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
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
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
1. Lack of efficiency compared to frictionless mechanics
2. Uncontrolled tipping
3. Deepening of overbite
4. Loss of anchorage
5. High friction and binding
1. Using a .022 slot, .019 x .025 archwires should be utilised as the base arches for space
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
Methods of force application
1. Easy to use
2. Less time consuming
1. Rapid force decay rate
2. Patient compliance
1. No cooperation
2. Constant force
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
Introduced in 1931
Stainless steel- 0.010”, coil diameter 0.040”
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 spring
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 mechanism
1. 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
• Precise control of space closure
• Adequate ‘rebound time’ for uprighting and arch levelling
• Some immediate improvement
• Need wire bending
• ST irritation
• Plaque accumulation
• High force
• Need short appoint
• Distortion of the wire with difficulties to control the movement in three plane of space
• No fail safe mechanics in most of the designs.
1. Continuous arch with loop
2. Segmented loop with Sectional arch
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
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
1. Two steps distalization (Separate canine and incisor retraction)
a. Alexander- Vari-simplex discipline
1. 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
6. 0.018 x 0.025” closing loop- anterior retraction
1. Triangular (Viazis) bracket- friction 10 times less
2. Bioforce wires- 11% reduction in friction
3. 2 parts
4. Alignment, leveling and space closure.
1. 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
Archwires – 0.019 x 0.025- good overbite control
Sliding mechanics with light forces either :
1. Active tiebacks
2. NiTi coil springs- 150gms force
1. 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
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
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
• The rates of space closure achieved with elastomeric chain and nickel titanium coil springs
• 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
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
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
2. however, elastomeric chain produces similar rates of closure when compared with
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 closure
A. 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
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
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
B. Biological factors:
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
Interference from opposing teeth: Occlusal interferences can halter space closure. This
can be due to bracket positioning errors as well.
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
Suggested sequence for dealing with a failure of space closure with
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
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.
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
2. By swapping the canine bracket.
3. The use of an alternative bracket system with less prescription inclination, for example,
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
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.