LOOP MECHANICS-

- Definition

-goals to space closure- burtsone – application of continuos force- 1961

- Anchorage and types

- Optimum orthodontic force

- Cortical anchorage R.W.bench 1978- bioprogressive therapy

- Muscular anchorage - BARTON H TAYOR- modified Tloop JCO 1981

Determinants of space closure

Classification of loops – design(vertical and horizontal), helices, function(uprighting,

distalising and stop loops

In friction mechanics the extraction space is closed with the help of elastic chain
which is attached to the tooth and the continuous archwire placed or otherwise,
canine, through application of a force, is expected to slide distally along and is guided
by a continuous arch wire

In frictionless mechanics retraction is accomplished with forces and couples built into
the loops or springs, which offer more controlled movement than friction mechanics

Burstone has outlined six goals to be considered for any universal method of space
closure: Burstone, C.J., Baldwin, J.J. and Lawless, D.T., 1961. The application of
continuous forces to orthodontics. The Angle Orthodontist, 

1. Differential space closure:

2. Minimum patient cooperation: Headgear and interarch or intermaxillary elastics should

not be a major component in controlling differential horizontal tooth movement during space
closure

3. Axial inclination control.

4. Control of rotations and arch width.

5. Optimum biologic response: This includes rapid tooth movement ,in addition, tissue
damage, particularly root resorption, should be at a minimum.

6. Operator convenience: The mechanism should be relatively simple to use, requiring only
a few adjustments for the completion of space closure.

ANCHORAGE CONSIDERATIONS
Anchorage is defined as “the nature & degree of resistance to displacement offered by
34
an anatomic unit when used for the purpose of effecting tooth movement” or
“Resistance to unwanted tooth movement”

Anchorage can be classified in to three types when using with preadjusted edgewise
appliances-CHARLES J. BURSTONE; The segmented arch approach to space
closure AJO 1982 Nov

Group A or maximum anchorage is one in which posterior segments remain in their

original position and the full space is used for anterior retraction. This category
describes the critical maintenance of the posterior tooth position. Seventy-five
percent or more of the extraction space is needed for anterior retraction.

Group B or moderate anchorage arch requires that approximately one half of the
space be used for retraction. This category describes relatively symmetric space
closure with equal movement of the posterior and anterior teeth to close the space.
This is the least difficult space closure problem.

Group C or minimal anchorage arch requires that approximately all space be closed
by protraction of the posterior teeth. Seventy-five percent or more of the space closure
is achieved through mesial movement of the posterior teeth. This is considered as
"critical" anterior anchorage.

The term optimal force is the idea that, there is a force level which will promote the
most efficient treatment response, without any untoward side effects like root
resorption.

Cortical Bone Anchorage- RUEL W. BENCH et al; Bioprogressive Therapy Part

6: Forces Used in Bioprogressive Therapy JCO 1978 Feb
Since an adequate blood supply that produces the cellular change is vital to move a
tooth, we should strive to maintain a generous blood supply and move teeth into the
less dense, more vascular trabecular bone and avoid the denser, avascular cortical
bone.

The concept of cortical bone anchorage implies that, to anchor a tooth, its roots are
placed in proximity to the dense cortical bone under a heavy force that will further
squeeze out the already limited blood supply and thus anchor the tooth by restricting
the physiological activity in an area of dense laminated bone. Because of its density
and limited blood supply, the cortical bone resists change and tooth movement is
limited. For efficient movement the mechanical procedures should steer the roots
away from the denser cortical bone and through the less dense channels of the
vascular trabecular bone.

Since each tooth is supported by cortical bone, an understanding of this bony structure
and support is necessary in order either to move the roots into the cortical bone to
anchor them or to avoid the cortical bone, if possible, for their efficient movement.

Musculature Anchorage- BARTON H TAYOR; Modified "T" Loop Archwire;

JCO 1981 Aug

Where the musculature is strong as characterized by the deep bite, low mandibular
plane, brachyfacial type, the teeth demonstrate a "natural anchorage". In the open bite
vertical dolichofacial patterns, the musculature seems weaker and less able to
overcome the molar- extruding and bite-opening effect of our treatment mechanics.

