Retraction loops and springs

RETRACTION
LOOPS AND
SPRINGS
www.indiandentalacademy.com

SPRING-?
PLAIN WIRE Vs WIRE
WITH A HELIX
FOR TOOTH
MOVEMENT

PROPORTIONAL
LIMIT
ELASTIC LIMIT

REASONS FOR THE
‘MASTER CIRCLE’-
THE COIL

Increases the proportional limit
Constant direction of force
Range of action
Flexibility of the wire [ position
of the coil ]

STIFFNESS-why is it
so important ?
Tipping –25-40gms

STIFFNESS-
directly proportional to the
flexural rigidity of the wire
critically dependent on the
geometry of the wire

FLEXURAL RIGIDITY
YOUNGS MODULUS-
composition &internal
microstructure
FACTOR I - second moment
of inertia of the cross section

FACTOR I→
Shape-round/rect etc
Dimensions of the cross
section of the wire
I= Πr 4
4www.indiandentalacademy.com

GEOMETRICAL SHAPE
resists deformation
in directions other
than which it is
activated

FORCE
DEFLECTION
D∝PL³
t 4www.indiandentalacademy.com

LOOPS
“A branch of
anything that returns
to the main part”

BASIC
REQUIREMENTS
Simple without complex
configurations
“Fail safe”

Stress raisers –
sudden change in cs
nicks or sharp bends
Force of correct magnitude
Constant force
Required m/f ratio

FACTORS AFFECTING SPRING
PROPERTIES OF A LOOP
BASIC TERMINOLOGIES-

LOAD DEFLECTION RATE
Definition
Stiffness
For active members – low
1.forces are low 2.greater
accuracy in force magnitude
For the reactive elements - highwww.indiandentalacademy.com

AXIAL LOAD
Definition
Torsion
Bending or flexure
Axial loadingwww.indiandentalacademy.com

MAXIMAL ELASTIC LOAD –
MEL
Definition
Active segment
Reactive segment

Elastic behavior
“Ability of a material
to return to its
original shape after
unloading”

Plastic behavior
“The occurrence of
permanent
deformation in a
configuration
during loading”www.indiandentalacademy.com

Elastic limit
“Greatest stress that
can be applied to an
alloy without
permanent
deformation. El and
MEL are analogous”www.indiandentalacademy.com

MAXIMAL ELASTIC
DEFLECTION
Definition
Measures deflection
EL&MEL-force applied
Reactive elementswww.indiandentalacademy.com

Modulus of elasticity
Definition
Determines LDR
{ LDR∝E }
E-constant / EL-altered

The ratio between the EL and E
determines the desirability of an
alloy-higher the ratio better the
spring properties
The ideal orthodontic wire for –
active
unit -↑ MEL { EL } &↓LDR
{ E } Reactive unit
- ↑EL & ↑Ewww.indiandentalacademy.com

SELECTION OF AN IDEAL
ARCH WIRE
1.WIRE CROSS SECTION
A. DIAMETER
MEL ∝ D3
LDR ∝ D4

For a rect wire
MEL ∝ bh
LDR ∝ bh3
.010/.020; force appld;
.010 104
=10000
.020 204
=160000
{16 times}

The overall stiffness of the
appliance is determined by ;
1. Wire stiffness [ws]
2. Design stiffness [as]
S= ws x as

Wire stiffness ;
1. Material stiffness [ E ]
2. Cross sectional stiffness- [ I ]
Design stiffness –can be changed by
increasing the wire between the
brackets which decreases the design
stiffness and hence the appl stiffness

B. Optimal cross
section for a
flexible member
For multidirectional
activations-round wire is
the structure of choice.

Disadvantages of
round wire;
properly oriented/ out
of plane.
it tends to rotate in
the bracket- gingiva or
cheek

For unidirectional
activations,flat wire is the
cross section of choice
because more energy can be
absorbed into a spring made
with a flat wire than with a
any other configuration.
Another advantage – problem
of orientation is solved.www.indiandentalacademy.com

2. PROPER ALLOY
AND SIZE
Primarily on LDR and
secondarily on the magnitude
of forces and moments
required.

The common mistake----
maximum elastic deflection
possible [ MED ∝1/D ]
.016/ .018; MED for .016
∝1/.016 [=62.5]
MED for .018 ∝
1/.018 [=55.55]

we find that the MED of .016
wire is only 1.15 times that of
.018 –not clinically
significant.
Therefore the primary reason
for selecting a particularwire-
stiffness [ LDR ]www.indiandentalacademy.com

Since the wire stiffness is
dependent on the material
stiffness,it is considered now
Since SS was most
commonly used Ms of SS
for comparative reasons is 1

Alloys Ms
S.steel 1
TMA .42
Nitinol .26
Blue eligiloy 1.19
Blue
Eligiloy[heat
treated]
1.19

Since Ws=Ms x Cs,for
the same cross section of
the wire, the stiffness of
TMA is .42 times that of
SS, for the same
appliance design

3.The length of the
wire
Influences MEL and LDR-
depending on configuration
and loading
VERTICAL LOADING
LDR ∝ 1/L3
MEL ∝ 1/Lwww.indiandentalacademy.com

LOADING WITH
COUPLE AT THE FREE
END
MDR ∝1/L2
MEM is not affected at
all by the changes in length

4.Amount of wire
loops/coils- lower the LDR
and increases the range of
action. MEL may or may
not be affected.

