Biomechanics of loop mechanics in enmasse space closure

BIOMECHANICAL
CONSIDERATIONS OF
LOOPMECHANICS IN ENMASSE
SPACE CLOSURE
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RETRACTION
FRICTIONLESS FRICTION

RETRACTION MODE
FRICTION
Cook book approach
Duration is increased
Pain associated is more
Number of appointments more
Anything with friction slows tooth movement
More tipping and extrusion compared to
frictionless
Confusion regarding force levels
Tendency to over activate elastic and spring forces

force system defined
variable wire used in same arch
prefabricated springs-accurately define
force systems
posterior extrusion,anterior intrusion or
combination
no of wire change reduced
frictional force eliminated
Orthodontic treatment becomes doctor
determined
FRICTIONLES
S

TYPES OF LOOPS USED
COMMONLY
T LOOP
M LOOP
OPUS LOOP
DOUBLE KEY HOLE LOOP
K-sir
TEAR DROP

DETERMINANTS OF SPACE CLOSURE
AMOUNT OF CROWDING
Extractions are done to relieve
crowding,maintenance of anchorage while
creating space for incisor alignment is necessary
in order to meet treatment objectives
ANCHORAGE
Using same mechanics for different anchorage needs
limits the ability to reach desired results.control
of molar position is very important. Utilizing a
force system determined appliance can improve
chance for success

AXIAL INCLINATION OF
CANINES,INCISORS
The same force applied to a tooth or a group
of teeth with different axial inclination will
result in different types of tooth
movement…

MIDLINE DISCREPENCIES
Midline defects should be corrected as early as possible.this
allows therapy to be completed symmetrically.
Asymmetric forces on left and right sides could result in
unilateral vertical forces,skewing of dental arches or
asymmetric anchorage loss
VERTICAL DIMENSION
Attention to vertical forces is essential for control of vertical
dimension in space closure. Undesired vertical extrusive
forces on the posterior teeth result in increase in lower
anterior facial height,increased linter labial gap and
excessive gingival display.the vertical forces in class2
elastics may result in these problems

BIOMECHANICS
FORCE
Force is defined as an act upon a body that
changes or tends to change the state of rest
or the motion of that body, though defined
in units of newton it is usually measured in
units of grams or ounces

MOMENT OF FORCE
When a force is applied at any point other
than center of resistance, in addition to
moving c res in the direction of the force a
moment is created, which is the rotating
tendency.
A moment may be referred in orthodontics as
rotation, tipping, or torquing

CENTRE OF MASS AND GRAVITY
Every body has a point which behaves as if
the whole mass is concentrated at that
single point, which is called the centre of
mass in a gravity free environment. The
same is called centre of gravity in an
environment where gravity is present

CENTER OF RESISTANCE
Since the tooth is
partially restrained, as
its root is embedded in
bone, its center of
gravity shifts apical
and is then referred to
as the center of
resistance

COUPLE
Two equal and opposite, non
collinear forces are called
couple
MOMENT OF COUPLE
The moment of a couple is
the product of one of the
forces times the distance
between the two forces.
the distance is called the
moment arm of the couple

MOMENT TO FORCE RATIO
the ratio of counterbalancing moment
produced to net force that is applied to a
tooth will determine the type of tooth
movement that will occur this is called
moment to force ratio
It is always mentioned that a MF ratio of 10:1
should be generated at the bracket in order
to achieve a bodily movement of the single
rooted tooth

If a bracket is 10mm from c res, a force
applied at bracket causes the tooth to tip
because of a moment that is 10mm times
the magnitude of the force. to counteract
this tendency to tip, a couple in the opposite
direction with a moment 10 times the
magnitude of the force would need to be
applied in addition to the force. this would
be an applied MF ratio of 10:1,reslting in
displacement of the tooth as if the force
alone had been placed thro c res
Why MF of 10:1?

TOOTH MOVEMENT
Uncontrolled tipping
A horizontal force at the level of a bracket
will cause movements of the root apex and
crown in opposite directions. This is the
simplest of tooth movement but is often un
desirable. The MF ratio for this type of
tooth movement is 0:1 to approx 5:1

CONTROLLED TIPPING
This is the desired type of tooth movement.
this is achieved by applying a force to move
the crown and application of moment to
control or maintain the position of root
apex. In this c rot is at root apex. An MF
ratio of 7:1 is generally necessary for
controlled tipping

TRANSLATION
Translation takes place when the crown and the root
moves in the same direction. The c rot is at
infinity.
A horizontal force applied at the center of resistance
of a tooth will result in this movement. However,
the bracket where the force application takes place
is at a distance from the c res. This force alone
applied at the bracket will not result in translation.
To achieve this, at the level of bracket, a couple
and a force that are equivalent to force system
thro c res is needed . An MF of 10:1 is needed

ROOT MOVEMENT
This is achieved by
keeping the crown of a
tooth stationary and
applying a moment
and force to move
only the root. The c rot
is at incisal edge. The
MF of 12:1 is needed

ROTATION
Pure rotation requires a
couple. No net forces
acts at c res, so only
rotation occurs.

