?et	 ?al.,	 ?2009a;	 ?Shen	 ?et	 ?al.,	 ?2011b;	 ?Peters	 ?et	 ?al.,	 ?2012;	 ?Shen	 ?et	 ?al.,	 ?2013a).	 ?	 ?As	 ?mentioned,	 ?the	 ?ideal	 ?temperature	 ?to	 ?provide	 ?heat	 ?treatment	 ?is	 ?proprietary,	 ?however	 ?an	 ? interesting	 ? study	 ? showed	 ? heat	 ? treatments	 ? from	 ? 430-??440?C	 ? were	 ? able	 ? to	 ?significantly	 ? increase	 ? the	 ? fatigue	 ?resistance	 ?of	 ?Ni-??Ti	 ? rotary	 ? files,	 ?while	 ? instruments	 ?exposed	 ?to	 ?temperatures	 ?above	 ?and	 ?below	 ?this	 ?level	 ?showed	 ?a	 ?lower	 ?level	 ?of	 ?fatigue	 ?resistance	 ? (Zinelis	 ? et	 ? al.,	 ? 2007).	 ? 	 ? Alapati	 ? found	 ? he	 ? could	 ? manipulate	 ? the	 ? Af	 ?temperature	 ?of	 ?ProFile	 ?rotary	 ?instruments	 ?(Dentsply	 ?Tulsa	 ?Dental,	 ?Tulsa,	 ?OK)	 ?after	 ?heat	 ? treatments	 ? (Alapati	 ? et	 ? al.,	 ? 2009b).	 ? 	 ? Conventional	 ?NiTi	 ? files	 ? have	 ? an	 ? austenite	 ?structure	 ? at	 ? room	 ? or	 ? body	 ? temperatures,	 ? while	 ? CM	 ? wire	 ? displays	 ? higher	 ? Af	 ? than	 ?conventional	 ? NiTi	 ? (Shen	 ? et	 ? al.,	 ? 2011b)	 ? and	 ? as	 ? a	 ? result	 ? a	 ? greater	 ? amount	 ? of	 ? the	 ?	 ?	 ? 35	 ?instrument	 ?rests	 ?in	 ?the	 ?martensite	 ?phase	 ?at	 ?these	 ?same	 ?temperatures	 ?(Alapati	 ?et	 ?al.,	 ?2009a;	 ?Ye	 ?and	 ?Gao,	 ?2012;	 ?Zhou	 ?et	 ?al.,	 ?2012).	 ?Shen	 ?has	 ?reported	 ?CM	 ?wire	 ?as	 ?having	 ?a	 ?lower	 ? critical	 ? stress	 ? for	 ? the	 ? reorientation	 ? to	 ? martensite	 ? than	 ? other	 ? superelastic	 ?wires.	 ?	 ?Additionally,	 ?CM	 ?wire	 ?has	 ?a	 ?lower	 ?ultimate	 ?tensile	 ?strength	 ?but	 ?a	 ?significantly	 ?higher	 ?maximum	 ?strain	 ?than	 ?superelastic	 ?wires.	 ?	 ?These	 ?properties	 ?lead	 ?to	 ?a	 ?greater	 ?degree	 ? of	 ? flexibility	 ? of	 ? CM	 ? wires	 ? which	 ? contrasts	 ? sharply	 ? with	 ? conventional	 ? NiTi	 ?wire	 ?(Shen	 ?et	 ?al.,	 ?2013b).	 ?	 ?	 ?	 ?	 ?The	 ?physical	 ?properties	 ?and	 ?phase	 ?state	 ?of	 ?CM	 ?wires	 ?have	 ?an	 ?effect	 ?on	 ?cyclical	 ?fatigue,	 ? however	 ? environment	 ? also	 ? plays	 ? a	 ? role.	 ? 	 ? Shen	 ? et	 ? al.,	 ? found	 ? that	 ?when	 ? CM	 ?wire	 ?was	 ?immersed	 ?in	 ?a	 ?water	 ?bath,	 ?the	 ?fatigue	 ?resistance	 ?of	 ?this	 ?material	 ?was	 ?even	 ?greater.	 ? 	 ?A	 ?possible	 ?explanation	 ?for	 ?this	 ?is	 ?the	 ?liquid	 ?media	 ?may	 ?be	 ?acting	 ?as	 ?a	 ?heat	 ?sink	 ?during	 ? the	 ? fatigue	 ?process	 ?(Shen	 ?et	 ?al.,	 ?2011a).	 ? 	 ?Repeated	 ?autoclave	 ?cycles	 ?do	 ?not	 ?appear	 ?to	 ?effect	 ?the	 ?maximum	 ?torque	 ?values	 ?of	 ?CM	 ?wire	 ?(Casper	 ?et	 ?al.,	 ?2011),	 ?but	 ?it	 ?is	 ?unknown	 ?if	 ?these	 ?repeated	 ?autoclave	 ?cycles	 ?cause	 ?changes	 ?in	 ?fatigue	 ?resistance	 ?or	 ?in	 ?the	 ?phase	 ?composition	 ?of	 ?the	 ?files.	 ?	 ?	 ?	 ?2.5.	 ?Aim	 ?	 ?	 ?	 ? The	 ?aim	 ?of	 ?this	 ?study	 ?is	 ?to	 ?provide	 ?a	 ?detailed	 ?understanding	 ?of	 ?the	 ?effects	 ?of	 ?cyclical	 ? fatigue	 ? on	 ? the	 ? torsional	 ? failure	 ? values	 ? of	 ? conventional	 ? nickel-??titanium	 ?Typhoon	 ?and	 ?Typhoon	 ?CM	 ?instruments.	 ?	 ?	 ?	 ?	 ? 36	 ?	 ?	 ?	 ?Chapter	 ?3.	 ?Hypothesis	 ?	 ?	 ?	 ?There	 ?is	 ?no	 ?influence	 ?of	 ?previous	 ?exposure	 ?of	 ?cyclical	 ?fatigue	 ?on	 ?the	 ?torsional	 ?failure	 ?of	 ?conventional	 ?nickel-??titanium	 ?files	 ?or	 ?controlled	 ?memory	 ?Typhoon	 ?files.	 ?	 ?	 ?	 ? 37	 ?	 ?Chapter	 ?4.	 ?Material	 ?and	 ?Methods	 ?	 ?	 ?The	 ? fatigue	 ? testing	 ? protocol	 ? has	 ? been	 ? described	 ? previously	 ? and	 ? was	 ? reproduced	 ?throughout	 ?the	 ?experimental	 ?period	 ?(Shen	 ?et	 ?al.,	 ?2011a;	 ?2012).	 ?	 ?	 ?	 ?4.1.	 ?Specimen	 ?Section	 ?	 ?	 ?	 ? Typhoon?	 ? (Clinician?s	 ? Choice	 ? Dental	 ? Products,	 ? New	 ? Milford	 ? CT)	 ? rotary	 ?endodontic	 ? files	 ? were	 ? selected	 ? for	 ? this	 ? study	 ? because	 ? the	 ? same	 ? cross	 ? sectional	 ?design	 ?was	 ? found	 ? in	 ? both	 ? the	 ?NiTi	 ? and	 ? CM	 ? files.	 ? 	 ? File	 ? sizes	 ? 25.04	 ? and	 ? 40.04	 ?were	 ?selected	 ? for	 ?use	 ? in	 ?both	 ? file	 ? types	 ? to	 ?show	 ?any	 ?potential	 ?differences	 ? in	 ?behavior	 ?of	 ?the	 ?different	 ?file	 ?sizes	 ?or	 ?types.	 ?	 ?	 ?4.2.	 ?Method	 ?to	 ?Cyclically	 ?Fatigue	 ?Files	 ?	 ?	 ?	 ?	 ?	 ? NiTi	 ? rotary	 ? instruments	 ? of	 ? Typhoon	 ? and	 ? Typhoon	 ? CM	 ? were	 ? subjected	 ? to	 ?rotational	 ?bending	 ?at	 ?the	 ?curvature	 ?of	 ?46?	 ?with	 ?a	 ?9.5-??mm	 ?radius	 ?in	 ?deionized	 ?water	 ?at	 ?the	 ?temperature	 ?of	 ?23??	 ?2?C.	 ?Only	 ?a	 ?16-??mm	 ?length	 ?from	 ?the	 ?tip	 ?of	 ?the	 ?instrument	 ?was	 ?immersed	 ?in	 ?the	 ?liquid	 ?medium	 ?during	 ?the	 ?test	 ?to	 ?avoid	 ?galvanic	 ?action	 ?between	 ?the	 ? instrument	 ?and	 ? its	 ?handle	 ? (Shen	 ?et	 ?al.,	 ?2012).	 ?NiTi	 ?and	 ?CM	 ? files,	 ? in	 ?both	 ?25.04	 ?and	 ? 40.04	 ? were	 ? fatigued	 ? to	 ? failure	 ? and	 ? the	 ?mean	 ? for	 ? each	 ? file	 ? size	 ? and	 ? type	 ? was	 ?determined.	 ? 	 ?Subsequently,	 ?each	 ? file	 ?size	 ?and	 ? type	 ?was	 ?exposed	 ? to	 ?25%,	 ?50%,	 ?and	 ?	 ?	 ? 38	 ?75%	 ?of	 ?their	 ?respective	 ?mean	 ?fatigue	 ?life	 ?while	 ?immersed.	 ?	 ?Both	 ?the	 ?mean	 ?number	 ?of	 ?cycles	 ?to	 ?fatigue	 ?(mNCF)	 ?and	 ?time	 ?were	 ?recorded.	 ?A	 ?three	 ?point	 ?bending	 ?apparatus	 ?was	 ?used	 ?to	 ?cyclically	 ?preload	 ?the	 ?files,	 ?similar	 ?to	 ?the	 ?one	 ?demonstrated	 ?in	 ?Figure	 ?4.1	 ?and	 ?Figure	 ?4.2.	 ?	 ?Figure	 ?4.1.	 ?Demonstration	 ?of	 ?a	 ?three-??point	 ?bending	 ?apparatus.	 ?	 ?	 ?	 ? 39	 ?	 ? 	 ?	 ?	 ?Figure	 ?4.2.	 ?Demonstration	 ?of	 ?a	 ?CM	 ?file	 ?in	 ?the	 ?three-??point	 ?bending	 ?apparatus.	 ?	 ?	 ?	 ? 40	 ?In	 ? order	 ? to	 ?have	 ? the	 ? file	 ? placed	 ? at	 ? the	 ? correct	 ? position,	 ? it	 ?was	 ?necessary	 ? to	 ?locate	 ? the	 ? handpiece	 ? carefully	 ?within	 ? a	 ? rectangular	 ? notch	 ? at	 ? the	 ? top	 ? of	 ? the	 ? three-??point	 ?bending	 ?apparatus	 ?(see	 ?Figure	 ?4.1).	 ? 	 ?This	 ?was	 ?held	 ? in	 ?place	 ?with	 ?Triad	 ?Light	 ?Curing	 ? Material	 ? (Dentsply	 ? International,	 ? York,	 ? PA).	 ? 	 ? The	 ? top	 ? two	 ? pins	 ? on	 ? the	 ?apparatus	 ?were	 ?sitting	 ?passively	 ?against	 ?the	 ?file,	 ?while	 ?the	 ?majority	 ?of	 ?the	 ?curvature	 ?of	 ?the	 ?file	 ?was	 ?introduced	 ?as	 ?a	 ?result	 ?of	 ?the	 ?location	 ?of	 ?the	 ?lowest	 ?pin.	 ?	 ?There	 ?was	 ?a	 ?small	 ?notch	 ?cut	 ?into	 ?the	 ?lowest	 ?pin	 ?to	 ?keep	 ?the	 ?file	 ?centered	 ?in	 ?its	 ?longitudinal	 ?axis	 ?while	 ?rotating.	 ?	 ?An	 ?ongoing	 ?test	 ?is	 ?demonstrated	 ?in	 ?Figure	 ?4.3.	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?Figure	 ?4.3.	 ?CM	 ?file	 ?being	 ?exposed	 ?to	 ?cyclic	 ?fatigue	 ?in	 ?a	 ?water	 ?environment.	 ?	 ?	 ?	 ?	 ? 41	 ?4.3.	 ?Method	 ?to	 ?determine	 ?angle	 ?of	 ?deflection	 ?and	 ?radius	 ?	 ?	 ? In	 ?order	 ?to	 ?determine	 ?the	 ?angle	 ?of	 ?file	 ?deflection	 ?and	 ?distance	 ?of	 ?the	 ?radius,	 ?the	 ? software	 ? program	 ? ?ImageJ?	 ?was	 ? used	 ? (National	 ? Institutes	 ? of	 ?Health,	 ? Bethesda,	 ?Maryland).	 ? 	 ? The	 ? determination	 ? of	 ? the	 ? angle	 ? of	 ? deflection	 ? and	 ? radius	 ? was	 ?accomplished	 ?by	 ? creating	 ? an	 ? arc	 ? and	 ? then	 ? subsequently	 ?measuring	 ? it	 ? as	 ? shown	 ? in	 ?Figure	 ?4.4.	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 	 ?Figure	 ?4.4.	 ?	 ?Drawing	 ?the	 ?arc	 ?prior	 ?to	 ?measurement.	 ?	 ?	 ?	 ? 42	 ?	 ? Once	 ?the	 ?arc	 ?had	 ?been	 ?created,	 ?the	 ?angle	 ?was	 ?determined	 ?using	 ?the	 ?software.	 ?	 ?The	 ?distance	 ?of	 ?the	 ?radius	 ?was	 ?determined	 ?by	 ?the	 ?use	 ?of	 ?the	 ?ruler	 ?in	 ?the	 ?calibrated	 ?photograph,	 ?as	 ?demonstrated	 ?in	 ?Figure	 ?4.5.	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 	 ?Figure	 ?4.5.	 ?Calculation	 ?of	 ?radius	 ?and	 ?curvature	 ?angle.	 ?	 ?	 ?	 ? 43	 ?4.4.	 ?Torsion	 ?Testing	 ?	 ?	 ? The	 ? files	 ? from	 ?each	 ?group	 ?had	 ?their	 ?handles	 ?removed	 ?to	 ? facilitate	 ? testing	 ? in	 ?the	 ?torsiometer	 ?by	 ?the	 ?use	 ?of	 ?crimping	 ?pliers.	 ?	 ?The	 ?handles	 ?of	 ?Typhoon	 ?files	 ?used	 ?in	 ?this	 ?experiment	 ?were	 ?glued	 ?on	 ?at	 ?time	 ?of	 ?their	 ?manufacture,	 ?so	 ?one	 ?option	 ?to	 ?remove	 ?the	 ? handle	 ? was	 ? the	 ? use	 ? of	 ? a	 ? flame,	 ? that	 ? could	 ? be	 ? used	 ? to	 ? soften	 ? the	 ? glue	 ? as	 ?demonstrated	 ?in	 ?Figure	 ?4.6.	 ?	 ?However,	 ?the	 ?handle	 ?could	 ?more	 ?simply	 ?be	 ?cut	 ?from	 ?the	 ?file	 ?with	 ?crimping	 ?pliers	 ?prior	 ?to	 ?insertion	 ?in	 ?the	 ?torsiometer.	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 	 ?Figure	 ?4.6.	 ?Removal	 ?of	 ?a	 ?file	 ?handle	 ?prior	 ?to	 ?a	 ?torsion	 ?test.	 ?	 ?	 ?	 ? 