ABSTRACT
http://dx.doi.org/10.1590/1678-775720150596
The im pact of clinical use on t he t orsional behavior
of Recipr oc and WaveOne inst r um ent s
Rafael Rodrigues Soares de MAGALHÃES1, Lígia Carolina Moreira BRAGA1, Érika Sales Joviano PEREIRA2, Isabella )DULDGD&XQKD3(,;27219LFHQWH7DGHX/RSHV%82123, Maria Guiomar de Azevedo BAHIA1
1- Universidade Federal de Minas Gerais, Faculdade de Odontologia, Departamento de Odontologia Restauradora, Belo Horizonte, MG, Brasil. 2- Universidade Federal da Bahia, Faculdade de Odontologia, Departamento de Clínica Odontológica, Salvador, BA, Brasil.
3- Universidade Federal de Minas Gerais, Faculdade de Engenharia, Departamento de Engenharia Metalúrgica e de Materiais, Belo Horizonte, MG, Brasil.
Corresponding address: Érika S. J. Pereira - Departmento de Clínica Odontológica - Universidade Federal da Bahia - Av. Araújo Pinho, 62 - Campus Canela
- 40110-150 - Salvador - BA - Brazil - Phone: +55 71 3283-8964 - Fax: +55 71 3283-8962 - e-mail: erikajoviano@gmail.com
Submitted: January 14, 2016 - Accepted: April 26, 2016
T
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possibilit y t hat t hey degraded wit h use. Mat erial and Met hods: Diam et er at each m illim et er, pit ch lengt h, and area at 3 m m from t he t ip w ere det erm ined for bot h t ypes of inst rum ent s. Tw ent y- four inst r um ent s, size 25, 0.08 t aper, of each syst em w er e divided int o t w o gr oups ( n= 12 each) : Cont r ol Gr oup ( CG) , in w hich new Recipr oc ( RC) and WaveOne Pr im ar y ( WO) inst r um ent s w er e t est ed in t or sion unt il r upt ur e based on I SO 3630- 1; and Exper im ent al Gr oup ( EG) , in w hich each new inst r um ent was clinically used t o clean and shape t he r oot canals of one m olar. Aft er clinical use, t he inst r um ent s w er e analyzed using opt ical and scanning elect r on m icr oscopy and subsequent ly t est ed in t or sion unt il fract ur e. Dat a w er e analyzed using one- way analysis of var iance at D= .05. Result s: WO inst r um ent s show ed
VLJQL¿FDQWO\KLJKHUPHDQYDOXHVRIFURVVVHFWLRQDODUHD$P= 0.000) and sm aller pit ch
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at D3 ( P 1RVLJQL¿FDQWGLIIHUHQFHVLQWRUVLRQDOUHVLVWDQFHEHWZHHQWKH5&DQG WO new inst r um ent s ( P= 0.134) w er e found. The clinical use r esult ed in a t endency of
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differ ence was obser ved bet w een t hem ( P= 0.327) . Dur ing t he pr eparat ion of t he r oot canals, t w o fract ur ed RC inst r um ent s and longit udinal and t ransver sal cracks in RC and WO inst r um ent s w er e obser ved t hr ough SEM analysis. Conclusion: Aft er clinical use, no
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Ke y w or ds: Endodont ics. I nst r um ent at ion. Root canal pr eparat ion.
I N TROD UCTI ON
Ni ck e l –Ti t a n i u m ( Ni Ti ) r o t a r y i n st r u m e n t s
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of t h e r oot can al sy st em ; h ow ev er, t h ey m ay exper ience pr em at ur e failur e caused by fat igue17,24
or by t or sional ov er load. Tor sional fract ur e is a r esult of t he binding of t he inst r um ent t ip inside t he r oot canal, w hich is t ypically sm aller t han t he inst rum ent t ip diam et er20. The rupt ure occurs when
t he t orsional st ress locks t he inst rum ent in dent ine w alls an d b ecom es h ig h er t h an t h e m ax im u m t orque; t he inst rum ent can wit hst and at t hat point15.
