Dental

Materials

Journal

11 (1): 1-10,

Super-Elasticity Ni-Ti

and

Alloy

1992

Thermal

Orthodontic

1

Behavior

Arch

of

Wires

Takayuki YONEYAMA*, Hisashi DOI*, Hitoshi HAMANAKA*, Yasuo OKAMOTO**, Masakuni MOGI** and Fujio MIURA*** * Division

of Metallurgy

University,

, Institute Kanda-Surugadai,

2-3-10

** 1st Department

for

Medical Chiyoda-ku,

of Orthodontics , Faculty Yushima, Bunkyo-ku, Tokyo 113, Japan

*** Department

of Orthodontics

Yokohama

on December

Accepted

on March

among

of Dentistry,

of Dental

Tokyo

Medicine,

Tokyo

Medical

and

Medical and Dental University,

Tsurumi

University,

2-1-3

Tsurmi,

Dental

1-5-45

Tsurumi-ku,

230, Japan

Received

Bending investigated

, School

and Dental Engineering, Tokyo 101, Japan

26, 1991

3, 1992

properties and thermal behavior of twenty commercial Ni-Ti alloy orthodontic arch wires were quantitatively to characterize their suitability for clinical use. There was substantial difference

the load-deflection

curves

obtained

by a three-point

bending

test.

Some

wires

elasticity; load decreased little with decreasing deflection. Others showed good spring-back load was nearly proportional to deflection. Thermal behavior due to phase transformation

exhibited

examined by differential scanning calorimetry (DSC). Some of the wires did not have the correct tion temperatures to exhibit super-elasticity at body temperature. Moreover, thermal behavior related to super-elasticity. However, wires without

There were super-elasticity

Key words:

wire, Super-elasticity,

Ni-Ti

alloy

clear thermal peaks in the DSC curves had no peak in the DSC curves. Thermal

super-

properties only; of the alloy was transformawas closely

of the super-elastic

wires.

behavior

INTRODUCTION Ni-Ti

alloy,

for its unique introduced

consisting

of nickel

mechanical

to clinical

properties orthodontics

and titanium of shape as Nitinol

in nearly

memory

equiatomic

in 19711).

It had

property due to high elastic strain and low elastic stiffness2-5). In 1982, a new super-elastic Ni-Ti alloy orthodontic wire was showed

super-elasticity

movement8-10). Ni-Ti

alloy

properties

were and

providing

Successively, investigated transformation

property15) and reversible the mechanical properties

light

continuous

rectangular

temperatures

force

wires11), bending

for orthodontics.

proportions,

and super-elasticity.

of Ni-Ti

alloy

was

spring-back

introduced6,7).

This wire

and efficient

tooth

method12,13) and coil springs14)

As for the relation

force control16,17) were reported. of the super-elastic Ni-Ti alloy

an excellent

for physiologic

is known

This

alloy

between

wires,

of

the mechanical

a thermomechanical

The effect of heat treatment wires was also examined18,19).

on

Owing to these papers, Ni-Ti alloy orthodontic wires received much attention and rapidly spread in clinical use. Accordingly, many manufacturers began to produce Ni-Ti alloy orthodontic wires. However, the transformation temperatures of marketed Ni-Ti wires vary20), and there are considerable differences in the bending properties21,22). In this study, differential scanning calorimetry (DSC) was used to measure twenty commercial Ni-

2

T. YONEYAMA,

Ti alloy

arch wires

super-elasticity

H. DOI, H. HAMANAKA,

and the bending

and thermal

Y. OKAMOTO,

properties

behavior

M. MOGI

were compared

of wires

MATERIALS

to clarify

and F. MIURA

the relation

between

for orthodontics

AND

METHODS

The wires used in this study are listed in Table 1. Common specifications

of the wires

are: round wire; upper arch form; 0.46mm (0.018inch) in diameter. The diameters were measured by a micrometer prior to the experiment. In this paper, abbreviated codes in Table Table

* **

1

N i-Ti

TITANIUM

NICKEL #

## ### #### @ @@ @@@ @@@@ +

ALIGN, •gA•h-Co. TITANAL

, Ormco Nickel-Titanium

tp

wire

NITINOL VITANOL,

Pacific,

Co.,

, Tomy

CA,

Carlsbad, Wilmington,

Glendora,

Inc., CA,

International

IN,

Orthodontics, ACTIV-ARCH

USA

CA,

USA DE,

Marcos,

USA CA,

USA

USA and

Equipment

Orthodontics, Inc.,

Inc., Tokyo,

Co.

