orthodontic controlled space closure

Orthodontic controlled
space closure
Prof dr Maher Fouda
Mansoura Egypt

It has already been
mentioned that the
stages of orthodontic
treatment with fixed
appliances can be
conveniently
divided into a number of
successive phases to
help plan the
treatment sequence.
The maxillary
and mandibular
fi rst premolars
were extracted.
All teeth were
sequentially
bonded and
banded with
0.018 × 0.025
inch pre-adjusted
edgewise
brackets (Roth-
type
prescription).
Initial alignment
phase was
completed in 4
months.

Following diagnosis and
treatment
planning (including
informed consent), these
are:
1. alignment and
levelling
2. space closure
3. finishing
4. retention and follow-up
5. normal visits to the general
dentist during orthodontic
treatment.
Maxillary and
mandibular anterior
teeth retracted with
a continuous tear
drop loop (0.017 ×
0.025) inch titanium
molybdenum alloy.

Controlled space
closure is an
important objective in
fixed appliance
treatment,
particularly when
teeth have
been extracted or
where there is
spacing present (e.g.
microdontia,
hypodontia).
Five months later, the maxillary and mandibular anterior teeth
were retracted with a continuous tear drop loop (0.017 ×
0.025 inch titanium molybdenum alloy) . The anterior and
posterior segments were stabilized separately. The loop was
activated 2 mm initially alpha 15°and beta 25° and reactivated
when a space of 1.5 mm was closed every month. This
procedure was repeated until the extraction space was closed.
After 9 months of retraction of the maxillary and mandibular
anterior teeth, the extraction space was closed.

Teeth are often
extracted for the
management of
dentoalveolar
disproportion (i.e.
crowding)
and for dentoalveolar
compensation to
manage mild to
moderate skeletal
discrepancies.
The upper and
lower arches
exhibited
moderate
crowding with
Class I canine
and molar
relation
bilaterally; 4
mm overjet
and 3 mm
overbite
Cephalometric evaluation showed a Class I skeletal base,
average growth pattern, and proclined upper and lower
incisors

A comprehensive space
analysis should be undertaken
when planning treatment.
Maxillary incisor
retraction, and space closure,
will often commence while a
deep overbite is reducing, or
has been reduced in the case
of complete overbites, and
typically when spacing
within
the labial segments (2-2 or 3-
3) has been consolidated.

Extraction space
closure can occur
during
the alignment and
levelling phase as
some space may
be needed for the
relief of crowding
and levelling of the
arches.
The lower arch was
moderately crowded.
She had an excess
overjet of 6 mm and
deepbite of 4 mm
with Class I canine
and molar on right
and left sides. The
upper dental midline
was canted to the
right, and lower
dental midline was
shifted to the right by
3 mm to the facial
midline. She had class
1 canine and molar
relation bilaterally.
Cephalometric examination
revealed mild skeletal Class II
tendency, average growth
pattern, and proclined upper
and lower incisors

It is important that space closure is
controlled, as uncontrolled
space closure can lead to a failure
to achieve a number
of important treatment objectives.
• Poor incisor positioning leading
to an unfavourable facial
profile and smile aesthetic
changes.
• Failure to correct the incisor
occlusion: overjet, overbite
and centrelines.
• Failure to correct the molar
occlusion: anteroposterior,
transverse and vertical.
archform and crossbite were corrected with archwire
expansion in SS archwires with palatal crown torque in
posterior segment to avoid palatal cusp hang. Space closure
was done on 19 × 25 SS, the upper right segment
used binary mechanics to avoid second molar rotation.
However, some mesial-in rotation of upper second molar was
desired to sock the mesiobuccal cusp in embrasure of lower
first and second molar. This would also occupy the increased
space available on upper right due to molar extraction.
Alignment with NiTi archwires included bend backs to avoid
proclination of incisors. The narrow

At Completion of Alignment and
Levelling
Once the arches have been aligned and
levelled, it is important
to undertake a comprehensive case re-
evaluation,
including reassessment of:
• patient concerns
• facial profile and smile aesthetics
• space available within each quadrant
• estimation of remaining facial growth
based on pubertal
stage
• overjet, overbite and centreline
position
• molar and canine relationship
• compliance with treatment to date. : Leveling and alignment
Nickel-Titanium archwires were used for leveling and alignment
with gradual archwire upgrade from 0.014-inch to 0.016 ×
0.022-inch [

All these factors combine to
determine the treatment
mechanics that may be most
appropriate from this stage
forwards. It may be worthwhile at this
stage to document
treatment progress by taking a full
set of extraoral and
intraoral photographs. These are
relatively inexpensive
records to take, with no patient risk,
and can help to confirm
the plan for the next stage of
treatment and to justify
why certain mechanics were used
from that point of record
taking.
upper and lower canines were retracted on stainless steel archwires (0.016 ×
0.016-inch) using elastomeric chain against second premolar, first and second
molars as part of the maximum anchorage preparation, elastomeric chains were
changed every 3 weeks.
After canines’ retraction was completed, incisors retraction was performed
using T-loop stainless steel
archwire (0.016 × 0.022-inch) with anterior step up, anterior
lingual root torque and Gable bends. After closing all the
spaces, finishing and detailing was performed

Objectives during Space Closure
There are a number of important
objectives that we should
aim to achieve during space closure. It is
useful to review
patient concerns before commencing
space closure as these
may have changed during alignment and
levelling. It is particularly
important to identify new concerns that
may be
unrealistic to manage and a frank
discussion at this stage
can help to reset patient
expectations, which will help to
improve satisfaction at the end of
treatment. 1: T-Loop archwire

A reassessment of the facial
profile will also help determine
How much upper incisor retraction
is advisable when
correcting an increased overjet in
Class II malocclusions.
In cases where the lips are
retrusive relative to the facial
profile, the nasolabial angle is
increased, particularly with
a backward inclination of the
upper lip, and it may be
advisable to only partially correct
an increased overjet.

In
cases were the
patient feels that
the upper lip has
been
pushed forward
excessively during
alignment and
levelling,
it would be
sensible to plan for
more incisor
retraction.