Determinants of space closure

The important factors that play a role in the space closure procedure are:16

• Amount of crowding:.
• Anchorage:

v Classification of anchorage
v Concept of differential anchorage

• Axial inclination of canines and incisors:

• Midline discrepancies and left–right symmetry

Vertical dimension:

DIFFERENTIAL FORCE SYSTEMS:

Variable Moments and Forces

The components of any force system are

1. Alpha moment.
This is the moment acting on the anterior teeth (often termed

anterior torque).

2. Beta moment.

This is the moment acting on the posterior teeth. An example is tip back bends placed
mesial to the molars that produce an increased beta moment.

3. Horizontal forces.

These are the mesio-distal forces acting on the teeth. The distal forces acting on the
anterior teeth always equal the mesial forces acting on the posterior teeth.

4. Vertical forces.

These are intrusive-extrusive forces acting on the anterior or posterior teeth. These
forces generally result from unequal alpha and beta moments.

When the beta moment is greater than the alpha moment, an intrusive force acts on the
anterior teeth while extrusive forces act on the posterior teeth. When the alpha
moment is greater than the beta moment, extrusive forces act on the anterior teeth
while intrusive forces act on the posterior teeth. The magnitude of the vertical forces
is dependent on the difference between the moments and the interbracket distance.

When translation of both the anterior and posterior teeth is required, the force system
should produce equal and opposite forces and moments. Since the moments and forces
are of equal magnitude and only opposite in direction, vertical force couples would
not be present; therefore, the bio-mechanic side effects would be negligible. The
moment-force ratios acting on the anterior and posterior teeth should approximate
10:1, which is the ratio needed for bodily tooth movement

If load deflection rate is large, stress levels, traumatic to the PDL, alveolar bone, and
roots, can be delivered at very small loop activations that are difficult to deliver
precisely. Also, large F/D, requiring small activations, deactivate after small tooth
movements; if the M/F is not constant, the PDL stress distributions change rapidly as
the tooth cycles from controlled tipping to translation to root movement. Most closing
loop designs offered to date optimize for low F/D at the expense of M/F. another way
to lower the F/D is by using arch wires formed from alloys with reduced Young's
Modulus.

34
The performance of closing loop is determined by
1. Spring properties.
2. Root paralleling moments.
3. Location of the loop relative to adjacent brackets. 4. Additional design
considerations.

Spring Properties

Wire material

Size of the wire

Distance between the attachments

Wires of greater springiness or smaller cross sectional area allows the use of simple
loop designs. All these factors affect the spring character of a closing loop.

Root paralleling moments.

While considering the extraction space closure, a closing loop must generate not only
closing forces, also it must produce appropriate moments to bring the roots parallel to
each other. But this requirement will limit the amount of wire that can be incorporated
to make the loop. When we incorporate a loop, the spring becomes springier, and
unable to produce necessary moments. So it is preferred to incorporate more wire
horizontally than vertically. This will also reduce the tissue impingement. That is why,
a loop which is 7-8 mm tall while incorporating 10-12mm or more wire is preferred.

If the legs of the loop were parallel to each other before activation, opening the loop
will produce an angle, that in it will generate a moment in the desired direction. It is
shown that unacceptably tall loops would be required to generate appropriate
moments in this manner, so additional moments must be generated by placing gable
bends, when the loop is placed in mouth

Location of the loop

The gable bend in the loops acts like a V bend in the arch wire. So when placed in the
mouth it is very sensitive to its position. That is when it is placed in the centre of the
span; it creates equal forces and couples on the adjacent teeth. If it is placed in the one
third way between the interbracket span, the teeth near to the loop will be extruded
and will feel a considerable moment to bring the root toward the V bend, the tooth
further away will be intruded and will receive a moment to move the teeth away from
the V bend.

Additional considerations
The design of the spring should be as simple as possible, because more complex
designs will be uncomfortable for the patient, more difficult to fabricate and more
prone to fracture or breakage.

A loop is more effective, when it is closed rather than opened during activation.
Moreover a loop is designed to opened to activate, can be made, so that when it closes
completely ,the vertical legs come in contact, preventing further movement, producing
a fail safe effect.

