Retraction mechanics in swa 2 /certified fixed orthodontic courses by Indian dental academy

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Contents
Introduction
Anchorage
Optimum force
Retraction mechanics
•Sliding mechanics
•Loop mechanics
•Biomechanical advances
Conclusion

ANCHORAGE IN ORTHODONTICS

NEWTON’S third law of motion :
“ Every action has an equal and
opposite reaction.”


DEFINITIONS :
Moyers :
 “ Resistance to displacement.”
 Active elements and reactive elements.
T.M. Graber :
 “The nature and degree of resistance to
displacement offered by an anatomic unit
when used for the purpose of effecting
tooth movement.”

DEFINITIONS :
Proffit :
 “Resistance to unwanted tooth
movement.”
 “Resistance to reaction forces that is
provided (usually) by other teeth, or
(sometimes) by the palate, head or neck
(via extraoral force), or implants in
bone.”

DEFINITIONS :
Nanda :
 “The amount of movement of posterior
teeth (molars, premolars) to close the
extraction space in order to achieve
selected treatment goals.”


DEFINITIONS :
BENNETT AND MCLAUGHLIN:
Anchorage control:
‘The manoeuvres used to restrict
undesirable changes during the opening
phase of treatment, so that leveling
and aligning is achieved without key
features of the malocclusion becoming
worse.’


CLASSIFICATION:
Moyers :
 According to the manner of force
application:
1. Simple anchorage :
Resistance to tipping.
2. Stationary anchorage :
Resistance to bodily movement.


CLASSIFICATIONS:

3. Reciprocal anchorage :
Two or more teeth moving in
opposite directions and pitted against
each other by the appliance.


CLASSIFICATIONS:
Moyers :
 According to the jaws involved:
1.

Intra maxillary :
Anchorage established in the same
jaw.


CLASSIFICATIONS:

2. Inter maxillary :
Anchorage distributed
to both jaws.
Baker’s anchorage (1904)


CLASSIFICATIONS:
Moyers :
 According to the site of anchorage:
1. Intra oral :
Anchorage established within the
mouth.


CLASSIFICATIONS:

2.

Extra oral :
Anchorage obtained outside the oral
cavity.
a.) Cervical : eg. neck straps
b.) Occipital : eg. Head gears
c.) Cranial : eg. High pull headgears
d.) Facial : eg. Face masks

CLASSIFICATIONS:


CLASSIFICATIONS:

3.

Muscular :
Anchorage derived from action of
muscles.
eg. Vestibular shields.


CLASSIFICATIONS:
Moyers :
 According to the number of anchorage units
:
1. Single or primary anchorage:
Anchorage involving only one tooth.
2. Compound anchorage:
Anchorage involving two or more teeth.


CLASSIFICATIONS:

3. Reinforced anchorage:

Addition of non dental anchorage sites.
eg. Mucosa, muscle, head, etc.


CLASSIFICATIONS:
Nanda :
 A anchorage : critical / severe
75 % or more of the extraction space
is needed for anterior retraction.
 B anchorage : moderate
Relatively symmetric space closure
(50%)
 C anchorage : mild / non critical
75% or more of space closure by
mesial movement of posterior teeth

CLASSIFICATIONS:
Burstone :





Group A arches
Group B arches
Group C arches


BIOLOGICAL ASPECTS OF
ANCHORAGE :
Factors affecting anchorage:





Number of roots
Shape, size and length of each root
multirooted > single rooted
longer rooted > shorter rooted
triangular shaped root > conical or
ovoid root
larger surface area > smaller surface
area

ANCHORAGE :

 Cortical anchorage:

Cortical bone vs. medullary bone
 Muscular forces:
Horizontal growers vs. vertical growers


OPTIMUM FORCE


Pressure in the PDL=
Force applied to a tooth
Area of distribution in PDL

 Tooth movement increases as pressure

increases upto a point, remains at same
level over a broad range and then may
gradually decline with extremely heavy
pressure.

