PropeOrthodonti

erties of ic Arch wires

Load and elongat

Fr

tion

rom Proffit et al. Contemporary Orthodontics

Stress, strain and

Stress (σ) = Force =F/AAreaArea

Strain (ε)= Change in lenO i i l lOriginal leng

σ/ε = E (Elastic Modulustested in tension or co

d elastic modulus

ngth = ∆l/Lthgth

s) when specimen ompressionp

L/E curve vs. S/S

L/E curve takes into considespecimen – aka extrinsic

S/S curve normalizes the gestiffnessstiffness

A homogenous material shoA homogenous material shomodulus, but materials ofhave different L/E curves

curve

eration the geometry of the stiffness

eometry out – aka intrinsic

ould only have one elasticould only have one elastic f different dimension will

Description of poiDescription of poiS/S curve and terProportional limitYield point

OrYield pointUltimate StrengthF il i t

StiSp

Failure pointp

Ra

ReFo

ints on a L/E andints on a L/E and rminologyrthodontic terms

iffnesspringinessp gange

esilienceormabilityy

L/E and S/S curveL/E and S/S curve…points

From Proffit et al. Contempp

definition of….definition of

porary Orthodonticsp y

Terminology…

From Proffit et al. Contemporary Orthodontics

Stiffness: slope of linear portion of the L/E curve, = Elastic modulus in S/S curveElastic modulus in S/S curve

Range: Distance a wire will bend elastically beforebend elastically before permanent deformation will occur

Strength = Stiffness x Range

Resilence formabResilence, formabtoughness

From Proffit et al. Contemporary Orthodontics

bility andbility and

Resilience: Area under the S/S curve out to the proportional limitlimit

Formability: Amount of d f i ipermanent deformation a wire

can withstand before failing

Ideal orthodontic

• High strength• Low stiffnessLow stiffness• High range

Hi h f bilit• High formability• Capable of taking weld• Measurements in 1/10• 0 016 inch wire is a co0.016 inch wire is a co

wire

d/solder000th of inch or mmommon sizeommon size

Archwire material

• Size• Shape• Shape• Composition

s

Size

• Diameter

From Proffit e

• Length2 l th 8 i i i– 2x length = 8x in springin

= 4x in range (s= strength by ½= strength by ½

(look at Fig 10-13 in text)

et al. Contemporary Orthodontics

( b )

N

ness (cube)square)

½

N

½

Shape

• Round– .014 up to .020

• Rectangularecta gu a– .016 x .016 (162) squar– .021 x .025

– Dimension is in inches

re

Length of wire

Remember: Increased length = inncreased range and flexibility

TypePreci

Composition Stainresist

C bCobaeg: Ecomm

Nicksuper

Beta-and N

UsuaRounRoun

From Proffit et al. Contemporary Orthodontics

Recta

es of metals/alloysious: Gold (in the past)

nless steel: 18-8, strength, springiness, corrosion tance. Can weld

l Ch i Ch i id h iblalt Chromium: Chair side heat treatments possible Elgiloy, available in different grades (not monly used today)

kel Titanium (aka NiTi): have shape memory and relastic, no formability at RT. Cannot weld

-Titanium (aka TMA): Intermediate between steelNiTi. Can weld

al sequence in orthodontics nd, Rect. NiTind SSangular TMA and/or SS

Stress/StraStress/Strassss

Stre

sSt

res

Load

/Lo

ad/

LL

NicNic

DeflectioDeflectio

ain Curvesain Curves

Stainless SteelStainless Steel

Beta-TitaniumBeta-Titanium

ckel Titaniumckel Titanium

on/Strainon/Strain ML Swartz

To get optimimalTo get optimimal teeth…Vary the Size shape compositioSize, shape, compositio

D-Rect

Start treatment with more flexibleallowing for controlled tooth/ro

forces to moveforces to move

n of the wiren of the wire

ML Swartz

NiTi

e wires and end with stiffer wires

NiTi

ot movements, and 3-D control

Shape, size are d

• Now add Pages 334• Do not need to know• Do not need to know

or Strength increase• But do need to know

decrease

described in text

4-337 to readingw if Stiffness Rangew if Stiffness, Range e by what factorw if they increase or

Video’s from Ormmco..Cu NiTi

Manufacture of Stai

Source: Ormco

inless Steel Blanks

NiTi manufacture…

Sour

…

rce: Ormco

SummaryKnow the points, areas and sand S/S curves

Extrinsic and intrinsic proper

Orthodontic wire materials, wused initially) and most stiff y

Effect of diameter and lengthiwire

ignificance of each on the L/E

rties, normalizing for geometry

which is most flexible (thus (towards end of treatment)

h on flexibility (springiness) of

National Board Pa

• Loops and helices areprimarily top y– align teeth– increase force of the wincrease force of the w– increase flexibility of th– hold soft tissues awayhold soft tissues away

art II Questions

e used in arch wires

wireswireshe wiresfrom orthodontic bracketsfrom orthodontic brackets

Questioons