BIOMECHANICS OF SPACE CLOSURE

Translatory movement causes the least tissue damage because the periodontal
stress is relatively uniformly distributed along the root surfaces –

CHARLES J. BURSTONE; The segmented arch approach to space closure AJO

1982 Nov

NANDA; Biomechanics of tooth movement

STANLEY BRAUN et al On the management of extraction sites; AJO1997 Dec

If an extraction site is closed with a translatory force system (M/F = 10) applied
equally to the posterior teeth and anterior teeth, type B closure will occur.

In type A closure, the clinician must increase the M/F ratio on the posterior teeth to
approximately 12 to 13. This results in a periodontal stress distribution related to root
movement, while the anterior teeth are simultaneously subjected to a M/F
approximating 10, resulting in translation. This purposeful differential stress
distribution between the posterior and anterior teeth takes advantage of the hierarchy
of relative velocities of tooth movement, namely, root movement which is a slower
process than translatory movement.

Because the system is in equilibrium, vertical forces occur, and a couple results (F X
d), which is equal to the difference in magnitude between the posterior moment (Mp)
and the anterior moment (Ma). These vertical forces are of concern for they have the
potential of altering the occlusal plane. It is therefore important to control the
differential between the posterior and anterior moments, so that the vertical forces are
ostensibly balanced by occlusal forces.

To achieve type C closure, the force system is reversed, with the larger moment
applied to the anterior teeth and the smaller moment applied to the posterior teeth.
This result in an M/F ratio approximating translation applied to the posterior teeth
versus an M/F ratio approximating root movement applied to the anterior teeth. Once
again, vertical forces are of concern. In case, where the mandibular anterior teeth had
been intruded earlier, one should consider the use of Class II elastics, to eliminate the
couple created by the larger anterior moment (Ma). In this case, the horizontal force
(F) in the M/F may be reduced by half (F/2)

From the occlusal aspect, the forces acting on the buccal surfaces of the posterior teeth
produce a moment. This moment tends to alter the arch form by decreasing the arch
width in the premolar region. This moment may be negated by an activated lingual
arch or by dividing the mesiodistal force buccolingually. The lingual force may be
supplied by an elastic. The closure force on the anterior teeth does not have an effect
on the arch width in the canine region.

RECOMMENDED FORCE LEVELS

Optimum orthodontic force has been defined by Nikolai as that which produces a
maximum of desirable biologic response with minimum tissue damage, resulting in
rapid tooth movement with little or no clinical discomfort.

Fortin recommends 147 gm as the optimum force for premolar translation in dogs.
With this force, very few areas of hyalinization were noticed and osteoclastic activity
was maximum.
Smith and Storey suggest a force of 150 to 200 gm as being optimum for translation
of human lower canines,

Reitan advocates 250 gm, and

Lee recommends 150 to 260 gm,

whereas Ricketts and associates prescribe 75 gm.

FRICTION MECHANICS
The disadvantages of sliding mechanics are

1. Due to friction, tooth movement is slower.

2. Increased time should be provided to allow distal root movement. So elastics
should not be changed too often. Constant high force level can cause
hyalinization of PDL and inhibit direct bone resorption around the canine. This
may ensue in anchorage loss.
3. Ceramic brackets are not advised with friction mechanics, as it will produce
more friction.
4. Even double width bracket will have more surface area than single width
bracket; friction produced by both the bracket is almost the same. In single
width brackets, distal root tipping moment is reduced, produces more crown
tipping, and hence more friction.

As the tooth moves, the applied force decreases due to elastic force decay. The applied
moment can increase or decrease, dependent on the arch wire configuration.
Therefore, the M/F changes as the tooth moves, and the tooth responds, typically
progressing from controlled tipping (center of rotation at the root apex) to translation
to root movement. Such progression may not produce the most efficient or the least
traumatic tooth movement. Wire-bracket friction is a variable factor as the moving
teeth displace along the arch wire with this approach, making it difficult to accurately
predict M/F.

Another weakness that allows the canine to tip during its distal movement is the
flexibility of the arch wire in the span between the anterior and posterior teeth.
Because of the reactive forces from the moment, the arch wire will bow and no longer
constitute a straight line along which the canine can slide. Interference from food
during chewing also may contribute to the bending of the arch wire.

