Cyclic
fatigue
resistance
of
Nickel-Titanium
reciprocating
instruments
tested
with
an
innovative
kinematics
Impatto
di
una
nuova
cinematica
sulla
resistenza
in
fatica
ciclica
di
strumenti
reciprocanti
Francesco
Iacono
a,
Chiara
Pirani
a,*
,
Luigi
Generali
b,
Maria
Rosaria
Gatto
a,
Maria
Giovanna
Gandolfi
a,
Carlo
Prati
aa
School of Dentistry, Endodontic Clinical Section, Master in Clinical Endodontology,Department ofBiomedical and NeuromotorSciences,UniversityofBologna,Italy
bDepartment of Surgery, Medicine, Dentistry and Morphological Sciences with Transplant Surgery, Oncology and
RegenerativeMedicineRelevance(CHIMOMO),SchoolofDentistry,EndodonticSection,UniversityofModenaandReggio Emilia,Modena,Italy
Received6March2018;accepted17March2018
KEYWORDS Cyclicfatigue; Endodontic instrumentation; Kinematics; Nickel-titanium instruments; Reciprocatingmotion. Abstract
Aim: ToevaluatecyclicfatigueresistanceofdifferentNickel-Titaniuminstrumentstestedwith aninnovativereciprocatingkinematics.
Methodology: EightyNickel-Titaniumreciprocatinginstruments weretestedin cyclicfatigue resistance:WaveOnePrimary(n=20),WaveOneGoldPrimary(n=20),ReciprocR25(n=20)and ReciprocBlueR25(n=20).Thecyclicfatigueofeachbrandwasmeasuredwithtwodifferent motorsandkinematicssettings:(1)X-SmartPlus(DenstplyMaillefer)usedin‘‘WaveOneAll’’or ‘‘ReciprocAll’’setting,accordingtomanufacturer’sinstruction;(2)a4:1contra-angle(Cefla, Imola, Italy)with an experimental kinematics(Goldspeed EVOE4 — Cefla, Italy)(EVO) with different rotation anglesand basedonasinusoidalacceleration.Thetimetofracture inan artificialstainless-steelcanal(908angleanda5-mmradiusofcurvature)wasdigitallyrecorded. Meanlife,beta(failurerate)andeta(characteristiclifei.e.thenumberofsecondsatwhich 63.2%of theproducthas failed)werecalculatedforeachgroupandcomparedwithWeibull analysis.
* Correspondingauthorat:EndodonticClinicalSection,DepartmentofBiomedicalandNeuromotorSciences(DIBINEM),UniversityofBologna, AlmaMaterStudiorum,Bologna,Italy.Tel.:+390512088126;fax:+39051225208.
E-mail:chiara.pirani4@unibo.it(C.Pirani).
Availableonlineatwww.sciencedirect.com
ScienceDirect
jo ur na l h o m ep a ge : w w w.e ls e v i er.c o m / lo c at e /gi e
https://doi.org/10.1016/j.gien.2018.03.004
1121-4171/ß2018Societa` ItalianadiEndodonzia.ProductionandhostingbyElsevierB.V.ThisisanopenaccessarticleundertheCCBY-NC-ND license(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Introduction
Overlastyears,severalstrategiesinendodontic
instrumen-tationhavebeenproposedbymanufacturerswiththeaimto
reduce procedural errors andfractures of Nickel-Titanium
(NiTi)instruments.1,2
Theuseofdifferentmovementsandkinematicsofthefiles
toshapethecanalshasbeenstudiedfromsixtiesand
seven-ties.AlsoProfessor FrancescoRiitanocontributedin
devel-oping an innovative device to reduce errors and fractures
duringinstrumentationprocedures.3,4
In2008Yared5relaunchedthereciprocatingmotion(RM)
by proposing theuseof a ProTaperF2 used for canal
pre-paration in a clockwise (CW) and counterclockwise (CCW)
direction. Thereafter several studies had shown a longer
lifespanof NiTiinstrumentsused inRMincomparisonwith
continuousrotation.6—8In2011WaveOne(Denstply
Maille-fer, Baillagues, Switzerland), and Reciproc (VDW, Munich,
Germany)havebeenlaunchedonthemarketwiththe
inten-tiontosimplifyandshortentheendodonticprocedures.9,10
Recently,theheattreatmentofM-WireNiTialloyinducedthe
developmentof Gold andBlue alloyandconsequentlythe
passage from WaveOne and Reciproc to WaveOne Gold
(Denstply Maillefer, Baillagues, Switzerland) and Reciproc
Blue(VDW,Munich,Germany).
Manufacturersrecommendtheuseofthese instruments
with a specific motor and pre-set reciprocation modes.
PAROLECHIAVE Cinematica; Faticaciclica; Strumenti Nichel-Titanio; Strumentazione endodontica; Movimento reciprocante.