44	 ?The	 ?subsequent	 ?groups	 ?of	 ?previously	 ?cyclically	 ?preloaded	 ?files	 ?were	 ?exposed	 ?to	 ? torsional	 ? loading	 ? tests,	 ?with	 ? the	 ?exception	 ?of	 ?one	 ?group	 ? that	 ?was	 ?not	 ?precycled	 ?and	 ? considered	 ? to	 ? be	 ? the	 ? control	 ? group.	 ? 	 ? The	 ? torque	 ? tests	 ? were	 ? performed	 ? in	 ? a	 ?torsion	 ? tester	 ? (also	 ? known	 ? as	 ? a	 ? torsiometer)	 ? until	 ? rupture	 ? to	 ? establish	 ? each	 ? file's	 ?mean	 ? value	 ? of	 ? torque	 ? to	 ? failure	 ? and	 ? maximum	 ? angular	 ? deflection	 ? of	 ? each	 ? group	 ?(Lopes	 ? et	 ? al.,	 ? 2013).	 ? The	 ? torsion	 ? tests	 ? were	 ? performed	 ? based	 ? on	 ? International	 ?Organization	 ? for	 ? Standardization	 ? ISO	 ? 3630-??1	 ? (ISO3630-??1,	 ? 2008)	 ? using	 ? a	 ? torsion	 ?machine.	 ? The	 ? rotation	 ? speed	 ? was	 ? set	 ? clockwise	 ? to	 ? two	 ? revolutions	 ? per	 ? minute	 ?(RPM).	 ? The	 ? end	 ? of	 ? the	 ? shaft	 ? was	 ? clamped	 ? into	 ? a	 ? chuck	 ? connected	 ? to	 ? a	 ? reversible	 ?geared	 ?motor.	 ? Three	 ?millimeters	 ? of	 ? the	 ? instrument?s	 ? tip	 ?were	 ? clamped	 ? in	 ? another	 ?chuck	 ?with	 ? brass	 ? jaws	 ? to	 ? prevent	 ? sliding.	 ? The	 ? torsional	 ? load	 ? and	 ? distortion	 ? angle	 ?were	 ?recorded	 ?until	 ?the	 ?file	 ?separated.	 ?	 ?4.5.	 ?Fractographic	 ?Examination	 ?	 ?The	 ? fracture	 ? surfaces	 ? of	 ? all	 ? fragments	 ? were	 ? examined	 ? under	 ? a	 ? scanning	 ? electron	 ?microscope	 ? (SEM;	 ? Stereoscan	 ? 260;	 ? Cambridge	 ? Instruments,	 ? Cambridge,	 ? UK).	 ? The	 ?region	 ? in	 ? which	 ? the	 ? dimple	 ? area	 ? could	 ? be	 ? found	 ? was	 ? outlined	 ? on	 ? the	 ?photomicrograph	 ? for	 ? fatigue	 ? failure	 ? groups,	 ? and	 ? measured	 ? with	 ? ImageJ	 ? 1.4	 ? g	 ?software	 ?(National	 ?Institutes	 ?of	 ?Health,	 ?Bethesda,	 ?MD)	 ?on	 ?each	 ?photomicrograph.	 ?	 ?	 ?	 ?	 ?	 ? 45	 ?4.6.	 ?Statistical	 ?Analysis	 ?	 ?	 ? The	 ?results	 ?were	 ?analyzed	 ?by	 ?using	 ?one-??way	 ?ANOVA	 ?with	 ?post	 ?hoc	 ?analysis	 ?	 ?(SPSS	 ?for	 ?Windows	 ?11.0,	 ?SPSS,	 ?Chicago,	 ?IL)	 ?at	 ?a	 ?significance	 ?level	 ?of	 ?P	 ?<	 ?.05.	 ?	 ?	 ?	 ?	 ? 46	 ?	 ?	 ?Chapter	 ?5.	 ?	 ?Results	 ?	 ?	 ?	 ? Within	 ?a	 ?water	 ?environment,	 ?both	 ?sizes	 ?25.04	 ?and	 ?40.04	 ?TYP	 ?CM	 ?instruments	 ?had	 ?a	 ?significantly	 ?higher	 ?number	 ?of	 ?revolutions	 ?in	 ?fatigue	 ?testing	 ?when	 ?compared	 ?to	 ? conventional	 ? nickel-??titanium	 ? instruments	 ? (P	 ? <	 ? .05).	 ? 	 ? Table	 ? 5.1	 ? represents	 ? the	 ?cyclical	 ?fatigue	 ?life	 ?of	 ?25.04	 ?and	 ?40.04,	 ?both	 ?in	 ?NiTi	 ?and	 ?CM.	 ?	 ?	 ?In	 ?size	 ?25.04,	 ?there	 ?was	 ?no	 ?difference	 ?in	 ?torque	 ?between	 ?the	 ?CM	 ?files	 ?and	 ?the	 ?conventional	 ? NiTi	 ? files	 ? (Table	 ? 5.2)	 ? (P	 ? >	 ? .05).	 ? The	 ? torque	 ? of	 ? size	 ? 40.04	 ? files	 ? was	 ?significantly	 ? higher	 ? than	 ? the	 ? torque	 ? of	 ? size	 ? 25.04	 ? files	 ? (P	 ? <	 ? 0.05).	 ? There	 ? was	 ? no	 ?significant	 ? difference	 ? of	 ? torque	 ? value	 ? TYP	 ? CM	 ? and	 ? TYP	 ? instruments	 ? of	 ? size	 ? 25.04	 ?between	 ?precycling	 ?and	 ?no	 ?precycling	 ?groups.	 ?	 ?In	 ?the	 ?40.04	 ?TYP	 ?group,	 ?the	 ?75%	 ?pre-??cycling	 ?group	 ?had	 ?a	 ?significantly	 ?lower	 ?torque	 ? than	 ? the	 ? no	 ? precycling	 ? group	 ? (P	 ? <	 ? .05).	 ? 	 ? In	 ? the	 ? TYP	 ? CM	 ? 40.04	 ? group,	 ? the	 ?preloading	 ? groups	 ? (25%,	 ? 50%	 ? and	 ? 75%)	 ? had	 ? a	 ? smaller	 ? distortion	 ? angle	 ? until	 ?fracture	 ?than	 ?the	 ?no	 ?preloading	 ?group	 ?(P	 ?<	 ?.05).	 ?	 ?	 ?The	 ? CM	 ? files	 ? of	 ? both	 ? sizes	 ? had	 ? a	 ? significantly	 ? higher	 ? distortion	 ? angle	 ? than	 ?conventional	 ? NiTi	 ? files	 ? of	 ? both	 ? sizes	 ? (P	 ? <	 ? .05).	 ? The	 ?mean	 ? and	 ? standard	 ? deviation	 ?were	 ?calculated	 ?as	 ?indicated	 ?in	 ?Tables	 ?5.1,	 ?5.2	 ?and	 ?5.3.	 ?	 ?	 ? 47	 ?	 ?	 ?	 ?Table	 ?5.1	 ?	 ?The	 ?number	 ?of	 ?revolutions	 ?until	 ?fracture	 ?of	 ?Typhoon	 ?NiTi	 ?and	 ?CM	 ?files	 ?at	 ?a	 ?curvature	 ?46?	 ?with	 ?a	 ?9.5mm	 ?radius	 ?in	 ?a	 ?water	 ?environment	 ?(mean	 ??	 ?S.D.)	 ?	 ?Brands	 ? Size	 ?25/.04*	 ? Size	 ?40/.04*	 ?Typhoon	 ?NiTi&	 ? 579	 ??	 ?119	 ? 320	 ??	 ?52	 ?Typhoon	 ?CM&	 ? 3968	 ??	 ?632	 ? 2143	 ??	 ?307	 ?	 ?*	 ?There	 ?was	 ?a	 ?statistically	 ?significant	 ?difference	 ?between	 ?the	 ?file	 ?sizes	 ?(p<0.05).	 ?	 ?&	 ?There	 ?was	 ?a	 ?statistically	 ?significant	 ?difference	 ?between	 ?the	 ?CM	 ?and	 ?NiTi	 ?files	 ?