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Space closure by frictionless mechanics 2 /certified fixed orthodontic courses by Indian dental academy
SPACE CLOSURE BY
INDIAN DENTAL ACADEMY
Leader in continuing dental education
Space closure is an important step in mechanotherapy,
solely dictated by clinical treatment objectives and is
irrespective of method employed
Space closure should be individually tailored based on the
diagnosis & treatment plan
Selection of any method should be based on desired tooth
Goals for any space closure method
Differential space closure capability
Axial inclination control
Control of rotation & arch width
Optimum biological response
Minimum patient cooperation
Determinants of space closure
Amount of crowding
Axial inclination of canine & incisors
Midline discrepancy & L/R symmetry
Amount of crowding:
Extractions are Usually done to relive crowding
In case of severe crowding anchorage control becomes
Maintaining anchorage while creating space for
decrowding is important
Anchorage classification & concept of differential
anchorage is important.
Using the same mechanics for different anchorage need
limits the results
Reinforcement methods can be used in critical
Using a force system determined appliance design can
improve chances of success.
Axial inclination of canines & incisors
Inclination of canine and incisor are particularly important.
When same force and moment applied to a tooth or a group
of teeth with different axial inclination will result in
different type of tooth movement.
Example in case of unfavorable positioned canine(root
mesial crown distal)
Axial inclination of canines & incisors
Midline discrepancy & L/R symmetry:
Mid line discrepancies with or without an asymmetric
L/R occlusal relationship corrected as early as possible
Asymmetrical forces on L/R could result in unilateral
vertical forces, skewing of dental arch or asymmetrical
Undesired vertical forces may result in ↑ Lower Facial
Height, ↑ interlabial gap & excessive gingival display.
Minor & major cuspid retraction:
Depend upon severity of crowding in anterior segment,
anchorage requirements & axial inclination of canine
• Minor : refers to uncontrolled tipping of canine when 1-2
mm arch length is required per side (lace back)
• Major :controlled tipping or translation of canine when
more than 3 mm arch length is required per side.
• If canine inclination is ideal then translation is preferred
Retraction mechanics divided into
• Sliding (Frictional) mechanics involves either moving
the brackets along the arch wire or sliding the arch wire
through bracket & tube
• Loop (Frictionless) mechanics involves movement of
teeth without the brackets sliding along the arch wire
but with the help of loops
Moderate Anchorage situation
Treatment with 18- slot:
either sliding or loop mechanics can be used.
Single or narrow twin brackets on canine & PM is ideally
suited for use of closing loops in continuous arch wire
Treatment with 22- slot:
As a general rule space closure done in two steps
First retracting the canine usually with sliding mechanics
2nd retracting four incisors usually with closing loop
Enmasse – using Opus or T loop but less than ideal
Maximum Anchorage situations
Treatment with 18- slot:
Friction from sliding is usually avoided, and employing closing
Anchorage is augmented & anchorage strain is reduced by:
Adding stabilizing lingual arch.
Reinforce maxillary posterior anchorage with Extra-Oral force.
Class III elastics from high pull head gear to supplement
retraction force in lower arch
Retraction of canine independently, preferably using a
segmental closing loop & then retracting incisors with 2nd
Maximum Anchorage situations
Treatment with 22- slot:
Like 18 – slot Anchorage is augmented & anchorage strain is
Canine can be retracted with sliding by
Reinforcing posterior anchorage with extra oral force
Application of extra oral force directly against canine
to slide them posteriorly.
Use of segmented arch mechanics for retraction
Segmented arch mechanics for tipping/ uprighting
Minimum Anchorage situations
Requires anchor control, to reduce incisor retraction by:
By incorporating as many teeth in anterior segment
Locating the extraction site more posteriorly.
Placing active lingual torque in incisor section of archwires
To breakdown posterior anchorage(moving one tooth a time)
Use of extra-oral force (face mask)
Use of implants/ onplants to protract posteriors.