Not only is a pure bodily distal movement of the canine difficult to achieve with so-
called sliding mechanics, the canine will also rotate. Because the force application is
not through the center of resistance of the tooth in the labiolingual direction either, a
moment is necessary to counteract tooth rotation. This moment is exerted by the
ligature tying the arch wire to the bracket. Because of the risk of friction, the ligature
tie cannot be very tight. Also, the ligature will probably yield during the control
intervals, resulting in rotation of the canine during its distal movement.

FRICTIONLESS MECHANICS-

This approach involves bending arch wire loops of various configurations, sectionally
(to deliver the desired M/F to an individual tooth) or in a continuous arch wire (to
deliver the desired M/F to several teeth). This approach is friction-free; when
activated, the arch wire loops distort from their original configuration; as the tooth
moves, the loop gradually returns to its preactivated position, delivering the energy
stored at the time of activation.

If only anteriors are retracted, loop is placed closer to the canine than molar and a
gable bend is placed near to molar. An increased gable bend in the posterior part
enhances posterior anchorage. If posteriors are to be protruded, gable bend is given
more in alpha and loop is placed more posteriorly
Loops are of two types-closed loop and open loop. A closed loop has low load
deflection rate due to reduced length of the wire. It is having more range of activation
than a open loop due to the additional wire and the BAUSCHINGER EFFECT
(range of activation is always greatest in the direction of last bend).the M:F ratio of
both the loops are the same . The main differences between the both are the activation.
Open loop is activated by pulling the legs apart, hence unbending the loop, whereas
the closed loop is activated by bringing the legs together, in the direction of last bend

Disadvantages of loop mechanics

1. a)  Minor error in loop mechanism will cause major errors in tooth movement.
2. b)  Retraction loops are more uncomfortable to the patients.
3. c)  More chair-side time required than friction mechanics
4. d)  More wire bending skill required
5. e)  Like sliding mechanics, this will produce mesial out rotation of

the canines when doing individual canine retraction. This can be prevented by
giving lingual elastics or an antirotation bend in retraction loop.
“T” LOOP
In the Segmented Arch Technique, developed by Burstone in 1962, frictionless
springs are used to attract the segments of teeth on either side of an attraction site.
These springs are pre-activated to deliver the required counter-moments as they work-
out (are deactivated). These counter-moments should be the same magnitude as the
tipping moments to achieve bodily tooth movement. The force systems from these
springs can be tested on a measuring apparatus before using them clinically.

According to Burstone, at least six goals should be considered for any universal
method of space closure:

1. Differential space closure. The capability of anterior retraction, posterior

protraction, or a combination of both should be possible.
2. Minimum patient cooperation. Headgear and interarch or intermaxillary
elastics should not be a major component in controlling differential horizontal
tooth movement during space closure. Their dependence on patient cooperation
is reflected in a lack of precision and may limit treatment possibilities.
Headgear and elastics may have other applications in treatment.
3. Axialinclinationcontrol.
4. Control of rotations and arch width.
5. Optimum biologic response. This includes rapid tooth movement with a
minimum lowering of the pain threshold. In addition, tissue damage,
particularly root resorption, should be at a minimum.
6. Operator convenience. The mechanism should be relatively simple to use,
requiring only a few adjustments for the completion of space closure.

To illustrate the characteristics of the force system, burstone introduced a composite

0.017 x 0.025” retraction spring, the T loop spring. When the spring is activated 6
mm, it delivers approximately 201 gm. of distal force at the start of retraction. After
the canine moves distally 1 mm, the force will be reduced by 33 Gm. to 168 Gm. The
load- deflection rate averages 33 Gm. per mm. The low load-deflection rate enables
the orthodontist to deliver optimal magnitudes of force. High- load deflection springs
as vertical loops dissipate force rapidly; hence, one must activate to very high force
levels in order to produce any significant tooth movement. At 6 mm activation, along
with the 201 gm of force, a moment which tends to move the canine root distally is
created. The moment value approximates 129 gm/mm.