Inc.,

Denver,

CO,

Japan

eop

Inc.,

Inc. , Unitek Minneapolis,

USA

USA

FL,

, TOOC , TP

USA

USA

Sarasota,

San

Supply

Mountain

MD,

USA

Inc.,

Organizers,

WI,

Hagerstown,

PA,

Greenwood,

Inc.,

Sheboygan,

America,

Bristol,

Inc.,

, Orthodontic , Rocky

SENTALLOY

+++

Wire

Diego,

Orthodontics,

Corp.,

ORTHONOL

plus

San

of

Inc.,

Technologies,

, Ortho

Ni-Ti

nt

$

, OIS

NITANIUM

++

++++

, Lancer

NI-TEK

, G & H

Inc.,

Orthodontics,

Corporation

Orthodontics,

, Glenroe

in this study

, American

, Dental

, Masel TITANIUM

MARSENOL

tested

WIRE

TITANIUM

ELASTINOL

****

arch wires

MEMORY

NICKEL

***

alloy

Corp., MN,

Monrovia, USA

CA,

USA

Gaithersburg, USA

MD,

USA

SUPER-ELASTICITY

1 are

used

package

in place

of the names

and used in the

following

OF Ni-Ti

of these two

wires.

ALLOY

Two

arch

WIRES

wires

3

were

taken

from

each

tests.

To investigate the bending property of Ni-Ti alloy arch wires, a three-point bending method was chosen because it characterizes super-elasticity more accurately than the approved ADA standard cantilever method. Moreover, the three-point bending test simulates the clinical application of the wire on teeth10). Straight 30mm portions of Ni-Ti alloy arch wires were used for the three-point bending test. The specimens were cut from both ends, consequently, four specimens were examined for each kind of wire. Figure 1 shows a schematic drawing of the device, viewed from above. The center pole was combined with a load cell* to measure the load on the wire; the two side poles were mounted on a movable stage connected Neither bracket

with a displacement transducer** to measure the deflection of the wire. nor ligature wire was used to avoid the influence of tightening. The

temperature of the specimen and the apparatus was kept at body temperature, 310K. The loading and unloading speed was approximately 0.2mm/s; the maximum deflection was 2.0mm. Figure 2 is a schematic drawing of a load-deflection curve of a super-elastic Ni-Ti alloy arch wire. To evaluate the bending properties of Ni-Ti alloy arch wires, three parameters were devised for the load-deflection curve -a load-deflection (L/D) ratio, a minimum load and a minimum deflection for super-elasticity. Since the unloading process is thought to be more closely related to orthodontic force than the loading process, these parameters were taken from the unloading curve. The L/D ratio is inclination K, taken from the straightest

Fig. 1

Schematic

drawing

point bending from above.

test

of

the

device,

* LU -5 KA , NMB,Tokyo, Japan ** 1303, NMB, Tokyo, Japan

threeviewed

Fig. 2

Schematic drawing of the loaddeflection curve of a super-elastic Ni-Ti alloy arch wire. Inclination K determines the L/D ratio. The load value of point E is the minimum load; the deflection of point F is the minimum deflection.

4

T. YONEYAMA,

H. DOI, H. HAMANAKA,

part in the super-elastic value is used to evaluate load value

of point

characterizes is the

deflection

cut

was

from

pieces,

373K.

value

sealed

with

arch in

wire

The

used

as

and

aluminum

the

heating

reference

rate

and F. MIURA

was

in the super-elastic

point

F;

load range,

The minimum

it demonstrates

the

and

deflection

required

minimum

force.

the

remaining

weighed cells,

The

load value

force due to super-elasticity.

inflection

super-elastic

calorimeter**. was

with the lowest

of the

performed

each

scanning Al2O3

E, the point

to obtain

DSC

M. MOGI

range, a generalized parameter of the super-elastic index22). This the changeability of the orthodontic force. The minimum load is the

the level of orthodontic

deflection

Y. OKAMOTO,

portions by

and

atmosphere

an

put

into of

material. 0.17K/s.

