Space closure

The ideal force-delivery system would meet the following criteria:

1. Be economical

2. Provide optimal tooth-moving forces that elicit the desired effects.

3. Require minimal operator manipulation and chairtime.

4. Be comfortable and hygienic for the patient.

5. Require minimal patient cooperation.

There are three types of movement during space closure

1. Alpha, anterior teeth movement

2. Beta, posterior teeth movement

3. Vertical

4. Horizontal (buccopalatal)

The ratio between moments to force ratio M/F will determine the

resultant movement (Tanne et al., 1988):

1. 7/1 cause tipping

2. 10/1 cause bodily

3. 12/1 cause root up righting

4. However in pd compromised condition, the centre of rotation will be more apically and the

need for more M/F ratio in order to control the transitional movement

Requirement before commence space closure GOLD STANDARD

1. Alignment complete

2. Derotations complete

3. Levelling complete

4. Full bracket engagement

5. Working archwires in place

6. Ligate with metal ligs

Types of space closure mechanics

A. Sliding mechanism to close space

Advantages

1. Simple Minimal wire bending

2. Less time consuming

3. Enhances patient comfort

4. Long appoint

5. Measurable force

6. No running out of space for activation

7. Maintain arch form

8. Vertical control

9. Root parallism

Disadvantage

1. Lack of efficiency compared to frictionless mechanics

2. Uncontrolled tipping

3. Deepening of overbite

4. Loss of anchorage

5. High friction and binding

Mechanics1. Using a .022 slot, .019 x .025 archwires should be utilised as the base arches for space

closure.

2. At the commencement of Phase 2, .018" round S.S. archwires will be in place. It is

necessary to fit an intermediate wire before the final rectangular arches can be placed, and

this should be either:

.020 round S.S. This is preferred when torque alignment is good, and vertical control is

required (deep overbite case).

.018 x .025 rectangular or .020 x .020 square Niti. This is preferable to reduce significant

torque difference in the slot line-up between adjacent teeth.

.017 x .025 steel is a third alternative to address both requirements of vertical control and

torque initiation.

Methods of force application

Elastics

Advantages

1. Easy to use

2. Less time consuming

3. Hygienic

Disadvantages:

1. Rapid force decay rate

2. Patient compliance

Magnet

Advantage

1. No cooperation

2. Constant force

Disadvantages

1. Bulky

2. Brittle

3. Corrosion

4. Toxic

Tiebacks (Berman ligature)1. Passive tiebacks : See Lacebacks section

2. Active tiebacks

Type one (distal module)

Type two (mesial module)

Reactivation: 4-6 wks. Trampoline effect

Coil springsIntroduced in 1931

Stainless steel- 0.010”, coil diameter 0.040”

Cobalt- chromium

NiTi

Springs should not be expanded beyond the manufacturers recommendations (22mm for the

9mm springs and 36mm for the 12mm springs).

Factors affecting force levels of coil spring1. Alloy

2. Wire size (Miura 1988)

3. Lumen size (Miura 1988)

4. Coil pitch. Fine pitch has lower super elasticity

5. Length of the spring

6. Amount of activation

B. Closing loop mechanism1. In the 18-slot appliance with single or narrow twin brackets on canines and premolars is

ideally suited for use of closing loops in continuous archwires.

2. Closing loop archwires should be fabricated from rectangular wire to prevent the wire from

rolling in the bracket slots.

3. Appropriate closing loops in a continuous archwire will produce approximately 60:40

closure of the extraction space if only the second premolar and first molar are included in

the anchorage unit and some uprighting (distal tipping) of the incisors is allowed.

4. Greater retraction will be obtained if the second molar is part of the anchorage unit, less if

incisor torque is required.

There are two ways to hold the archwire in its activated position. 1. By bending the end of the archwire gingivally behind the last molar tube.

2. The alternative is to place an attachment—usually a soldered tieback

Advantages• Precise control of space closure

• Adequate ‘rebound time’ for uprighting and arch levelling

• Some immediate improvement

Disadvantages• Need wire bending

• ST irritation

• Plaque accumulation

• High force

• Need short appoint

• Tipping

• Distortion of the wire with difficulties to control the movement in three plane of space

• No fail safe mechanics in most of the designs.

Types 1. Continuous arch with loop

2. Segmented loop with Sectional arch

Design

1. Vertical loop

2. T loop (Keng 2011 compare the T closing loop of NiTi and TMA and found no difference

except that NiTi one is more resistance to deformation

3. Mushroom loop

4. PG Retraction Spring

Specific recommendations for closing loop archwires

1. 16× 22 wire, delta or T-shaped loops, 7 mm vertical height, and additional wire

incorporated into the horizontal part of the loop to make it equivalent to 10 mm of vertical

height.