This r isk m ay be r educed by per for m ing cor onal enlar gem ent and by cr eat ing a glide pat h befor e using any NiTi r ot ar y inst r um ent3.
Tw o brands of NiTi inst r um ent s, adopt ing t he
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concept , w er e r ecent ly int r oduced int o t he m ar ket : Recipr oc ( VDW, Munich, Ger m any) and WaveOne ( Dent sply- Maillefer, Ballaigues, Swit zerland) . These
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is pr oduced by an innovat ive t her m om echanical t r e a t m e n t p r o c e s s1 2 , 1 4 , 1 8 , 1 9. T h e y e m p l o y a
per iodically r ever sing t he r ot at ion, and ult im at ely incr eases t he lifespan of t he inst r um ent14,27. I n t he
r ecipr ocat ing m ot ion, t he values of clockw ise and count er clockw ise r ot at ions ar e differ ent for each inst rum ent . A large rot at ing angle, count erclockwise ( CCW) t o t he cut t ing dir ect ion, det er m ines t hat t he inst r um ent advances in t he canal t o engage and cut t he dent in, w her eas a sm aller angle, clockw ise
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im m ediat ely disen gaged an d saf ely pr ogr esses along t he canal pat h, w hile r educing t he scr ew ing
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Pr evious st udies show ed t hat t he r ecipr ocat ing inst rum ent s prom ot ed m inim al apical t ransport at ion, m aint aining t he original canal curvat ure bet t er t han r ot ar y inst r um ent s, alt hough t hey ar e associat ed w it h pr oducing higher debr is ext r usion4,6.
Several st udies assum ed t hat t he r ecipr ocat ing
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NiTi inst r um ent s, w hen com par ed w it h cont inuous r ot ar y m ot ion9,13,15,16,22. Kim , et al.14 ( 2012) st udied
f l ex u r a l f a t i g u e a n d t o r si o n a l r esi st a n ce a n d dem onst rat ed t hat Reciproc had t he longest fat igue life w hile WaveOne pr esent ed t he highest t or sional r esist ance. The sam e out com e for WaveOne was also dem onst rat ed in anot her st udy by Elnaghy and Elsaka8 ( 2015) , w hile Ha, et al.10 ( 2015) found
n o differ en ce in t or sion al r esist an ce com par in g Recipr oc and WaveOne inst r um ent s.
How ever, ver y lim it ed infor m at ion is available on t he t or sional behavior of inst r um ent s used in
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t im e a NiTi inst r um ent encount er s r esist ance it under goes t or sional loading. The load is gr eat er whenever t he dent in is hard or t he canal diam et er is sm all. This t or sional load exer t ed on t he sur face of t he inst r um ent can pr event it s r ot at ion t o a gr eat er or lesser ext ent . I n ext r em e cases, t he inst r um ent m ay fract ur e w hen t he r esist ance is so high t hat it const rains t he m ovem ent of t he inst r um ent2.
To evaluat e t he m agnit ude of t he t or sional load t o which t he inst rum ent s are subj ect ed when used in
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Consider ing t hat t he inst r um ent pr ogr ess in t he canal w it hout pr e- enlar gem ent and being awar e t hat t he am ount of t or que generat ed dur ing t he shaping of r oot canals clear ly depends on t he size of t he cont act ar eas bet w een t he inst r um ent s and t he canal walls20, t he pur pose of t his r esear ch was
t o analyze t he effect of t he clinical use on t or sional r esist ance of Recipr oc and WaveOne inst r um ent s.
M ATERI AL AN D M ETH OD S
The inst r um ent s em ployed in t his st udy w er e Reciproc ( RC/ R25) ( VDW Gm bH, Munich, Germ any) , and WaveOne ( WO/ Pr im ar y ) ( Dent sply- Maillefer, Ballaigues, Sw it zer land) bot h t ypes size 25, 0.08
t aper.