The Liquid

of

the

electronic

the

the

nitrogen

Two

temperature used

for

segments

were

chamber chamber

was

20mm

They

measuring

measuring scanning

wires.

balance*.

of

was

argon

was

between

the

cooling

cut a

were into

four

differential gas,

and ƒ¿173K

and

process.

A schematic drawing of a DSC curve of a Ni-Ti alloy wire is shown in Fig 3. In this study, three parameters were taken from the curve -the reverse transformation finishing temperature (Af point), the endothermic peak (Hendo) and the endothermic energy (Qendo). This endothermic reaction is caused by the reverse transformation of Ni-Ti alloy.

Fig. 3

Schematic drawing of a DSC curve of a Ni-Ti alloy arch wire. Af indicates the reverse transformation finishing temperature. Hendo and Qendo show the endothermic energy,

* **

respectively.

ED -200 , Shimadzu, Kyoto, Japan DSC -7000 , ULVAC, Tokyo, Japan

peak and the endothermic

SUPER-ELASTICITY

OF Ni-Ti

ALLOY

WIRES

5

RESULTS Bending

property

Figure There

4 shows

are

unloading wires

processes.

called

nearly work

two typical

conspicuous

flat

load-deflection areas,

Figure

5 shows

the work-hardened

proportional with these

to the

curves

where

the

load

of super-elastic changes

two of the load-deflection

type.

There

increasing

and

during

curves

is no flat area

decreasing

Ni-Ti

little

the

arch wires. loading

of the Ni-Ti

in these

deflection.

alloy

curves,

and

alloy arch

and the load is

Super-elasticity

does

not

wires.

The three parameters

-the

L/D ratio, the minimum load and the minimum deflection

-

of commercial Ni-Ti alloy arch wires were calculated and are shown in Table 2. SB showed the lowest L/D ratio of 0.16kN/m; SY, VT and OR exhibited relatively low values. However, GL, OO, US and JJ showed considerably higher L/D ratios. Those of OT, LA and UT were markedly The blanks, wires. load,

minimum because

Points

load

points

deflection

showed

value

and the

E and F were

E and F were located

SB had the lowest

minimum VT

higher and were nearly constant

value

showed

deflection

indistinguishable

the unloading

value

in some

curves.

SY, OR and VT showed

tendency:

of OT,

in the load-deflection

at the same position

of 0.50N; a similar

minimum

throughout

SB exhibited

LA and curves

UT

are

of these

As for the minimum

relatively

the lowest

process.

low values. value;

The

SY, OR and

low values.

Differential Scanning Calorimetry Figure 6 shows a typical DSC curve of a Ni-Ti alloy arch wire with super-elasticity. There are two endothermic peaks on the heating curve owing to the rhombohedral phase transition23) and the reverse transformation. The Af points of Ni-Ti alloy arch wires are shown in Table 3. Most of them were between 290K and 305K, below body temperature,

Fig. 4

Typical load-deflection -Ti alloy arch wires elasticity.

curves of Ni with super-

Fig. 5

Typical load-deflection curves of Ni -Ti alloy arch wires without superelasticity.

6

T. YONEYAMA,

Table

H. HAMANAKA,

2

Summary

of three-point

Standard

deviations

in parentheses.

Fig. 6

310K.

However,

higher

than

The

H. DOI,

bending

curve

of GL and OO

test of Ni-Ti

of a Ni-Ti

were

slightly

alloy

M. MOGI

alloy

arch

higher,

and F. MIURA

arch wires

wire

with

and that

super-

of US was noticeably

310K.

values

Fig. 3, were

those

Typical DSC elasticity.

Y. OKAMOTO,

of the endothermic

calculated

peak

and are shown

and the energy

in Table

of Ni-Ti

3. SB showed

alloy

arch wires,

the highest

peak

shown

and energy;

in

SUPER-ELASTICITY

Table

3

Standard

Summary

of DSC of Ni-Ti

deviations

in parentheses.

Fig. 7

SY,

VT,

OR

endothermic 1.0•~10-2s-1. thus

the

and peak There

Af

point

Typical DSC curve elasticity.