To decrease the LDR
without decreasing the
MEL,the additional
amount should be at the
point where bending
moment is a maximum

THE BENDING MOMENT
The cantilever BA is
subjected to a vertical load
The ideal point to
incorporate a coil

In a clinical situation-area
of greatest bending
moment-teardrop loop
Not the amount
of wire but the
placement

5. Direction of loading
straight piece wire-loaded –
permanent deformation.
attempt to increase the bend in
the direction- resistance?and why?
once a bend is made-MEL is
not the same-BAUSCHINGER
EFFECT.

Activation of the spring-
closing the coil rather than
opening.
reverse curve in the arch
wire-the last bend and the
direction of activation should
be the same.www.indiandentalacademy.com

applying these principles to
the closing loop- ‘fail safe’
range of action-
1mm/month and not more
than 2mm/month

Moment to force ratio
Ratio of the force to the moment.
uncontrolled tipping-5:1
controlled tipping -7:1
translation -10:1
root movement -12:1www.indiandentalacademy.com

Depending on the anchorage
Type A-maximum anchorage
Type B-moderate anchorage
Type C-minimum anchorage

Moderate anchorage cases
50-50
forces and moments
vertical forces
m/f ratio-10:1

Maximum anchorage cases
retractive forces to the anterior
teeth and no forces to the posteriors.
such a situation – is it possible.?
intra oral anchorage-Newton's
third law – how do we tackle the
situation www.indiandentalacademy.com

Two ways of achieving this-
altering the forces
altering the moments
both the above ways
aiming to increase the m/f ratio
of the post and decreasing the
m/f of the antwww.indiandentalacademy.com

1. Altering the forces
a. ant segment.
moment should be a constant-
the only option
increase in force should not be
associated with a reactionary
increase www.indiandentalacademy.com

how do we do that?
a.class II elastics
b.j-hook from headgear

b.Post segment.
moment should be
constant- the only option
force opposite to that
acting on the post segments
headgear-distal

2. Altering the moments
force constant- increasing
the post moment- β and
decreasing the ant moment-α
how do we do that?

3. Position of the loop
mesio distal positioning-
important
midway-equal and opp
activation moments.
what is an activation
moment? www.indiandentalacademy.com

off centered to distal-
tip back moment and
intrusive force-maximum
anchorage cases.
mesially off centered-
increases the ant moment-
minimum anchorage cases.www.indiandentalacademy.com

Loops
various types of loops are used.
what are α and β bends.-
moments.
a regular 10mm high loop-
1mm activation-m/f ratio 3:1

to achieve 10:1activation
should be reduced to .2mm-
but force levels?
how do we increase the m/f
ratio;
height of the loop-limited
space www.indiandentalacademy.com

loop design varied-t loop
vs. regular vertical loop
pre-activation or gable
bends-within the loop or
where the loop meets the
archwire.

As we try to engage the wire-
activation moment- neutral position-
with this added moment m/f ratio
of the loop is increased
the α moment-distal root
movement and β moment –mesial
root movementwww.indiandentalacademy.com

Unequal α and β
moments- vertical forces
If the α moment is greater-
anchorage of ant segment
and a net extrusive force

if the β moment is greater-
post anchorage and a net
intrusive force
if the α and β moments
are equal- no verticalforces

The T loop
Burstone – university of
Connecticut
18x25 SS / 17 x 25 TMA
Segmental or continuous

Segmental;support- 18 x 25SS
t loop; auxiliary tube-18 x
25 vertical tube / 1mm 22 x 28
tubes soldered

Dimensions of the t loop
The distal leg–1mm shorter - ??

Passive form
Neutral position
activation moment
Activation always considered
from neutral position

The activation
moment
“The moment arising because
of a change in configuration of
the spring that would occur
because of the mesiodistal
forces to the spring”

Activation – pulling apart –
angulation of the horizontal arms
↑The mesio distal force
↑The deflection
↑The activation moment
M/f ratio – constant for a particular
configurationwww.indiandentalacademy.com

The off centered v bend
Maximum anchorage cases-
differential anchorage
Closer the v bend-higher the appl
moment

Apex of the v-length of
the wire
Shorter the wire-higher
the bending moment

Centering the t loop- moments ?
Off centered t loop- anchor teeth
Clinically the spring – 1-2 mm
closer to one side
Subtle changes in the position of
the v bend critically changes the
moment magnitudes- precisionwww.indiandentalacademy.com

Activation of the t loop – 6 mm
Progress of tooth movement
Group b – centered t loop-initial
m/f 6:1- controlled tipping of ant
and post segments

2mm of deactivation-spring
activation 4mm-m/f raises to
10:1- bodily movement
Further closure 1-2 mm m/f
12:1-root movement
Clinical situation –should
not be reactivated till all
three stages are completedwww.indiandentalacademy.com