Results: InstrumentstestedwiththekinematicsEVOpresentedhighervaluesofetainallgroups. Reciproc Blueshowed thehighest eta value (233.05) and Wave One Goldthe lowerfailure probability(46.98%).WaveOneinstrumentsshowedsimilarfatigueresistancewhentestedwith EVOorX-Smart.
Conclusion: Tested kinematics with different angles and based on sinusoidal reciprocating accelerationhad apositiveimpact onfatigue lifetimeofreciprocating instruments.Present findingssuggestthepossibilityoffutureimprovementsintheclinicaluseofreciprocatingfiles. ß2018Societa` ItalianadiEndodonzia.ProductionandhostingbyElsevierB.V.Thisisanopen accessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/ 4.0/).
Riassunto
Obiettividello studio: Scopodello studioe` statoquellodivalutare l’impattodiuna nuova cinematicacondifferentiangolidirotazioneecontrorotazionesuglistrumentidisegnatiperil movimentodireciprocazione.
MaterialieMetodi: Lafaticaciclicadi80strumentiNiTireciprocantie` statamisuratainun canalemetallicoartificialeconangolodi908econraggiodi5mm,condiversecinematichedi reciprocazione.
Sonostati testati8gruppidistrumenti(n=10): Gruppo1:WaveOne Primaryinmodalita` ‘‘WaveOneAll’’utilizzandoilmotoreX-SmartPlus(DentsplyMaillefer);Gruppo2:WaveOneGold Primary(DentsplyMaillefer)in‘‘WaveOneAll’’conX-SmartPlus;Gruppo3:ReciprocR25(VDW)in ‘‘ReciprocAll’’conX-SmartPlus;Gruppo4ReciprocBlue(VDW)R25in‘‘ReciprocAll’’con X-SmartPlus.Altri4gruppideglistessistrumentisonostatitestatiutilizzandolanuovacinematica direciprocazione (EVOE4,Cefla,Imola,Italy)conangolidifferentiebasatasulconcettodi accelerazionesinusoidale,utilizzandounospecificomotoresperimentaleconuncontrangolo4:1 (CEFLA,Imola,Italy).Gruppo5:WaveOnePrimaryinmodalita` ‘‘WaveOne’’utilizzandoilsistema EVOE4(Cefla);Gruppo6:WaveOneGoldPrimaryin‘‘WaveOne’’conEVOE4;Gruppo7:Reciproc R25inmodalita` ‘‘Reciproc’’conEVOE4;Gruppo8:ReciprocBlueR25in‘‘Reciproc’’conEVOE4. L’analisistatisticaWeibulle` statautilizzatapercalcolareeconfrontarelamedia(meanlife), beta(failurerate)eeta(ilnumerodisecondicuiil63.2%deglistrumentihafallito). Risultati: GlistrumentitestaticoncinematicaEVOE4hannodimostratountempomedio(mean life)difratturaperfaticaciclicasuperioreaglistrumentitestaticonlecinematiche convenzio-nalidireciprocazione,in ognigruppo.I ReciprocBluehannomostrato ipiu` elevativaloridi resistenza(233.05eta)mentreiWaveOneGoldhannodimostratola piu` bassaprobabilita` di fallimento(46,98%).
Conclusioni: Lanuovacinematicadireciprocazionebasatasuangolidifferentiedaccelerazione sinusoidaleha dimostrato avere unimpatto positivo sullaresistenza allafaticaciclica degli strumenti testati. Inoltre e` stato confermato che i nuovi trattamenti termici delle leghe miglioranoleproprieta` meccaniche deglistrumenti. Irisultatidiquestostudioaprononuovi scenarisulledinamichediutilizzodeisistemireciprocantiadoggidisponibili.
ß2018Societa` ItalianadiEndodonzia.ProductionandhostingbyElsevierB.V.Cetarticleest publie´ enOpenAccesssouslicenceCCBY-NC-ND( http://creativecommons.org/licenses/by-nc-nd/4.0/)
Nevertheless,severalpossibilitiesexistforkinematicsofRM,
andtheperformancesareconsequentlyinfluenced.11,12For
example,decreasingthereciprocationrangeofthe
instru-mentsresultsinincreasedcyclicresistancewithless
trans-portation but in longer preparation time.13 To date,
relatively few studies evaluated the differences between
severalmodifiedkinematicsofreciprocation(differentspeed
and/orangles).11—13
Recentlyanewendodonticmotor(Cefla,Imola,Italy)has
beenengineeredwithdifferentfeaturesintermsofengaging
anddisengagingrotationanglesandintroducingtheconcept
ofsinusoidalaccelerationto everyrotationreversalofthe
reciprocatingmovement.Thismotorispartofaninnovative
dentalunit(Cefla,Imola,Italy).