OI

exhibited

compared was could

no not

peak be

the

high

DSC

ALLOY

WIRES

7

arch wires

alloy

arch wire

values.

endothermic

in the

detected.

alloy

of a Ni-Ti

relatively with

OF Ni-Ti

US, OO,

energy; curves

of

the LA,

OT

without

JJ

super-

and

GL

Hendo/Qendo and

UT,

showed

ratio as

shown

is

a less in

low than

Fig.

7,

8

T. YONEYAMA,

H. DOI,

H. HAMANAKA,

Y. OKAMOTO,

M. MOGI and F. MIURA

DISCUSSION Super-elasticity

and

endothermic

Super-elasticity transformation.

behavior

of Ni-Ti Clinical

alloy

orthodontic

process. The bending property tion, which is an endothermic and the endothermic

peak

occurs force

in association is thought

in the unloading process. There

of a super-elastic

with

stress

to be displayed

induced through

martensitic the unloading

process is affected by the reverse transformawas a close relation between super-elasticity Ni-Ti

alloy

wire18).

Figure 8 shows the relation between the L/D ratio and the endothermic energy of Ni-Ti alloy arch wires. The L/D ratio demonstrates the changeability of the orthodontic force in the super-elastic range. The lower a wire's ratio is, the less changeable the force it can display. The wires showing high endothermic energy on the DSC curves exhibited low L/D ratios; the orthodontic force of these wires remained nearly constant in the unloading process. This property is considered physiologically desirable for tooth movement10). On the other hand, the three wires showing no endothermic energy exhibited high L/D ratios; orthodontic force decreased with decreasing deflection. These wires possess good springback property, however, the orthodontic force is changeable. The L/D ratio is also related closely to the endothermic peak. If a wire shows a low endothermic peak compared with the endothermic energy, the L/D ratio is not as low as expected from the energy measurement. The open squares represent these in Fig. 8. Ni-Ti alloy wires need to show clear thermal peaks due to transformation Optimum treatment super-elastic

to exhibit

orthodontic

stage,

and so forth.

Ni-Ti

Fig.

force

alloy

8

In some

wires

Relation

with heat

with

the

recent

L/D

ratio

and

The

open

squares

wires

whose than wires.

ratio 1.0•~10-2s-1;

of endothermic the

kind

studies,

treatment

wires.

arch

other

super-elasticity.

between

alloy

less

varies

span

changing

the

between orthodontic

was investigated12,13,16,19)

endothermic

energy

represent peak

open

of tooth,

circles

to

the

of

values

endothermic represent

Ni-Ti of

energy those

of

the is the

brackets, force

The minimum

of

SUPER-ELASTICITY

load is thought suitable

to be an effective

orthodontic

super-elastic orthodontics, deflection

force.

continuous

parameter

The

force.

because

it means

is restricted

relative

OF Ni-Ti

ALLOY

for choosing

minimum

deflection

As for this

parameter,

a wider

range

9

the super-elastic is the

required

a lower

of continuous

to the minimum

WIRES

value

force.

wire with the most deflection

to exhibit

is better

for clinical

However,

the minimum

load.

Transformation temperature The transformation temperatures of Ni-Ti alloy have a great influence on the mechanical properties. Super-elasticity is caused by the stress induced martensitic transformation, and the unloading process used for orthodontic force relates to the reverse transformation from the martensitic phase to the parent phase. Therefore, this property is observed at a temperature above the transformation temperature range. Since the three-point bending test was carried out at 310K, a representative body temperature, the Af point of the wires must be below this temperature to exhibit super-elasticity. In a recent study, transformation temperatures of a commercial Ni-Ti alloy orthodontic wire were in a range too high to exhibit super-elasticity even after heat treatment20). As shown in Table 3, three among the twenty wires tested had no peak on the DSC curves, and another three wires had inadequate transformation temperatures for super-elasticity. The mechanical properties and the thermal behavior of Ni-Ti alloy vary with composition, history of heat treatment, degree of machining, and so forth. The reasons for the differences among the commercial Ni-Ti wires are probably in the material itself and/or the production method. Ni-Ti alloy is easily oxidized and contaminated at high temperatures; the properties of the alloy are very sensitive to impurities and the proportion of nickel and titanium. Since the characteristics of Ni-Ti alloy depend on the internal structure, they are damaged by machining and are changed by heat treatment temperature and time. Ni-Ti alloy wire possesses ideal properties for tooth movement, correct and careful production.

