Space Closure3 / orthodontic courses by Indian dental academy

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Space closure typically occurs more easily in high-angle patterns with weak musculature than in low-angle patterns with stronger musculature. The rate of closure can be increased, particularly in high-angle cases, by slightly raising the force level or using thinner archwires. However, more rapid space closure can lead to loss of control of torque, rotation, and tip.

Effects of Overly Rapid Space Closure

INDIAN DENTAL ACADEMY

Leader in continuing dental education www.indiandentalacademy.com

www.indiandentalacademy.com

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Loss of torque control results in upper

incisors being too upright at the end of

space closure with spaces distal to the

canines and a consequent unaesthetic

appearance. The lost torque is difficult

to regain. Also, rapid mesial movement

of the upper molars can allow the

palatal cusps to hang down, resulting in

functional interferences, and rapid

movement of the lower molars causes

"rolling in"


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Reduced rotation control can be seen mainly in the teeth adjacent to extraction sites, which also tend to roll in if spaces are closed too rapidly Reduced tip control produces unwanted movement of canines, premolars, and molars, along with a tendency for lateral open bite. In high-angle cases, where lower molars tip most freely, the elevated distal cusps create the possibility of a molar fulcrum effect www.indiandentalacademy.com

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In some instances, excessive soft-tissue hyperplasia occurs at the extraction sites ,this is not only unhygienic, but it can prevent full space closure or allow spaces to reopen after treatment. Local gingival surgery may be necessary in such cases.


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Proper alignment of bracket slots is essential to eliminate frictional resistance to sliding mechanics. The common procedure is to use .018" or .020 " round wire for at least one month before placing .019"´.025" rectangular wires. Leveling and aligning continues for at least a month after insertion of the rectangular wires, and that space closure cannot proceed during that period.

Inhibitors to Sliding Mechanics


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Therefore the rectangular wires are tied passively for at least the first month, until leveling and aligning is complete and the archwires are passively engaged in all brackets and tubes

Conventional elastic tiebacks are than placed ,In some cases, this phase takes three months.


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First-order or rotational resistance

at the mesiobuccal and distolingual aspects of the posterior bracket slots is produced by rotational forces on the buccal aspects of the posterior teeth.

The most effective way to counteract this resistance is to apply intermittent lingual elastic forces— one month from cuspid to first molar, the next month from cuspid to second molar.

There are three primary sources of friction during space closure


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Second-order or tipping resistance

at the mesio-occlusal and distogingival aspects of the posterior bracket slots is caused by

excessive and overactivated tieback forces, which lead to • tipping of the posterior teeth, • inadequate rebound time to upright these teeth,• and a resultant binding of the system.

The importance of light forces (50-150g) and minimal activation length (to provide time for uprighting) cannot be overemphasized.


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Third-order or torsional resistance

occurs at any of the four areas of the bracket slot where the edges of the archwire make contact.

Like tipping resistance, this is produced mainly by

excessive and overactivated tieback forces, which cause the upper posterior lingual cusps to drop down and the lower posterior teeth to roll in lingually


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Since forces are directed from the first molars to anterior hooks on the archwire, small spaces occasionally open between the first and second molars.

This can be managed in one of three ways: A damaged lower premolar or first molar bracket, either from careless use of biting sticks during bonding or from improper diet, can hinder space closureInterference from opposing teeth sometimes restricts lower arch space closure, particularly if bracket placement was incorrect or a full-unit Class II molar relationship existed.

Problems During Space Closure


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As spaces close, the distal ends of the archwires will protrude

more and more, and these protruding wires will tend to become

bent gingivally by chewing forces

Certain tissue factors can hinder full space closure with any kind

of mechanics. Soft-tissue build-up can result from poor plaque

control or overly rapid space closure. The alveolar cortical plate,

mesial to the lower first molars, tends to narrow after extraction of

the second premolars, especially in lower-angle situations.

Retained roots, ankylosed teeth, and bone sclerosis are other

possible factors to be considered.


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1. Inadequate leveling, resulting in archwire binding

2. Posterior torque such that torquing and sliding cannot occur

simultaneously

3. Blockage of the distal end of the main archwire by a ligature wire

4. Damaged or crushed brackets that bind the main archwire

5. Soft tissue resistance from build-up in extraction sites

6. Cortical plate resistance from a narrowing of the alveolar bone in

extraction sites

7. Excessive force, causing tipping and binding

8. Interferences from teeth or the opposing arch

9. Insufficient force

Constant attention is required to prevent any of the following inhibiting factors:


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BIOMECHANICS OF CANINE RETRACTION ON A CONTINUOUS ARCHWIRE

ROBERT J NIKOLAI SEMIN ORTHOD 2001www.indiandentalacademy.com

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Friction is a function of the relative roughness of two surfaces in contact. It is the force that resists the movement of one surface past another and acts in a direction opposite the direction of motion.