Concerning the smile, an
assessment of the incisor
inclination in profile view
can help to determine if
this
needs to be maintained
during upper incisor
retraction or
whether some
retroclination or
proclination is required to
achieve the best aesthetic
outcome.

A tangent to the
labial
face of the
central incisor
crown should be
approximately
parallel to the
true vertical with
the patient in
natural head
position (Figure
15.1).
Ideal aesthetic upper
incisor inclination. Judged
clinically, with the
patient’s head in their
natural head position, a
tangent to the labial face
of the upper central
incisor crown (red
line) should be 0–5∘ to the
true vertical (green line).
The inset
photos show aesthetically
pleasing (a), proclined (b)
and slightly
upright (c) incisors. This
assessment cannot be
made
cephalometrically and
should be made clinically.

A clinical
assessment is
important
as cephalometric
analysis alone does
not provide all the
required
information about
the most aesthetic
appearance
and can be
misleading.

is reduced at rest and
during smiling,
particularly when
the overbite is reduced,
consideration may be
given to
some (1–2mm) extrusion
of the upper incisors to
help
improve the incisor
show and increase the
overbite.
Where the upper
incisor display

Ideal aesthetic upper incisor
inclination. Judged
clinically, with the patient’s head
in their natural head position, a
tangent to the labial face of the
upper central incisor crown (red
line) should be 0–5∘ to the true
vertical (green line). The inset
photos show aesthetically
pleasing (a), proclined (b) and
slightly
upright (c) incisors. This
assessment cannot be made
cephalometrically and should be
made clinically.

Where
the incisor show is
increased at rest and during
smiling,
care has to be taken to
minimise any mechanics
that may
extrude the upper incisors
further (e.g. Class II
intermaxillary
elastics) and consideration
can be given to reducing a
deep overbite by upper as
well as lower incisor
intrusion.

An assessment of the amount
of space remaining within
each quadrant, measurement
of the overjet, overbite,
centreline
positions, molar relationship
and likely remaining
anteroposterior mandibular
growth will give an indication
of the likely anchorage
requirements in order to
achieve
the desired occlusal outcome.

This will then allow
an
assessment of how
much space within
each arch should
be closed by incisor
retraction or molar
protraction (i.e.
differential space
closure)..

In Class II malocclusion,
the
aim is often to maximise
maxillary incisor
retraction and
mandibular molar
protraction in order to
facilitate molar
and incisor
anteroposterior
correction to achieve
dentoalveolar
compensation for the
skeletal discrepancy.

In class III malocclusion,
the opposite is usually
the case
(i.e. maximum lower
incisor retraction and
maximum
upper molar protraction).
It should be remembered
that
there is a limit to how
much the inclination of
incisors
can be changed for
dentoalveolar
compensation.

Excessive
change may lead to non-
axial loading, with
concomitant
risk to periodontal health,
roots protruding outside
of the
labial plate of alveolar
bone, poor smile
aesthetics and
reduced access to oral
hygiene on the lingual
surfaces of
excessively retroclined
lower incisors.

Another important
aim of space closure
is to achieve
the desired aesthetic
and occlusal
objectives by
maximising
bodily tooth
movement, achieving
root parallelism
and controlling the
arch form.

An important
principle of
treatment is often to
maintain the lower
incisor position
as the pretreatment
position is
considered the most
stable
position. However,
there is no
guarantee that this
position
will automatically
confer stability and
retention is still
necessary.
Superimposed cephalometric tracings showing dentofacial changes
after 19 months of treatment (red) compared to pre-treatment (black).
The protrusive lower lip was corrected, resulting in a more balanced
facial profile. Maxillary incisor axial inclination was increased 5˚ and
mandibular incisors were retracted ~5mm. The mandibular second
molar(s) was protracted and substituted for the missing 1st molar(s).

One can then
argue that if there
is no guarantee of
stability, and
retention is still
required,
small changes in
lower incisor
position may be
acceptable.

In cases where the lower incisors have been held back
by abnormal soft tissue activity (e.g. lip trap, significant
digit sucking) that is removed as part of treatment, where
it is thought that the lower incisors have been trapped
by a deep and complete overbite (e.g. Class II division 2
malocclusion) and in Class III camouflage cases where
the lower incisors are retroclined and positioned behind
the upper incisors, it may be more acceptable to produce
larger changes in lower incisor inclination.

The aims of treatment are
to maintain the lower
incisor position, it can
be useful to take a lateral
cephalometric radiograph
when
a few millimetres of space
are still left to close in the
lower
arch. In this way the final
mechanics of space
closure can
be planned to achieve the
desired goal.
Unilateral Class II biomechanics with
a maxillary 0.018″ stainless steel
archwire and a mandibular 0.017″ x
0.025″ stainless steel archwire to
coincide dental midlines. The
mandibular second molars were
bonded shortly after this visit.

Classification of Anchorage
Anchorage may be classified according to Burstone’s
Classification.
• Group A: space closure by predominantly incisor retraction
(75%) with some allowance for molar protraction
(25%).
• Group B: approximately equal amounts of incisor retraction
and molar protraction.
• Group C: space closure by predominantly molar protraction
(75%) with some allowance for incisor retraction
(25%).

A number of
factors
affect
anchorage
loss, so it is
difficult
to make
hard and
fast rules .
Adolescent female, aged 16 years with a skeletal class II hyper divergent. She had
a cleft lip, 14, 24, 35 and 44 were extracted as part of an interceptive treatment by
extractions at the age of 12 years but not followed by orthodontic treatment because
of noncooperation. The spaces are lost by protraction of the posterior teeth with
persistence of dental class II and crowding

On some
occasions,
anchorage
requirements
may be
asymmetrical, so
treatment
mechanics may
vary between the
left and right
sides.
The mesiodistal width of upper and lower deciduous molar
were recorded at 8.5 and 9.0 mm respectively before
treatment; the first
molar protraction was performed by segmented arch using
modified Nance and lingual holding arches as an
anchorage unit; b-c and e-f, at 6 months
of the treatment.