1. Staged approach:
Methods of canine retraction:
Frictionless: Paul Gjessing spring, Burstone T loop,
Delta loop, L loop, Omega loop
Extra oral: Head gear - Four hooked for both the arches
Retraction using Rare earth magnets
Rapid canine retraction through Distraction of PDL
Methods of en-masse retraction of four incisors:
Frictionless : P.G spring, Burstone T loop, Delta loop,
L loop, Retraction utility arch,
Omega loop arch wire or
Closing loop arch wire
Extra oral : Head gears
Intrusion & retraction of four incisors:
Burstone three piece intrusion arch
Rickets Retraction & intrusion utility arch
2. Enmasse retraction of six anteriors:
Frictionless – Closing loops,
Burstone T loop continuous arch wire,
Opus loop (Siatkowaski)
Simultaneous retraction & intrusion of six anteriors:
K - Sir Arch
Sliding / Friction Mechanics:
Tooth is retracted or slides through the arch wire, it
involves either moving the brackets along the arch wire or
sliding the arch wire through bracket & tube.
It is used for both individual canine and enmasse
Friction is present due to surface irregularities of arch wire
Various methods used:
Elastic modules with ligature wire
Closed coil springs
J hook head gear
Mulligan V bend sliding mechanics
Employing tip-Edge brackets on canines.
Minimal wire bending time
More efficient sliding of arch wire through posterior
No running out of space for activation
Less time consumption for placement
Disadvantages of sliding mechanics:
1. Variable force.
2. Confusion regarding ideal force levels.
3. E-chain absorbs water and saliva when exposed to oral
environment causing degradation of force by 50%-70% by
the 1st day.
4. Excess Stretching of E-chain causes breakdown of internal
bond leading to permanent deformation.
5. Tendency of overactive elastic causing initial tipping & inadequate
rebound time for uprighting if forces are activated too frequently
6. Staining of E-chain
7. Dependent on patient cooperation in case of elastic bands
8. Due to friction and binding between bracket and arch wire
applied force should be higher than the required optimum force
because of decay in force
9. Generally slower than loop mechanics due to friction
Due to all these problems in friction or sliding mechanics,
frictionless mechanics stands in better position for retraction, as
monitoring of optimum force can be done effectively and it is
active for a longer duration of time.
Loop / Frictionless Mechanics:
Loop (Frictionless) mechanics involves movement of teeth
without the brackets sliding along the arch wire but with the
help of loops
Force generated intrinsically by arch wire
By incorporating loops in arch wire
Energy is stored in loops and release it in slow and
There is no friction between archwire and bracket
Biomechanics of frictionless mechanics:
The teeth in an arch wire will invariably assumes the
passive position of the arch wire.
When a bend is placed in the middle of the archwire and
engaged into brackets two equal and opposite moments are
When offset bend is placed differential moments are
produced. (as anchor bend in Begg technique.)
Greater clockwise moment
(extrusion) in posterior
segment (near to the v- bend)
& smaller anti-clockwise
moment (intrusion force) in
anterior segment (away from
the v- bend) is produced.
This same principles apply in Frictionless mechanics
where instead of a bend a loop is placed in the wire.
Bends are placed on the mesial & distal legs of loop, called
Alpha (α) & Beta (β) bends respectively.
These bends produce Alpha and Beta moments when wire is
placed into bracket
If β moment > α moment
anchorage enhanced by mesial root movement of
posterior extrusion & anterior Intrusion
If α moment > β moment
anchorage of anterior segment is increased by distal root
anterior Extrusion & posterior Intrusion
If both equal
no vertical force
Moment is determined by the loop design
Activation of loops produces the force in frictionless
Activated by pulling the distal end of wire through molar
tube and cinching back or by soldering a tie back mesial to
molar tube on archwire
Moment to force ratio (M/F) determines the type of tooth
Moment to force ratio for various tooth movements:
10 : 1
>10 : 1
According to Charles Burstone - moment to force ratio for
translation is about 10:1.