2. Gable bends of 40 to 45 degrees total (half on each side of the loop). The gable bend should

be reactivated after 4mm of retraction.

3. Loop placement 4 to 5 mm distal to the center of the canine tooth, at the center of the space

between the canine and second premolar with the extraction site closed.

The performance of a closing loop, from the perspective of engineering theory, is determined by three major characteristics (Siatkowski, 1997):

1. Spring properties (i.e., the amount of force it delivers and the way the force changes as the

teeth move); the spring properties of a closing loop are determined almost totally by the

wire material (at present, either steel or beta-Ti), the size and cross section (should be

rectangular) of the wire, and the distance between points of attachment (This distance in

turn is largely determined by the amount of wire incorporated into the loop and the

distance between brackets).

2. The moment it generates, so that root position can be controlled; If the center of resistance

ofthe tooth is 10 mm from the bracket, a canine tooth being retracted with a 100 gm force

must also receive a 1000 gm-mm moment if it is to move bodily. If the bracket is 1 mm

wide, a vertical force of 1000 gm must be produced by the archwire at each side of the

bracket. This requirement to generate a movement limits the amount of wire that can be

incorporated to make a closing loop springier because, if the loop becomes too flexible, it

will be unable to generate the necessary moments even though the retraction force

characteristics are satisfactory. It is mainly depends on the wire size, length, interbracket

distance and the loop configuration. Additional moments must be generated by gable

bends (or their equivalent) when the loop is placed in the mouth. Sadowski 1997.

3. Its location relative to adjacent brackets (i.e., the extent to which it serves as a symmetric

or asymmetric bend in the archwire). if it is in the centre of the span does a V-bend

produce equal forces and couples on the adjacent teeth. If it is one-third of the way

between adjacent brackets, the tooth closer to the loop will be extruded and will feel a

considerable moment to bring the root toward the V-bend, while the tooth farther away

will receive an intrusive force but no moment. If the V-bend or loop is closer to one

bracket than one-third of the distance, the more distant tooth will not be intruded but will

receive a moment to move the root away from the V-bend (which almost never is

desirable). For routine use with fail-safe closing loops (as described later), the preferred

location for a closing loop is at the spot that will be the center of the embrasure when the

space is closed. This means that in a first premolar extraction situation the closing loop

should be placed about 5 mm distal to the center of the canine tooth. The effect is to place

the loop initially at the one-third position relative to the canine.

4. Additional feature in the closing loops

“Fail safe.” This means that although a reasonable range of action is desired from each

activation, tooth movement should stop after a prescribed range of movement, even if the

patient does not return for a scheduled adjustment.

Convenience: It also is important that the design be as simple as possible because more

complex configurations are less comfortable for patients, more difficult to fabricate

clinically, and more prone to breakage or distortion.

Open or close loop: A third design factor relates to whether a loop is activated by opening

or closing. All else being equal, a loop is more effective when it is closed rather than

opened during its activation. On the other hand, a loop designed to be opened can be made

so that when it closes completely, the vertical legs come into contact, effectively

preventing further movement and producing the desired fail-safe effect. A loop activated

by closing, in contrast, must have its vertical legs overlap. This creates a transverse step,

and the archwire does not develop the same rigidity when it is deactivated. Bauschinger

effect- range of activation is always greater in the direction of the last bend, Closed loop-

greater range of activation than open loop

Enmass or two steps distalization (Separate canine and incisor retraction)

1. Two steps distalization (Separate canine and incisor retraction)

a. Alexander- Vari-simplex discipline1. Power chain + 0.016” round wire

2. Heavy forces- 250-300gms- cuspids rotate & tip lingually

3. Power chain changed every 4 wks

4. 4-6 months

5. Then

6. 0.018 x 0.025” closing loop- anterior retraction

b. Viazis1. Triangular (Viazis) bracket- friction 10 times less

2. Bioforce wires- 11% reduction in friction

3. 2 parts

4. Alignment, leveling and space closure.

5. Finishing.

c. Proffit1. Canine retraction by segmental loop made from 16*22 SS or 17*27 TMA

2. Sliding on .018*25 or sliding on 19*25 or 18*25 SS using NiTi CCS or PCS

3. The ideal force to slide a canine distally is 150 to 200 gm, since at least 50 to 100 gm will

be used to overcome binding and friction

4. incisor retraction again either by closing loop or sliding mechanics

2. En-masse anterior retraction

a. MBT Archwires – 0.019 x 0.025- good overbite control

Sliding mechanics with light forces either :

1. Active tiebacks

2. NiTi coil springs- 150gms force

b. Proffit1. En mass retraction can be done using the segmented arch approach for space closure is

based on incorporating the anterior teeth into a single segment, and both the right and left

posterior teeth also into a single segment, with the two sides connected by a stabilizing

lingual arch.