Some principles of anchorage management where the molar position is to be
largely maintained, movement of molars and
incisors is desired and where the incisor position is largely to be maintained.

Types of Space Closure
Space can be
closed using
loop
(frictionless) or
sliding
(friction)
mechanics.

Closing loops were
used for space
closure with the
standard edgewise
technique because
the presence of
archwire bends (i.e.
first-, second- and
third-order bends)
did not allow sliding
mechanics.

Loop
mechanics involves
incorporation of loops,
within a continuous
or segmented archwire,
and the springback
properties
of the activated loop
generate the required
forces to move
groups of teeth without
resistance from frictional
forces.
tear drop loop (0.017
× 0.025 inch titanium
molybdenum alloy)

Design features within
the loop are required
to produce the
necessary
counterbalancing
moments to control
the type
of tooth movement
(i.e. bodily movement
versus tipping).

Generating differential
moment-to-force
ratios between the active and
anchorage units facilitate the
delivery of differential tooth
movement (i.e. tipping versus
bodily movement), which will
facilitate differential space
closure. With a properly
designed loop, a good range
of
activation can also be
generated.
OPUS LOOP DESIGN

The introduction of the
preadjusted edgewise
appliance
by Lawrence Andrews largely
eliminated the need for
archwire bends, giving rise to
the straight-wire technique,
which allows for the use of
sliding mechanics, where
the archwire and bracket slots
slide past each other with
resistance from friction,
binding and possibly notching.

Forces are delivered
using elastics or coil
springs (closed
or open) and the
guiding archwire
generates the
necessary
counterbalancing
moment necessary
for bodily tooth
movement .

The forces applied must
overcome
frictional resistance and
provide the necessary force
for tooth movement. Frictional
forces are variable within
the cycle of tooth movement,
as teeth tip and then upright,
so the forces applied to the
periodontal ligament also vary
and are unknown.

Because the applied force within the
periodontal ligament is unknown and the interbracket distance
between the canine and second premolar bracket is
short, the ability for differential space closure by applying
differential moment-to-force ratios between the anchorage
and active units is small and mainly Group B anchorage is
achieved unless additional anchorage reinforcement techniques
are employed, for example headgear, intermaxillary
elastics or temporary anchorage devices (TADs).

The advantages and disadvantages of sliding and loop
mechanics for space closure.

Sliding Mechanics with the Preadjusted
Edgewise Appliance
The 0.018-inch versus 0.022-inch Slot
Globally, the majority of
orthodontists use the 0.022-inch
dimension bracket (working
archwire 0.019 × 0.025-inch
stainless steel) compared to the
0.018-inch dimension
bracket (working archwire 0.016 ×
0.022-inch stainless
steel). This dimension refers to the
height of the bracket
slot.
A 0.022 × 0.028-inch bracket slot is
shown, with a 0.019 × 0.025-inch
rectangular archwire.

Edgewise Appliance
A perceived
advantage of the
0.022-inch slot is that
it allows a larger-
dimension working
archwire to be used
which may be
mechanically more
efficient.

Edgewise Appliance
There is good
evidence that no one slot size
is superior to another in
terms of treatment duration,
quality of occlusal outcomes,
patient satisfaction, root
resorption and pain
experience.
Therefore, the choice is due to
operator preference as both
systems can produce good
results.
The rectangular slot
had its greatest
dimension in
the horizontal
plane. Its height
and depth
dimensions were
0.022 × 0.028
inches,
respectively.

Edgewise Appliance
Working Archwires
0.019 × 0.025-inch Stainless
Steel
In the majority of cases
a customised 0.019 ×
0.025-inch
stainless steel archwire
is used for space
closure within
a 0.022-inch
dimension bracket
system.
0.019 inch × 0.025 inch stainless steel archwire for arch
coordination and space closure

Edgewise Appliance
Working Archwires
0.019 × 0.025-inch Stainless Steel
This dimension
of archwire theoretically provides
0.003 inch (approximately
0.08mm) of vertical clearance to
help reduce
frictional forces and allow sliding
mechanics to occur
whilst providing sufficient rigidity
to allow bodily tooth
movement and good control of
arch form during space
closure.
The play (deviation angle) can be
defined as an angular rotation
of the wire, from its passive position
(cross-section of the wire parallel to
the slot walls) until the position
where the diagonal corners of the
wire
contact the opposite wall of the slot
Torque play between an archwire and the bracket slo

Edgewise Appliance
Working Archwires
Stainless steel also has
favourable surface
characteristics
due to the low level of
asperities (microscopic
peaks), which also helps to
reduce frictional forces to
facilitate sliding mechanics

Edgewise Appliance
Working Archwires
The vertical
clearance is theoretical
because there is good
evidence that
archwire and bracket
slot dimensions are
not accurate due
to manufacturing
errors.
Depiction of the torsional play angle (γ) between the
bracket’s slot and the archwire (a)

Edgewise Appliance
Working Archwires
The 0.003 inch of theoretical
vertical clearance also introduces
approximately 10∘ of
slop into the system. The degree of
slop may be less in
reality, and archwires may perform
better than expected,
because of residual tip that may
remain uncorrected when
the archwire is first placed (Figure
15.2) and which may
occur during treatment as teeth
move.
A 0.19 × 0.025-inch archwire in a 0.022-inch
slot. (a) Theoretically, the 0.003 inch (0.08
mm) of vertical clearance (red
area) would introduce approximately 10∘ of
slop (play in the third dimension). (b) In
reality there may be less slop as teeth may
be
slightly tipped so the archwire does make
contact in some areas (red spots).

Edgewise Appliance
Working Archwires
If any degree of
slop is undesirable during
maxillary incisor retraction, this
can be compensated for by using
a high torque bracket
prescription (e.g. MBT > Roth >
Andrews) or by placing
palatal root torque into the
archwire anteriorly.
Slot play. A bracket can rotate in
either direction around the flat
archwire until the slot play is used up
and the wire locks between the slot
walls (slot lock). The amount of slot
play is specific to each individual
wire-slot combination

• nitial and contact positions of the archwire put into the bracket. The
archwire can rotate by 4.7
within the clearance gap

Edgewise Appliance
Working Archwires
Use of light
retraction forces will also
help to lessen the moment
that
causes incisor
retroclination as the size
of the moment is
proportional to the force
applied.