To the best of ourknowledge,no research had
investi-gatedthe influenceof thisnew kinematics on the fatigue
resistanceofNiTiFiles.Thereforetheaimofthisstudywasto
test the cyclic fatigue of different generations of NiTi
designedforthereciprocation,assessingtheimpactofthe
newkinematicsontheirfatigueresistance.
Materials
and
methods
Asample of80 NiTi reciprocating instruments wastested:
WaveOnePrimary(n=20),WaveOneGold Primary(n=20),
ReciprocR25(n=20)andReciprocBlueR25(n=20),
Instru-mentsweredistributedin8experimentalgroups(n=10)as
showninTable1.
Thecyclicfatigueresistanceofeachbrandwasmeasured
with two different motors and kinematics settings as
reported in Table 1: (1) X-Smart Plus (Denstply Maillefer,
Baillagues,Switzerland)endodonticmotorusedrespectively
in ‘‘WaveOneAll’’ or ‘‘Reciproc All’’setting, according to
manufacturer’s instruction; (2) a 4:1 contra-angle (Cefla,
Imola,Italy)withthemodifiedkinematics(GoldspeedEVOE4
—Cefla,Italy)(EVO).
A custom-made device, specifically designed for cyclic
fatiguetests,wasused(Fig.1).Instrumentsweretestedina
metalblockmadefromstainlesssteelAISI300witha
simu-lated tapered canal (908 angle of curvature and a-5mm
radius).Aslippingplexiglasstopfacecoverallowed
visuali-zationoftheinstrumentsinthecanal.Thecanalwasfilled
withglycerine,reducingfrictionandheatrelease.The
elec-trichandpiecewasmountedonamobileapparatusproviding
a preciseand standardized placement of each instrument
insidetheartificialcanal.Allthefileswerereciprocateduntil
theoccurrenceofthefractureandthetimetofracturewas
visuallyrecordedwithadigitalstopwatch(3MESPE,St.Paul,
MN,USA).
Meanlife,beta(failurerate)andeta(characteristiclife
i.e.thenumberofsecondsatwhich63.2%oftheproducthas
failed)werecalculated foreachgroupandcomparedwith
Weibullanalysis.
Results
Themeanlife,beta(failurerate)andeta(characteristiclifei.e.
thenumberofsecondsatwhich63.2%oftheproducthasfailed)
were calculated for each group and were compared with
Weibullanalysis(Table2).Themeanlifeofinstrumentstested
with the kinematics EVO was generally higher,presenting a
greaterproportionofinstrumentswithhighervaluesofetainall
groups. Reciproc Blue were significantly the most resistant
instruments,irrespectiveofkinematics,andlastedsignificantly
longer than Reciproc.WaveOne Golddemonstrated a higher
resistance than WaveOne with EVO motor, showing alsothe
lowest failure probability (beta) among groups (46.98%).
WaveOneinstrumentsshowedsimilarfatigueresistancewhen
testedwithEVOorX-SmartKinematics.
Discussion
Inthisresearchtheinfluenceofdifferentkinematicsonthe
fatiguelifeoffour differentreciprocatinginstruments was
tested.FatigueresistanceofNiTiinstruments isassociated
withthepropagationofasuperficialcrackbecauseof
alter-natingtensileandcompressivecyclesincurvedcanal,14and
isinfluenced bymovementkinematics (continuousor
reci-procatingmotion).15RMpermitstotheinstrumentto
com-plete one full rotation after more reciprocating cycles
(depending on thedifferent angles),6,11 whichmeans that
moretimeisneededforoneentirerotationwhencompared
withcontinuousrotation.Inparticular,anglesofrotationand
contra-rotation, acceleration, deceleration and speed are
well-known parameterthatmayaffect theenduranceand
thepreparationtime11—13ofNiTireciprocatinginstruments.
Findingsofthepresentstudydemonstratedthatkinematics
EVOsignificantlyinfluencesthecyclicfatigueresistance of
Table 1 Group (n=10) of the tested instruments with differentmotorsandkinematicssettings.
Instrument Motor Kinematics Group1 WaveOne X-Smart WaveOneAll Group2 WaveOne EVOE4 WaveOne Group3 WaveOneGold X-Smart WaveOneAll Group4 WaveOneGold EVOE4 WaveOne Group5 Reciproc X-Smart ReciprocAll Group6 Reciproc EVOE4 Reciproc Group7 ReciprocBlue X-Smart ReciprocAll Group8 ReciprocBlue EVOE4 Reciproc
Figure1 3Dreconstructionofthefatiguetestdeviceusedin thepresentstudy.
testedfiles.Infact,themeanlifeofinstrumentstestedwith
thekinematicsEVOwashigherandwithagreaterproportion
ofinstrumentswithhighervaluesofetainallgroups.