A regular 10mm high vertical loop offers a M:F ratio of
only 3:1 when it is activated by 1mm.
To get M:F ratio of 10:1, activation should be reduced to
0.2mm, but the force level is not sufficient for retraction
M/F could be increased by (Burstone & Koenig)
By ↑ vertical dimension of loop (but it has limitation as
available space in the vestibule)
↑ horizontal dimension in apical part of loop
↑ Apical length of the wire
Angulations of loop legs
↓ inter bracket distance
Positioning loop close to tooth to be retracted bodily
The most effective way to increase M:F ratio is placing
Pre Activation Bends Or Gable Bends.
These bends can be placed within the loops or where loop meets
the arch wire.
As we try to engage the wire into bracket we pull the horizontal
arm of the loop down producing a moment called the activation
moment and the loop is said to be in NEUTRAL POSITION
The M:F ratio increases as spring gets deactivated as the
Sequence of tooth movement with changes in M/F ratio:
Controlled tipping (8:1)
Root movement (12:1)
So spring should not be activated too frequently
SPACE CLOSING LOOPS
Closing loop arch wires should be fabricated from rectangular
wire to prevent wire from rolling in the bracket slot
The performance of the loop, from the perspective of
engineering theory, is determined by 3 major characteristics
1. Spring properties
2. Moment it generates
3. Its location
[William. R. Proffit]
1. SPRING PROPERTIES
The amount of force it delivers and the way the force changes
as the teeth move.
It is determined almost totally by the
Wire material - Stainless steel
Size of the wire
Distance between points of attachment
distance between bracket
amount of wire incorporated
Changing the size of the wire produce largest change in
its characteristics, but the amount of wire incorporated in
the loop is also important
[William. R. Proffit]
2.Moment it generates
To close an extraction space while producing bodily tooth
movement closing loop must generate not only closing
force but also appropriate Moments to bring the root apices
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
Loop design is also affected.
Placing some of the wire within the closing Loop in a
horizontal rather than vertical direction improves its ability
to deliver the moments needed to prevent tipping.
To generate appropriate moments additional moments must
be generated by Gable bends
Its location is very important for its performance in
As gable bends are incorporated, the closing loops
functions as the V bend in the arch wire. Effect of V bend
is very sensitive to its location
There can be 3 locations of V bend
2.Closure to anterior
3.Closure to Posterior
If it is in the center of the span a V-bend produce:
Equal forces and
Equal couples on the adjacent teeth
If it is one-third of the way between adjacent brackets,
the tooth closer to the loop - extruded &
moment - root toward the V-bend,
tooth farther away - intrusive force but no moment
4.Additional design principle
Fail safe: this means that, although a reasonable range of
action is desired from each activation, tooth movement
should stop after that, even if patient does not come for
Design should be as simple as possible
During activation of loop it is considered more effective
when it is closed rather than opened
INDIVIDUAL CANINE RETRACTION:
It is important to do individual canine retraction in
maximum anchorage cases.
Correct positioning of the canine after retraction is
imperative for function, stability and esthetics
This requires the creation of a bio mechanical system to
deliver a predetermined force and a relatively constant
moment-to-force ratios in order to avoid distal tipping and
For translation of canine :
The displacement of canine depends on the relationship
between the line of force and the center of resistance (CR)
Application of force through CR.
Anti-tip and anti-rotation moment-to-force conditions
necessary for translation of canines with average dimensions.
Anti-Tip:- 11:1 Anti-Rotation:- 4:1
Anti tip couple
Anti rotational couple
Burstone called it the Attraction Spring
Canine Retraction - severe crowding cases and
high anchorage (group-A) cases.
Enmasse Retraction - four incisors after canine retraction
Wire selection for loop:
18- slot: 16 x 22 SS or 17 x 25 TMA
22- slot: 18 x 25 SS or 19 x 25 TMA
Base arch wire: 21 x 25 in SS
The pre-activated spring with the anti tip (M/F- 11:1) and anti
rotation (M/F- 4:1) is placed
Activated by pulling it and giving a distal cinch back.