2. A retraction spring is used to connect these stable bases,

3. Because the spring is separate from the wire sections an auxiliary rectangular tube, usually

positioned vertically, is needed on the canine bracket or on the anterior wire segment to

provide an attachment for the retraction springs. The posterior end of each spring fits into

the auxiliary tube on the first molar tooth.

Evidences about mechanics of space closure

A. NITI coil spring versus tie back, Samuel 1993

1. Spring better

2. There was no difference in tooth position produced by the two systems after space closure.

3. There was no evidence of greater patient discomfort with the springs

B. Heavy versus light NITI, Samuel 1998

1. 150gm and 200gm are the same

2. 100gm produce less effect

C. Spring versus PCS versus active tieback, Dixon and O’Brien 2002

1. The NT coils produced more space closure per unit time.

2. From their results, the time required to close a 6 mm extraction space would average 17

months with an active ligature, 10 months with elastic chain and 7.5 months with NT coil.

3. Additionally from this study, there was lack of effect of inter-arch elastics on the rate of

space closure. It was surprising that we did not find any effect of Class II or Class III

elastics on rates of space closure. Theoretically, it would seem that inter-arch elastics

should speed up space closure, however, there may some explanation for their lack of

effect:

The study lacked statistical power to detect an elastic effect.

The elastic force may not have been sufficient to influence rates of tooth movement

Patients may not be co-operating totally with full time elastic wear

The inter-arch elastics are moving blocks of teeth in each arch in an anterior or posterior

direction without significantly adding to the space closing effect.

For certain force levels, the addition of elastics may not increase the rate of tooth movement

at the histological level.

D. Spring versus PCE, Nightingale and S. P. Jones, 2003

The problem of this study is being a split mouth study

Indeed, it is well known that elastomeric systems lose force during the duration of their

use. This is thought to be due to

1. Water causing the weakening of intermolecular forces

2. Chemical degradation

3. Elastomeric relaxation

4. Tooth movement resulting in decreasing stretch placed upon the elastomeric chain

Conclusions

• The rates of space closure achieved with elastomeric chain and nickel titanium coil springs

were similar.

• However, one might well disagree with the conclusion that there is no clinical significance

in a difference between 0.84 mm/month closure with elastic chain and 1.04 mm/month for

NT coils. This difference of 0.2 mm/month may not sound much, but would equate to 11.4

weeks difference in the time required to close a 6 mm space

E. Comparison of NiTi Coil Springs vs. Class II Elastics in Canine Retraction, Sonis

1994

Nickel titanium closed coil springs produced nearly twice as rapid a rate of tooth

movement as conventional elastics rated at about the same force level.

F.Comparison of NiTi Coil Springs vs. active tie Elastics in Canine Retraction, Sumaya

2011

NITI better than active tie

G. Force degradation in nickel titanium

Angolkar et al (1992) force decay in nickel titanium ranged from 8% to 17% of the

original force over 28 days.

H. Force degradation in elastomeric chain

1. Baty 1994 loss of 50% to 70% of the force in the first day with only 30% to 40%

remaining at 3 weeks.

2. He also reported that pre-stretching the chain in order to reduce the rapid decay in force

only increased the residual force at 3 weeks by 5% clinically insignificant

3. Bishara 1974 show that PCE loss half of its force after 24 h and the remaining force

stay for 4 weeks so he recommend over extension of the PCE

I. Fluoride release

1. Storie et al (1994). They found that the fluoride-releasing chain was unable to deliver a

satisfactory force level for more than one week compared to 3 weeks for the conventional

chain used for comparison

J. Enmas and two step retraction

Heo 2007, no difference between

K. Factors influencing efficiency of sliding mechanics to close extraction space: a

systematic review. Barlow , 2008

1. The results of clinical research support laboratory results that nickel-titanium coil

springs produce a more consistent force and a faster rate of closure when compared with

active ligatures as a method of force delivery to close extraction space along a continuous

arch wire;

2. however, elastomeric chain produces similar rates of closure when compared with

nickel-titanium springs.

