Retraction by frictional mechanics

RETRACTION BY
FRICTIONLESS MECHANICS
www.indiandentalacademy.com

INTRODUCTION
Tooth movement occurs by various
mechanisms
EXTRENSIC
Force is basic component
Extrinsic - elastics, E-chain,Niti springs e.t.c
Intrinsic - Loops bend in arch wire
INTRINSIC

EVOLUTION
As early as 1915 (in first issue of I.J.O),
Ray.D.Robinson demonstrated about
Efficiency of loop arch wire
Dr.Robert H.W Strang (1933) pioneered
the loop design for edgewise mecanics
On the other hand Dr.P.R.Begg (1952)
advocated their usage in the initial phase of
Begg treatment www.indiandentalacademy.com

With advancement in techniques of
scientific testing and better understanding of
physiological principles of tooth movement
improvisation of loop design continued
through 60’s and 70’s
Eminent orthodontist like Dr.Joseph
Jarabak,Dr.Charles Burstone,Dr.Robert
Ricketts must be credited for their single
contributions

In the last decade some other contributors
are
Dr.Raymond Siatkowski-OPUS LOOP/AJO/1997
Dr.Poul Gjessing - P.G.RETRACTION
SPRING/ AJO/1985,92

CENTER OF MASS
Each body has point in its mass
Which we call center of mass in
Gravity-free environment.
CENTER OF GRAVITY
In an environment where
Gravity is present

FORCE-It is defined as “An act upon a body
that changes or tends to change the state of
rest or the motion of that body”.
by :R.J NIKOLAI

CENTER OF RESISTANCE
Depends on alveolar bone
support,root length,no. of
roots.It is at the approximate
mid point of embedded
portion of root.
POINT OF FORCE APPLICATION

CENTER OF ROTATION
 Line drawn through long axis
of initial and final tooth
movement where it meets is
called center of rotation
 It can be at 1.At CR
2.Apical to CR
3.At root apex
4.At infinity
 Tooth movement will depend
on the location of center of
rotation

Defined as the rotational tendency when force is
applied away from the center of resistance
A force acting at a distance
Mathematically given as M = f x d
Where M is the moment F is the force
And D is the perpendicular distance of the line of action
to the center of resistance
MOMENT

Direction of a moment
The direction of the moment of a force can be
determined by continuing the line of action around
the center of resistance towards the point of origin.www.indiandentalacademy.com

COUPLE-It is two parallel
forces of equal magnitude
acting in opposite direction
and separated by a distance.
MOMENT OF COUPLE
It is the product of one of
the force times the distance
between two forces

What is friction mechanics?
Tooth is retracted or slides through the arch wire.
It is used for booth individual canine and enmasse
retraction
Friction is present due to surface irregularities of
arch wire and bracket
Various methods used
1. Elastic modules with ligature wire
2. Elastomeric chains Stainless steel
3. Closed coil springs Niti
Co-cr-ni alloyswww.indiandentalacademy.com

4. J hook head gear
5.Mulligan V bend sliding mechanics
6.Employing tip-Edge brackets on canines.
Disadvantages of sliding mechanics
1. It gives variable force.
2. E-chain absorbes water and saliva when exposed
to oral environment causing degradation of force
by 50%-70% by 1st
day
3. Excess Stretching of E-chain causes breakdown
of internal bond leading permanent deformation.
4. Permanent staining of E-chainwww.indiandentalacademy.com

5.Dependent on patient cooperation in case of
elastic bands
6.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
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.www.indiandentalacademy.com

What is frictionless mechanics?
Force generated intrinsically by arch wire
By in cooperating loops in arch wire
Energy is stored in loops and release it in slow
And continuous fashion
There is no friction between archwire and bracket

ANCHORAGE
Definition “Refers to the nature and degree of
resistance to displacement offered by an anatomic
unit when used for the purpose of effecting tooth
movement”
“amount of movement of the posterior teeth(molars,
Premolars) to close the extraction space in order to
achieve selected treatment goal”

ANCHORAGE CLASSIFICATION
According to Ravindra Nanda
GROUP A
GROUP B
GROUP C

GROUP A ANCHORAGE

GROUP B ANCHORAGE

GROUP C ANCHORAGE

FACTORS DETRRMINING THE TOOTH
MOVEMENT REQUIRED DURING
SPACE CLOSURE
AMOUNT OF CROWDING-
-Extractions are Usually done to relive crowding
-Anchorage control becomes very crucial
-Maintaining anchorage while creating space
for decrowding is important

ANCHORAGE-
-Anchorage classification during treatment
planning is very important for desired results.
various methods like (headgear,lip-bumper,lingual-
arch,trans palatal arch e.t.c)
AXIAL INCLINATION-
-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 movementwww.indiandentalacademy.com

-example in case of unfavorable positioned canine
(root mesial crown distal)
MIDLINE DISCREPANCIES AND LEFT OR
RIGHTASYMMETRIES
-These problems should corrected as early as
possible
-Asymmetric forces could result in unilateral vertical
forces causing asymmetric anchorage loss

VERTICAL DIMENSION
-Attention should be given to vertical forces during
space closure .
-undesirable vertical extrusive forces may result in
increased lower facial height,increased inter labial
gap,excessive gingival display

RETRACTION
STAGEDENMASSE
FRICTIONLESS SLIDING
TIP AND UPRIGHT
SIMULTANEOUS
INTRUSION
AND RETRACTION
STAGE 1 STAGE 2
CANINE ANTERIORS
FRICTIONLESS SLIDING
FRICTIONLESS
SLIDING

Mechanism of action of retraction
Key hole loop
(frictionless)
Cl-3 elastic
(friction)
Individual
Canine
retraction

INDIVIDUAL CANINE RETRACTION
The canines are key stones of occlusion.
Correct positioning of the canine after retraction i
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 dista
tipping and rotation.