Befor e t he m echanical t est ing, all t he brand new inst r um ent s r eceived fr om t he m anufact ur er s w e r e p h o t o g r a p h e d u si n g a h i g h - r e so l u t i o n d i g i t a l ca m e r a ( 2 0 D ; Ca n o n , To k y o , Ja p a n ) . Their dim ensional charact er ist ics w er e assessed against t he Am er ican Nat ional St andar ds I nst it ut e/ Am er ican Den t al Associat ion Sp ecif icat ion No. 1 0 1 . Th e m easu r em en t s ( n = 1 2 f or each t y pe) w er e obt ained using I m age Pr o Plus 6.0 ( Media Cy b e r n e t i cs; Si l v e r Sp r i n g , MD ) . Li n e s w e r e
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out er m ost diam et er s at each m illim et er fr om t he t ip w er e m easur ed. The sam e m et hod was used t o det er m ine t he pit ch lengt h. To v isualize and m easur e t he cr oss- sect ional ar ea at 3 m m fr om t he t ip ( A3) , t hr ee inst r um ent s of each t ype w er e random ly select ed and cut t o approxim at ely 2.7 m m fr om t he t ip using a m et allographic cut t er ( I som et 1000; Buehler, I llinois, USA) . The cr oss- sect ional sur faces w er e polished w it h sandpaper t o 3.0 m m fr om t he t ip and t hen im aged using a scanning elect ron m icroscope ( SEM) ( JSM 6360; Jeol, Tokyo,
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a r e a s f o r e a ch i n st r u m e n t w e r e d e t e r m i n e d using t he sam e soft war e descr ibed above. Such dim ensional and geom et r ical charact er ist ics ar e
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on t or sional behavior16. Thr ee inst r um ent s of each
sy st em w er e ex am ined by SEM t o assess t heir su r f ace ch ar act er ist ics v er if y in g if t h er e w er e sur face defect s, such as m icr ocracks, even in new inst r um ent s.
The inst r um ent s w er e t hen div ided int o t w o groups, each one cont aining t welve new inst rum ent s of each t ype: ( i) Cont r ol Gr oup ( CG) , in w hich a t or sion t est was per for m ed t o est ablish t he m ean
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at fract ur e, and ( ii) Exper im ent al Gr oup ( EG) , in w hich t he inst r um ent s w er e em ployed clinically, in
vivo, by an exper ienced endodont ist t o shape t he
r oot canals ( 3 or 4 per t oot h) of one upper or low er m olar random ly dist ribut ed bet ween t he t wo groups
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# 1 0 an d # 1 5 ) ( Den t sp ly - Maillef er, Ballaig u es, Sw it zer land) , pat ency was est ablished. Dir ect and angled radiographs of each t oot h w er e obt ained using a paralleling t echnique t o evaluat e anat om y, as w ell as t o det er m ine t he canal radius and angle
RIFXUYDWXUHDVGH¿QHGE\3UXHWWHWDO23 ( 1997) ,
and it s approxim at e lengt h. These param et ers were m easur ed by pr oj ect ing t he radiographic im ages
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was m easur ed along t he out er canal wall.
The inst r um ent at ion was com plet ed gent ly w it h an “ in- and- out ” m ot ion, and each canal was pr epar ed unt il t he w or king lengt h was r eached ( 0.5 m m of t he canal pat ency lengt h) , w hen t he inst r um ent was im m ediat ely w it hdraw n. The inst r um ent s w er e operat ed using t he m anufact urer ’s pre- program m ed set t ings for a Silver Recipr oc engine ( VDW Gm bH, Munich, Ger m any) : “ Recipr oc all” m ode for RC size 25 and “ WaveOne all” m ode for WO Pr im ar y. The inst rum ent was rem oved from t he canal aft er t hree pecks or w hen r esist ance was encount er ed, and it was used in a lat eral br ushing m ot ion. A 5.25% sodium hypochlorit e solut ion was used for irrigat ion and RC- Prep ( Prem ier Dent al Product s, Norrist own,
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inst r um ent w er e cleaned aft er each gr oup of t he t hr ee “ in- and- out ” m ovem ent s.
