Jmema1ional EniWdontic Journal (1995) 28. 2 39-243
`
`Torsional and stiffness properties of nickel-titaniun1 K files
`J. J. CAMPS & W. J. PERTOT
`Depar/ment of Restorative Dentistry @d Endodontics, Faculty ofDentistry, Marseille, France
`
`Summary
`
`'fhe purpose of this study was to compare stiffuess and
`resistance to frdcture of four brands of nickel titanium K
`files. Instruments of si?.es 15 to 40 were tested according
`to ANSI/ADA Specification No. 28. Resistance to frac(cid:173)
`ture was determined by tlvisting and measuring the
`maximum torque and angular deflection at fuilure.
`Stifiiless was determined by measuring the moment
`required to bend the instrument 45". The permanent
`dcfomtation angle remaining between the tip and the
`flutes of the instruments after bending ceased was also
`re.corded. Nickel titanium K flies satisfied and far
`exceeded specification slundards for st:iffuess. They also
`satisfied and exceeded
`tne standards for angular
`de!iection at failure. They met or e_xceeded the maxi(cid:173)
`mum torque at failure standards in a!l si?.es exeept for the
`size 40 of the Maillefer Niti. and the si2e 30 of the Mac
`Spadden Niti. Nickel titanium K files presented a null
`permanent dcfomtation angle. Clinical studies are
`required to evaluate the influence of low bending
`moment on other properties :Such as breakage and canal
`transportation.
`
`Keywords: Endodontic file, Nickel, Stiffness, Titanium,
`'rl\'ist
`
`Introduction
`
`Nickel titanium alloys (Ntti) present many interest(cid:173)
`ing properties: a shape memory effect. supcrelasticity.
`good biocompaHbility and high corrosion resi:.;t1mce
`(Yoneyama et al. 1993a). Surgical applications such as
`shape memory intramedullary nails, shape memory
`bone plates and many others have been reported
`{Yoneyama ei al. 1993b}. One of the most successful
`applications in the dental field is supcrela(>iic Nitl arch
`>vires for orthodontics.
`
`Correspondence: Dr )can Camps. labormoire de Recherche. Unit~
`!MBB, Far.ul!c d'Odontologie. 27 boulevard Jean Moulin, 1338~
`Marseille Cedex 5. France.
`
`C 199 5 Blacl:wcll Science Ltd
`
`For many years orthodontists have been using nickel
`titanium (Niti) wires because of their excellent flexibility
`and their resistance to stress fatigue (Andreasen &
`Hilleman 1971). Today four distinct products are avail(cid:173)
`able: Nitinol (NI for nickel. Tf for titanium and NOL for
`Naval Ordinance Laboratory (Lipsbatz et al. 1992)).
`cobalt-substituted nitinol
`(Andreasen & Hilleman
`1971}, Chinese Niti (Burston et al. 1985) and Japanese
`Niti (Mihura et al. 1986). T\venty-four brands of Niti
`orthodontic wires are available in I.i'K supply houses
`(Robinson 1992). Despite its valuable properttes. the use
`of Niti in endodontics has been limited for years ('Nalla
`et al. 1988). Re.cently, a \\>ide variety of new Niti
`endodontic instruments have been brought onto the
`market A Niti version of the Canal Master U (Brasseler.
`Savannah, GA. USA) is now available. Compared with
`stainless io'tee] Canal Master D. its fle..xibility is at least
`seven times higher in all sizes (Camps & Pertot 1994).
`The Lightspeed (Lightspeed technology Inc.. San
`Antonio, TX. USA) and the Sensor files (NT Co. fnc ..
`Chattanooga, TN, USA) are new instruments. with a
`special design, to be used in a low-speed handpiece. The
`Lightspeed remains centered in the curvature owing to
`ils very short cutting blades (Glosson et al. 1995). fu
`addition to these special instruments some classical K
`files made '"ith this new metal have also been produced.
`but no study has reported on their torsional properties.
`The purpose of this study was to evaluate the torsional
`and stiffness properties of Niti K files and to compare
`results with a stainless ~:;tee I K flle.
`
`Materials and methods
`Fi\•e types of file were tested and stainless steel Colorinox
`K files served as the control (Maillefer SA, Ballaigues,
`Switzerland). Four types of Niti K flies were tested:
`Brasseler (Savannah, GA. USA). JS Dental OS Dental Inc.
`Ridgefield, cr. USA). Mac Spadden (NT Co Inc.