Since relatively low forces are capable of retracting six teeth, there is little logic to
separate retraction of canines followed by retraction of the four incisors. For that
reason, only patients who have anterior arch-length problems with anterior crowding
require separate canine retraction. The force system that is used for retraction of the
canine is similar to that for en masse space closure. The composite retraction spring is
used in Group A arches, and the attraction spring is employed in Group B and C
arches. The difference lies in rotational control of the canine, which is achieved with a
nonsliding mechanism. Antirotation bends are placed in the retraction assemblies to
prevent the canine from rotating as it retracts. It is also possible to use an arch wire to
prevent rotation.

THE ASYMMET "T" ARCHWIRE

This loop system made of .016"X.022" TMA (for .018" brackets) or .0l9"X.025"
TMA (for .022" brackets) has proven effective in achieving the same tooth
movements produced by the Broussard system.

This Asymmet "T" archwire has a loop that is placed distal to the upper lateral
incisors.

Because of the resiliency of the TMA wire, the shorter, mesial portion of the loop can
be closed and the longer, distal portion opened to create a step between anterior and
posterior segments that allows simultaneous bite opening and anterior space
closure.
The vertical portion of the loop should be 5mm, the anterior loop 2mm, and the
posterior loop 5mm. The archwire should have an exaggerated reverse curve of Spee
and strong distal molar rotation. Bend the loop slightly inward to prevent irritation of
the cheek, and curve the distal ends of the archwire outward to allow easy insertion
into a pre-rotated molar tube. Trim off the curved ends after final placement and
activation of the wire.

Intra-oral Activation

In the initial phase of Class II, division 2 treatment, where the upper incisors are
extruded and in linguoversion, the loop acts to advance the upper incisors and to add
to the torque that is already incorporated in the incisor brackets. The reverse curve of
Spee accentuates the leveling process and creates overjet, making the lower incisors
accessible for bracketing.
This advancing/torquing moment can be achieved by pinching a small, inverted gable
bend at the top of the closing loop with a tapered optical or three-loop tier plier. The
intraoral activation opens the loop at its base, which tends to advance the upper
incisors; it also adds lingual root torque through the upward gable bend, which
enhances bite opening.

OPUS LOOP

To achieve net translation for the purpose of extraction space closure, orthodontists
have had to add residual moments to the closing loop arch wire with angulation bends
(gable bends) anterior and posterior to the loop, a posterior gable bend and angulations
within the loop, or a posterior gable bend and anterior wire-bracket twist (anterior root
torque).

Adding these residual moments has several disadvantages:

1. The teeth must cycle through controlled tipping to translation to

root movement to achieve net translation.

2. The correct residual moments are difficult to achieve precisely

in linear materials.

3. The resulting ever-changing PDL stress distributions may not yield the most
rapid, least traumatic method of space closure.

If a closing loop design can achieve inherent, constant M/F of 8.0 to 9.1 mm without
residual moments were available, en masse space closure with uniform PDL stress
distributions can be achieved. Such a mechanism would be less demanding of operator
skill to apply clinically and might provide more rapid tooth movement with less
chance of traumatic side effects.
Theoretical investigations using Castigliano's theorem were undertaken for vertical
loops, T-loops, and L-loops, each with increased projected M/F. Detailed perusal of
the mathematical trends suggested a new design, the “Opus loop.” Specific vertical
loops and Opus loops were then simulated by use of Ansysed 5.0-56 FEM software,
the new design being further optimized.

SPRING DESIGN

Opus loops 10 mm high, 10 mm long, and 0.5 mm radius in 0.016 ́ 0.022 inch S.S.
wire, 0.018 ́ 0.025 inch S.S. wire, and 0.017 ́ 0.025 inch TMA were simulated via the
Ansysed FEM software. The anterior end was fixed and the posterior end 13 mm
distal was constrained from moving in all but the horizontal direction, a reasonable
simulation of actuality when closing loops are placed in a continuous arch. When
centered in the interbracket distance, the M/F at the bracket connected to the helix end
of the loop always exhibited at least three times the M/F of the other end.