Aft er use in each pat ient , t he inst r um ent s w er e washed and ult rasonically cleaned for 5 m inut es in acet one. The RC and WO inst r um ent s of t he EG were observed by opt ical m icroscopy ( Mit ut oyo TM,
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t he pr esence of dist or t ion, unw inding defect s, and any m acr oscopic defor m at ion. Befor e t he t or sion t est , t he sam e t hr ee inst r um ent s of each syst em , pr eviously exam ined by SEM, w er e r eexam ined in t he sam e posit ion and ar ea t o assess t he effect of t he clinical use on t heir sur face charact er ist ics.
The t or sion t est s w er e per for m ed based on I SO
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descr ibed in det ail elsew her e1. Tor que values w er e
assessed by m easu r in g t h e for ce ex er t ed on a sm all load cell by a lever ar m linked t o t he t or sion axis. A r esist ive angular t ransducer connect ed t o a pr ocess cont r oller m easur ed and cont r olled t he rot at ion angle. The rot at ion speed was set clockwise t o 2 r pm . The end of t he shaft was clam ped int o a Figure 1- (a) Mean values of diameter (mm) as a function
of distance (mm) from the tip; (b) Mean values of pitch length (mm) as a function of pitch number
a
b
chuck t hat was connect ed t o a r ever sible gear ed m ot or. Thr ee m illim et er s of t he inst r um ent ’s t ip was clam ped int o anot her chuck w it h brass j aw s t o pr event it fr om sliding. Cont inuous r ecor dings o f t o r q u e a n d a n g u l a r d ef l ect i o n , a s w el l a s m easurem ent s of t he m axim um t orque and angular
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design ed com pu t er pr ogr am . To det er m in e t h e
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param et er s am ongst t he differ ent gr oups, dat a obt ained w er e subj ect ed t o a one- way analysis of
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RESULTS
The m ean values ( ± st andar d dev iat ions) of diam et er at 3 m m fr om t he t ip ( D3) for RC and WO w er e 0.504± 0.010 m m and 0.499± 0.020 m m , respect ively ( Figure 1a) . Moreover, t he pit ch lengt h increased along t he act ive part of bot h inst rum ent s, wit h a st eeper increase recorded in RC inst rum ent s. I n general, RC pr esent ed lar ger pit ch lengt hs t han WO inst r um ent s, as illust rat ed in Figur e 1b.
I n t h i s st u d y, b o t h f i l e sy st em s u sed h a d differ en t cr oss- sect ion s, w it h RC pr esen t in g an S- sh ap ed cr oss- sect i on an d WO p r esen t i n g a concave t riangular- shaped cross- sect ion. Sim ilarly, t he m ean values of ar ea at 3 m m fr om t he t ip,
A3, for RC and WO w er e 0.112± 0.005 m m2 and
0.123± 0.005 m m2, respect ively. However, alt hough QR VWDWLVWLFDOO\ VLJQL¿FDQW GLIIHUHQFHV UHJDUGLQJ
t he D3 ( P= 0.521) w er e pr esent , WO inst r um ent s
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RC ( P= 0.000) .
T h e m e a n v a l u e s o f m a x i m u m t o r q u e d et er m i n ed f o r RC an d WO n ew i n st r u m en t s ( CG) w er e 1. 763± 0. 226 Ncm and 1. 852± 0. 293 Ncm , r espect ively ( Figur e 2) . Alt hough new WO inst r um ent s show ed higher values for m axim um t o r q u e t h a n RC i n st r u m e n t s, n o st a t i st i ca l l y
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( P 7KH DQJXODU GHÀHFWLRQ YDOXHV ZHUH 295± 35° and 241± 28° for RC and WO inst rum ent s,
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( P= 0.000) .
Radius and angle of cur vat ur e m ean values ( ± st andar d deviat ions) charact er izing t he geom et r y of t he r oot canals of RC and WO inst r um ent s w er e 5.3± 1.9 m m ; 5.5± 2.2 m m and 23± 11°; 24± 15°,
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differ ence ( P> 0.05) in r oot canal geom et r y am ong t he gr oups.