VARIABLES AFFECTING FRICTIONAL RESISTANCE DURING TOOTH MOVEMENT

PHYSICAL

ARCHWIRE

LIGATION

BRACKET

ORTHODONTIC APPLIANCE

BIOLOGICAL

SALIVA

PLAQUE

ACQUIRED PELLICLE

CORROSSION

NANDA& KULHBERGwww.indiandentalacademy.com

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ARCHWIREcrossectional size/shapematerialsurface texturestiffness

LIGATIONligature wireselastomericsself ligating brackets

BRACKETmaterialmanufacturing processslot width and depthfirst/second/third order bends

ORTHODONTIC APPLIANCEinterbracket distancelevel of bracket slots between adjacent teethforces applied for retraction

BIOLOGICAL

Saliva Plaque Acquired pellicle Corrosion


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The segmental arch technique as developed by Burstone utilizes T loop space closure springs for anterior retraction, symmetric closure or posterior protraction.

The segmental T loop as described by Burstone is one of the most versatile space closure devices available.

One of the main principles of the segmental arch technique is considering the anterior segment and posterior segment as one large tooth respectively. The right and left buccal units are connected by a transpalatal arch forming one big posterior unit.

The basic configuration of the TMA loops consists of a .017X.025” TMA wire.

CHARLES J BURSTONE AJO-DO 1982www.indiandentalacademy.com

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The rate of decay of the force applied by a spring is called the load-deflection rate, and it averages 33 Gm. per millimeter in the Burstone’s T loop.

The low load-deflection rate is important in this spring, since it enables the orthodontist to deliver optimal magnitudes of force.


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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.

Since the load-deflection rate is so high, it would be impossible for a clinician to activate the loop to produce an optimum magnitude of force. To deliver 200 Gm. of force, the required activation would be 0.2 mm. Not only is it practically impossible to activate such a small distance, the force of 200 Gm. would be dissipated rapidly over the remaining 0.2 mm. of activation. Thus, orthodontists who use high-force load-deflection mechanisms must use high force values that have undesirable sequelae, which include anchorage loss, pain, and undermining resorption.


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In contrast, a retraction spring with a low load-deflection rate of 33 Gm. per millimeter allows for the delivery of optimal force levels, since an error in activation of 1 mm. results in an error of only 33 Gm. Furthermore, as teeth move distally, the reduction in force is small, giving greater constancy of force at optimal levels.

Early in treatment, the posterior teeth are joined together to form a

posterior anchorage unit.

The anchorage unit consists of the right and left posterior teeth which

are connected by a buccal stabilizing segment and a transpalatal lingual

arch in the maxillary arch and a low lingual arch in the mandibular arch

During space closure, it is to be considered that there are only two teeth

— an anterior tooth comprising the incisors and the canines which have

been connected and a posterior tooth which includes molars and

premolars www.indiandentalacademy.com

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.

The attachment on the posterior tooth (segment) is a 0.018 by 0.025 inch

auxiliary tube on the first molar, and the one on the anterior tooth (segment)

is an auxiliary vertical tube on the canine bracket


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STANDARD FORM OF .017x.025 TMA LOOPS

WITHOUT PREACTIVATION BENDS

PREACTIVATION FORM OF THE SPRING DESIGNED TO PRODUCE EQUAL AND

OPPOSITE ALPHA AND BETA MOMENTS WHEN POSITIONED

IN CENTERED POSITION

Stanley Braun,. Sjursen, Jr., Legan, AJO-DO 1995www.indiandentalacademy.com

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To understand its design one must

first understand its passive form of

the spring and then its activation.

In the passive state there are no

moments or forces acting on it. In

its active state it applies a force

system on the teeth,

The activation of a spring requires

forces and moments to engage the

spring in its brackets and tubes.


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Neutral position:

The neutral position in an activated

loop is found by applying the

activation moments and without any

horizontal forces. In other words the

ends are twisted to bring the each

attachment to its horizontal position.

in this position the spring has zero

horizontal force

The horizontal force is got by pulling

the spring open from this position.