`Chattanooga, TN. USA) and Maillefer (Maillefer SA.
`Ballaigues, Switzerland). For each type of file the instru(cid:173)
`ments in sizes 15 to 40 were tested according to
`ANSI! ADA Specification No. 28. Ten instruments of
`
`239
`
`GOLD STANDARD EXHIBIT 2029
`US ENDODONTICS v. GOLD STANDARD
`CASE IPR2015-00632
`
`

`
`240
`
`J. ]. Camps & W. J. Pertot
`
`each size were tested for resistance to fracture by twisting
`and for sti!Iness by bending. For the twist test. maximum
`torque and angular deflection were measured at the time
`of instrument fracture. For the stiffness test. bending
`moment was measured when the instrument attained a
`45" bend. Four parameters were measured:
`the
`maximum torque at failure (in g.m) in clockwise rotation
`which rt.'Presented the moment when failure occured:
`the maximum angular dellection at failure in clockwise
`roiation (in degrees) which represented the number of
`degrees at which the instrument failed; the maximum
`bending moment {in g.m} required to bend the instru(cid:173)
`ment 45"; and the permanent deformation angle which
`represented the angle between the tip of the instrument
`and its cutting blades after the 45" bending ceased.
`For the twist test (maximum torque and angular
`deflection at failure). prior to testJng. the handle of each
`instrument >vas removed \Yhere it met the shaft. The
`shaft end was then damped ln a chuck connected to a
`reversibly geared motor revolving at 2 r.p.m. (Baure CM
`2024. St Aubin. Switzerland). A digital display and
`amplifier controlled the operation of the motor. Three
`mill.imetres of the tip of the instrument were clamped in
`another chuck 1.vith brass jaws connected to a digital
`torque meter memocouple (Maillefer SA) and to a strip
`chart (UNSF.JS L 4100} for recording. The digital torque
`meter memocouple measured torque with an accuracy
`of± l g.cm and angular deflection with an accuracy of ·
`±2'\ The files were then tighteneJ between the two
`chucks moving freely on two large horizontal parallel
`rods.
`For stiffness tests (maximum bending moment and
`permanent deformation angle} the same equipment was
`used with a few modillcations. The handle of the instru(cid:173)
`ment was not remov<:.>d and its tip was insertt>d .3 mm
`into a chuck. which was perpendicular to the axis of t11e
`geared motor. The amplifier was set at an angular
`deflection of 45° at which point the test stopped
`automatically. The bending moment was then mea(cid:173)
`sured and recorded automatieaHy by the memocouple.
`
`The permanent deformation angle \•:as read directly on
`the strip chart.
`As the number of samples of each size tested was less
`than 30. a normality test was performed for each instru(cid:173)
`ment type. size and measurement in order to verify
`distribution normality and variance equality. An
`analysis of variance (ANOVA) was performed to compare
`the torque. angular deflection. bending moment and
`permanent deformation angle of the instruments.
`Duncan's multiple range test compared data relating to
`each type offile. Significance was determined at the 9 5%
`confidence level. This analysis was performed wlth a
`microcomputer statistics program (PCSM, Delta consul(cid:173)
`tants, Lyon. Prance).
`
`Results
`For each group the normality test showed a normal
`distribution and as variance equality was vertlled ANOVA
`could be performed.
`
`Resistance to fracture by twisting
`i\1aximum torque m frlilure. Except for the sl?.e 40 of the
`Maillefer Niti. and the si7£ 3 0 ofthe Mac Spadden Nlti. aU
`instruments met or exceedr..>d the ANSI/ADA No. 28
`standards (Table 1). For all of types of tile. maximum
`torqLle at failure l.ncrea~d with file size, !\NOVA showed n
`statistically significant diflerence among the torques at
`failure of the five types of file (P<O.OOl ). Duncan's lest
`showed that. except for si7.e 15, Co!orinox K files
`presented a higher torque at failure than all the Niti files
`(Table 2). The Niti files showed no statistJcally
`significant difference for sizes 20. 2 5 and 3 5. For size
`15 files. MaiUefer Niti and JS Dental Niti presented the
`lowest torque at failure. Among the size .30 files Mac
`Spadden Niti file presented the lowest torque at failure.
`and for si7.e 40 the Malllefer Niti and Mac Spadden Niti
`files presented the lowest torque at failure.