Edgewise Appliance
Working Archwires
Extension arms/hooks (also termed
power arms)
of varying heights can
also be used to control
movement of the
anterior segment during
en masse incisor
retraction.
Extension hooks, shown anteriorly
on the maxillary
archwire, are available in variable
lengths. Space closing forces
applied to an extension hook help to
facilitate bodily incisor
retraction.

Edgewise Appliance
Working Archwires
power arms)
When an extension arm is placed mesial
to the
canine at the level of 0mm (bracket slot
level), palatal
tipping of the incisors is observed as
well as downward
deflection of the wire (extrusion), but
when a extension
arm of 5.5mm is used bodily tooth
movement with minimal
deflection of the archwire may be
achieved.

Edgewise Appliance
Working Archwires
0.019 × 0.025-inch Stainless Steel Extension arms/hooks (also termed
power arms)
In the
treatment of Class II division 1
malocclusion with excessively
proclined upper incisors but with
their root apices
in a relatively good position,
controlled palatal crown
tipping, in which the incisor
retroclines around its apex as
the centre of rotation, is required. In
this case, the use of
an extension arm height of 4–5mm is
recommended.

Edgewise Appliance
Working Archwires
power arms)
For
Class II division 2, lingual
root tipping of the
incisors is
desirable, which could be
carried out by raising the
height
of the extension arm to
above 5.5 mm. To achieve
bodily
anterior tooth movement, an
extension arm of 5.5mm can
be used.

Edgewise Appliance
Working Archwires
Extension arms/hooks (also termed power arms)
The 0.025-inch depth of the
archwire is important for
providing
sufficient torque control by
helping to create a
counterbalancing
moment that reduces tipping
and facilitates
bodily incisor retraction. The
counterbalancing moment is
created by engagement of the
rectangular archwire with the
opposing walls (gingival and
occlusal) of the bracket slot.
A central incisor bracket viewed in profile view with an engaged
0.019 × 0.025-inch stainless steel archwire. As the
incisor is retracted it tips backwards, because of the clockwise
space closing retraction force moment (F) and slop present,
until the
archwire makes contact with the bracket (red circles). An
anticlockwise counter-moment is generated (F), which prevents
further
tipping and allows for bodily retraction. The 0.025-inch
dimension of the archwire is important in creating a sufficient
counter-moment as the size of the moment is proportional to
the depth of the wire.

Edgewise Appliance
Working Archwires
power arms)
A central incisor bracket viewed in profile view with an engaged 0.019 × 0.025-
inch stainless steel archwire. As the
incisor is retracted it tips backwards, because of the clockwise space closing
retraction force moment (F) and slop present, until the
archwire makes contact with the bracket (red circles). An anticlockwise
counter-moment is generated (F), which prevents further
tipping and allows for bodily retraction. The 0.025-inch dimension of the
archwire is important in creating a sufficient
counter-moment as the size of the moment is proportional to the depth of the
wire.

Edgewise Appliance
Working Archwires
It is important that the lower
archwire is customised in
width in order to produce
minimal changes in lower
intercanine
and intermolar width, as this
is known to be prone to
relapse. The maxillary
archwire is then customised
using
the corresponding maxillary
template.
The lower rectangular HANT wire
has been
removed.
A wax template is softened in warm
water and
molded over the lower arch to record
indentations of the
brackets.
The wax template viewed
from the labial.
The .019/.025 rectangular steel wire
is bent t o the
indentations.

Edgewise Appliance
Working Archwires
power arms)
Custamization is
facilitated by using
clear templates
that can be placed
over
the pretreatment
lower study model.

Edgewise Appliance
Working Archwires
power arms)
If at the time of
archwire placement
the 0.019 ×
0.025-inch wire
slides freely through
the slots, then
space closure can
commence
immediately.

Edgewise Appliance
Working Archwires
power arms)
If there is
resistance to insertion due to
friction, usually as a
consequence
of inadequate torque or molar
rotation control,
then the archwire should be
ligated and allowed to
become
passive for six to eight weeks
before space closure is
commenced.

Edgewise Appliance
Working Archwires 0.018-inch or 0.017 × 0.025-inch Stainless Steel
Archwires
In certain
situations, an
undersized
archwire may
be used
for space
closure.
Effect of space closure with conventional
sliding mechanics without miniscrew. Anterior
and posterior segments rotate around CR of
each segment, archwire forced to bend near
rotation of entire arch. These changes can
easily be prevented with precurved archwires.

Edgewise Appliance
Archwires
• In Class III cases,
an undersized
archwiremay be
used in
the lower arch
where retroclination
of the lower
incisors
is desired for
dentoalveolar
compensation.
The treatment was initiated by banding the first molars and the
lower left second molar and bonding of the other teeth using
0.018 slot preadjusted edgewise ceramic brackets with Roth
prescriptions. A letter for referral to extract the upper first
premolars and the lower right first premolar was given to the
patient, and an atraumatic extraction of these teeth was done.

Edgewise Appliance
Archwires
In such cases , a circle-
loop or U-bend can be
placed mesial to the
space
to be closed for the
application of intra-
arch space closing
forces or use of Class
III intermaxillary
elastics.
Build-Up composite resin was applied on both of the lower
molars. Leveling and alignment were done by using a 0.012″
NiTi wire, followed by 0.014″ NiTi, 0.016″ NiTi, 0:016 × 0:022″
NiTi, and finally 0:016 × 0:022″ stainless steel wires for space
closure.

Edgewise Appliance
Archwires
It
is important that
the archwire is
customised after
placement
of a circle-loop
or U-bend as
these do distort
the
arch form.
Space closure was done by using class III elastics and
elastomeric chains. Finishing and detailing were done by using
0:016 × 0:022″ and 0:017 × 0:025″ stainless steel wires and
intermaxillary elastics. All the third molars were extracted
except the lower left one.