(p<0.05).	 ?	 ?	 ?	 ?	 ? 48	 ?	 ?	 ?Table	 ?5.2	 ?(a)	 ?	 ?Torque	 ?and	 ?distortion	 ?angle	 ?at	 ?fracture	 ?by	 ?torque	 ?of	 ?	 ?25.04	 ?Typhoon	 ?NiTi	 ?and	 ?CM	 ?files	 ?fatigued	 ?0	 ??	 ?75%	 ?of	 ?the	 ?number	 ?of	 ?rotations	 ?to	 ?failure	 ?by	 ?fatigue	 ?(mean	 ??	 ?S.D.)	 ?	 ?	 ?mNCF:	 ?the	 ?total	 ?number	 ?of	 ?revolutions	 ?to	 ?failure.	 ?	 ?*	 ?There	 ?was	 ?a	 ?statistically	 ?significant	 ?difference	 ?between	 ?in	 ?distortion	 ?angle	 ?between	 ?the	 ?CM	 ?and	 ?NiTi	 ?files	 ?(P<0.05).	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?Size	 ?25.04	 ?Typhoon	 ?CM	 ? Typhoon	 ?NiTi	 ?Cyclic	 ?pre-??cycling	 ?of	 ?mNCF	 ?	 ?mNCF	 ? Torque	 ?(N?	 ?mm)	 ? Distortion	 ?Angle*	 ?(?)	 ? 	 ?	 ?	 ?	 ?	 ?mNCF	 ? Torque	 ?(N?	 ?mm)	 ? Distortion	 ?Angle*	 ?(?)	 ?0	 ? 0	 ? 3.85	 ??	 ?0.47	 ? 792	 ??	 ?50	 ? 0	 ? 3.63	 ??	 ?0.89	 ? 500	 ??	 ?61	 ?25%	 ? 992	 ? 3.56	 ??	 ?0.40	 ? 743	 ??	 ?58	 ? 147	 ? 3.30	 ??	 ?0.33	 ? 486	 ??	 ?39	 ?50%	 ? 1984	 ? 3.36	 ??	 ?0.35	 ? 747	 ??	 ?75	 ? 290	 ? 3.44	 ??	 ?0.36	 ? 479	 ??36	 ?75%	 ? 2976	 ? 3.33	 ??	 ?0.66	 ? 778	 ??	 ?93	 ? 434	 ? 3.48	 ??	 ?0.44	 ? 482	 ??	 ?25	 ?	 ?	 ? 49	 ?	 ? Table	 ?5.2	 ?(b)	 ?	 ?Resistance	 ?to	 ?torque	 ?of	 ?40.04	 ?Typhoon	 ?NiTi	 ?and	 ?CM	 ?files	 ?after	 ?cyclic	 ?precycling	 ?of	 ?the	 ?mNCF	 ?	 ?	 ?mNCF:	 ?the	 ?total	 ?number	 ?of	 ?revolutions	 ?to	 ?failure;	 ?	 ?*	 ?There	 ?was	 ?a	 ?statistically	 ?significant	 ?difference	 ?in	 ?distortion	 ?angle	 ?between	 ?the	 ?CM	 ?and	 ?NiTi	 ?files	 ?(P<0.05).	 ?&	 ?There	 ?was	 ?a	 ?statistically	 ?significant	 ?difference	 ?in	 ?torque	 ?of	 ?40.04	 ?NiTi	 ?files	 ?between	 ?no	 ?cyclic	 ?precycling	 ?of	 ?the	 ?mNCF	 ?and	 ?75%	 ?cyclic	 ?precycling	 ?of	 ?the	 ?mNCF	 ?(P<0.05).	 ?	 ?	 ?	 ??,	 ??	 ?There	 ?was	 ?a	 ?statistically	 ?significant	 ?difference	 ?in	 ?distortion	 ?angle	 ?in	 ?CM	 ?files	 ?between	 ?those	 ?that	 ?were	 ?not	 ?precycled	 ?and	 ?those	 ?that	 ?were	 ?precycled.	 ?	 ?No	 ?difference	 ?was	 ?found	 ?within	 ?the	 ?CM	 ?precycled	 ?files,	 ?regardless	 ?if	 ?they	 ?were	 ?precycled	 ?to	 ?25%,	 ?50%	 ?or	 ?75%.	 ?	 ?	 ?	 ?	 ?	 ?Size	 ?40.04	 ?Typhoon	 ?CM	 ? Typhoon	 ?NiTi	 ?Cyclic	 ?pre-??cycling	 ?of	 ?mNCF	 ?	 ?mNCF	 ? Torque	 ?(N?	 ?mm)	 ? Distortion	 ?Angle*	 ?(?)	 ? 	 ?	 ?	 ?	 ?	 ?mNCF	 ? Torque	 ?(N?	 ?mm)	 ? Distortion	 ?Angle*	 ?(?)	 ?	 ?0	 ? 	 ?0	 ? 	 ?11.29	 ??	 ?0.78	 ? 	 ?924?	 ?108?	 ? 	 ?0	 ? 	 ?13.38	 ??	 ?2.60&	 ? 	 ?412	 ??	 ?37	 ?	 ?25%	 ? 	 ?536	 ? 	 ?12.16	 ??	 ?1.14	 ? 	 ?750	 ??	 ?60? 	 ?80	 ? 	 ?12.12	 ??	 ?1.59	 ? 	 ?430	 ??	 ?44	 ?	 ?50%	 ? 	 ?1072	 ? 	 ?12.13	 ??	 ?1.11	 ? 	 ?738	 ??	 ?106?	 ? 	 ?160	 ? 	 ?12.43	 ??	 ?1.38	 ? 	 ?417	 ??	 ?36	 ?	 ?75%	 ? 	 ?1608	 ? 	 ?11.26	 ??	 ?1.52	 ? 	 ?712	 ??	 ?109?	 ? 	 ?240	 ? 	 ?10.63?	 ?1.38&	 ? 	 ?447	 ??	 ?44	 ?	 ?	 ? 50	 ?	 ?	 ? 	 ?	 ?Table	 ?5.3	 ?Time	 ?to	 ?failure	 ?by	 ?cyclic	 ?fatigue	 ?in	 ?a	 ?water	 ?environment	 ?at	 ?9.5mm	 ?radius	 ?and	 ?46?	 ?curvature	 ?(mean	 ??	 ?S.D.)	 ?	 ?Brands	 ? Size	 ?25/.04*	 ? Size	 ?40/.04*	 ?Typhoon	 ?NiTi&	 ? 1	 ?min	 ?9	 ?sec	 ?	 ??	 ?14	 ?sec	 ? 38	 ?sec	 ??	 ?6	 ?sec	 ?Typhoon	 ?CM&	 ? 7	 ?min	 ?56	 ?sec	 ??	 ?1	 ?min	 ?16	 ?sec	 ? 4	 ?min	 ?16	 ?sec	 ??	 ?37	 ?sec	 ?	 ?	 ?*	 ?There	 ?was	 ?a	 ?statistically	 ?significant	 ?difference	 ?between	 ?the	 ?file	 ?sizes	 ?(p<0.05).	 ?	 ?&	 ?There	 ?was	 ?a	 ?statistically	 ?significant	 ?difference	 ?between	 ?the	 ?CM	 ?and	 ?NiTi	 ?files	 ?(p<0.05).	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 51	 ?Fractographically,	 ? the	 ? images	 ?represent	 ?different	 ?patterns	 ? that	 ?were	 ? largely	 ?dependent	 ?on	 ? the	 ? composition	 ?of	 ? the	 ? file.	 ? 	 ? Typically,	 ? the	 ? files	 ?made	 ? from	 ?CM	 ?wire	 ?had	 ? a	 ? much	 ? smaller	 ? dimpled	 ? area	 ? displayed	 ? through	 ? the	 ? scanning	 ? electron	 ?microscope.	 ? 	 ? TYP	 ?CM	 ? instruments	 ?had	 ?a	 ?higher	 ?number	 ?of	 ? crack	 ?origins	 ? than	 ?TYP	 ?files	 ? in	 ? fatigue	 ?failure	 ?groups	 ?only	 ?(Figure	 ?5.1).	 ?The	 ?values	 ?of	 ? the	 ?area	 ?occupied	 ?by	 ?the	 ? dimple	 ? region	 ? as	 ? part	 ? of	 ? the	 ? total	 ? surface	 ? area	 ? of	 ? the	 ? fractured	 ? cross-??section	 ?were	 ?smaller	 ?on	 ?TYP	 ?CM	 ?instruments	 ?(Figure	 ?5.1A)	 ?than	 ?on	 ?TYP	 ?instruments	 ?(Figure	 ?5.1B)	 ? in	 ? only	 ? the	 ? fatigue	 ? failure	 ? groups.	 ? This	 ? was	 ? evident	 ? in	 ? both	 ? file	 ? sizes.	 ? 	 ? The	 ?appearances	 ?of	 ? the	 ? fractured	 ?surface	 ?after	 ? the	 ? torsion	 ? test	 ?all	 ?exhibited	 ? the	 ? typical	 ?pattern	 ?of	 ? torsional	 ? fracture	 ?characterized	 ?by	 ?circular	 ?abrasion	 ?marks	 ?and	 ?skewed	 ?dimples	 ?near	 ?the	 ?center	 ?of	 ?rotation	 ?(Figure	 ?5.1C-??F).	 ?	 ? A	 ? closer	 ? image	 ? in	 ? Figure	 ? 5.2	 ? A	 ? and	 ? B	 ? is	 ? the	 ? same	 ? 25.04	 ? NiTi	 ? file	 ? at	 ? 100%	 ?fatigue.	 ? 	 ? Figure	 ? 5.2	 ? A	 ? shows	 ? the	 ? fractured	 ? file	 ? while	 ? Figure	 ? 5.2	 ? B	 ? shows	 ? the	 ?delineation	 ?of	 ?the	 ?dimpled	 ?as	 ?opposed	 ?to	 ?the	 ?non-??dimpled	 ?area.	 ?	 ?Note	 ?that	 ?a	 ?dimpled	 ?area	 ? represents	 ? the	 ?majority	 ?of	 ? the	 ?area	 ? in	 ? this	 ? cross	 ? section	 ?view	 ?of	 ? the	 ?NiTi	 ? file.	 ?	 ?Figure	 ?5.3	 ?is	 ?a	 ?conventional	 ?NiTi	 ?40.04	 ?file	 ?that	 ?has	 ?a	 ?dimpled	 ?area	 ?quite	 ?similar	 ?to	 ?that	 ?shown	 ?in	 ?Figure	 ?5.3B,	 ?with	 ?the	 ?majority	 ?of	 ?the	 ?file	 ?displaying	 ?dimples.	 ?	 ?In	 ?Figure	 ?5.4,	 ?a	 ?40.04	 ?CM	 ?file	 ?is	 ?shown	 ?that	 ?has	 ?a	 ?much	 ?less	 ?dimpled	 ?area	 ?than	 ?the	 ?same	 ?sized	 ?conventional	 ? NiTi	 ? files.	 ? 	 ? The	 ? images	 ? selected	 ? for	 ? these	 ? figures	 ? are	 ? typical	 ? and	 ?representative	 ?from	 ?those	 ?of	 ?their	 ?group.	 ?	 ?	 ?	 ? 52	 ?	 ?Figure	 ?5.1.	 ?	 ?A	 ?photomicrograph	 ?of	 ?a	 ?fracture	 ?surface	 ?of	 ?(A)	 ?Typhoon	 ?CM	 ?instrument,	 ?and	 ?(B)	 ?Typhoon	 ?instrument	 ?with	 ?the	 ?region	 ?of	 ?fatigue	 ?crack	 ?propagation	 ?and	 ?dimple	 ?area	 ?outlined	 ?(dotted	 ?line)	 ?with	 ?crack	 ?origins	 ?(arrows)	 ?in	 ?fatigue	 ?test;	 ?(C)	 ?Typhoon	 ?CM	 ?instrument,	 ?and	 ?(D)	 ?Typhoon	 ?instrument	 ?in	 ?torsion	 ?test	 ?without	 ?preloaded	 ?group;	 ?the	 ?75%	 ?cyclically	 ?preloaded	 ?of	 ?(E)	 ?Typhoon	 ?CM	 ?instrument,	 ?and	 ?(F)	 ?Typhoon	 ?instrument	 ?in	 ?torsion	 ?test.	 ?	 ?	 ? 53	 ?	 ?	 ?Figure	 ?5.2.	 ?Demonstration	 ?of	 ?conventional	 ?NiTi	 ?before	 ?(above)	 ?and	 ?after	 ?outlining	 ?(below)	 ?of	 ?dimpled	 ?area.	 ?	 ? 54	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ?Figure	 ?5.3.	 ?	 ?40.04	 ?NiTi	 ?dimpled	 ?area	 ?demonstration.	 ?	 ?The	 ?dimpled	 ?area	 ?represents	 ?the	 ?majority	 ?of	 ?the	 ?area	 ?in	 ?this	 ?cross-??sectional	 ?view,	 ?which	 ?lie	 ?within	 ?the	 ?boundaries	 ?of	 ?the	 ?dotted	 ?line.	 ?	 ?	 ?	 ?	 ?	 ?	 ? 55	 ?	 ?	 ?	 ?	 ?	 ?	 ?Figure	 ?5.4.	 ?Demonstration	 ?of	 ?40.04	 ?CM	 ?dimpled	 ?area.	 ?	 ?	 ?Note	 ?that	 ?the	 ?crack	 ?origins	 ?are	 ?from	 ?each	 ?point	 ?of	 ?the	 ?triangle	 ?in	 ?this	 ?sample.	 ?	 ?	 ?	 ?	 ?	 ?	 ?	 ? 56	 ?	 ?Chapter	 ?6.	 ?Discussion	 ?	 ?	 ?	 ? The	 ? aim	 ? of	 ? this	 ? study	 ?was	 ? to	 ? provide	 ? deep	 ? insight	 ? into	 ? the	 ? effect	 ? of	 ? cyclic	 ?fatigue	 ? on	 ? torsional	 ? failure	 ? of	 ? Typhoon	 ?CM	 ? instruments	 ? by	 ? varying	 ? the	 ? amount	 ? of	 ?cyclic	 ? preloading.	 ? Cyclic	 ? fatigue	 ? of	 ? NiTi	 ? rotary	 ? instruments	 ? has	 ? been	 ? studied	 ?extensively	 ?under	 ?simulated	 ?conditions	 ?(Chan	 ?&	 ?Cheung,	 ?1996;	 ?Plotino	 ?et	 ?al.,	 ?2009).	 ?	 ?The	 ? fatigue	 ? resistance	 ? of	 ? TYP	 ? CM	 ? files	 ? has	 ? been	 ? evaluated	 ? as	 ? an	 ? isolated	 ? process.	 ?	 ?The	 ? literature	 ? has	 ? limited	 ? information	 ? about	 ? torsional	 ? resistance	 ? of	 ?thermomechanically	 ?treated	 ?files,	 ?and	 ?very	 ?little	 ?specifically	 ?about	 ?TYP	 ?CM	 ?files.	 ?The	 ?torsional	 ? property	 ? of	 ? another	 ? CM	 ? instrument,	 ? Coltene	 ? Hyflex	 ? CM	 ? (Coltene	 ?Whaledent,	 ? Cuyahoga	 ? Falls,	 ? OH),	 ? manufactured	 ? from	 ? a	 ? similar	 ? alloy	 ? has	 ? been	 ?recently	 ? reported	 ? (Pettiette	 ? et	 ? al.,	 ? 2001;	 ? Peters	 ? et	 ? al.,	 ? 2012).	 ? It	 ? is	 ? also	 ? known	 ? that	 ?rotary	 ? instruments	 ? experience	 ? both	 ? cyclic	 ? fatigue	 ? and	 ? torsional	 ? stress	 ?simultaneously	 ? when	 ? actively	 ? cutting	 ? dentin	 ? in	 ? curved	 ? canals	 ? (Blum	 ? et	 ? al.,	 ? 1999;	 ?Cheung	 ?and	 ?Liu,	 ?2009).	 ?	 ?	 ?There	 ?is	 ?a	 ?scarcity	 ?of	 ?reports	 ?that	 ?examine	 ?the	 ?combined	 ?effect	 ?of	 ?these	 ?two	 ?factors	 ? for	 ? instrument	 ? fracture.	 ? In	 ? the	 ? present	 ? study,	 ? the	 ? torsional	 ? tests	 ? were	 ?performed	 ?on	 ?the	 ?third	 ?millimeter	 ?from	 ?the	 ?instrument's	 ?tip	 ?based	 ?on	 ?the	 ?position	 ?of	 ?the	 ?files	 ?that	 ?were	 ?previously	 ?submitted	 ?to	 ?the	 ?maximum	 ?curvature	 ?during	 ?flexural	 ?fatigue	 ? tests.	 ? When	 ? flexural	 ? fatigue	 ? and	 ? torsion	 ? were	 ? combined,	 ? these	 ? effects	 ?occurred	 ?at	 ?the	 ?same	 ?segment	 ?of	 ?the	 ?file.	 ?It	 ?should	 ?be	 ?emphasized,	 ?however,	 ?that	 ?the	 ?	 ?	 ? 57	 ?complexity	 ?of	 ? the	 ?clinical	 ?situation	 ?cannot	 ?be	 ? fully	 ?reproduced	 ? in	 ?vitro.	 ?Regardless,	 ?the	 ? test	 ? method	 ? in	 ? the	 ? present	 ? study	 ? may	 ? be	 ? one	 ? step	 ? closer	 ? to	 ? a	 ? more	 ?comprehensive	 ?representation	 ?of	 ?clinical	 ?conditions.	 ?	 ? Thermomechanical	 ? processing	 ? is	 ? a	 ? frequently	 ? used	 ?method	 ? to	 ? optimize	 ? the	 ?microstructure	 ?and	 ?transformation	 ?behavior	 ?of	 ?NiTi	 ?alloys,	 ?which	 ?in	 ?turn	 ?have	 ?great	 ?influence	 ? on	 ? the	 ? reliability	 ? and	 ? mechanical	 ? properties	 ? of	 ? NiTi	 ? files	 ? (Pruett	 ? et	 ? al.,	 ?1997;	 ? Zuolo	 ? and	 ? Walton,	 ? 1997;	 ? Arens	 ? et	 ? al.,	 ? 2003;	 ? Hou	 ? et	 ? al.,	 ? 2011;	 ? Shen	 ? et	 ? al.,	 ?2011b;	 ? Zhou	 ? et	 ? al.,	 ? 2012).	 ? 	 ? Typhoon	 ? CM	 ? rotary	 ? instruments	 ? were	 ? recently	 ?characterized	 ?by	 ?an	 ?austenitic	 ?finish	 ?temperature	 ?of	 ?approximately	 ?55?C,	 ?indicating	 ?that	 ?at	 ?body	 ?temperature,	 ?the	 ?instrument	 ?would	 ?contain	 ?a	 ?significant	 ?proportion	 ?of	 ?martensitic	 ?alloy	 ?(Pruett	 ?et	 ?al.,	 ?1997;	 ?Parashos	 ?et	 ?al.,	 ?2004;	 ?Cheung	 ?et	 ?al.,	 ?2005;	 ?Shen	 ?et	 ?al.,	 ?2009b;	 ?Gao	 ?et	 ?al.,	 ?2010;	 ?Shen	 ?et	 ?al.,	 ?2011b).	 ?The	 ?martensitic	 ?form	 ?of	 ?NiTi	 ?has	 ?high	 ?resistance	 ?to	 ?fatigue.	 ?Therefore,	 ?it	 ?was	 ?not	 ?surprising	 ?that	 ?TYP	 ?CM	 ?instruments	 ?were	 ? more	 ? resistant	 ? to	 ? cyclic	 ? fatigue	 ? than	 ? the	 ? TYP	 ? instruments	 ? in	 ? both	 ? air	 ? and	 ?aqueous	 ?media	 ?(Sattapan	 ?et	 ?al.,	 ?2000a;	 ?Shen	 ?et	 ?al.,	 ?2011a)	 ?(Ha?kel	 ?et	 ?al.,	 ?1999;	 ?Shen	 ?et	 ?al.,	 ?2006;	 ?2012).	 ? 	 ?This	 ?was	 ?also	 ?confirmed	 ?by	 ?the	 ?present	 ?findings	 ?in	 ?an	 ?aqueous	 ?media.	 ?As	 ?a	 ?general	 ?rule,	 ?flexible	 ?instruments	 ?have	 ?been	 ?assumed	 ?to	 ?be	 ?less	 ?resistant	 ?to	 ? torsional	 ? load	 ? (Pruett	 ? et	 ? al.,	 ? 1997;	 ? Sattapan	 ? et	 ? al.,	 ? 2000a;	 ? Kramkowski	 ? and	 ?Bahcall,	 ?2009;	 ?Larsen	 ?et	 ?al.,	 ?2009;	 ?Alapati	 ?et	 ?al.,	 ?2009a;	 ?Gao	 ?et	 ?al.,	 ?2010;	 ?Gambarini	 ?et	 ?al.,	 ?2011;	 ?Kim	 ?et	 ?al.,	 ?2012;	 ?Wycoff	 ?and	 ?Berzins,	 ?2012;	 ?Ye	 ?and	 ?Gao,	 ?2012;	 ?Lopes	 ?et	 ?al.,	 ?2013).	 ?	 ? Torsional	 ? strength	 ? is	 ? related	 ? to	 ? how	 ? much	 ? a	 ? file	 ? can	 ? twist	 ? before	 ?fracture	 ? and	 ? is	 ? a	 ? desirable	 ? property	 ? during	 ? the	 ? preparation	 ? of	 ? narrow	 ? and	 ?	 ?	 ? 58	 ?constricted	 ? canals,	 ? as	 ? most	 ? typically	 ? this	 ? is	 ? when	 ? the	 ? file	 ? is	 ? subjected	 ? to	 ? high	 ?torsional	 ? loads.	 ? 	 ? In	 ? the	 ? present	 ? study,	 ? TYP	 ? CM	 ? files	 ?without	 ? cyclic	 ? preloading	 ? had	 ?similar	 ?torque	 ?values	 ?than	 ?instruments	 ?made	 ?of	 ?conventional	 ?NiTi.	 ?	 ?For	 ?the	 ?angle	 ?of	 ?rotation	 ? before	 ? fracture,	 ? the	 ? TYP	 ? CM	 ? files	 ? without	 ? cyclic	 ? preloading	 ? generally	 ?possessed	 ? high	 ? values	 ? that	 ? were	 ? superior	 ? to	 ? the	 ? conventional	 ? TYP	 ? files.	 ? 	 ? In	 ? this	 ?study,	 ? torque	 ?at	 ? failure	 ?was	 ?determined	 ?according	 ? to	 ? ISO3630-??1,	 ? specifically	 ? those	 ?torque	 ?values	 ?that	 ?were	 ?sufficient	 ?to	 ?break	 ?the	 ?instrument	 ?at	 ?D3	 ?when	 ?rotated	 ?with	 ?two	 ?rpm.	 ?	 ?However,	 ?clinical	 ?torque	 ?stresses	 ?occur	 ?at	 ?higher	 ?revolutions	 ?per	 ?minute,	 ?and	 ? file	 ? binding	 ? effects	 ? are	 ? influenced	 ? by	 ? canal	 ? anatomy,	 ? operator	 ? skill	 ? level,	 ? and	 ?other	 ?factors	 ?(Blum	 ?et	 ?al.,	 ?1999;	 ?Parashos	 ?et	 ?al.,	 ?2004).	 ?	 ?Therefore,	 ?the	 ?data	 ?obtained	 ?here	 ?cannot	 ?be	 ?directly	 ?extrapolated	 ?to	 ?clinical	 ?conditions	 ?and	 ?conclusions	 ?from	 ?the	 ?present	 ?study	 ?must	 ?be	 ?drawn	 ?with	 ?caution.	 ?	 ? Previous	 ? studies	 ? showed	 ? that	 ? cyclic	 ? fatigue	 ? had	 ? a	 ? significant	 ? effect	 ? on	 ?torsional	 ?fracture	 ?resistance	 ?on	 ?ProFile	 ?and	 ?ProTaper	 ?instruments	 ?