`
`Table l Mtmns (standard 'le\iatlons) oftlw torque at failun:. in g.ru. ofth••livc brands ofK fiks{n"' 10 iu each sl7Jo] and minimum valuf'S t>f!hc
`:\NSI! ADA specification No. 28
`
`J5
`
`20
`
`15
`
`30
`
`35
`
`40
`
`MailleferNitl
`l1r;w;cler Niti
`JSD~ntalNiti
`Mac Spadd->JJ Nltl
`Colodnux
`ANSI/AD/> No. 2S
`
`l051 044)
`1909 (280)
`1448 (89i
`1830 (7l/
`2(!33 (167)
`800
`
`1873 (l04)
`2407(222)
`2727()34)
`1211 (16ll
`3788 (271)
`1800
`
`33301265)
`3243 (3;!9)
`3517(242)
`3409(509)
`6273 (~55)
`3000
`
`5361 !494)
`6629 \295)
`6638 {268)
`4064{330)
`939(}(535)
`450()
`
`7042(642)
`9682{1\36)
`.8431 (928)
`7824(327)
`13121 (767)
`65()()
`
`SJ18 (114)
`!4270(948}
`1216 (879)
`9999(B7)
`18769 (1132}
`woo
`
`

`
`Niti file bending and torsion
`
`2 41
`
`Table 2 Duncan's grouping ofth<: torque at failure. Groups with the
`same letter were not signiflcan!ly different
`
`Table 4 Duncan's grouping or the angular dellcction at failure.
`Groups with the ~11me letter were not sigullkantly different
`
`Maillefer Nili
`Brasseler NiH
`jS Dental Ni!i
`Mac Spadrlen Nlti
`Colorinox
`
`15
`
`A
`B
`/IB
`H
`ll
`
`20
`
`25
`
`A
`A
`A
`A
`B
`
`A
`A
`A
`A
`B
`
`3{}
`
`B
`B
`B
`A
`c
`
`35
`
`40
`
`A
`A
`A
`A
`B
`
`A
`B
`ll
`A
`c
`
`MallleferNitl
`Brasseler Nitl
`]S Dental Nlli
`Mac Spadden Niti
`Colorinox
`
`j 5
`
`A
`A
`B
`B
`A
`
`20
`
`/U3
`A
`c
`c
`B
`
`25
`
`30
`
`A
`B
`B
`B
`B
`
`A
`A
`B
`B
`c
`
`35
`
`A
`B
`c
`c
`c
`
`40
`
`AB
`A
`B
`c
`c
`
`}v1aximum angular tlt~!ledion at. ft{i]ure. All illes satisfied
`and exceeded Specification No. 28 minimum values for
`angular dellecUon at 1:1Hure (Table 3 ). Whatever the
`type of file. maximum angular deflection at failure did
`not increase with file si7.e. ANOVA showed a statistically
`significant difference among the angulations at failure of
`the five types of file (P<O.OOJ ). Duncan's wsts showed
`that JS De.nta! and Mac Spadden presented the highest
`angu!Hr deflection at failure for the sizes 15. 20. 2 5 and
`35 (Tab!e 4}. For si7£S 15, 30 and 40. Mailiefer and
`Brasseler Nlti files presented
`the lowest angular
`deflection at failure. Except for sizes 15 and 10. the
`Colorlnox files presenied the highest angular deflection
`at failure.
`
`Stif!iwss test
`
`,\Jaximum bendirzq moHumt. The bending moment of all of
`the instruments. ln all sizes. satisfk>d and 1.vere bdow the
`maximum values set out in the specifications {Table 5).
`A,t;OVA showed a statistically significant difference
`among the angulations at failure for the five types of file
`{[><0.001). Duncan's
`tbat bending
`tesL"i showed
`moments were significantly greater for Colorinox than
`for Niti files in all sizes (Table 6}. The nickel t.itanlnm
`instruments were about cight times more flexible than
`those made with stainless steel. Exc.ept for size 40. no
`statistically signlficm1t differences were found between
`the bending moment of the four brands of Niti files. Of
`the size 40 files. MaHlefer and Mac Spadden presented
`the lowest bending moment
`
`Permanelll dr;formarion angle
`All the Nitl instruments showed a null permanent defor(cid:173)
`mation angle: when the stress ceased the instruments
`went back to their original position without modifica(cid:173)
`tion. Th.e Colorinox presented a permanent deformation
`angle that increased with file size (Table 7).