3. Clinical and laboratory research suggest little advantage of 200 g nickel-titanium

springs over 150 g springs.

What do I use to close space?

1. Big space, spring

2. 2-3mm use active tie

3. Small, PCE

Obstacles to space closureA. Mechanical factors:

1. Excessive friction

Situations in which friction may be excessive during space closure include the following:

Active forces between bracket and wire (unlevelled arch), Working archwires should

be in place for at least a month to ensure proper levelling and freedom from posterior

torque pressure.

The end of the arch wire is inside the molar tube

A bracket or tube may have distorted or been inadvertently crimped with distal-end

cutters

Ceramic brackets produce more friction (Kusy et al 1990)

Sometimes excessive space-closing force plus vigorous curve of Spee produces a

marked bowing of the wire and this in itself may produce such friction

Multiple brackets distal to the space to be closed will increase friction

Conventional ligation increase friction – especially with elastomeric modules and

especially if they are in a figure-of-8 configuration

2. Incorrect force levels: Forces above the recommended levels can cause tipping and

friction, and thus prevent space closure. Inadequate force may be a cause of slow or non-

space closure in adults. Force levels need to be in balance during space closure and sliding

mechanics.

B. Biological factors:

I. Intramaxillary causes:

Soft tissue resistance: Gingival overgrowth in the extraction sites can prevent space

closure, and can cause space to reopen after appliance removal. It can also be a problem

when closing a midline diastema. Care is needed to maintain good oral hygiene and avoid

too rapid space closure, as these can contribute to local gingival overgrowth. In few cases

local soft tissue surgery may be indicated.

Roots too close

Necking of the bone

II. Intermaxillary causes:

Interference from opposing teeth: Occlusal interferences can halter space closure. This

can be due to bracket positioning errors as well.

overbite

III. Individual variation: In many instances, no definite cause can be found,, The study by

Pilon (1996), also referred to in the chapter on Anchorage, strongly supports the view that

tooth movement varies markedly between individuals because of variation in inherent

metabolic factors.

Suggested sequence for dealing with a failure of space closure with sliding mechanics

1. Check for causes as listed above and remove them as appropriate

2. if no cause can be found, and especially if the wire seems hard to swivel, assume that the

friction is too high

3. Take all sensible steps to lower friction

4. Have thinner wires through the brackets

5. If the overbite situation permits, remove almost all the curve of spee

6. Ensure that any elastomeric ligatures on the sliding teeth are in a plain “O” configuration on

one tie-wing only

7. Consider propping the bite with glass ionomer cement on the lower molars

8. Increase the force for one visit. If space-closing coils are being used, the addition of

elastomeric chain is often effective, providing an initial increase in force which then

reduces to the level previously provided by the coil alone

9. Consider attaching the coilspring/elastics to the first molar, leaving the second molar out of

space closure for a visit or two

10. Alternative mechanics for space resistant to closure

Further increase in force is not advisable

A. Switching to closing loops as the means of space closure.

B. If sliding through ceramic brackets (this usually applies to anterior spaces), change the

archwire. The archwire surface may have been roughened by the ceramic bracket material

C. Tiebacks with 2 modules

D. Wonder or bi-dimensional wire

This dual diameter wire has a rectangular anterior segment to maintain torque control in that

region but with buccal segments which are round in cross section (usually 0.018"). Such

wires are now available with the buccal segment section being 0.016" x 0.022" . This would

probably retain sufficient rigidity to adequately control overbite and buccal segment

alignment whilst significantly reducing friction on those teeth which were sliding

E. Self-ligating brackets

F. Sectional mechanics

G. Hycon device-

A centimeter segment of 21 x 25 wire –soldered 7mm screw device

Placed in double or tripe tube of molar

Screw with large head- ligature tie

Activation- twice a week one full turn

Space closure- 1mm/month

H. Prevention is better than cure,

• Extractions and space closure, If treatment goals can be achieved without extractions, then

this removes space closure as a problem

• consider early retraction of upper canines to a class 1 relationship. This prevents occlusal

interference with lower canine brackets

I.Surgery assisted space closure (Chung 2013)

There are three basic types of corticotomy that might be planned in adult patients with

missing lower first molars in atrophic alveolar ridge.

Traditional or circumscribed corticotomy involves 2mm vertical and horizontal cuts in the

cortical bone circumscribing the teeth to be

moved. It can be used in cases of thin bony

root coverage.

