Space closure Degree of space closure Moment to force ratio Segmental mechanics for space closure - Canine retraction - Incisors retraction Sliding mechanics for space closure Role of friction in sliding mechanics Factor influencing the sliding mechanics Mini-implant and space closure

1. 1
Dr. Mohammed Alruby
Mechanics of extraction space closure
Prepared by
Dr: Mohammed Alruby

2. 2
Dr. Mohammed Alruby
Space closure
Degree of space closure
Moment to force ratio
Segmental mechanics for space closure
- Canine retraction
- Incisors retraction
Sliding mechanics for space closure
Role of friction in sliding mechanics
Factor influencing the sliding mechanics
Mini-implant and space closure

3. 3
Dr. Mohammed Alruby
Space closure:
Bring opposing teeth together or segment of teeth by applying a force between them, this force is
occlusal and buccal to center of resistance
Greater amount of space closure will greater degree of side effects
Degree of space closure:
- Minor: less than 2mm
- Moderate; less than 4mm
- Severe: greater than 4mm
Large space closure need more anchorage control over the desired tooth movement
Anchorage type;
1- Absolute: no movement at anchorage unit
2- Maximum: minimum movement at anchorage unit
3- Moderate: same movement at anchorage unit as active
4- Minimum: major movement at anchorage unit
Moment to force ratio: M/F:
M / F ratio is a good way to describe or predict the quality of tooth movement
M / F ratios:
5: 1 ------------------ required for tipping
7: 1 ------------------ required for controlled tipping
10: 1 -----------------required for translation
12: 1------------------required for root correction
Loop design and M / F ratio:
Mechanical properties of closing loops depend on many factors, such as loop height, shape, design and
position, wire material.
Loop height:
As loop height increase, M / F ratio increase
6mm loop height ----------2 M / F ratio
10mm loop height ---------4 M / F ratio
Loop shape:
M / F ratio by T loop is higher than vertical loops
M / F ratio by helix loop is higher than that without helix
Loop placement:
Higher moment produced at bracket closure to the loop
Types of space closure mechanics
1- Segmental mechanics for space closure
a- Canine retraction:
Definition: movement of canine in distal direction from position close to lateral incisor to position next to
premolars along gentle curvature of the arch
Set up: there is an anterior-posterior space approximately 8mm distal to canine before space closure (21
X 25 stst) wire in (22 slot) can used to hold the arch as a separate unit
Pre-activation of the loop: before loop is inserted pre-activation bends is done known as alpha bend
(anterior curvature) and beta bend (posterior curvature).
This bend is necessary to create a moment (Mc) that will counter act the moment of the force (Mf)
The greater the degree of bend the greater Mc generated
Activation of the loop: the final activation of loop is done only when it is placed in the bracket slot and
the wire is pulled distally through posterior tube and cinched.
The amount of distal pull is guided by the amount of space to be closed as:
for 8mm extraction ----- 8mm activation is good

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Dr. Mohammed Alruby
phase I: tipping:
in initial phase of retraction which the spring is fully
activated
the center of rotation close to apex of canine so there is
crown movement with little movement of root
anchorage demand on molars is minimal
if pre-activation bend is not done in wire loop there is
uncontrolled tipping of canine will occur
Mc< Mf
phase II: translation:
as the canine is distalize and the
distance between two attachment
decrease, the force level drops
need more anchorage demands,
both molars and canines tend to translate
Mc = Mf

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Dr. Mohammed Alruby
Phase III: root movement:
Force level continue to drop
More root movement than crown,
root correction, Mc > Mf
Anchorage reinforcement
needed because there is some anchorage loss
B- incisors retraction:
Will proceed in a similar way as for
canine retraction, during retraction
there is more tipping movement so
high Mc in posterior teeth is needed
and less Mc at incisors.
Phase I is more sufficient to close
the space when incisors retracted
Mc > Mf --------in molars
Mc < Mf ---------in incisors
2- Sliding mechanics for space closure:
Definition; pull or pushing the teeth along continuous arch wire, with a force delivery system adequate to
produce movement
Advantages: shorten treatment period, prevent excessive force application,
improve patient comfort, more control during space closure
a- Canine retraction:
Before start canine retraction, all teeth must be levelled and aligned to a degree that arch wire chosen
for retraction sits passively through the bracket slot
Phase I: unsteady state: uncontrolled tipping
This the initiation of canine retraction, single force applied to canine to produce moment Mf acting on
(C Res) center of resistance of canine causing tip
There is some degree of play between arch wire and bracket slot
Tipping occurs in uncontrolled manner creating C Rot apical to C Res (If CRot apical to CRes so no Mc)
Phase II; controlled state; controlled tipping:
No clearance or play between arch wire and bracket, two point of contact between bracket and arch wire
Mc opposite to Mf so no tipping. Mc< Mf
Mc continue to increase and C Rot moves toward apex in pre-angulated bracket slot, the initial clearance
is zero
Phase III: steady state: translation state:
Contact between arch wire and bracket edge increase leading to increase in Mc with in force level so
Mc = Mf
Phase IV: restorative state:
= Constant decayed in distal movement ------ decrease force level ------ decrease Mf so Mf < Mc (with
correction of root angulation (2nd
order bend))
= Tremendous amount of friction at bracket wire interface that lead to relocation of C Rot gingival to C
Res anywhere between bracket and C Res
= If the force of retraction not decayed, this phase is not reached and there are only 2 phases (tipping
only)
= it is the root movement stage: Mc > Mf
N: B: canine movements phases:
1- Uncontrolled tipping: Mf present and no Mc
2- Controlled tipping: Mf > Mc
3- Translation: Mf = Mc

