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