Opus loops do have the potential to steepen the cant of occlusal plane in the maxillary
arch and flatten it in the mandibular arch,but less so than with other closing loop
designs. Although steepening occlusal plane is advantageous for over-treatment of
Class III relationships, it should be monitored
P G CANINE RETRACTION SPRING

Poul Gjessing in 1985 introduced a new design of canine retraction spring which,

1. Promotestranslationsagittallyandhorizontallythroughanantitip moment-to-force
ratio of approximately 11:1 and an antirotation moment-to-force ratio of
approximately 4:1, both being relatively constant over a certain range of
activation;
2. Results in a low load-deflection ratio during generation of retraction forces in
the range of 50 to 200 gm;
3. Results in no adverse interaction between antitip and antirotation moments
during activation;
4. Could be used in both 0.018 and 0.022 inch edgewise systems
5. Have limited dimensions and allow for faciolingual adjustments
 without altering the above-mentioned characteristics.

SPRING DESIGN

The spring is made from 0.016 X 0.022 inch stainless steel wire where the
predominant active element is the ovoid double helix loop extending 10 mm apically.
It is included in order to reduce the load/deflection of the spring and is placed
gingivally so that activation will cause a tipping of the short horizontal arm which is
attached to the canine, in a direction that will increase the couple acting on the tooth.
Height is limited by practical considerations, so that a double loop is necessary to
incorporate sufficient wire. The gently rounded form avoids the effect of sharp bends
on load/deflection and, through the use of the greatest amount of wire in the vertical
direction; reduction of horizontal load/deflection is maximized. At the same

time, minimizing horizontal wire increases rigidity in the vertical plane.

The smaller loop occlusally is incorporated to lower levels of activation on insertion

in the brackets in the short arm (couple) and is formed so that activation further closes
the loops.

The mesial and distal extensions of the looped wire segment are angulated both in the
vertical and in the horizontal plane. When the spring is in place, but prior to activation
of the driving force (neutral spring position, F = 0 gm), static antitip and antirotation
couples will be exerted to the canine.

The distal driving force is generated by pulling the distal, horizontal leg through the
molar tube. A desirable force level of approximately 160 gm is obtained when the two
sections of the double helix are separated 1 mm. During the activation the force is
matched by an additional couple (activation couple) arising from the double- helix
loop which, in theory, acts as four lever arms.

Incorporation of a segment of a circle ("sweep") in the distal leg of the spring is an

adjustment with the purpose of eliminating undesirable ß moments acting at the
second premolar bracket and tending to move the root apex too far mesially.
CLINICAL APPLICATIONS

The spring is constructed to resist rotational and tipping tendencies during retraction
— not to correct rotations and/or extreme deviations in inclination of the canine.
Therefore, leveling of the buccal segments must be terminated prior to insertion of the
spring. The second molars should also be ligated.

The circular loop is pulled forward to contact the distal aspect of the canine bracket
and is secured by a gingival bend of the anterior leg. Faciolingual loop inclination for
patient comfort is obtained by adjustment of the mesial and distal legs. To prevent
jiggling in the 0.022 inch brackets, a 90° twist of the anterior leg is recommended, so
that the 0.022 inch dimension is vertical and corresponds to the vertical dimension of
the bracket.Activation to 140 to 160 gm is obtained by pulling distal to the molar tube
until the two sections of the double helix are separated 1 mm. Activation is repeated
every 4 weeks, and the canine is expected to undergo approximately 1.5 mm of
controlled movement with each activation. Minor rotations of the canine, which may
take place during retraction in case of anatomic deviations in root anatomy, are easily
corrected with lingual elastics subsequent to retraction. At this stage, the residual
moment inherent in the spring will result in an uprighting effect.

PG SPRING FOR CANINE RETRACTION

The PG retraction system has been designed to facilitate segmented treatment of

extraction cases. The basic element of the system, which is available in right and left
versions, is a prefabricated, highly standardized, stainless steel retraction spring that is
adjustable to fit both .018" and .022" edgewise appliances.

The PG Universal Retraction Spring is designed for controlled retraction of either

canines or upper incisors. No clinical alteration of the spring is needed, and the force
system produced is independent of interbracket distance. The spring is precalibrated to
deliver predictable moment-to-force ratios in three planes of space. The magnitude of
the force delivered, which is kept within desirable physiological limits, can be
identified by "reading" the morphology of the spring during activation.

Clinical Application of PG spring

1. Alignment of the buccal teeth.

The buccal segment must be leveled prior to insertion of the

spring.