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Dr. Mohammed Alruby
4- Root correction: Mf < Mc
B- incisors retraction:
During space closure the incisors also allow the same phases as during canine retraction but the more
dominant is I, II phases (tipping) due to greater play angle
When we need to do more control for incisors retraction from the phase I by introduce Mc from the first
phase of retraction by:
1- Torqueing the arch wire (twist the arch)
2- Increase the stiffness and size of main arch
3- Decrease Mf produced without compromising the force magnitude and this can achieve by change
the point of force application relative to C Res of the teeth by using (power arm) design as the
power arm close to C Res of canine during retraction
Play angle:
it is the angle between the bracket and the arch wire
(line tangent bracket and line tangent wire surface)
In 16 X 22stst-------- angle measured 16 to 18 degrees
In 17 X 25 stst ------angle measured 13 to 14 degrees
In 19 X 25 stst ----- angle measured 6 to 8 degrees
In 21 X 25 stst ----- angle measured 2 to 3 degrees

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Dr. Mohammed Alruby
N: B:
= in a continuous arch system, there is a limiting possibilities of unpredictable canine movement.
= During phase I, II movement of canine retraction, there is elastic deflection on the wire that create an
extrusive force on incisors that cause lingual tipping
= we can prevent that by: using high stiffness wire or using light force retraction or
using overlay intrusion arch
N: B:
According to the third law of motion:
= The retraction force on canine exert the same force on molars, this force will create moment on molar,
causing it to tip mesially and this depend on:
Surrounding bone, tooth characteristics, additional teeth ligated to the molars
= by using heavier force; lateral open bite will occur due to tipping of canine and molars crown with no
root correction that prevent tooth to enter phase III and IV of sliding movement.
Role of friction in sliding mechanics:
= in sliding mechanics, some of the applied force is dissipated as friction and the remainder is transferred
= maximum biological tissue response occurs only when the applied force is sufficient magnitude to
overcome friction and lie within the optimum range of force necessary for tooth movement
= factors may cause friction:
1- Bracket width
2- Wire size
3- Materials
4- Tightness of ligation
5- Saliva
Factors influencing the efficiency of sliding mechanics
1- Arch wire properties:
= Stiffness of the continuous arch wire support the teeth, keeping it from the uncontrolled tipping when
force is placed on it as using stst then niti wires.
= The tooth will tip the wire contacts, the bracket at opposite corner of the slot, stop the tipping motion,
this contact at corner appear to produce a counter acting moment that pulls the root of the tooth in the
same direction as the crown moved.
2- For delivery system:
Niti coil spring produced significant faster rate of retraction than active ligation or intra-oral elastics (O
elastics) (3/16)
Niti coil spring produced similar rate of space closure as power chain elastics
3- For ligation methods:
Self-ligating bracket SLB produce low friction compared with conventional bracket.
Mini-implant and space closure mechanics
== Mini-implant (M I) serve as anchorage unit in situation where there is need for absolute anchorage,
and used to produce constant and predictable force system, so, accurate and precise movement of active
units can be achieving without possibility of anchorage loss
== Basic principle of mini-implant M I:
When using conventional mechanics, force application is usually parallel to the occlusal plane, the force
ideal only in one plane, however in M I usually placed apical to occlusal plane between the roots, so the
force is applied as an angle.
== this angulated force broken into two compartments:
a- Horizontal retraction force (r)
b- Vertical intrusive force (I)

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Dr. Mohammed Alruby
= the force by M I is much closer to C Res of anterior unit, therefore the mf is significantly less tha that
of conventional mechanics, this means, there is less tendency of teeth to tip
= in conventional mechanics, active part is the moved part and passive unit is the anchorage unit, but by
using M I which is third counterpart, the selective moment between posterior and anterior segment is
possible.
Total force > retraction force > intrusive force (F > r > I)
N: B: during retraction of anterior segment by using M I,
there is two distinct force component:
1- Large retractive force (r)
2- Smaller intrusive force (I)
3- Causing enmass retraction with some
intrusion of anterior segment