The m ean values of t or sional r esist ance aft er clinical use ( EG) ar e also sum m ar ized in Figur e 2. The graphs illust rat ed a decr ease in t or sional st r engt h for bot h inst r um ent s evaluat ed. How ever, st at ist ical analysis of t he m axim um t or que values
for t he RC and WO new inst rum ent s and aft er clinical
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and P UHVSHFWLYHO\7KHDQJXODUGHÀHFWLRQ
values decr eased aft er clinical use, except for RC inst r um ent s. How ever, st at ist ical analysis show ed
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pair s of inst r um ent s exam ined: new WO x used WO ( P= 0.067) and new RC x used RC ( P= 0.192) .
As illust rat ed in Figur e 3, t he lat eral sur faces of all RC and WO inst r um ent s subm it t ed t o r oot canal shaping exhibit ed longit udinal m icr ocracks, i.e., cracks parallel t o t he longit udinal axis of t he inst r um ent . I n addit ion, t ransver sal m icr ocrack s alon g t h e cu t t in g ed g e w er e ob ser v ed in t h e inst r um ent s aft er clinical use. Fr om t hese im ages, it is not ew or t hy t hat bot h inst r um ent s pr esent ed sim ilar crack pat t erns. A predom inance of larger and w ider cracks in t he region bet w een 1.0 and 2.5 m m fr om t he inst r um ent t ip was obser ved.
Fi g u r e 3 r e v e a l s a h i g h co n ce n t r a t i o n o f t y pical t ransv er sal and longit udinal m icr ocrack s on t he sur face of a RC inst r um ent t hat fract ur ed dur ing clinical use. I n t his invest igat ion, t w o RC inst r um ent s exper ienced int racanal failur e dur ing
clinical use ( Figur e 4) .
D I SCUSSI ON
Se v e r a l f a ct o r s, su ch a s a n a t o m y o f t h e r oot can als, size, t aper, design , alloy ch em ical com posit ion, and t herm om echanical process applied dur ing m anufact ur ing m ight affect t he t or sional b eh av i or of Ni Ti i n st r u m en t s1 5. No si g n i f i can t
differ ence in radius and angle of cur vat ur e could
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of geom et r ical fact or s on t he t or sional behav ior was avoided.
I t is im por t ant t o em phasize t he dim ensions of t he inst r um ent s at 3 m m fr om t he t ip because t his is t he point of appr ehension of t he inst r um ent s for t orsional t est s ( according t o I SO 3630- 1) , and where t he m axim um curvat ure is found in m ost root canals in clinical pract ice w it h t he gr eat est m echanical solicit at ions26. Alt hough sim ilar diam et er s at D3 ZHUHSUHVHQWHG:2KDGDPHDQ$VLJQL¿FDQWO\
higher ( P= 0.000) t han t he one obser ved for RC inst r um ent s. As discussed in t he lit erat ur e, t he m axim um t or que values incr eased pr opor t ionally
w it h A315. I t is also generally accept ed t hat t he
lar ger t he pit ch lengt h, t he sm aller is t he t or sional r esi st an ce o f an en d o d o n t i c i n st r u m en t7. WO
inst r um ent s pr esent ed sm aller pit ch lengt h t han RC inst r um ent s. These charact er ist ics of sm aller pit ch lengt h and higher A3 lead t o a t endency of a higher t or sional st r engt h for WO inst r um ent s. These r esult s cor r oborat e a r ecent clinical t r ial t hat accessed t he fract ure incidence of t he reciprocat ing
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post er ior t eet h. The overall inst r um ent separat ion incidence concer ning t he num ber of canals shaped was found t o be as low as 0.13%5.