Edgewise Appliance
Working Archwires
0.018-inch or 0.017 × 0.025-inch Stainless Steel
Archwires
• To close final
spaces (1–2mm)
where space closure
has
been very slow, an
undersized archwire
may be used
to reduce friction,
aid sliding and
facilitate final space
closure.

Edgewise Appliance
Archwires
Care must be taken when using smaller archwires with
reduced rigidity for space closure as there is greater likelihood
of tooth tipping and loss of arch form (e.g. distobuccal
rotation of the molars), particularly if space closing forces
are high, as high forces generate bigger moments (moment
= force × distance). Greater first molar control, for tipping
and rotation, can be achieved by incorporating the second
molars into the appliance in such cases .

Edgewise Appliance
Archwires
(a) Rigid archwires help to control mesial molar tipping and mesiolingual
rotation because of the moments generated
when a force is not passed through the centre of resistance. (b) If smaller
dimension archwires are used for space closure, or where
second premolars have been extracted, incorporation of the second molars
will help to control the movement of the first molar by
preventing tipping and rotation.

Method of Force Application
Space closing forces
are usually applied
between a
hook on the archwire,
between the lateral
incisor and
canine bracket, and
the first or second
molar tube hook.
Type two active tiebacks (mesial
modules) in upper and lower arches.
The elastomerics are stretched
maximally in this photograph - ideally, in
most treatments, slightly less stretching
is appropriate. For final space closure, it
is sometimes helpful to place two
elastomeric modules.

Space closing forces are usually
applied between a
hook on the archwire (crimpable or
soldered), between the
lateral incisor and canine, and a
hook on the first or second
molar tube. In this case a space
closing NiTi coil is being used
for space closure.
Either a soldered or
crimpable hook is placed
mesial to the canine in case
separate canine retraction
is required. Soldered hooks
tend to be more secure than
crimpable hooks but they
have the downside that a
greater
inventory of archwires is
needed with differing hook
positions.

space closing forces can
be applied using a
number of different
methods :
• elastomeric chain (e.g.
power chain, E-Links) (see
Appendix II)
• closed coil springs (NiTi
or stainless steel)
• active ligature tie-backs
(o-ligs)
• elastics (e.g. 3/16-inch
diameter) (see Appendix
II).

Space closing forces can be applied using a number of
methods. (a) Power chain, which is usually stretched between
50
and 100% of its length. (b) Closed coil springs (NiTi), which are
available in a variety of lengths and force levels. (c) Closed coil
springs
can also be attached using ligature wire anteriorly to prevent
them from being overstretched in some cases.

(d) Active ligature
tie-backs (o-ligs), which are made by threading a elastomeric module
onto 0.010-inch ligature wire. The forces are applied to either
the first or second molar depending on how much posterior
anchorage is required. (e) Once space closure is complete a passive
ligature wire can be used to maintain the space closure and this is
also facilitated by gently bending the end of the archwire distal to
the last molar, which helps maintain the arch length.

Evidence would
suggest that NiTi
closing springs may
result in more rapid
space closure
compared to
elastomeric
chain, with a mean
difference of 0.2mm
per month.

Active ligature tie-backs appear
to be least effective.
Elastomeric techniques may be
less efficient because of the
rapid decay of elastic forces
within the oral environment.
There does not appear to be any
difference
in anchorage loss between
elastomeric chain and
closed coil springs.
The completed type one
active tieback. It is helpful to
carry one arm of the ligature
wire under the archwire. An
elastomeric module is
stretched to twice its
unstretched size .

There are no studies
comparing root
resorption, pain
difference and cost-
effectiveness between
the two techniques.
Elastics (3/16 inch) may
be less effective
than springs but this may
be related to patient
compliance
in wearing them.

Force Levels
Although there is no
definitive evidence for the
optimal
force required during
space closure, a force
delivery system
that generates 150–200 g
of orthodontic force is
usually
prescribed. It would appear
that 150 or 200 g forces are
equally effective.
A force measuring gauge. This
device can be used
to measure the magnitude of
applied forces to ensure correct
amounts are applied. A number
of gauge sizes are available for
different force ranges (see also
Appendix II).

Force Levels
Lower forces are probably
preferable in
those with periodontal disease
as the centre of resistance
for tooth movement is moved
apically, because of bone loss,
which creates bigger moments
that will also translate into
greater tipping per unit of
applied force. Force levels can
be measured using a force
measuring gauge .

Incorporation of Second Molars
Second molars are incorporated
into fixed appliances for
a number of reasons,
The main reasons for
incorporating second molars
into a fixed appliance are:
• to provide more anchorage
• to help control movement
of the first permanent
molars
• to close space mesial to
the second molar.
Space closure mechanism, final
phase of mesialization of tooth
47 consisting of an edgewise
stainless steel archwire (19×25),
continuous laceback ligature
and two elastic power chains

A convenient way to
reinforce anchorage is to
undertie adjacent teeth
with a stainless steel
ligature. When the second
molar is added to the
appliance and tightly
connected to the first molar,
this so-called molar block
has twice as much root
surface as 1 molar.
Space closure: A, with
miniscrew and closed-coil
spring; B, with molar block and
active tie-back.

This technique is especially
suitable when the first premolars
are extracted because then also
the second premolars can be
added to the anchorage block,
further increasing the anchorage
value. In that way, the root surface
ratio between the anchor blocks
and the front teeth is changed.
Theoretically, this results in less
mesial movement of the anchor
teeth.

Anchorage
The second molars may be
bonded or banded in order to
provide anchorage support for
greater incisor retraction.
Incorporation of second
molars will increase
anchorage
by increasing the root surface
area of the anchorage unit
and also by reducing mesial
tipping of the first permanent
molar.

Anchorage
For the second molar to be
incorporated into the
anchorage unit, space closing
forces can be applied directly
to it, or the molars can be tied
together as a block with
a stainless steel undertie, and
the forces can be applied
to the first molar hook.

Anchorage
Incorporation of second
molars
does increase frictional
resistance to space
closure so it is
often wise to leave a 0.019
× 0.025-inch archwire
ligated in
position for one visit
without placing space
closing forces
to allow greatest passivity.