The recently engineered EVO motor by Cefla imparts
differentengaginganddisengagingrotationalangles(angles
ofthismotionare patentpendingandcannotbefully
dis-closed)and confersa sinusoidal acceleration during every
rotationreversalofthereciprocatingmovement.The
ratio-nalebehindthiskinematicsistogenerateasmoother
transi-tion between rotation and contra-rotation, permitting a
moreaccuratecontrolofthetorqueandreducingthestress
oftheinstrumentthroughanincrementalangular
accelera-tionofthespeed.Furtherinvestigationsshouldevaluatethe
impactofthisinnovativekinematicson thetorsionalloads
whichtheinstrumentsaresubjectedduringcanal
instrumen-tationandtheeffectofthisreciprocatingkinematicsonroot
canaldentinalsurfacethroughscanningelectronmicroscope
(SEM).Infact,severalstudies16—18confirmedSEMasa
sui-tablemethodforthecomparisonofdentinsurface
morphol-ogyafterinstrumentation,asshowninFig.2.
Accordingto other studies,19,20 inthe present research
thecyclicfatigueresistanceofreciprocatinginstrumentswas
reportedastimetofracture(seconds).Thistominimizethe
errors of questionable dataavailable on the pre-set
kine-maticsfromthoseclaimedbythemanufacturers, mainlyin
terms of engaging/disengaging angles and rotational
speed.21Furtherstudiesshoulddeeperinvestigatethe
para-metersofthetestedkinematicstobetterunderstandtherole
ofdifferentanglesandspeedonthecycliclifeof
reciprocat-inginstruments.
Aspartofthisstudy,Weibullanalysiswasconductedwith
respectto‘‘lifedata’’,measuredinhours,miles,cyclesor
anyothermetric,definingtheperiodofsuccessfuloperation
ofaparticularproduct.22,23Thistypeofanalysisfocuseson
informationrelated to extreme-value distribution andthe
lowervaluesthatmaybemorecrucialforcliniciansandhas
beenalreadyusedasanadequatemodelforevaluatingthe
cyclicfatigueresistanceofNiTifiles.24,25
Another interesting aspect of the present study is the
comparisonofNiTiinstrumentssubjectedtodifferent
ther-momechanicaltreatments.Isitwellknownthatoneofthe
mostsuccessfulstrategytoimprovethemechanical
proper-tiesof NiTi files is to optimize the microstructure of NiTi
alloysthroughdifferentthermomechanicalprocesses.24This
determinesthecharacteristicsofthemicrostructuralphases
and adjuststhe transition temperatures of the alloy.26—30
WaveOnefileshavebeenenhancedfromM-wiretoGoldalloy
treatment.31,32 In this in vitro research the comparison
betweenWaveOneGoldandWaveOneresultedina
statisti-callyhigherfatigue resistance of WaveOneGold only with
EVO, while no significant differences were found with
X-Smart.EventheheattreatmentofReciprochasbeen
chan-gedfromM-wiretoBluealloy.Accordingtotheliterature33—
35
ourfindingssuggestedanimprovedfatigueresistanceof
thenew Reciproc Blueinstruments that resultedthemost
resistantfilesirrespectiveofthetestedkinematics.
Conclusions
The findings of this in vitro research showed the positive
impact of new kinematics on fatigue life of reciprocating
instruments, suggesting the possibility of future
improve-mentsintheclinicaluseofreciprocatingfiles.Furtherstudy
shoulddeeper evaluatethe kinematicsevaluating alsothe
impactofthesinusoidalreciprocatingmotiononthe
instru-mentsduringcanalinstrumentation.
Clinical
relevance
Presentresultsdemonstratedthatinnovativekinematicshas
apositiveimpactonfatiguelifeofreciprocatinginstruments,
thus suggesting new scenario in the clinical use of NiTi
reciprocatingfiles.
Table2 Weibullanalysisoffatigueresistanceofthetestedgroups.Meanlife,beta(failurerate)andeta(characteristiclife,i.e. thenumberofsecondsatwhich63.2%oftheproducthasfailed)arereported.
Group Instrument/kinematics Meanlife(s) beta eta
Group1 WaveOne—XSmart 76.482 2.311 85.81
Group2 WaveOne—EVOE4 81.537 3.666 90.51
Group3 WaveOneGold—X-Smart 77.88 8.206 82.38
Group4 WaveOneGold—EVOE4 127.71 7.715 136.07
Group5 Reciproc—X-Smart 126.45 6.181 135.73
Group6 Reciproc—EVOE4 171.23 2.808 196.70
Group7 ReciprocBlue—X-Smart 132.73 7.972 136.43
Group8 ReciprocBlue—EVOE4 215.88 5.651 233.05
Figure2 ESEMmicrograph(1500)of themiddlethird ofa rootcanalinstrumentedwithWaveOne.
Conflict
of
interest
Theauthorsdeclarenottohaveanyconflictofinterest
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