Activation on insertion is 6- 7mm
Activation on insertion is 6-7mm
The M/F ratio is 8:1 – controlled tipping
Now as the tooth moves the activation reduced to 4mm the
force is reduced.
M/F ratio is further increased to 10:1 - bodily movement
The activation is reduced to 2mm – force is further reduced
M/F ratio increased to 12:1 – root uprighting
So spring should not be activated too frequently
Spring usually activated every 4-6 weeks
Composite T loop attraction spring:
Composite TMA 0.018 - 0.017 x 0.025 in retraction spring.
A 0.018 in round T spring is welded directly to a 0.017 x
0.025 in base archwire.
Used in the segmented arch technique for both canine and
Developed by Ricketts in Scotland in 1976.
Rate of canine retraction by Ricketts was 1.38mm/month
- Mesial crown tipping
- Disto-palatal rotation
POUL GJESSING CANINE RETRACTION
. Poul Gjessing of Denmark 1985
. The spring is constructed to resist rotational and tipping
tendencies during retraction
made from: 016 x 022 in SS wire.
predominant element - OVOID DOUBLE HELIX LOOP
extending 10 mm apically, and 5.5 mm in width.
smaller occlusal loop - 2 mm diameter, incorporated to lower
the levels of activation.
Anti-tip bend (Alpha) 15˚.
Beta-bend 12˚ for II premolar,
30˚ for I molar.
Anti rotation bend 35˚.
Distal sweep for molar.
PG CANINE RETRACTION SPRING
Anti rotation bend
Anti tip bend
Ovoid Double Helix Loop - reduce the load deflection of
Placed gingivally - activation will cause a tipping of the
short horizontal arm (attached to the canine)
In a direction that will increase the couple acting on the
Smaller loop - occlusally - lower levels of activation on
insertion in the brackets in the short arm (couple)
Formed so that activation further closes the loops.
sweep in the distal leg - eliminates undesirable ß moments
acting at second premolar bracket
(which tend to move the root apex too far mesially)
By pulling the distal, horizontal leg through the molar tube.
Force level of approximately 160 gm is obtained when the
two sections of the double helix are separated 1 mm.
Activation is repeated every 4 weeks, and the canine is
expected to undergo approximately 1.5 mm of controlled
movement with each activation.
Specially designed 0.017 x 0.022 inch heat-treated Elgiloy
springs (Rocky Mountain Orthodontics, Denver, Colo.)
inserted into buccal and gingival tubes, which are part of
the molar and canine brackets
special canine brackets
similar to traditional retraction springs except for the extra helix in the
anterior (a) portion.
helix, in conjunction with the gables placed in the posterior (b) legs of
the spring, provides the required couple "counter-moment" for the
moment of the force
allows for the translation of the canine or molar during space closure.
• Three angles in the spring to consider
• Ø1 and Ø2 - bends posterior & anterior to contraction helices
• Ø3 - angle of the anterior leg of the helix.
0° - Anterior retraction
15° - Reciprocal attraction
30° - Posterior protraction
15° - Anterior retraction
30° - Reciprocal attraction
45° - Posterior protraction
NITI CANINE RETRACTION SPRING:
(Yasoo Watanabe, JCO/2002)
Made from .016" ×.022" Titanal wire, with anti-tip and antirotation bends incorporated in closing loop.
Major advantage of this spring is the ability to use it
without a preliminary leveling stage,
Because it can simultaneously retract the canines and level
the posterior teeth.
Its light, continuous force allows an activation of as much
as 10mm to complete canine retraction without reactivation
of the closing loop.
Spring provides continuous forces and moments over a
broad range of activation.
And the closing force can be maintained within normal
biological and physiological limits.
Retracting group of teeth together as a single unit.