however, it cannot be used in clinics without

CONCLUSION Bending arch

wires

metry.

properties were

The wires

orthodontic showing

no

showing

high endothermic

remained

nearly

peak

exhibited

a good

wires

behavior

of twenty

by a three-point

force

creased with decreasing high for super-elasticity. super-elastic

and thermal

investigated

constant

bending energy

commercial test

Ni-Ti

and differential

alloy

orthodontic

scanning

exhibited

excellent

super-elasticity;

in the unloading

process.

However,

spring-back

property

only;

the

orthodontic

calorithe

the wires force

de-

deflection. The transformation temperatures of some wires are too Therefore, correct production is indispensable for the use of

in clinics.

REFERENCES

1) 2)

Andreasen, G.F. and Hilleman, T.B.: An evaluation of 55 cobalt substituted nitinol wire for use in orthodontics, J Am Dent Assoc 82: 1373-1375, 1971. Andreasen, G.F. and Morrow, R.E.: Laboratory and clinical analyses of nitinol wire, Am J Orthod 73: 142-151, 1978.

10

T. YONEYAMA,

3) 4)

5) 6) 7)

8) 9) 10) 11) 12) 13) 14)

15) 16) 17)

18)

19)

20) 21)

22)

23)

H. DOI,

H. HAMANAKA,

Y. OKAMOTO,

M. MOGI

Lopez, I., Goldberg, J. and Burstone, C. J.: Bending characteristics 569-575, 1979. Kusy,

R.P.:

Angle

Orthod

Effects

of composition

51: 325-341,

and cross

section

on the elastic

and F. MIURA

of nitinol wire, Am J Orthod 75: properties

of orthodontic

wires,

1981.

Kusy, R.P.: On the use of nomograms to determine the elastic property rations of orthodontic arch wires, Am J Orthod 83: 374-381, 1983. Watanabe, K.: Studies on new superelastic NiTi orthodontic wire, (Part 1) Tensile and bend test, J Japan Soc Dent Appar Mat 23 (61): 47-57, 1982. (in Japanese) Watanabe, K.: Studies on new superelastic NiTi orthodontic wire, (Part 2) Bend and successive 90 degrees bends test in accordance with the ADA specification No.32 for Orthodontic Wires, J J Dent Mater 2 (5): 594-603, 1983. (in Japanese) Ohura, Y.: Orthodontic studies on super elastic NiTi wire, 1. Mechanical properties, J Jap Orthodont Soc 43 (1): 71-80, 1984. (in Japanese) Burstone, C.J., Qin, B. and Morton, J.Y.: Chinese NiTi wire-new orthodontic alloy, Am J Orthod 87: 445-452, 1985. Miura, F., Mogi, M., Ohura, Y. and Hamanaka, H.: The super-elastic property of the Japanese NiTi alloy wire for use in orthodontics, Am J Orthod Dentofac Orthop 90 (1): 1-10, 1986. Okamoto, Y.: Studies on super-elastic NiTi alloy square and rectangular wires for orthodontic use, 1. Mechanical properties, J Stomatol Soc Jpn 54 (1): 57-67, 1987. (in Japanese) Ohura, Y.: Orthodontic studies on super-elastic NiTi alloy wire, 2. Bending and controlling the amount of force, J Jpn Orthod Soc 47 (1): 92-104, 1988. (in Japanese) Miura, F., Mogi, M. and Ohura, Y.: Japanese NiTi alloy wire, use of the direct electric resistance heat treatment method, Eur J Orthod 10: 187-191, 1988. Miura, F., Mogi, M., Ohura, Y. and Karibe, M.: The super-elastic Japanese NiTi alloy wire for use in orthodontics, Part III. Studies on the Japanese NiTi alloy coil springs, Am J Orthod Dentofac Orthop 94 (2): 89-96, 1988. Lee, J.H., Park, J.B., Andreasen, G.F. and Lakes, R.S.: Thermomechanical study of Ni-Ti alloys, J Biomed Mater Res 22: 573-588, 1988. Okamoto, Y.: Studies on super-elastic NiTi alloy square and rectangular wires for orthodontic use, 2. Reversible control of force level, J Stomatol Soc Jpn 55 (1): 5-14, 1988. (in Japanese) Okamoto, Y., Hamanaka, H., Miura, F., Tamura, H. and Horikawa, H.: Reversible changes in yield stress and transformation temperature of a NiTi alloy by alternate heat treatments, Scripta Metall 22: 517-520, 1988. Hamanaka, H., Yoneyama, T., Doi, H., Okamoto, Y., Mogi, M., and Miura, F.: Mechanical properties and phase transformation of super-elastic Ni-Ti alloy wires, Part 1: Relation between super-elasticity and phase transformation, J J Dent Mater 8 (2): 207-215, 1989. (in Japanese) Hamanaka, H., Yoneyama, T., Doi, H., Okamoto, Y., Mogi, M. and Miura, F.: Mechanical properties and phase transformation of super-elastic Ni-Ti alloy wires, part 2: Changes of properties through heat treatment, J J Dent Mater 8 (2): 216-223, 1989. (in Japanese) Airoldi, G. and Rivolta, B.: Ni-Ti wires applied in orthodontics, Transactions of the 3rd World Biomaterials Congress 11: 265, 1988. Yoneyama, T., Doi, H., Hamanaka, H., Okamoto, Y., Karibe, M., Mogi, M. and Miura, F.: Transformation temperatures of orthodontic Ni-Ti wires by DSC, J J Dent Mater 7 (Special 12): 69-70, 1988. (in Japanese) Yoneyama, T., Doi, H., Hamanaka, H., Noda, T., Okamoto, Y., Karibe, M., Mogi, M. and Miura, F.: Evaluation of super-elasticity characteristics of orthodontic Ni-Ti alloy wire, J Stomatol Soc Jpn 56 (1): 93-101, 1989. (in Japanese) Miyazaki, S. and Otsuka, K.: Deformation and transition behavior associated with the R-phase in Ti-Ni alloys, Metall Trans 17A (1): 53-63, 1986.