`
`Discussion
`
`Under the conditions of this study nickel titanium instru(cid:173)
`ments satislled ANSI/ ADA SJX'4:ification No. 28
`standards. Only the size 4:0 Maillefer Nitl and the si7.e 30
`the Mac Spadden. Niti files presented reduced torque
`values at failure: these flies may be brittle and must be
`used carefully.
`Stainless :>'te,el K files presented a higher torque at
`failure than Nlti K files but with the same rotation at
`failure. If the tips of d1e stainless steel files were locked in
`the canal they were more resistant to fracture than Niti
`K files. This is surprising as Niti is a snperelastic metal
`fKapHa & Sachdeva 1989l and undergoes iess perma(cid:173)
`nent deformation than stainless steel when subjected to
`the same amount of stress (Hudgins er al. J 99J) (Fig. 1 ).
`For instance, Canal Master U made with N!ti presents a
`rotation at failure superior w that of stainless skoel Canal
`Master U (Cmnps & Pertot 1994} and its handle can be
`turned several Urnes before breakage occurs. This is
`probably because of the machining procedures (Seta ct
`al. 1990) which are more important with K files than
`·with Canal Master U and generate more stress within the
`metal.
`
`Table 3 Means {standard deviations) of the angular de!lection at failure. in degrees. of the five brands (11 := W ln each size! nfK files ami minimum
`vaiur"s of the t\NSI/;\DA specification No. 28
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`Ma(!lcfcr Niti
`Br.•s.<wler Ni.ti
`JS Dental Nitl
`Mac Spaddcn Nit!
`Colorinox
`ANSI! ADA No. 28
`
`756(74.31)
`643(95.87)
`1218 (77.22)
`1116 (85.7)
`673.17 (86.83)
`3&0
`
`661{61.86)
`479.4 (66.14}
`9333(104.9)
`944.1 Hi8.54)
`799.31 (132.44)
`360
`
`637.7 {97 .24)
`815.9 (70.98)
`777.3 (56.12)
`852.7 (63.35)
`799.14 () 29.1ll
`360
`
`512(40.55)
`563 (37.38)
`781.9 (115.7)
`771i.4 (66.31)
`978.44 (195.68)
`360
`
`480.9\36.83)
`641.3 (139.8)
`947.9 (127.'))
`961.9 (131.581
`894.4( 1 B.l 8)
`360
`
`521.6 (61.491
`490.8 (86.381
`688.1 (149.38)
`850(211.65)
`839 (160.66}
`360
`
`0 19'15 Hiarkwcii Science Ltd. llllmllllimrnl End:ulonllc !""'""'!. 28
`
`

`
`242
`
`f. f. Camps f:r \·V. J. Pertot
`
`Tllble 5 Means (standard deviations) of1he bending moment at 45° of the five brands ofK ftles (n=lO in each size) and maximum values of the
`t\NS!f ADA specification 28
`
`15
`
`20
`
`Ma!llefer N!tl
`Brasse!er Niti
`JS Dental N.lti
`Mac Spaddcn Niti
`C<:>lorirmx
`ANSIIADANo. 28
`
`438(53)
`796 (100)
`68:9(48)
`878 {52)
`2232 (181)
`5000
`
`834(65)
`1103 {112)
`1338i,110l
`987 (73}
`4254(244)
`8000
`
`1-_:.
`
`1535 (160)
`1700 \179)
`1877 (1931
`1668 (237)
`7095 (376j
`12000
`
`30
`
`35
`
`40
`
`2157 (llO)
`2940{118)
`3231 {992)
`1593 {132}
`11174(575)
`15000
`
`2779 (155)
`4594{313)
`4143 (479)
`3600!452)
`15587 (6l2)
`19000
`
`3545 0 75)
`7005 (471)
`5866(41>0)
`4348(695)
`21983 (811)
`25000
`
`Niti K files presented a bending moment five or six
`times lower than stainless steel K files: they are five or six
`times more flexible. The poor flexibility of stainless steel
`or carbon steel endodontic instruments turns curved
`canal preparation into a daily challenge. :\ flexible
`instrument may avoid canal transportation during
`enlargement. Conversely, a nonflexible instrument leads
`to errors during preparation such as ledges. Zips, canal
`and apical foramen transportation and strip perfora(cid:173)
`tions. Canal preparation vvith this type of instrument is
`time consuming because of the importance of the forces
`generated on dentine by the instrument and the
`opposite forces generated by dentine reacting on the
`instruments. Furthermore. these forces generate stresses
`along the cutting blades which may result in instrument
`breakage. The Niti K files presented a lower torque at
`failure than stainless steel K files, which is a disadvan(cid:173)
`tage. but their bending moment is S<J low that they may
`he sa!er clinically. Studies nmst be undertaken to
`evaluate canal transportation during curved canal
`
`Tllble 6 Duncan ·s grouping of the bending moment. Group$ with the
`same letter were nnt significantly different
`
`]5
`
`20
`
`25
`
`30
`
`MailleferNiH
`Brasse!er Nili
`JSDentalNiti
`Mac Spadden Nit!