2. Adjustment of faciolingual loop inclination.

The correct faciolingual position of the spring is obtained by

adjusting the anterior and posterior extensions before insertion.

3. Bracket engagement.

The anterior extension of the spring is engaged in the canine bracket. The posterior
extension must be engaged in both the premolar

and the molar brackets to obtain optimum transverse control of the canine and
alignment of the canine, premolar, and molar. The anterior extension is pulled
mesially until the small circular helix contacts the distal aspect of the canine bracket
and the wire is secured by bending the anterior extension gingivally.

4. Activation
The spring is activated by pulling distal to the molar tube until

the two loops separate. The wire is secured with a gingival bend in the posterior
extension. Reactivation to the initial spring configuration should be done every four to
six weeks. This amount of activation produces the recommended initial load of 100g.
It is critical to avoid overactivation of the spring, because a few millimeters of
overactivation will result in reduced M/F ratios and thus unwanted tipping and
rotation.
 24
PG SPRING FOR CONTROLLED INCISOR RETRACTION

The position of the upper incisors has a striking effect on the esthetic appearance of
the face and on an individual's self-esteem. As with canine retraction, a segmented
approach provides the necessary three-dimensional control of the incisors to be
moved. The PG Universal Spring has been calibrated to optimize biological reactions
of the anterior teeth and to prevent unplanned side effects in the posterior segments.

BIOMECHANICS

Class II cases frequently have a deep bite caused by over eruption of the incisors.
Orthodontic repositioning of the maxillary incisors therefore requires an upward and
backward force vector.

During retraction, the four incisors are united to form the anterior segment (active
unit). The anterior segment is pitted against the two posterior, reactive units, each
comprising the canine, second premolar, first molar, and eventually second molar. The
force is delivered by a retraction spring connecting the lateral incisor bracket to the
gingival molar tube.

APPLIANCE DESIGN

The appliance design is identical to the one used to design the spring for canine
retraction.

Because the magnitude of intrusive forces produced at the anterior segment are
determined by the posterior curvature of the spring, this curvature was adjusted to
deliver the required force magnitude of 10-25g per side. The resulting curve is close to
the original design used for equal distribution of the beta moment through the
premolar bracket and molar tube during canine retraction. Therefore, only minor
changes were necessary to optimize the spring for both incisor and canine retraction.

Clinical Application

1. Alignmentoftheincisors.
The PG Universal Retraction Spring can be used with any
edgewise system,with triple tubes at the upper first molars. The occlusal tube is used
for canine retraction. During the final sequence of canine retraction, the upper incisors
are aligned with archwires engaged in the incisor brackets, bypassing the canine and
premolar brackets (occupied by the canine retraction spring), and proceeding through
the gingival molar tube.

A vertical step is added distal to the lateral incisors to compensate for differences in
the vertical level of the buccal and over erupted incisor segments).

2. Consolidation of the segments.

Alignment of the incisors is followed by stabilization of the

buccal and anterior segments with heavy rectangular wires, To avoid interdental
spacing, the stabilizing arches, which pass through the occlusal molar tubes, are bent
close to the mesial and distal aspects of the terminal brackets and tubes.

3. Adjustment of the spring for incisor retraction.

Before engagement, the spring is modified by making a 90°

twist in the anterior extension, 3mm in front of the small circular loop. The twisted
extension should be angulated 105° to allow for a 15° play between the wire and the
vertical slot.

The anterior and posterior points of force application are the centers of the lateral
incisor bracket and the triple molar tube, respectively. The posterior extension of the
spring is always inserted in the gingival auxiliary molar tube, but the anterior
extension can be attached to the lateral bracket in several ways. The most practical is
to use .018"X.025" lateral incisor brackets with vertical Broussard-type slots. These
accommodate the .017"X.022" PG springs.

Although a vertical slot provides excellent control of the spring's inclination, it is not a
necessity. The anterior extension can be placed behind the tie wings of a standard
edgewise lateral incisor bracket and tied to the sectional arch mesial and distal to the
bracket. A gingivally directed bend in the anterior extension prevents the activated
spring from sliding distally.