Can effectively be employed in moderate and minimum
Simultaneous intrusion and retraction of the anterior teeth,
maintaining torque control may also be employed
En-masse retraction is done with a continuous arch wire with
one closing loop each side distal to cuspid.
Differential force technique and location of loop can be placed
depending on the type of anchorage.
VARIOUS RETRACTION ARCHWIRES:
Various loop designs are available for retraction
All are having pre-determined vertical heights
Ranging from 7-10mm in vertical direction to keep it
closure to center of resistance of tooth
OPEN VERTICAL LOOP:
Originated by Dr. Robert W. Strang (1933).
Used for retraction of anterior teeth
CLOSED VERTICAL LOOP:
Only being difference is horizontal overlapping.
- Dr. Harry bull (1951)
Introduced a variation of standard vertical loop
Loops legs were tightly abutting each other
He recommended that these loops should be made from
.0215 x .025 stainless steel
VERTICAL OPEN LOOP WITH HELIX:
Dr Morris Stoner
Main purpose is to increase the working range
As mentioned by Dr Morris Stoner
Loop named because of resemblance to the Greek letter ‘omega’
The loop is believed to distribute the stresses more evenly
CLOSED VERTICAL LOOP WITH HELIX:
It was described by Dr. Proffit.
0.018 slot - 16 x 22 inch
0.022 slot - 18 x 25 inch
Approximately 200 angulations on either side
T-LOOP FOR ENMASSE RETRACTION:
Utilizes loops for space closure for
2.Symmetric space closure
T-LOOPS FOR ENMASSE
RETRACTION AND INTRUSION:
ASYMMETRICAL ‘T’ LOOP:
- JAMES. J. HILGERS (JCO/1992)
made of .016“ x 022" TMA (for .018" brackets) or
.0l9“ x 025" TMA (for .022" brackets),
with 5mm vertical step,
2mm anterior loop, and 5mm posterior loop.
archwire should have - exaggerated reverse curve of Spee
& strong distal molar rotation
Pre activation of Asymmetric "T" loop:
A. Short mesial loop compressed
B. Long distal loop opened.
C. Loop after pre activation.
Broussard combination closing and bite opening loop
with step between anterior and posterior segments.
Hilgers modification with reduced loop size for patient
comfort and crossed "T" for greater mechanical
Apical addition of wire in Archial configuration
More patient friendly- reduces the horizontal part of wire
Beta-titanium CNA M loop- 0.017 x 0.025 in
Activation up to 5 mm
Reactivation- every 6-8 wks
Bypass premolars - ↑ IBD
Preformed M loop space closing archwires:
Pre activation- separating the legs by 3mm.
Gable bends - mesial to increase anterior moment
- distal to increase anchorage moment
Torque in distal leg eliminated - wire passive in 3rd order in
Loop reactivated until there is at least 3 mm of space closure
After space closure, wire left in mouth for 1-2 visits- root
Double keyhole loop:
Roth treatment mechanics
Introduced by John Parker - 0.019 x 0.026 in
Complete space closure with one set of archwires
Allows operator to select how space will be closed
Activation- cinching wire distal to last molar tube, activated
every 3-4 weeks
POUL GJESSING RETRACTION ARCH:
- P.GJESSING (AJO/1992)
The PG retraction spring can be used as a module for
controlled retraction of both canines and incisors.
The suggested horizontal force - 100 gm for incisor
The incisor segment intrusion is induced with a magnitude
of 10 to 25 gm on each side between subsequent
Similar to canine spring with
Includes vertical slot in the lateral
750 bend 3mm mesial to the helix
to be inserted in the vertical slot
Activated by pulling distal end
separating the double helix and
producing 100gms force.
Activated every 4-6 weeks
- RAYMOND.E.SIATOWSKI (AJO/1997 )
Used for en-masse retraction of all six anterior Teeth
Wire sizes: 0.016 X 0.022 S.S, or 0.018 X 0.025 S.S. wire.