`Colorlnox
`
`A
`A
`A
`A
`ll
`
`A
`A
`A
`A
`!}
`
`A
`A
`A
`A
`l~
`
`A
`A
`:\
`A
`!3
`
`35
`
`A
`A
`A
`A
`H
`
`40
`
`A
`B
`B
`:\
`c
`
`Tabk 7 Mea.ns (standard deviations), in degrees. of the permanent
`dclormatlon angle of th.: K Oles, Colorino>:
`
`l5
`20
`25
`30
`35
`40
`
`9.94 (6.99)
`1L95(8.87)
`1B(S.D3)
`15.33(5.96)
`15.33 (5.96)
`18.14(4.77)
`
`preparation with Niti K files together with the incidence
`of instrument breakage.
`Niti K files presented a null permanent deformation
`angle. On the contrary. stainless steel K files presented a
`permanent deformation angle ranging from 9.94" to
`18.14". This means that if the tip of a stainless steel file is
`bent at a 45° angle and left free. il does not go back to its
`pos!tlon but malnra!ns an angle of JOG with the flutes.
`This presents a disadvantage in a linear motion, during
`instrument withdrawal (Wildey et al. 199 2 }. but most of
`all in rotary motion. The stress generated by the rotation
`of an instrument in a curved canal is increased by the
`
`(a) A scanning eleL'tron mi~Toscope view <,fa Malllcfer Niti K
`fig. 1
`lile tip before deformation. {b) t\ scanning ck'Ctmn mic-roscope vlew of
`the llutr.s of a Maillefcr Niti K file that underwent inelastic defonmulon
`without fracture.
`
`

`
`permanent deformation angle: its tip undergoes a stress
`equal to the canal curvature added to the permanent
`deformation angle. It would be interesting to know
`whether stainless steel K files intended for rotary motion
`(Roane et al. 1985}, such as fllex-R. present a permanent
`delormaUon angle.
`Niti K files presented interesting stillness properties
`that ought to remain unchanged by sterilization proce(cid:173)
`dures (Mayhew & Kusy 1988). Temperatures of about
`600°C are required to effect a change in flexibility (Lee
`eta/. 1988 ). The encouraging fearures presented by Niti
`K fik>s in this study must be followed by studies that
`investigate the effects on canal curvature, eflidency. and
`clinical resistance to fracture.
`
`Conclusions
`
`l. Nickel titanium K files satisfied ANSI/ ADA specifi(cid:173)
`cation No. 28 values tor moment at failure. except !i.1r
`size 40 Mail!e!er Nitl. and si;r,e 30 Mac Spadden Nitt
`2. NJckel titanium K flies satislk>cl ANSI! ADA specilica(cid:173)
`tion No. 28 values for rotation at failure and for
`bending moment at a 4 5" angle.
`3. Nickel titanium K Illes presented a lower torque at
`failure than the stainless steel K Hies and the same
`rotation at failure.
`4. Nickel titanium K files presented a bending moment
`five times lower than stainless stet'l K files and a null
`permanent deformation angle.
`
`References
`
`ANlJR£ASSN G!'. H!l.tlll.!AN TB (1971) An cvnlualimt uf 55-L"<Jhah
`substltued Nitinol wire for uSt:~ in orthodontics. Jount«i of Amerkan
`Dental (i$sadtHion 82. 1373·"'5.
`,>\NSl (l98Sl Revised :lmrricml Nutimml Sumdimls llistitutd :1moimn
`Denwl th .. ~ti;iation 1.):r~:~{k«tim: No. 28 for Root Ctma1 Files ami
`Hwmers. TWJC K. Nm'l' Yo,-k. USA: Amerlcun National Standards
`lnstllute.
`lltlRSTON Cj. QtN B. MowrnN )Y (1935) Chinese NiH wire. A n~·w ortho(cid:173)
`dontic aHoy. Amfr-kmt Journal tifDrtlwdon!i~~-(( 87, 445=52.