111

本 号 掲 載 論 文 の 和 文 抄 録

矯 正 用Ni-Ti合

金 ア ー チ ワ イ ヤ ー の 超 弾 性 と熱 量 変 化 米 山 隆 之 ＊,土 居

寿 ＊,浜 中 人 士 ＊

岡 本 安 生 ＊＊,茂 木 正 邦 ＊＊,三 浦 不 二 夫 ＊＊＊ ＊東京 医 科 歯 科 大学 医用 器 材 研 究所 金 属材 料 部 門 ＊＊ 東 京 医 科 歯 科大 学 歯 学 部矯 正 学 第 一講 座 ＊ ＊＊鶴 見大 学 歯 学 部 矯正 学 教 室

い ワイ ヤ ー も存 在 した。 示 差走 査 熱 量 計 に よ って 熱 量 変

歯 科 矯 正 臨 床 に お い て 広 く用 い られ て い るNi-Ti合 金 アー チ ワイ ヤー の 特性 を明 らか に す る 目的 で,20種

の

市 販 ワ イヤ ー に つ いて,曲 げ特 性 お よび 熱量 変 化 を定 量 的 に検 討 した。 その 結 果,2点

支 持 中 央荷 重 法 の 抗 曲試

化 の測 定 を行 った結 果,い

くつ か の ワイ ヤ ー で は,体 温

で 超弾 性 を発 揮 す る た め には 変態 点 が 不適 切 であ った 。 さ らに,熱 量 変 化 は超 弾 性 と密接 に関 連 して い る知 見 を

験 に よ る荷 重-た わ み 曲線 に著 しい 相違 を認 め た。超 弾

得 た。す なわ ち,超 弾 性 を示 す ワ イヤ ー のDSC曲

性 を発 揮 した ワ イ ヤー で は,除 荷 過 程 に お い て荷 重 の 変

明 瞭 な 熱量 変 化 の ピー クが 存 在 したの に対 し,超 弾 性 を

化 が小 さい 領域 が認 め られ た の に対 し,荷 重 とたわ み が

示 さな い ワ イヤ ー で は ピー クが 認 め られ な か った 。

比 例 的 に変 化 し,良 好 な ス プ リン グ特 性 しか認 め られ な

線 には