The anterior toe-in of the spring, as calibrated for rotational control in canine
retraction, establishes a good relationship between the anterior portion of the spring
and the lateral incisor bracket. Horizontal adjustments for fitting the anterior extension
in the vertical slot and the posterior extension in the molar tube have no significant
effect on the sagittal and vertically directed force system. The faciolingual inclination
of the double helix is adjusted as for canine retraction

4. Bracket engagement.
The posterior extension is placed in the gingival auxiliary tube
of the molar bracket. The anterior extension is placed in the vertical slot of the lateral
incisor bracket, pulled as far occlusally as possible, and locked with a mesial bend.

5. Activation.
The spring is activated by pulling the posterior extension

distally until the double helix is distorted. This configuration will produce an initial
horizontal force of about 100g. The posterior extension is secured with a gingival
bend distal to the molar tube. The spring is reactivated every four to six weeks by
returning the double

helix to its initial configuration 115

K-SIR ARCH
(KALRA SIMULTANEOUS INTRUSION AND
33
RETRACTION ARCH)

The K-SIR (Kalra Simultaneous Intrusion and Retraction) archwire is a modification

of the segmented loop mechanics. It is a continuous 0.019"X0.025" TMA archwire
with closed 7mm X 2mm U-loops at the extraction sites.

The main indication for the K-SIR archwire is for the retraction of anterior teeth in a
first-premolar extraction patient who has a deep overbite and excessive overjet, and
who requires both intrusion of the anterior teeth and maximum molar anchorage

APPLIANCE DESIGN

To obtain bodily movement and prevent tipping of the teeth into the extraction spaces,
a 90° V-bend is placed in the archwire at the level of each U-loop. This V-bend, when
centered between the first molar and canine during space closure, creates two equal
and opposite moments to counter the moments caused by the activation forces of the
closing loops.
A 60° V-bend located posterior to the center of the interbracket distance produces an
increased clockwise moment on the first molar, which augments molar anchorage as
well as the intrusion of the anterior teeth.

To prevent the buccal segments from rolling mesiolingually due to the force produced
by the loop activation, a 20° antirotation bend is placed in the archwire just distal to
each U-loop.
Activation

A trial activation of the archwire is performed outside the mouth. This trial activation
release s the stress built up from bending the wire and thus reduces the severity of the
V-bends.

After the trial activation, the neutral position of the each loop is determined with the
legs extended horizontally. In neutral position, the U-loop will be about 3.5mm wide.
The archwire is inserted into the auxiliary tubes of the first molars and engaged in the
six anterior brackets. It is activated about 3mm, so that the mesial and distal legs of
the loops are barely apart.

The second premolars are bypassed to increase the interbracket distance between the
two ends of attachment. This allows the clinician to utilize the mechanics of the off-
center V-bend.

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 cause controlled 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 eight weeks
until all space has been closed.

Control of Reactive Forces

Off-center V-bends will generate an extrusive force on the molars, which is usually
undesirable. One of the keys to preventing unwanted side effects of an appliance is to
keep the reactive forces at a minimum while exerting an optimum level of force on the
teeth to be moved.

The K-SIR archwire exerts about 125g of intrusive force on the anterior segment and a
similar amount of extrusive force distributed between the two buccal segments—
generally the first permanent molars and the second premolars, connected by segments
of TMA wire. The force of 125g is effective for intrusion of the anterior teeth, while
the reactive extrusive force on the buccal segments is countered by the forces of
occlusion and mastication. Extrusion of the buccal segments is not usually noted,
either clinically or cephalometrically.

Another way to reduce the effects of the reactive force is to add teeth to the anchorage
unit. Including the second molar will, of course, also increase anchorage in the
anteroposterior direction. If even more anchorage is needed to resist both anterior
movement and the extrusive force on the buccal segments, a high-pull headgear can be
added to the molars. In practice, I rarely use a headgear with this archwire, except in
extremely critical anchorage situations.

A major advantage of the K-SIR appliance, compared to archwires that provide

similar mechanics, is its simplicity of design, with a minimal amount of wire in the
loop configuration. It is, therefore, easy to fabricate, comfortable for the patient, and
less likely to cause tissue impingement. The .019" X .025" TMA provides sufficient
strength to resist distortion, as well as enough stiffness to generate the required
moments.