Anchorage
Debonding of the
second molar
tube can be a
particular concern
and it may be wise to
consider
banding rather than
bonding to reduce
breakages.

Control of the First Molar
Incorporation of the
second molar helps to
provide the
necessary anchorage to
prevent mesial tipping
and mesiolingual
rotation of the first
molar, particularly when
the
second premolars have
been extracted or are
missing or
when an undersized
archwire is used for
space closure.
Space closure with 0.019 x
0.025" SS Posted archwires
Angle’s skeletal Class I base with
an Angle’s dentoalveolarClass I
malocclusion, with decreased
mandibular plane angle and bi-
dental protusion , mesiobuccal
rotation in relation to 15 and
spacing in relation to 21 and 22
with upper midline shift

(a) Rigid archwires help to
control mesial molar tipping
and mesiolingual rotation
because of the moments
generated
when a force is not passed
through the centre of
resistance. (b) If smaller
dimension archwires are used
for space closure, or where
second premolars have been
extracted, incorporation of the
second molars will help to
control the movement of the
first molar by
preventing tipping and rotation.

This will also help to fully
express the
torque in the first molar
tube by providing the
necessary
anchorage. In second
premolar extraction cases,
incorporating the second
molar will maximise space
closure
by bodily tooth movement
of the first permanent
molar, which will help to
achieve good root
parallelism at
the completion of treatment.
Orthodontic tooth
movement is initiated with
0.022 slot MBT bracket
system in both the arches.
0.016 NiTi was the initial
wire, followed 0.017 × 0.025
NiTi, 0.019 × 0.025 NiTi,
0.019 × 0.025 SS.

Because of these
principles, when
the first permanent
molar has been
extracted,
incorporation of the
third molar,
if it has erupted,
will help to better
control the second
molar.

A problem
can arise
when the
third molar is
absent,
which is the
case in most
children.

In such cases,
unwanted
rotation of the second
molar during space
closure can be
minimised by using
the double traction
technique where
space closing forces
are applied both
buccally and lingually
to the second molar
to minimise moments
tending to
cause rotation .
(a) The single traction
technique. (b) The double traction
technique.
Elastomeric chains were attached on
the buccal and lingual surfaces to
achieve more efficient space closure
(yellow arrows) and avoid iatrogenic
rotation of the terminal right molar.

Mesial tipping in
such cases
can also be
reduced by
sweeping a gentle
curve into the
posterior part of
the archwire.

Close Space Mesial to the
Second Molar
In many cases, when
applying space closing
forces to the
first molar, when the
second molar is not
bonded, the pull
from the trans-septal fibres
will pull the second molar
forward and maintain
contact between the two
teeth.

Close Space Mesial
to the Second Molar
Occasionally the
second molar will
not follow, for
example
if there is an
occlusal
interference, and
the tooth must be
incorporated into
the appliance to
encourage its
mesial
movement.

Two-stage Space Closure
versus En Masse
Retraction
Space closure, using
sliding or loop
mechanics, can be
achieved either by
separately retracting the
maxillary
canines followed by the
four incisors (two-step)
or by en
masse retraction of the
whole anterior canine-
to-canine
segment
simultaneously.
Maxillary and mandibular
incisors proclined, molars
and canines are in Class 1
relationship (left).
Maxillary and mandibular anterior
teeth retracted with a continuous
tear drop loop (0.017 × 0.025) inch
titanium molybdenum alloy.
: Canine
retraction
Incisors
retraction
:Leveling
and
alignment
(

Two-stage Space
Closure versus En
Masse
Retraction
It has been claimed
that the
two-step technique
may be superior in
anchorage
preservation
as smaller forces may
be used for separate
canine
and incisor retraction,
which may reduce the
strain on the
anchorage unit.
Post-treatment
photographs
En masse retraction of anterior teeth (
: Leveling and alignment
Initial intraoral photographs

Two-stage Space Closure
versus En Masse
Retraction
In reality, clinicians
are unlikely to
control
the forces used with
such accuracy. The
evidence would
suggest that two-
stage space closure
does not result in
less
anchorage loss.

Two-stage Space
Closure versus En
Masse
Retraction
The two-stage
techniquemay
also be less
patient friendly
as it produces
unaesthetic
spaces mesial to
the canines
before incisor
retraction can
commence.

Two-stage Space Closure versus En Masse
Retraction
Evidence also suggests that the
en masse/TAD combination
is superior to the two-stage
technique with
regard to anchorage preservation
and amount of incisor
retraction. Limited evidence
suggests that en masse
retraction requires less treatment
time and that no significant
differences exist in the amount of
root resorption
between the two techniques.

Two-stage Space Closure versus En Masse
Retraction
If using TADS for anchorage for en
masse retraction,
it should be remembered that
altering the vertical positioning
of a TAD placed between the first
and second
premolar roots can alter the
vertical component of force
to the incisors during en masse
retraction to produce
differing outcomes . (a) A TAD has been placed high to generate a
larger component of vertical force to cause
incisor intrusion as well as
retraction in this patient who was unhappy with
her ‘gummy’ smile. (b) End of treatment.

Two-stage Space Closure versus En
Masse
Retraction
If space closing forces
are placed between a
high TAD (>10mm
above the archwire)
and a 6-mm extension
arm, retraction,
anticlockwise
rotation as well as
intrusion are achieved,
which can be
useful for improving
excessive upper
incisor display during
rest/smiling.
Altering the line of force application can change the center
of rotation and/or the type of tooth
movement. Orange: uncontrolled tipping, Blue: controlled
tipping, Pink: translation, Purple: root movement,
Green: root movement with crown moving forward. Red
dot: center of resistance, other dots: center
of rotations corresponding with the line of force.

Two-stage Space Closure versus En
Masse
Retraction
Placing the TAD lower
(<8mm from the
archwire) would cause
retraction, clockwise
rotation and
extrusion. Intermediate
positioning (8–10mm
from the
archwire) may produce
bodily retraction.