It is important to do individual canine
retraction in maximum anchorage cases.
Making it possible to apply predetermined and
precise forces which can meet the biomechanical
requirements for planned tooth movements.
Friction and binding of the tooth are
eliminated.
Tipping and rotations can be controlled.

THE CR OF CANINE :
Shown to be located in the center of the root one third
of the distance from the alveolar crest to the apex.

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.

Force application Distal tipping

Force application Rotation

Antitip and antirotation moment-to-force
conditions necessary for translation of
canines with average dimensions.www.indiandentalacademy.com

Force application
Anti tip couple

Anti rotational couple
Force application

VARIOUS CANINE RETRACTION
LOOPS
1. CUSPID RETRACTOR(R.M.RICKETT/AJO/76)
2. T-LOOP (BURSTONE/AJO/1976)
3. P.G SPRING (P.GJESSING/AJO/1985)
4. CUSPID RETRACTOR
(R.HASKELL/AJO/1990)

CUSPID RETRACTOR
(RICKETT’S/AJO/1976)

EN-MASSE RETRACTION
It literally means retracting group of teeth
Together as a single unit.
As segmented technique developed by Burstone,
it utilizes loops for space closure for
1.Anterior retraction
2.Symmetric space closure
3.Posterior protraction

3-PHASES OF TOOTH
MOVEMENT
A.TIPPING
B.TRANSLATION
C.ROOT UPRIGHTING

En-masse space closure can effectively be
employed in moderate and minimum anchorage
cases
Simultaneous intrusion and retraction of the
anterior teeth,maintaining torque control may
also be employed.However,demand on the
Anchorage should be evaluated carefully

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 loop designs are available for retraction
and all are having pre-determined vertical heights
ranging from 7-10mm in vertical direction to keep
it closure to centre of resistance of tooth

CLOSING LOOPS
Closing loop arch wires should be fabricated
from rectangular wire to prevent wire from rooling
in the bracket slot
The performance of the loop,from the
perspective
of engineering theory,is determined by 4 major
characteristics
1. Spring properties
2. Moment it generates
3. Its location
4. Additional design principle

1. SPRING PROPERTIES
 It is determined almost totally by the
A. wire material
B. size of the wire
C. distance between point of attachment
 Changing the size of the wire produce largest
change in its characteristics,but the amount of
wire in cooperated in the loop is also important

FROM
WILLIAM.R.PROFFIT
IInd edition

2.Moment it generates
To close an extraction space while producing
bodily tooth movement closing loop must generate
not only closing force but also approximate
MOMENT
To generate a moment limits the amount of wire
that can be in cooperated into it,which will make it
more springier and it will unable to generate
necessary MOMENT
MOMENT

3.Its location
Its location is very important for its performance
in closing space.
As gable bends are in cooperated ,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
1.Equal distance
2.Closure to anterior
3.Closure to Posterior

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.
if patient does not come for scheduled appointment
Design should be as simple as possible
During activation of loop it is considered more
effective when it is closed rather than opened

BIOMECHANICS (looped arch wire)
The teeth in an arch wire will invariably assumes
the passive position of the arch wire.
When we place bend in the middle of the wire
and engage into bracket two equal and opposite
moments are produced
When offset bend is placed differential force is
produced
This same principles apply in FRICTIONLESS
mechanics where instead of bend loop is placed in
the wire

Bends placed on the mesial and distal legs of loop
are called as ALPHA and BETA respectively
These bends produce ALPHA and BETA moments
when wire is placed into bracket
Activating the loops produces the forces in
frictionless mechanics.Pulling the distal end of the
arch wire through molar tube and cinching it back
does this.
MESIAL LEGDISTAL LEG

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
3:1when it is activated by 1mm
To get M:F ratio of 10:1 activation should be
reduced to .2mm,but force level is not sufficient for
retraction
In order to increase moment,height can be
increased but it has limitation as available space in
the vestibule

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

Thus with this added moment M:F ratio of loop
is increased.
The ALPHA MOMENT produces distal root
movement of anterior teeth,while the BETA
MOMENT produces mesial root movement of
posterior teeth.
If ALPHA = BETA NO VERTICAL FORCE
If ALPHA not BETA ,VERTICAL FORCE

If BETA moment is >ALPHA posterior anchorage
is enhanced by the mesial root movement of
posterior teeth and net extrusive effect on posteriors
and intrusive force on anterior teeth.
If ALPHA moment is > BETA anchorage of
anterior segment is increased by distal root
movement and net extrusive effect on anterior teeth
and intrusive effect on posterior.
M:F ratio increases as spring gets deactivated
Spring should not be activated to frequentlywww.indiandentalacademy.com

MOMENT TO FORCE RATIO FOR
VARIOUS TOOTH MOVEMENTS
M/F 5 : 1 Uncontrolled tipping
M/F 8 : 1 Controlled tipping
M/F 10 : 1 Translation
M/F >10 : 1 Root movement

FACTORS THAT INFLUENCE M:F RATIO
Height of the loop
Horizontal loop length
Apical length of the wire
Placement of the loop
Helix in-cooperation
Angulations of loop legs
Burstone and KOEING 1976 AJOwww.indiandentalacademy.com

Retraction by frictional mechanics

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