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Differential moments are obtained by the principle of off center V bends which results in unequal moments. the closer the V bend is to the tooth the higher the moment. the segmented T loops approximated a V bend. Clinically the spring needs to be positioned at least 1-2mm closer

to one side than another to obtain a moment differential.www.indiandentalacademy.com

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ure With the introduction of beta-titanium wire (TMA), it has been

possible to simplify the design so that a T loop by itself will have

a relatively low load-deflection rate and a large maximum

springback. The heavier base arch which fits into the auxiliary

tube of the first molar is important, since it allows positive

orientation of the spring and, more significantly, it is capable of

withstanding, without permanent deformation, the higher

moments that are needed for anchorage control. Furthermore, the

use of a heavier base arch tends to increase the moment-to-force

ratio on the anterior teeth, since any bending in the occlusally

positioned part of the spring tends to minimize this ratio.

To aid the clinician in achieving the proper angulation, templates

are used. Rather than to measure the angles, it is more

expeditious to duplicate the shape of the spring from a template. www.indiandentalacademy.com

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The T loop described in

Biomechanics by Nanda is designed

for an activation upto 6 mm.at full

6mm activation tooth movement

occurs in three phases: tipping,

translation and root movement.

For a symmetric centered spring an

initial activation produces a M/F

ratio of 6/1 which results in tipping

movement of the teeth into the

extraction space.


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With 2mm deactivation or spring activation = 4mm the M/F ratio is 10/1 which results in translation of the segments towards each other. With 1-2mm space closure (spring activation =2mm) the M/F ration increases to 12/1 and higher resulting in tooth movement. Clinically the spring should not be re activated till all three phases are complete.


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This demonstrates another method that may be used for controlling the forces and moments produced by segmented 0.017 ´ 0.025-inch TMA T-loop springs or closing loops in general.

Previously, the approach described for achieving differential alpha/beta moments with segmented T-loops used asymmetric angulations of the preactivation bends.

However, with this method the moment differential does not remain constant with spring activation, i.e., the moment differential is dependent on both spring activation and the differences in the preactivation angulations.

OFF CENTERED T LOOPS

Andrew Kuhlberg, Charles J. Burstone AJO-DO 1998www.indiandentalacademy.com

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Off-center positioning maintains

the constancy of the moment

differential throughout the range of

spring deactivation (space closure).

This concurs with Burstone and

Koenig who demonstrated a

moment differential and vertical

forces with off-center vertical

loops.


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The effect of off-center placement of T-loops with a standard shape at a standardized activation and interbracket distance. A centered T-loop produces equal and opposite moments with negligible vertical forces. Off-center positioning of a T-loop produces differential moments. More posterior positioning produces an increased beta moment. More anterior positioning produces an increased alpha moment. A standard shaped T-loop can be used for differential anchorage requirements by altering the activation and mesial-distal position of the spring.


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The center position of the spring can be found by:distance = (interbracket distance –activation)/ 2

where distance = length of the anterior and posterior arms (distance from the center of the T loop to either the anterior or posterior tubes)

interbracket distance=distance between the canine and molar brackets.

Activation= millimeters of activation of the springwww.indiandentalacademy.com

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With the use of a vertical tube at

the canine a 90 degrees gingival

bend at the calculated distance

eases placement and monitoring

throughout space closure

The T loop is places in the

molar auxiliary tube and then

inserted into the canine bracket.

The distal end is pulled back

until it is the desired length

which results in the desired

activation.


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ure Force systems related to type A, B, and C extraction site closure


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The T loop is positioned closer to the posterior segment (1-2 mm off centering) is sufficient .activation of 4 mm is necessary. This reduces the horizontal forces without altering the moment differential. The force system acting on the anterior segment favors tipping. The moment difference remains as the space closes and the spring deactivates.The spring must be re activated when 2 or less mm of activation remains.

MAXIMUM POSTERIOR ANCHORAGE:

(Group A anchorage)


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Because the beta moment is greater than the anterior moment a vertical intrusive force acts on the anterior teeth which can exaggerate the tipping tendency and steepen the occlusal plane. Similarly the posterior occlusal plane can be steeped buy the extrusive force. Maintaining adequate horizontal force helps to reduce this effect. A High pull headgear can also be used to control the posterior occlusal plane. It is likely that root correction will be required at the end of space closure. www.indiandentalacademy.com

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TPA

FIRST ORDER VIEW OF A T-LOOP SPRING WITH A

V-BEND INCORPORATED FOR ROTATIONAL CONTROL


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This is the most difficult of all space closures. The increased alpha moment has a tendency to deepen the overbite.

The loop must be placed 1-2mm closer to the anterior teeth.

Care must be taken that the wire segment achieves full bracket engagement because play can reduce the moment differential.

Space closure with tipping of the buccal segments will occur.