T loop
WIRE MATERIAL- TMA
DIMENSION-.017*.025”
ACTIVATION-6mm

GENERAL CONCEPTS FOR T LOOP USE
Passive form of the appliance
and its activation must
first be understood.
There are no forces or
moments acting on the
spring in this state.
The activation requires
application of forces and
moments to engage the
spring in the brackets or
tubes

Next the neutral position of the spring must be
understood
This is found out by applying the activation
moments to the spring without any
horizontal forces
The anterior and posterior arms are bought to
its respective attachment on the occlusal
plane.
In this position there is no horizontal forcewww.indiandentalacademy.com

The horizontal force is produced by
pulling the T open from this position.
The activation of the spring is always
considered with respect to neutral
position and this can be found out by
applying the activation moments

When proper
preactivation bends
are placed, the spring
is designed such that
the spring forms a T in
the neutral position

Differential anchorage is obtained by
applying unequal alpha and beta moments.
The higher moment is applied to the
anchorage teeth.
The differential moment is applied by
applying the concepts of the off center V
bend
V bend results in unequal moments
The closer the V bend to the teeth the higher
the moment.

For obtaining differential anchorage off
centering the spring by 1 or 2 mm is enough
For full 6 mm activation, tooth movement
occurs in three phases- tipping, translation,
and root movement.
For a symmetric centered spring MF is
6:1,this results in tipping of anterior and
posterior.
Now the space closed will be 2mm in other
words the deactivation and the activation
remains at 4mm

Now the MF ratio increases to 10:1 resulting
in bodily movement.
Now the activation remains at 2 mm only and
the MF increases to 12:1 and higher.
This results in root movement
The spring does not need reactivation until all
three phases of tooth movement have been
expressed

Group A space closure
The biomechanical aspect for this space
closure is to increase the posterior MF ratio
Utilizing the V bend principle the T loop is
positioned closure to molar tube.
Too much of off centering is not required,
only 2 mm is sufficient.
ACTIVATION- 4 mm
This reduces the horizontal forces without
affecting the moment difference.

The force acting on the anterior segment
favors tipping.
The spring must be reactivated only when 2
mm or less of activation remain.
Since beta moment is more than alpha
moment, a vertical intrusive force acts on
the anterior segment and it steepens the
anterior occlusal plane.

Likewise beta moment steepens posterior
occlusal plane.
Maintaining adequate horizontal force reduces
these effects.
The posterior occlusal plane can be controlled
with the use of a high pull head gear.

GROUP B SPACE CLOSURE
Equal and opposite moments and forces are
needed.
The T loop spring centered between the
canine and molar attachments produces this
force system.
The center position of spring can be found by
Distance= inter bracket distance-activation/2
here the distance= distance from center of T
loop to either anterior or posterior tubes.

Interbracket distance= the distance between
molar and canine brackets
Activation= mm of activation which is usually
is 6
At this 6 mm of activation MF is 6:1 with the
horizontal force being 320-340gm.
The tooth movement follows tipping, bodily
movement, and root movement.

space closure should be monitored
periodically.
To check the remaining activation the spring
is removed from the canine bracket and
remaining activation at neutral positioning
is measured
The progress of space closure is assessed by
observing the amount of remaining space,
axial inclination of anterior and posterior
occlusal relationship.

GROUP C SPACE CLOSURE
The alpha moment is increased relative to the
beta moment.
The side effect is an extrusive force on the
anterior thus deepening the bite.
In this T loop is positioned close to the
anterior segment
Space closure proceeds with mesial tipping of
buccal segment.
Activation of 4 mm is needed. The spring
should be reactivated every 2 mm.

CONTROL OF MECHANICAL SIDE
EFFECTS DURING SPACE CLOSURE
First order side effects is
molar mesial in and
canine distal in
rotation. This can be
prevented by joining
molars rigidly by a
palatal arch.

The third order control of canine is important
in group A space closure.
The intrusive force tips the crown bucally and
increases the overjet.
In this the use of intermaxillary elastics to aid
in canine eruption or symmetric centered T
loop wit head gear control should be used.