Frictionless Mechanics with the
Preadjusted Edgewise Appliance
Loops can be placed
into continuous
archwires to generate
opening and closing
forces and moments to
control tooth
movement (i.e. bodily
movement versus
tipping).

Generation of Forces
When placed into a
stainless steel archwire
and activated,
a loop will display
characteristics such as
elastic deformation and a
proportional
limit beyond which
permanent deformation
will
occur.

The ideal properties of a
loop are:
• a large range of
activation
• a high proportional limit
to reduce the risk of
permanent
deformation
• a low load (force)–
deflection rate, so that
light constant
forces are delivered over
as large a range as
possible.
The T-loop was first introduced by Charles H.
Burstone at the University of Connecticut in 1982. It is
fabricated from 0.017 x 0.025 inch TMA or 0.16 x
0.022 inch SS wires. It was specially designed for
canine retraction in segmented arch technique and
enmasse or separate incisor retraction. It has a
horizontal loop of
10 mm length and 2 mm diameter. Mesial leg is of 5 mm
height and distal leg is of 4 mm height. Anti-rotation
bends of 120° is given between the legs during pre-
activation. T-loop is activated horizontally by 4mm

The load (force)–deflection
characteristics are dependent
on a number of factors, including
the following.
1. Young’s modulus of the alloy
used (stainless steel >
cobalt chromium > beta-titanium >
NiTi), which is
calculated from the gradient of the
stress–strain graph.
The greater the modulus of
elasticity, the higher the load
(force)–deflection rate.
Tear drop loop in upper arch and lower arch

on a number of factors,
including the following.
2. Wire cross-section:
rectangular wires have a
higher load
(force)–deflection rate than
round wires.
3. Wire dimension: thicker
wires have a higher load
(force)–deflection rate than
thinner wires. However,
reducing wire dimensions
reduces wire strength, so
an increase in wire length can
be used to reduce the
force–deflection rate of thicker
wires.
The ‘Mouse loop was
fabricated and pre-
activation bends were
placed. The loop was
placed in the pre-
activation state for four
weeks
The space of the
deciduous canine
was was closed after
5 appointments.

on a number of factors, including the
following.
4. Length of wire: force
varies inversely to the
third power
of the length. Helical
coils can be used to
increase
the effective length of a
wire and reduce the load
(force)–deflection rate.
The straight 0.017 x 0.025”
TMA wire is bent gingivally at
an angle of 65º and from this
bend a height of 8mm was
measured and marked. At this
mark a helix of the diameter of
2 mm was fabricated with the
bird beak plier. This arm was
considered as beta arm (B).
The pre-activation bends
were incorporated in the
loop. The alpha arm was 25◦
(a) and beta arm was 30◦ (B)

Generation of Moments
Because force cannot be delivered directly through the
centre of resistance of teeth, application of forces will
create moments, or a force tending to cause rotation,
which will lead to tipping movements. The generation
of a counterbalancing moment to these forces, by careful
loop design, helps to control tooth movement. Creating
different degrees of counterbalancing moments between
anchorage and active units can help to control anchorage
balance and the degree of tipping within each unit (see
Chapter 2).
Activated
vertical closIng
loops.

A closing loop must generate not only a closing force but also
appropriate moments to bring the root apices together at
the extraction sites. When a closing loop is activated, its
horizontal legs attempt to rise at an angle to the plane of the
arch w ire .
Forces and moments produced by an activated Bull loop system

The horizontal legs are constrained by brackets and therefore
deliver a moment to those brackets. The moment produced by a
closing loop during activation is termed activation or Inherent
Moment. The activation moment is dependent on the change in
angle that the horizontal arms of the loop make with the
bracket ... when a loop is pulled apart.

The ratio of these moment to the activation force is termed inherent
M/F, a constant for any given loop geometry. Inherent M / F increases
as loop height increases. Because of intraoral an atomic limitations.
loops cannot be made with enough height to achieve inherent M/F to
translate individual teeth or groups of teeth.
Moment-to-
force ratio
(M/F)
equation for a
vertical
closing loop
with helix.

To achieve a higher M/F ratio.
an angulation or
a gable type bend must be put in the loop. The additional moment
produced by gabling in a Ioop is termed residual moment. To achieve
net translation, residual moments in the form of gable bends or
anterior lingual root torque and posterior gable bend must be added.

Adding these residual moments has several disadvantages: ,. The teeth
must cycle through controlled tipping to translation to root movement
to achieve net translation. 2. Whenever residual moments are added.
the loop's neutral position (zero activation position) becomes ill
defined. making it difficult to achieve proper activations. 3. The
resulting ever·changing periodontal slress distributions may not yield
the most rapid, least traumatic method of space closure.
Tear Drop Loop

Loop Designs
Many designs of loop exist
because no
single loop has all the ideal
properties. The simplest form
of loop, the open vertical loop
(U-loop), does not have
good force–deflection
characteristics and cannot
generate
sufficient counterbalancing
moments to control tooth
movement, so variations on
its design exist. The focus of
the remainder of this chapter
will be on the T-loop, as this
is probably one of the most
studied loop designs.
Various loop designs, other than the T-loop, exist:
(a) reverse vertical loop, (b) open vertical loop, (c)
closed vertical loop,
(d) bull loop, (e) reverse vertical loop with helix, (f)
open vertical loop with helix, (g) closed vertical
loop with helix and (h) tear drop
loop.

T-Loop
The T-loop was first
described in 1976 by
Burstone and
Koenig. Incorporating a
horizontal section of wire at
the
apex of an open vertical loop
(U-loop)was found to bemore
biomechanically favourable in
terms of load–deflection
characteristics and comfort
than incorporating multiple
helices at the apex.

T-Loop
Increasing the horizontal width of
the T-loop, within anatomical
limits, also improved the
load–deflection characteristics as
well as increasing the
moment-to-force ratio. Figure
15.13 shows the shape and
dimensions of a clinically useful
passive T-loop made from
0.017 × 0.025-inch beta-titanium
wire.Stainless steel is
less preferable as it exerts
approximately 40% greater force.
The shape and size of a
simple T-loop made from
0.017 × 0.025-inch beta-
titanium wire.