`
`Niri file bending ancl torsion
`
`2 4 3
`
`CAMPS j. PISR'for \lv'j (1 994) Torsional and sti!Tnt:ss properties of Canal
`Master U stainless steel <md nitinol instruments. Jmmwl of
`EmlodanHcs 20. 39 5-8.
`Gwssot' CR. H!il.Lf.R RH. Dovr. S!l. DEL R!O CE (1</95} Comparison
`of root canal prepat'a!ion using Ni· Ti hand. Ni-T1 cngine-<lriven.
`and K-Fiex endodontic instruments. Jtmma/ ,~f Emiodamics 2 L
`146-51.
`HtlDGl:-IS lf, lhCllY MD. ERJCKSO!" 0991) The effect nf long-term
`deflection ()n perrnanent defonnaUon of Nickel-titanium &rch\virL"K
`The Angk0rr/uki.ontis160. 283-7.
`KAI'H.>~ S, S.'ltlWEI' A R ( 1989) Mechanical propenics and clinical
`applications of ortiwdon!ic wires. Ameriwn Journal of Oniwrlamli:s
`and Demofitda/ Onlw;>edits 96.1 no- 9
`Lf:Eji'L :\l'!ll\F.ASB!:\ GF. LAKES RS (19SSl Thern10!UcCanlcal study of
`Ni-ri alloys. journal af Biomtdiwi M<ttetitlis Research 11. 5 i 3-- S8.
`MAYHEW Mj. KliSY RP t 1981!) Elk'C!s of swrilizatkm on the mechanical
`properties and the surface topography nfnickel·timnium arch wires.
`Amerimn ]ourmtl of Orrltocwmics and Dcmojitcial Ortlwpedics 9 J.
`231-,6.
`M!!WRA F. )\,fOG! JVL 0Hl'RA Y. flAMAKAK,\ H 11986} The >'UperelastiC
`property <>f th" japanese l'ili alloy wire for use in ortho(cid:173)
`dontics . . 1mrrican Journal of Ortlwdonllt.~ a11d Denw.filcial Or!lmpedits
`90.1 .. 10.
`IJFSH.IIT?: J .. l3ROCKHnns PJ. Vh$T VC 09921 Cllulcal note No. l L
`Mechanical properties
`in bending of shape-memory wires.
`AU$!rclfi<m lJtnuil jmmml3i. 315···· 6.
`Rnr.N~ rn. &llll>f.A CL..l)t::;CAN$01\ MG (1985} The "halanc~·d f()rce"
`(;um:ept for ins!rumentation of curved canals. joumal of BmlmLm!ics
`11. 203-.. Jl.
`Rom;;;;o;; SN (l992l Superela.<;~.k wires. A romparl>on of wires avail(cid:173)
`able from the UK supply houses. British Journal of Ortlwdol!tics 19.
`323-9.
`SETO llG. N!rHOU.S JL HARIKGTnK GW ( 1990i Torsional pmperties of
`twistt:.-d and machined endodontic JllL>s. Jaumali\{ EndoamHics 16.
`355-60.
`WALL-\ f:L BK/iNTl.EY WA. Giii\STE11' H (!988} t\n initial in\'est.lgation
`of the bending and wr;ional properties of nitlnol root canal tiles.
`]ounwl o.fEm!mlomics 14. 346- 5L
`WIWEV \VL. SE!:\U F$. Mo;;n~mmnY S (1992) Anotlter look at root
`mnal instrum~nJ.ation Oral Sw·gery. Ornll<;ledirine m>d Om! Pmlwi~>,n;
`74.499-507.
`YoNf:BMA T. KorAKtM.KnEAYA>H!l'. Dm H. Ht.MA~'M'.A H{l993a)
`lnfh::cnc(; ofrnqld nhJterlaL~ and h!?Alt treatment on tensile properUe..-.;
`of Ni· Ti alloy;<;. Bulletin of Tok!J<' Medifine Drmaf University 40.
`16i-72.
`YllNEY.AMA T. Do! H. HAMMvR.~ H (l993b) Bending properties and
`transformation H'mperature or heat treated ~~-Ti alloy wire for
`ort!wdonUc uppllancL'S. }11uma! of BiiJIIl<'dical Materi1tls J:kssearclt 2 7.
`399-401.
`
`I9951llad:wdl Scioncc fJd. ln!mmUmwl Endod,,nfir Jouma!. l!l