Continuous arch T loop space closure
The force system is not well defined as with
segmental T springs but careful use of alpha and
beta moments helps to achieve good results in
group B and C closure
In group A high pull head gear to control the
posterior is needed.
T loops on each side is made distal to the cuspids
using a preformed arch wire(TMA.0175*.025” or
SS .016*.022”)
For SS wires the activation must be half of that
described here

As shown T loops are
made 6-7 mm high
and 10mm wide and
are positioned distal to
cuspids

Desired alpha and beta moments are placed
anterior and posterior legs.
The recommended beta activation for A,B,C
anchorage are 40, 30 ,20 degrees
respectively
.
After activations are placed, the loop should
be opened 2mm before insertion, if this is
not done the vertical legs of the T loop will
be overlapped in neutral postion.

The wire is inserted into molar auxiliary tube and
ligated to the anterior teeth
.
It is advisable to connect the buccal segments with a
palatal arch.
With this configuration the beta end of T loop
bypasses premolar brackets and is not inserted into
any posterior brackets except the molar tubes.
It delivers a force range of 250-300gm.

Control of side effects
Tipping of teeth into extraction space
Increase alpha and beta moments
Flaring of anterior teeth
Reduce alpha moment
Mesial in rotation of buccal segment
Mesial out rotation in arch wire, palatal arch, lingual
arch
Excessive lingual tipping of anterior teeth
Increase alpha moment

MUSHROOM LOOP
Similar to T loop with apical addition of wire
In the arch wire configuration to decrease
the load deflection rate and therefore
produces lower and continuous force
compared to other designs
MATERIAL-BETA TITANIUM
DIMENSION-.0175”*.025” OR .016”*.022”
ACTIVATION-5mm
FREQUENCY OF ACTIVATION-6-8
WEEKS

The decreased force and increased moment
when activated increases the MF and
therefore allows for greater root control and
anchorage
The beta titanium has lower stiffness than
steel and promotes a more constant force
delivery

If posterior anchorage in the objective, the
loop is offset to the posterior.
If reciprocal movement is required the loop is
placed equi distant between anterior bracket
to extraction site and molar tube.
The premolar should be bypassed and enaged
in the molar directly

This allows for force moment delivery to the
active(anterior) and reactive (posterior) teeth
directly rather being lost to canine and premolar.
It is advisable to stabilize posterior teeth with TPA
Once engaged the loop may be activated 5mm,this
will deliver enough force to simulataneously
retract anterior teeth enmasse with little impact on
posterior anchorage
Reactivation is needed every 6-8 weeks

OPUS LOOP
WIRE MATERIAL- SS,TMA
DIMENSION-16*22,18*25 SS
AND 17*25 TMA
The loop consisted of anterior end,
posterior end, vertical leg, and
the helix
Ref: Ajo 1997 oct,continuos archwire closing loop design
,optimization and verification part 1 Raymond E siatkowsi,
DMD

The original design goal of this loop is to
produce a closing loop capable of delivering an
inherent MF of between 8-9.1mm, the range
needed to achieve necessary translatory
movement of groups of teeth when a continuous
arch wire is used
no previously designed closing loop has been
capable of delivering MF of these levels
To achieve net translation orthodontist have had
to add residual moments to the closing loop arch
Ref: Ajo 1997 oct,continuos archwire closing loop design ,optimization and verification part 1
Raymond E siatkowsi, DMD

The gable bends anterior and posterior to the
loops, a posterior gable bend and
angulations with in the loop, or a posterior
gable bend and anterior twist. Adding these
residual moments has several disadvantages
The teeth must cycle through controlled
tipping to translation to root movement to
achieve net translation.
Correct residual moments are difficult to
achieve
The resulting ever changing PDL stress
distributions may not yield the most rapid,
least traumatic method of space closure

When the loop centered in the interbracket
distance, theMF at the bracket connected to
the helix end of the loop always exhibited at
least three time the MF of the other end.
Angulation of the vertical legs was then
varied in 5 degree increments untilMF was
equal at both ends.
This occurred when the legs were angled at
70 degrees to the plane of brackets.
The MF increased as the loop placed closer to
the brackets than the other.

MF increases more when the helix end is
closer than the other end
An activated symmetric closing loop acts as a
v bend located at the loop’s center.

Since there are no residual moments the neutral
position is which there is no force exerted, it is
exactly the spacing of the vertical legs as bent.
If the horizontal spacing between the vertical legs is
1 mm when the arch wire is formed, there will be
no activation force when that spacing is 1 mm
after the arch wire is tied in.
It is therefore possible to achieve precisely the
defined activation force desired by simply
increasing the horizontal spacing by activation
amount in mms

• Ref: Ajo 1997 oct,continuos archwire closing loop design
,optimization and verification part 1 Raymond E siatkowsi, DMD

OPUS LOOP FOR MAXIMUM ANCHORAGE
Ref: Ajo 1997 oct,continuos archwire closing loop
design ,optimization and verification part 1 Raymond
E siatkowsi, DMD