T-Loop
The T-loop is activated by
pulling the archwire through
the molar tube and cinching it
back. This has the effect
of expanding the loop and as
long as it is not deformed
beyond the proportional limit it
will spring back and
deliver a space closing force.
As well as a horizontal force,
an ‘activation moment’ will also
be created (as outlined
in Figure 15.14) as the base of
the spring becomes angled
upwards upon activation.
Activation of a T-loop is achieved by
pulling the
wire through the buccal tube and
cinching. This will deform the
spring and create a space closing
force. The base of the spring
(arrows) are also angled upwards to
generate activation
moments, in the direction shown by
the curved arrows, which
will reduce the degree of tipping
during incisor retraction and
also tip back the molars producing
greater anchorage.

T-Loop
This form of spring will
only
produce a moment-to-
force ratio of 4–5mm
which is only
adequate to tip the teeth,
so gable bends also
need to be
placed into the loop in
order to achieve
ratios of 10 : 1 which are
necessary for
translation.
If gable bends (arrows) are
placed into a passive
T-loop , residual moments
are created
which can beta-titanium
wire .

T-Loop
These
moments, termed
residual moments, are
generated when
the archwire is
engaged and are not
dependent on spring
activation.

T-Loop
Differential tooth
movement can be created
by placing asymmetrical
gable bends, which
produce
asymmetrical residual
moments between the
active and
anchorage units, and
positioning the spring
asymmetrically
across an extraction space.
. Pre activation of asymmetric T loop.

Segmented Arch Mechanics
In the segmented arch technique,
the arch is segmented
into an anterior and posterior unit.
The
If gable bends (arrows) are placed
into a passive
T-loop as shown in Figure 15.13,
residual moments are created
which can be sufficient to produce
incisor retraction by bodily
movement.
posterior teeth can be connected
with a transpalatal arch
to create a single posterior
anchorage unit. A T-loop can
be used to apply space closing
forces and differential space
closure can be achieved by placing
asymmetrical gable
bends and positioning the T-loop
asymmetrically where
it will create greater moments
closer to the side that it
is positioned.

There is no
evidence that this
technique is
more conservative
of anchorage than
sliding mechanics
for space closure
and it has the
drawbacks of
segmental
mechanics.
The case was treated using “Hybrid Segmental
Mechanics” with extraction of all four 1st
premolars with initial segmental retraction of
maxillary canines and mandibular right canine
using 0.017x0.025" TMA

Advantages and disadvantages of loop and
sliding mechanics.
Checking neutral position. Equal and opposite
moments are applied to spring, no horizontal forces
are applied so that horizontal arms become parallel,
position of vertical arms are checked.

Monitoring Space Closure
The normal rate of space closure
is variable during sliding
mechanics, with figures ranging
from 0.5 to 2mm per
month for NiTi coil springs and
elastomeric chain, with
NiTi coil springs appearing to be
slightly more efficient.
Many appliance and patient-
related factors probably
contribute to this variability,
including the force delivery
system, friction and bone biology.

There is evidence that
the bracket type (self-ligating
versus conventional) does
not affect rate of space closure.
There is good evidence
that space closure occurs more
rapidly during the pubertal
growth spurt, which occurs at age
14 (±2) years in males
and 12 (±2) in females.

Delaying dental
extractions as
close as possible to the
time of space closure
may accelerate
the rate of closure by
the regional
acceleratory
phenomenon and by
reducing the bone
density .

The rate of space closure should be
monitored. This may
be undertaken by measuring the size of
the extraction space
at each visit, or by measuring the
decrease in arch length by
measuring the excess archwire
protruding through the distal
tube at each visit. Small asymmetries in
the rate of space
closure are normal; however, if the
asymmetry is significant
(>25%) this may indicate a local
problem.
The space
closure
procedure
using
convention
al sliding
mechanics
is applied
close to the
bracket
slot, with
the line of
force action
parallel to
the
orthodontic
archwir

The most common local
problem that may hinder
sliding
mechanics, and
therefore space closure,
is frictional resistance.
If the archwire cannot be
removed or inserted with
minimal force, then
friction is likely to be a
cause.
In cases with
severe deep
overbite, the
miniscrew is
inserted above
the center of
resistance of
the teeth to
favor overbite
correction
The line of force
applied from the
miniscrew to the
hook prewelded
to the archwire
creates vertical
components,
favoring the
correction of a
deep overbite

There are
numerous causes of
elevated friction:
• poor alignment (e.g.
torque discrepancies,
rotated second
molars)
• kinked ( twisted)archwire
• distorted bracket or tube
(e.g. molar tubes)
• calculus deposits on
archwire and/or bracket.
Intraoral picture of the fixed orthodontic
appliances with the accidentally bent
rectangular NITI 0.017 x 0.025 inch
between the last two mandibular teeth
(teeth number 47 and 46)

The archwire–bracket slot
relationship is altered in
either of two ways: the
operator may actually twist
the archwire when using
standard edgewise brackets,
or the archwire may be
indirectly twisted by the
builtin torque in preadjusted
edgewise (PAE) brackets.

If friction is thought to
be the main factor,
then often
changing to a new
archwire or placing a
slightly undersized
archwire (0.017 ×
0.025 inch), and
waiting a visit before
reapplying forces, will
often help.

If it does not then other
factors should be considered, such as:
• occlusal or appliance interferences
• deep overbite
• retained roots
• root clash
• dense bone island
• low maxillary sinus
• thick gingival tissue
• ankylosis
• late-forming supernumeraries at the
site of space closure.
Short roots due to: A) incomplete root formation,
B) external apical root resorption, C) alveolodental
trauma, and D) short root anomaly
DPT demonstrating pipette-shaped and blunted roots
of the upper central and lateral incisor teeth.

Once space
closure is complete
it is necessary to
maintain
the closed space.
This can be
achieved with a
passive
ligature tie and
turning the end of
the archwire
gingivally.
Once space closure is complete a
passive
ligature wire can be used to maintain
the space closure and this is also
facilitated by gently bending the end
of the archwire distal to
the last molar, which helps maintain
the arch length.

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