MAXIMUM ANTERIOR ANCHORAGE :( Group C anchorage)


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the activation must be around 4mm and should be activated every 2mm.

The major side effects are loss of anchorage and extrusion of the anteriors.

Class III elastics or protraction headgear may help in the protration of the upper buccal segments.

For mandibular molars class II elastics may help.


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Segmental T loop space closure principles can also be applied to space closure on a continuous arch.

the force system is not as well defined a the segmental but careful use of the alpha and beta moments helps to achieve comparable results especially for group B and C anchorage cases.

For group A cases high pull headgear is necessary to control tooth position.

T loops one on each side are made using preformed arch wires .017 X .025 TMA or .016 X .022 Stainless steel arch wire.


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The activations given are for TMA wires and the Stainless

steel wires activation is reduced by half.

The T lops are made 6-7mm tall and 10mm wide and are

positioned distal to the cuspids.

Desired alpha and beta moments are place anterior and

posterior to the T loop vertical legs.

Recommended beta activations for A, B, and C anchorages are

40 degrees, 30 degrees and 20 degrees.


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After the activations are placed the loops should be open

approximately 2mm before placing in the mouth. the wire is inserted

into the molar auxiliary tube and ligated to the anterior teeth. The t loop

bypasses the premolars brackets and is not inserted in them.

For TMA loops the activation can be 3mm distal to the molar tube

which gives it a range of force of 250-300gms.

The patient should be monitored but no further activations are

necessary for 2-3 months. Too frequent reactivation can prevent root

movement and cause excessive tipping


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From the Occlusal view the first order side effect of rotation of the molars and canines are observed.

Rotation of the molars can be prevented by use of a transpalatal arch. (rectangular wires only not round wires TPA)

Control of canine rotation can be achieved by a variety of techniques.

CONTROL OF THE MECHANICAL SIDE EFFECTS OF SPACE CLOSURE:


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For enmasse retraction a rigid anterior segment can reduce this tendency. A canine bypass connecting he canines but bypassing the incisors can also control rotation. thirdly a anti rotation bend can be incorporated into the spring.

With asymmetric space closure vertical forces may be produced. these may produce undesired extrusive or intrusive tooth movements. these vertical forces may also produce third order side effects.

With group A space closure the third order side effect on the canine is troublesome the intrusive force causes a buccal flaring which increases the overjet at the canine and/or increases the intercanine width.


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CONTROL OF THE SIDE EFFECTS OF SPACE CLOSURE:

Careful monitoring is essential during space closure.

A frequently overlooked side effect of space closure is the first order

side effects.

The mesially directed buccally located force of the molar may lead to

the erroneous supposition that there is anchorage loss.

Distalization is not necessary . A mesially out directed force is all that is

needed to regain the original molar position.

A transpalatal arch provides an excellent mean to prevent this or actively

corrects it.


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CORRECTION OF THE SIDE EFFECTS

Tipping of the anterior and posterior teeth into the extraction spaceIncrease the alpha and beta moments

Flaring of the anterior teethReduce the alpha moment or increase the distal activation

Mesial in rotation of the buccal segmentsMesial out rotation of the palatal arch, archwire or lingual arch

Excessive lingual tipping of the anterior teethIncrease the alpha moment


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Rotating moments caused by buccal forces during extraction site closure.


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The OPUS loop was designed to deliver an inherent M/F ratio sufficient for enmasse space closure via translation of teeth of average dimensions with no bone loss.

Because its inherent M/F ratio is high enough no preactivation bends is needed before insertion

The neutral position is the passive position of the spring as it sits before insertion.

Simple cinch back activations can take care of the tooth movement thresholds to meet anchorage objectives.

Raymond E SiatkowskiSemin Orthod 2001

AJO-DO 1997www.indiandentalacademy.com

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No closing loop design previously has been capable of delivering at constant M/F of 8.0 to 9.1 mm most having inherent M/F of 4-5 mm or less. To achieve net translation, 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).


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ure Adding these residual moments has several disadvantages:

1. The teeth must cycle through controlled tipping to translation to root movement to achieve net translation (lower Young's Modulus materials go through fewer of these cycles for a given distance of space closure). 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 capable of achieving 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 could 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 effectswww.indiandentalacademy.com

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The opus loop achieves a M/F ratio of 8-9.1mm without addition of activation bends in the loop or archwire itself. Therefore its neutral position is the same as the inactivated position before it was tied into the brackets. Having the loops neutral position accurately allows known forces systems to be applied to the teeth via simple cinch back activations.


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Thank you

For more details please visit www.indiandentalacademy.com

Space Closure3 / orthodontic courses by Indian dental academy

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