The tear drop loop

Only ant retraction-closer to
canine-gable bend larger in post
segments
Both retraction and protraction-
midway-gable of equal
dimensions
Only post protraction-closer to
post-gable larger in ant segmentswww.indiandentalacademy.com

As tooth moves- α and β moments
decrease-↑ in m/f ratio because of
lower appl forces
Since the m/f ratio increases as the
spring deactivates-should not be
reactivated too often
Frequent reactivation –prevents
achieval of m/f to produce translationwww.indiandentalacademy.com

The opus loop
Dr Raymond E Siatkowski-
1997 AJO NOV
Castigliano’s theorem – m/f
Unique property-non varying
m/f –8.1-9 inherently

Design of the opus loop

As the tooth moves the
appld force decreases-
moment can ↑ or ↓
M/f changes as tooth
moves and the tooth
responds–
Controlled tipping-
translation-root movementwww.indiandentalacademy.com

Factors affecting the m/f of the
opus loop
1. Wire size and young's
modulus have little effect
on inherent m/f.[but a
major impact on LDR]
2. The greatest effect on
m/f-height of the loopwww.indiandentalacademy.com

3. Increasing the number of
apical helixes-lesser effect on
m/f
4. Varying the loop diameter
does not significantly affect the
m/f. It is maximized –loop dia
3.5mm

Position of the opus loop
Midway-m/f at the bracket –
helix end-3 times m/f at the
other end
So it is always placed close
to the ant end-1.5mm

Angulation of the vertical leg
Varied in 5 degree increments-
m/f was equal
Occurred-70 degrees to the
plane of the bracket
Because no residual moments-
neutral position-exactly the
spacing of the vertical legswww.indiandentalacademy.com

The experimental results
with the opus loop show
that the opus loop has to
be bent with great
accuracy to achieve
the design potential

The K-sir arch
Simultaneous intrusion and
retraction of the ant teeth –varun
kalra
Modification of the segmental
loop mechanics

K-sir arch
Continuous 19x25
TMA arch wire with
closed 7x2mm U
loops at the extraction
sites

To obtain bodily movement a
v-bend-archwire at the level of
each u loop
This v-bend when centered-two
equal and opposite moments to
counter the moments caused by
the activation forceswww.indiandentalacademy.com

90 degree v bend

A 60 degree v-bend –post to the
center of the IB distance-
↑clockwise moment on the
molar-augments anchorage
To prevent the buccal segments
–rolling mesiolingually –
20degree antirotation bend just
distal to each u loopwww.indiandentalacademy.com

60 degree v bend

Activation
Trial activation-releases the
stresses and decreases the
severity of the v-bend
After trial activation neutral
position is determined with
the legs extended horizontallywww.indiandentalacademy.com

Trial activation

In the neutral position
– U loops are 3.5mm wide
Archwire activated by
3mm so that mesial and
distal legs are barely apart

Neutral position

When loops activated-the
tipping moments
produced by the
retraction loop >
moments produced by the
v bend.this will initially
cause controlled tipping

As the loops deactivate-
force levels ↓-the m/f ↑to
cause first bodily and then
root movement
The arch-not reactivated
shortly-only every 6-8
weeks

The k-sir arch exerts about
125gms of intrusive force-ant
segment and a similar amount of
extrusive force distributed to the
two buccal segments, connected
by segments of TMA wire

This force is
sufficient for
intrusion of ant
while the
reactionary force is
countered by the
masticatory force

The main indication of the
k-sir-retraction of the
anteriors in a first premolar
extraction case who has a
deep bite and excessive
overjet and who requires
both intrusion of anteriors
and max molar anchoragewww.indiandentalacademy.com

Advantages of the k-sir
arch
1.Simplicity of design
2.Easy to fabricate.
3.Comfortable-less likely to
cause tissue
impingement

4. Because of the
friction less
mechanics and the
off centered v-bend-
molar anchorage is
excellent

THE L LOOP

THE OPEN VERTICAL
LOOP

Dr Morris Stoner and
Bruce S Haskell
mentioned that Robert W
Strang was the originator
of this loop for retraction
mechanics

THE CLOSED
VERTICAL LOOP

A similar design
with horizontal
extensions
overlapping each
other is termed as
a closed loop

THE VERTICAL OPEN
LOOP WITH A HELIX

Another modification of
vertical loop- Dr Morris
Stoner. The helix is
incorporated at the apex and
its main purpose is to
increase the working range
Can be open or closed
variety www.indiandentalacademy.com

THE DELTA LOOP

It was described by Dr
Proffit.
16 x 22-0.018 slot
18 x 25-0.022 slot
Approximately 20 degree
angulation on either side

THE DOUBLE DELTA
LOOP

THE OMEGA LOOP

As mentioned by Dr
Morris Steiner this loop is
named so because of the
resemblance to the Greek
letter omega. The loop is
believed to distribute the
stresses more evenly

THE BULL LOOP

According to Salzmann Dr
Harry Bull-1951-introduced a
variation of the standard
vertical loop,the only
difference being that the loops
were tightly abutting each
other. He recommended that
these loops- 0.0215 x 0.025 SS

Retraction loops and springs

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