(Bahia	 ?and	 ?Dias,	 ?2006;	 ?Kim	 ?et	 ?al.,	 ?2012).	 ?Particularly,	 ?instruments	 ?cycled	 ?to	 ?75%	 ?of	 ?fatigue	 ?life	 ?had	 ?a	 ?significant	 ?decrease	 ?in	 ?their	 ?torsional	 ?resistance.	 ?	 ?In	 ?the	 ?present	 ?study,	 ?cyclic	 ?fatigue	 ?was	 ?not	 ?detrimental	 ? to	 ? the	 ? file?s	 ?ability	 ? to	 ?withstand	 ?the	 ? torsional	 ? load	 ?of	 ?TYP	 ?and	 ?TYP	 ? CM	 ? files	 ? on	 ? size	 ? 25.04.	 ? 	 ? In	 ? the	 ? larger	 ? size	 ? (40.04),	 ? the	 ? 75%	 ? preloading	 ? TYP	 ?instruments	 ?had	 ?reduced	 ?torsional	 ?strength;	 ?in	 ?the	 ?25.04	 ?group	 ?this	 ?was	 ?not	 ?the	 ?case	 ?and	 ?furthermore	 ?precycling	 ?of	 ?	 ?25.04	 ?TYP	 ?CM	 ?instruments	 ?showed	 ?a	 ?slight	 ?reduction	 ?in	 ? the	 ? instrument?s	 ? distortion	 ? angle	 ? when	 ? compared	 ? to	 ? the	 ? no	 ? precycling	 ? group.	 ?	 ?However,	 ?in	 ?the	 ?clinical	 ?situation,	 ?there	 ?is	 ?no	 ?simple	 ?way	 ?to	 ?estimate	 ?the	 ?amount	 ?of	 ?	 ?	 ? 59	 ?cyclic	 ?fatigue	 ?accumulated	 ?in	 ?those	 ?multiple-??use	 ?instruments.	 ?Interestingly,	 ? in	 ?both	 ?sizes,	 ? TYP	 ? CM	 ? files	 ? displayed	 ? a	 ? similar	 ? torque	 ? value	 ? to	 ? TYP	 ? files	 ? but	 ? rotated	 ? at	 ? a	 ?greater	 ?angle	 ?before	 ?fracturing	 ?in	 ?both	 ?the	 ?preloading	 ?and	 ?no	 ?preloading	 ?groups.	 ?	 ?In	 ?size	 ?40.04	 ?the	 ?angle	 ?of	 ?distortion	 ?was	 ?significantly	 ?less	 ?in	 ?the	 ?precycled	 ?groups	 ?when	 ?compared	 ? to	 ? the	 ? no	 ? precycling	 ? group,	 ? however	 ? the	 ? torque	 ? was	 ? not	 ? significantly	 ?different.	 ?	 ?Nevertheless,	 ?a	 ?high	 ?angle	 ?of	 ?rotation	 ?before	 ?fracture	 ?in	 ?TYP	 ?CM	 ?files	 ?may	 ?be	 ? beneficial	 ? because	 ? it	 ? may	 ? provide	 ? clinicians	 ? with	 ? an	 ? indication	 ? of	 ?plastic/permanent	 ? deformation.	 ? The	 ? clinician	 ? may	 ? consider	 ? it	 ? a	 ? warning	 ? that	 ? the	 ?ultimate	 ?yield	 ?strength	 ?of	 ? the	 ?metal	 ?may	 ?be	 ?approaching	 ?and	 ? that	 ? fracture	 ?may	 ?be	 ?imminent.	 ?Even	 ? though	 ? the	 ? total	 ?number	 ?of	 ? rotations	 ?of	 ?TYP	 ?CM	 ? instruments	 ?with	 ?the	 ?75%	 ?preloading	 ?group	 ?was	 ?significantly	 ?higher	 ?than	 ?TYP	 ?instruments	 ?in	 ?the	 ?no	 ?precycling	 ? group,	 ? the	 ? torsional	 ? resistance	 ? of	 ? TYP	 ? CM	 ? instruments	 ?were	 ? similar	 ? to	 ?TYP	 ?instruments.	 ?	 ? Parashos	 ? et	 ? al.	 ? (2004)	 ? found	 ? cyclic	 ? fatigue	 ? to	 ? be	 ? the	 ? more	 ? common	 ?mechanism	 ? of	 ? file	 ? fracture	 ? in	 ? clinical	 ? practice.	 ? Sattapan	 ? et	 ? al	 ? (2000a)	 ? conversely	 ?found	 ?that	 ? torsional	 ?stress	 ?was	 ?slightly	 ?more	 ?prevalent	 ?as	 ? the	 ?cause	 ?of	 ? fracture.	 ? In	 ?clinical	 ?practice,	 ?files	 ?can	 ?fracture	 ?as	 ?a	 ?result	 ?of	 ?either	 ?mechanism,	 ?often	 ?with	 ?little	 ?to	 ?no	 ? warning.	 ? Examination	 ? of	 ? the	 ? fracture	 ? surface	 ? at	 ? high	 ? magnification	 ? using	 ?scanning	 ? electron	 ?microscopy	 ? is	 ? essential	 ? to	 ? reveal	 ? features	 ? that	 ?may	 ? indicate	 ? the	 ?possible	 ?origin	 ?of	 ?cracks	 ?and	 ? the	 ?mode	 ?of	 ?material	 ? failure	 ? (Shen	 ?et	 ?al.,	 ?2009a).	 ? 	 ?As	 ?previously	 ?discussed,	 ?cyclic	 ?fatigue	 ?fracture	 ?is	 ?characterized	 ?by	 ?numerous	 ?patches	 ?of	 ?linear	 ? fatigue-??striation	 ? marks	 ? and	 ? torsional	 ? failure	 ? is	 ? characterized	 ? by	 ? circular	 ?	 ?	 ? 60	 ?abrasion	 ?marks	 ?on	 ?the	 ? fracture	 ?surface.	 ?CM	 ?files	 ?had	 ?fatigue	 ?resistance	 ?superior	 ?to	 ?files	 ?made	 ?from	 ?conventional	 ?NiTi	 ?alloy.	 ?	 ?Hence,	 ?it	 ?is	 ?not	 ?surprising	 ?that	 ?the	 ?values	 ?of	 ?the	 ? area	 ? occupied	 ? by	 ? the	 ? dimple	 ? region	 ? as	 ? part	 ? of	 ? the	 ? total	 ? surface	 ? area	 ? of	 ? the	 ?fracture	 ?cross-??section	 ?were	 ?significantly	 ?smaller	 ?on	 ?instruments	 ?made	 ?from	 ?CM	 ?wire	 ?than	 ? on	 ? instruments	 ? made	 ? from	 ? conventional	 ? NiTi	 ? wire	 ? in	 ? the	 ? cyclic	 ? fatigue	 ? test	 ?(Shen	 ?et	 ?al.,	 ?2011a;	 ?2012).	 ?Their	 ?findings	 ?lend	 ?support	 ?to	 ?the	 ?results	 ?obtained	 ?here.	 ?The	 ?patterns	 ?established	 ?in	 ?this	 ?study	 ?for	 ?the	 ?fractured	 ?files	 ?supply	 ?a	 ?consistent	 ?base	 ?for	 ? the	 ? interpretation	 ? of	 ? fracture	 ? occurring	 ? under	 ? complex	 ? loading.	 ? The	 ? results	 ?showed	 ? that	 ? in	 ? the	 ? case	 ? of	 ? both	 ? heat-??treated	 ? NiTi	 ? instruments	 ? and	 ? conventional	 ?superelastic	 ? NiTi	 ? instruments	 ? in	 ? which	 ? the	 ? torsional	 ? test	 ? was	 ? applied	 ? after	 ? an	 ?incomplete	 ? flexural	 ? fatigue	 ? test,	 ? the	 ? fractography	 ? corresponded	 ? to	 ? the	 ? torsional	 ?fracture	 ? pattern.	 ? These	 ? data	 ? are	 ? in	 ? accordance	 ? with	 ? previous	 ? studies	 ? (Kim	 ? et	 ? al.,	 ?2012)	 ?that	 ? found	 ?the	 ?fractured	 ?conventional	 ?NiTi	 ? files	 ?after	 ?torsional	 ? tests	 ?showed	 ?typical	 ? features	 ? of	 ? torsional	 ? failure;	 ? there	 ?was	 ? little	 ? difference	 ?with	 ? regard	 ? to	 ? the	 ?brands	 ? or	 ? amount	 ? of	 ? precycling.	 ? From	 ? a	 ? clinical	 ? point	 ? of	 ? view,	 ? the	 ? results	 ? of	 ? this	 ?investigation	 ?also	 ?allow	 ?for	 ?speculation	 ?that	 ?an	 ?instrument	 ?fracture	 ?may	 ?be	 ?a	 ?result	 ?of	 ? a	 ? combination	 ? of	 ? cyclic	 ? fatigue	 ? and	 ? torsional	 ? load,	 ? although	 ? the	 ? fractographic	 ?examination	 ? reveals	 ? that	 ? an	 ? instrument	 ? fails	 ? from	 ? torsional	 ? fracture.	 ? The	 ?information	 ?from	 ?the	 ?foregoing	 ?case	 ?will	 ?aid	 ?clinicians	 ?in	 ?their	 ?understanding	 ?of	 ?the	 ?fracture	 ? process	 ? under	 ? clinical	 ? conditions.	 ? Further	 ? research	 ? is	 ? recommended	 ? for	 ?examining	 ? the	 ? effect	 ? of	 ? torsional	 ? fatigue	 ? on	 ? the	 ? cyclic	 ? fatigue	 ? fracture	 ? of	 ? NiTi	 ? CM	 ?files.	 ?	 ?	 ? 61	 ?Chapter	 ?7.	 ?Conclusions	 ?	 ?	 ?	 ? CM	 ? files	 ? behaved	 ? differently	 ? in	 ? a	 ? test	 ? environment	 ? than	 ? conventional	 ? NiTi	 ?rotary	 ?files.	 ?	 ?The	 ?present	 ?findings	 ?indicate	 ?that	 ?the	 ?fatigue	 ?life	 ?of	 ?CM	 ?instruments	 ?is	 ?significantly	 ? longer	 ? than	 ? conventional	 ? superelastic	 ?NiTi	 ? instruments.	 ?During	 ? cyclic	 ?testing	 ? to	 ? failure,	 ?CM	 ? files	 ?did	 ?not	 ?always	 ? fracture	 ?all	 ? the	 ?way	 ? through;	 ? sometimes	 ?the	 ? three	 ?millimeter	 ? tip	 ? of	 ? the	 ? file	 ? remained	 ? connected	 ? to	 ? the	 ? rest	 ? of	 ? the	 ? file	 ? as	 ? it	 ?rotated	 ?in	 ?the	 ?three-??point	 ?bending	 ?apparatus,	 ?similar	 ?to	 ?an	 ?upside	 ?down	 ?helicopter.	 ?	 ?It	 ? is	 ? theorized	 ? that	 ? this	 ? is	 ? because	 ? a	 ? high	 ? portion	 ? of	 ? the	 ? file	 ? is	 ? of	 ? martensitic	 ?composition	 ?at	 ?testing	 ?temperatures.	 ?	 ?TYP	 ?CM	 ?files	 ?displayed	 ?a	 ?torque	 ?resistance	 ?similar	 ?to	 ?TYP	 ?files	 ?but	 ?rotated	 ?a	 ?greater	 ?amount	 ?angle	 ?before	 ? fracture	 ? in	 ? the	 ?preloading	 ?and	 ?no	 ?preloading	 ?groups.	 ?	 ?	 ?It	 ?was	 ?not	 ?uncommon	 ?during	 ?torsion	 ?testing	 ?to	 ?observe	 ?the	 ?file	 ?unwind	 ?and	 ?then	 ?re-??wind	 ?on	 ?itself	 ?multiple	 ?times	 ?before	 ?fracture.	 ?	 ?There	 ?was	 ?no	 ?significant	 ?difference	 ?of	 ?torque	 ?value	 ?and	 ?distortion	 ?angle	 ?on	 ?both	 ?TYP	 ?CM	 ?and	 ?TYP	 ?instruments	 ?of	 ?size	 ?25.04	 ?between	 ? the	 ? precycling	 ? and	 ? no	 ? precycling	 ? groups.	 ? Cyclic	 ? fatigue	 ? had	 ? an	 ? effect	 ? on	 ?torsional	 ?fracture	 ?resistance	 ?in	 ?size	 ?40.04.	 ?	 ?Moreover,	 ?when	 ?40.04	 ?was	 ?precycled	 ?to	 ?75%	 ? of	 ? their	 ? cyclic	 ? fatigue	 ? life,	 ? TYP	 ? instruments	 ? showed	 ? a	 ? reduction	 ? in	 ? their	 ?torsional	 ?resistance	 ?compared	 ?with	 ?the	 ?no	 ?precycling	 ?group;	 ?precycling	 ?of	 ?TYP	 ?CM	 ?instruments	 ?reduced	 ?the	 ?distortion	 ?angle.	 ?	 ?	 ?	 ? 62	 ?It	 ?is	 ?possible	 ?that	 ?precycling	 ?files	 ?prior	 ?to	 ?torque	 ?testing	 ?to	 ?an	 ?amount	 ?greater	 ?than	 ?75%	 ?would	 ?show	 ?interesting	 ?fractographic	 ?combination	 ?patterns.	 ?	 ?The	 ?problem	 ?this	 ?presents	 ? is	 ? that	 ?as	 ? the	 ?mean	 ?cyclical	 ? failure	 ?rate	 ? is	 ?approached,	 ?more	 ?samples	 ?would	 ?be	 ?lost	 ?prior	 ?to	 ?torsional	 ?testing.	 ?	 ?	 ?Thermo-??mechanically	 ? treated	 ? files	 ? are	 ? the	 ? latest	 ? generation	 ? of	 ? endodontic	 ?rotary	 ?systems.	 ?	 ?Within	 ?the	 ?limitations	 ?of	 ?this	 ?study,	 ?TYP	 ?files	 ?appear	 ?to	 ?significantly	 ?increase	 ?their	 ?fatigue	 ?performance	 ?with	 ?generally	 ?no	 ?loss	 ?of	 ?torsional	 ?strength.	 ?This	 ?should	 ?be	 ?of	 ?benefit	 ? to	 ?the	 ?daily	 ?routine	 ?of	 ?the	 ?clinician,	 ?since	 ? 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