OPUS LOOP FOR MODERATE ANCHORAGE
Ref: Ajo 1997 oct,continuos archwire closing
loop design ,optimization and verification
part 1 Raymond E siatkowsi, DMD

OPUS LOOP FOR MINIMAL ANCHORAGE

KALRA SIMULTANEOUS INTRUSION AND
RETRACTION ARCH
WIRE MATERIAL-
TMA
DIMENSION- .019*.025
TMA
APPLIANCE DESIGN-
Ref:Jco 1998 SIMULTANEOUS INTRUSION AND RETRCTION
OF ANTERIOR TEETH
VARUN KALRA DDS, PHD

K-SIR is a continuous .019”*.025” TMA
archwire with closed 7mm*2mm U loops at
the extraction sites
To prevent tipping into the extraction sites a
90 degree V bend is placed at the level of
each U loop.
This V bend when centered between molars
and canine creates two equal and opposite
moments to counter the moments caused by
the closing loops
Ref:Jco 1998 SIMULTANEOUS INTRUSION AND RETRCTION OF ANTERIOR TEETH
VARUN KALRA DDS, PHD www.indiandentalacademy.com

A 60degreeV bend located
posterior to the center of
interbracket distance produces
an increased clockwise moment
of molar,which preserves
anchorage an aids intrusion of
the teeth
Ref:Jco 1998 SIMULTANEOUS INTRUSION AND RETRCTION OF ANTERIOR
TEETH

To prevent the buccal
segments from rolling
mesiolingually a 20
degree anti rotation
bend is placed in the
archwire just distal to
each U loop

ACTIVATION
Trial activation done outside
the mouth to release the
stress built up while
giving the V bends
Ref:Jco 1998 SIMULTANEOUS INTRUSION AND RETRCTION OF
ANTERIOR TEETH

Neutral position- legs
extended.U loop will
be about 3.5m wide.
The archwire is inserted
into molar tube and six
anterior brackets
It is activated about
3mm, so that mesial
and distal legs of loop
are barely apart

The second premolars are bypassed to
increase the interbracket distance between
the two ends of attachment.
When the loops are first activated, the tipping
moments generated by the retraction force
will be
greater than the opposing moments produced
by the V-bends in the archwire.
This will initially causecontrolled tipping of
the teeth into the extraction sites.

As the loops deactivate and the force
decreases, the moment-to-force ratio will
increase to cause first bodily and then root
movement of the teeth
The archwire should therefore not be
reactivated at short intervals, but only every
six to eightweeks until all space has been
closed.
The archwire should be in place for 4-5
months

CONTROL OF REACTIVE FORCES
Off-center V-bends will generate an extrusive
force on the molars, which is usually
undesirable.
The reactive forces should be kept minimum
while exerting an optimum level of force on
the teeth to be moved.
The K-SIR archwire exerts about 125g of
intrusive force and extrusive force
distributed between the two buccal
segments

one way to reduce the effects of the reactive
force is to add teeth to the anchorage unit.
Including the second molar will increase the
anchorage
Ref:Jco 1998 SIMULTANEOUS INTRUSION AND RETRCTION OF ANTERIOR TEETH

DOUBLE KEY HOLE LOOP
Introduced by John parker of alameda,california
They are made of rectangular wires,usually .
019*.026 dimension.
They are used along with asher face bow which
is an appliance that connects directly to the
anterior teeth.
it is used for intrusion and retraction of anterior
teeth

The concept behind this loop is;
 to allow the operator to use one set of arch
wires for complete space closure
Allow an easy medium between severe
tipping and sliding mechanics
Allow the operator to select the mode of
space closure

TEAR DROP LOOP
MATERIAL- SS
DIMENSION-.018*.025
The height of the tear
drop loop is 5mm
The loop is placed
immediately distal to
the lateral incisor
brackets.

The wire distal to the canine is reduced to .
016*.023, the purpose of reducing the
posterior portion is so it can easily slide
through the bicuspid brackets and molar
tubes.
ACTIVATION- after insertion the wire
should extend 5mm distally from the molar
tube.
A 442 type wire bending plier is used.

The distal extension of archwire is grasped
with the pliers and pulled through the molar
buccal tube, and then tipped distal to the
tube at 45 degree in superior direction.
The closing loop itself should be activated by
1mm.
it is important to activate only 1 mm per
appointment (every 4 weeks)

CONCLUSION
Most approaches of space closure
describe the technical features of the
appliance.
The method of their use follows a stereo
typed pattern rather meeting the
individual needs of the patient.
Space closure must be individually
planned whether it is friction or
frictionless, it must be based on
diagnosis and treatment plan
This in turn should be based on desired
tooth movementwww.indiandentalacademy.com

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Biomechanics of loop mechanics in enmasse space closure

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