Triangular corticotomy describes the removal

of triangular portions of the buccal and

lingual cortical plates. It can be implemented

when more efficient root movement is

required or where the buccal cortical bone is

too thin for decortication or indentation.

Indented decortication, a modification of the

technique described by Wilcko and

colleagues,involves making several

perforations on the buccal, lingual, and

occlusal surfaces of the cortical plate with a

round bur . The bone layer covering the root

surface must be thick enough for this

procedure. In each of the three types of

corticotomy, a flap is reflected by making a

crevicular incision and vertical incisions mesial and distal to the target tooth. Appropriate

cuts are then made through the full thickness of the cortical bone using a round bur at

800rpm under profuse saline irrigation.

Laceback

Lacebacks uses

1. Bodily distal movement of a normally inclined canine to provide space for labial

segment alignment. Masticatory forces are thought to be responsible for reactivating the

laceback and so encouraging further distal movement of the canine crown. This distal

movement of the canine is said to provide some 6– 7 mm of space over a 6-month period.

Sueri et al 2006 applied the MBT technique with extraction of the first premolars to study

the effectiveness of laceback ligatures on maxillary canine retraction. Canine distalization

was successfully achieved with laceback ligatures. Canine and molar movements were

significantly smaller in laceback cases.

2. Canine uprighting and prevention of canine proclination: Their mode of action is

believed to cause a slight distal tipping of the canine with compression of the periodontal

ligament in the area of the alveolar crest in the direction of movement. This flexes an

initial archwire and, as it returns to its original shape, the root apex moves distally as the

canine is said to ‘walk along the arch wire’.

3. Use asymmetrically for centerline correction

4. Protection of a flexible arch wire across an extraction site.

5. Prevent increase OB

6. Limit incisor proclination. But

Robinson in 1989, in a prospective study found a 2.47 mm difference in the lower incisor

antero-posterior position between cases treated with or without lacebacks. In the laceback

group there was a mean 1.0 mm distal movement of the incisors and a mean 1.76 mm

mesial movement of the first molars (so the OA loss is 0.76mm). In contrast the non-

laceback group demonstrated a mean 1.47 mm proclination of the incisors compared with

a mean 1.53 mm forward movement of the molars (so the OA loss is 3mm).

Irving, McDonald, 2004, found that the use of laceback ligatures conveys no statistical or

clinical difference in the anteroposterior or vertical position of the lower labial segment or

in the relief of labial segment crowding. The use of laceback ligatures creates a

statistically and clinically significant increase in the loss of posterior anchorage, through

mesial movement of the lower first molars.

On the other hand, Usmani, & O’Brien, 2002 found that canine lacebacks have an effect

and they cause some retroclination of upper incisors and prevent increase in overjet during

the initial aligning phase of Edgewise fixed appliance treatment. However, it should be

emphasized that this effect is small and may not be of clinical significance. Furthermore, if

the canine was distally tipped, the overjet was still likely to increase regardless of the use

of canine lacebacks. However, the benefits do not appear to be worthwhile. As a result, we

can suggest from our findings that upper canine lacebacks are not of benefit, as a routine

procedure, even if the canines are distally angulated.

Fleming 2012 in his systematic review found no difference in the use of LB

Management of distally inclined canine in deep overbite cases

When the canine is initially distally angulated, overbite control can be compromised and

center line displacement may result during the aligning and leveling phase of treatment.

These problems may be overcome by Khambay, 2006

1. Partial bonding of anterior teeth to allow the canine to upright without proclining the

incisors

2. By swapping the canine bracket.

3. The use of an alternative bracket system with less prescription inclination, for example, the

MBT

4. The Tip-edge systems

5. The use of lacebacks.

Force generated during laceback placement

Khambay, 2006 found that:

1. In vitro, there was a large inter-operator variation in the forces produced during laceback

placement.

2. With the in vitro model used in this study, few operators applied similar forces when

placing lacebacks on two separate occasions.

3. Khambay 2006, Magnitude and reproducibility of forces generated by clinicians during

laceback placement ranged from 0 to11.1 N.

SIATKOWSKI, R. E. 1997. Continuous arch wire closing loop design, optimization, and verification. Part I. American journal of orthodontics and dentofacial orthopedics, 112, 393-402.

TANNE, K., KOENIG, H. A. & BURSTONE, C. J. 1988. Moment to force ratios and the center of rotation. American Journal of Orthodontics and Dentofacial Orthopedics, 94, 426-431.