Alt hough t hese inst r um ent s ar e less suscept ible t o t h e “ t aper lock ” effect du e t o t h e clock w ise m ot ion of det ach m en t , on ce u sed as a sin
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op er at e u n d er h ig h er t or sion al load s ow in g t o incr eased cont act ar ea w it h dent in w alls, w hich m ay exceed it s t or sional st r engt h and event ually lead t o fract ur e2,20. The clinical applicat ion caused
a t endency of decr easing t he m axim um t or que but consum ed less t han 10% of t he t orsional resist ance of t he RC and WO inst r um ent s. Com par ed w it h Figure 4- Secondary electron images obtained by scanning electron microscopy. New Reciproc (a) and fractured Reciproc after clinical use (b). Presence of high concentration of typical longitudinal/parallel (wide arrows) and transverse (thin arrows) microcracks on the surface of a RC instrument fractured during clinical use (c, d)
a
c
b
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differ ence in t he t or sional r esist ance was obser ved aft er t he clinical use ( P> 0.05) . I t was pr eviously r epor t ed t hat clinical use in 10 cur ved canals or 5 m olar s, low er ed t he m ean values of m axim um t or que com par ed w it h t he new inst r um ent s1,25,26. 7KLVVLJQL¿FDQWGHFUHDVHLQWRUVLRQDOUHVLVWDQFHZDV
not obser ved in t his st udy and m ay be explained by t he r educed clinical use ( only 1 m olar ) or by t he r ecipr ocat ing m ot ion of t hese inst r um ent s. The
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( 295°) and WO ( 241°) inst rum ent s were far beyond t he am plit ude of r ot at ion em ployed in t he CCW m ovem ent ( 170°/ 150°) , w hich m ay also explain t he low incidence of failur e dur ing t he clinical use. I n a recent st udy, a very low incidence of fract ure in Recipr oc inst r um ent s and defor m at ion aft er clinical use was also observed21. According t o t he lit erat ure,
t h is low f r equ en cy of f r act u r e can be possibly underst ood as an im provem ent in fat igue resist ance associat ed w it h t h e r ecipr ocat ion k in em at ics1 6,
t he inst r um ent cr oss- sect ional design22, and t he
super elast ic M- w ir e alloy12,18,19.
I n accordance wit h t he m anufact urer and during t he clinical use, t hese inst rum ent s were used under apical pr essu r e. Lon git u din al cr ack s in RC an d
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or ient at ion on t heir sur faces under t or sional load w er e obser ved t hr ough SEM analy sis. Accor ding t o Bah ia, et al.2 ( 2 0 0 8 ) , d u r in g cy clic t or sion ,
planes w it h a m ax im um shear st r ess ar e eit her per pendicular and/ or parallel t o t he longit udinal axis indicat ing t hat inst r um ent fract ur e m ay occur as a r esult of t r i- axial st r esses, w hich could be t he case in fract ur ed RC inst r um ent s t hat pr esent ed bot h t y pes of cr ack s ( Figu r e 4 ) . Nev er t h eless, t he fract ur e t hat occur r ed in bot h RC inst r um ent s m ay be explained by t he low er m ean A3 values and t he lar ger pit ch lengt h in com par ison w it h WO inst r um ent s, t hus pr om ot ing a sm aller m ass at t he t ip of t he RC inst r um ent s.
CON CLUSI ON S
Wit hin t he lim it at ions of t his st udy, no st at ist ically si g n i f i can t d i f f er en ces i n t o r si o n al r esi st an ce bet w een Recipr oc and WaveOne inst r um ent s w er e obser ved, alt hough dat a suggest a t endency t o higher t orsional st rengt h for WaveOne inst rum ent s. Geom et r ic fact or s such as t he pit ch lengt h, t he diam et er, and area at 3 m m from t he t ip, in addit ion t o t he m anufact ur ing pr ocess, m ay have an im pact on t he clinical behavior of t hese inst rum ent s. Finally, w e obser v ed t hat t he clinical use in one m olar
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t or sional r esist ance for t he analyzed inst r um ent s.
ACKN OW LED GEM EN TS
This w or k was par t ially suppor t ed by Fundação de Am par o à Pesquisa do Est ado de Minas Gerais ( FAPEMI G) , Belo Horizont e, MG, Brazil, Coordenação de Aper feiçoam ent o de Pessoal de Nível Super ior ( Capes) , Brasília, DF, Brazil, Conselho Nacional de
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da Un iv er sidade Feder al de Min as Ger ais, Belo Ho r i zo n t e, MG, Br azi l . Th e au t h o r s d en y an y
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