0.017 X 0.025 inch TMA
Development of opus loop:
M/F required for translation
Individual teeth: 7.1-10.2 mm
Groups of teeth: 8.0-9.1 mm
Most closing loops have inherent M/F 4-5 mm or less
To achieve net translation, need to add residual moments
Gable bends anterior & posterior
Posterior gable bend & anterior wire-bracket twist
Development of opus loop:
Disadvantage of gable bend:
Cycle of Tipping- translation- uprighting (lower Young's
Modulus materials go through fewer of these cycles for a
given distance of space closure).
Correct magnitude of residual moments are difficult to
Changing areas of stress distribution in the pdl may not
yield most rapid, least traumatic method of space closure
Development of opus loop:
Study: design and verify loop design capable of delivering
M/F inherently without adding residual moments.
Castigliano’s Theorem: to derive M/F ratio in terms of
Using Castigliano's theorem, and refined, using FEM
simulations, and verified experimentally a new design, the
Opus Loop was developed.
capable of delivering a target M/F within the range of 8.09.1 mm inherently, without adding residual moments.
more precise force systems with non varying M/F can be
Groups of teeth therefore can be moved more accurately
en masse space closure with uniform PDL stress distributions more rapid tooth movement with less chance of traumatic side
neutral position is the same as the inactivated position - allows
known forces systems to be applied to the teeth
loops must be bent accurately to achieve their design potential.
All the dimensions are critical to the performance of the loop
- ROBERTO MARTINA (JCO/1997 )
kind of utility arch - simultaneously retract, torque, and intrude
or control the extrusion of the maxillary incisors.
made of .016" × .022" TMA for .018" bracket slots
anterior segment inserted into incisor brackets, and
two buccal segments into gingival first molar tubes
Two loops - connect the anterior and posterior segments
- extended as far vertically as possible
A distal activation of 2mm on each end of the arch will produce
the 100g of horizontal force needed for incisor retraction
To achieve a moment-to-force ratio of 10, placing a 3rd-order
activation (root-palatal torque) in the anterior segment of the
3rd-order activation should produce an intrusive force of
about 20g on each molar.
Extrusive force exerted on the anterior teeth.
To compensate this side effect - tipback / arc (preferably)
bent into each buccal segment to produce an intrusive force
- VARUN KALARA(JCO/1998)
K-SIR: Kalra Simultaneous Intrusion and Retraction archwire
continuous .019" X .025" TMA archwire
with closed 7mm X 2mm U-loops at the extraction sites
To obtain bodily movement and prevent tipping of the teeth
into the extraction spaces, a 90° V-bend is placed in the
archwire at the level of each U-loop
Centered 90° V-bend creates two equal and opposite
moments that counter tipping moments produced by
Off-center 60° V-bend placed about 2mm distal to U-loop.
Off-center V-bend creates greater moment on molar, increasing
molar anchorage and intrusion of anterior teeth.
20° anti-rotation bends placed in the archwire just distal to U-loop
A trial activation of the archwire is performed outside the mouth
trial activation releases the stress built up from bending the wire and thus
reduces the severity of the V-bends
Neutral position of loop
determined with mesial and
distal legs extended horizontally.
In neutral position, loop is
3.5mm rather than 2mm wide.
The archwire is inserted into the auxiliary tubes of the first molars and
engaged in the six anterior brackets
Second premolar bypassed - ↑ IBD
First molar and second premolar are connected by segment of
.019" X .025" TMA wire
It is activated about 3mm, so that the mesial and distal legs of the loops
are barely apart
archwire exerts 125 gm intrusive force on anteriors & similar amount of
extrusive force distributed between two buccal segments
archwire should not be reactivated at short intervals, but only every
six to eight weeks until all space has been closed.
Simplicity of design- ease of fabrication
Comfortable to the patient
TMA- low forces, low LDR, long range of action
En masse retraction- Shortens treatment time- prevents appearance of
unsightly space distal to incisors.
A good understanding of mechanics is required
when using retraction loops or springs, because
minor errors in mechanics can result in major
errors in tooth movement