 Anchorage control : Concentration of
desired force and dissipation of

 PRESSURE RESPONSE CURVE :


ANCHORAGE :
Anchorage situations :

Differential effect of very large
forces:
More movement of arch segment
with the larger PDL area.
Questionable response.


MECHANICAL ASPECTS OF
ANCHORAGE :



Tooth movement is brought about after
overcoming the frictional resistance
during sliding of wire in the bracket.
 Frictional force is proportional to the
force with which the contacting surfaces
are pressed together
 Affected by the nature of the surface
 Independent of the area of contact

Orthodontic

space closure should be
individually tailored based on the
diagnosis and treatment plan.


Two Schools of Thought
for retraction of anteriors following Premolar
extraction

Separate canine and anterior retraction
En-mass retraction

First School of Thought


Second School of Thought


 Storey, Smith and Stuwed have show
that :

5-55% of the total extraction space can
be taken up by the anchor molar.

 According to Salzman

during space closure following extraction
some amount of anchor loss will definitely
take place.


 Begg stated that
a differential force application (reciprocal
light force) moves the anterior teeth while
posterior teeth remain stationery.


RETRACTION MECHANICS

FRICTION

CONTINUOUS

FRICTIONLESS

SEGMENTAL

CONTINUOUS


SEGMENTAL

Components Affecting Sliding
Mechanics

1. WIRE MATERIAL: cobalt chromium,

beta titanium and nickel titanium wires
produces more friction than stainless steel
wires.

2. WIRE CROSS SECTION: rectangular
wire produces more friction than round
wires.

3. WIRE DIMENSIONS: larger diameter
wires produces more friction than smaller

4. BRACKET COMPOSITION: The

composition of bracket eg., ceramic
brackets, causes more friction than the
stainless steel bracket.


Which slot?
18 or 22


Which wire in which slot?


Position of hooks:
Turk et al in 2005
CRe dependent on:
Bone support
Root morphology
Incisor inclination

Ligation techniques:
Steel or elastomeric ligatures
Or self ligating bracket


Edwards et al in 1995
compared four ligation
techniques
Similar results- Spiller et al
and Bazakidau also.
Berger JL in 1990 compared
Speed bracket with
conventional ligation

Type of force:
1. active tieback
2. power chain
3. niti close coil spring
4. screw type mechanism

Active tiebacks


Type one tieback.

Active tie-backs consist of an elastic
module and ligature tie combination.

Type Two tieback.

2

Active tie-backs consist of an elastic
module and ligature tie combination.

Amount of force given by
the module
Prestreching


Elastic chain


Pletcher coil spring


Niti coil springs


Hycon


O brien et al in 2002 did a RCT to
compare 3 methods of space
closure:
1.Active tiebacks- 0.35mm/month
2.Powerchain – 0.58mm/month
3.Niti coil spring- 0.81mm/month

Anchorage :
1.Band second molars
2.Headgear
3.Curve of spee in the stainless
steel wire
4.TPA ?????
5.Implants

Wise et al in 1994
Bobak V et al in 1997


Implants

Placement of maxillary microscrew.


Mandibular microscrew.

Initial maxillary canine retraction force applied with
tieback between micro-implant & canine.

After 2 months of treatment, maxillary
anterior retraction force applied with
nickel titanium coil spring.


Sliding mechanics

Enmass

cuspid followed
by anteriors


CANINE RETRACTION
WITH SLIDING
MECHANICS


CANINE RETRACTION

Minor Cuspid
Retraction
Uncontrolled
tipping of 1-2 mm


Major cuspid
retraction
Controlled
tipping or
translation of
more than
3 mm.

Minor Cuspid Retraction
Minor Cuspid Retraction :- uncontrolled
tipping of the canine, when 1-2mm of arch
length per side is required.
It can be carried out with the use of
lace backs.


 Bennett and McLaughlin introduced

lacebacks to prevent forward tipping of
canine during levelling and aligning
 These are constructed using 0.009” or
0.010” ligature wire, tied in figure-ofeight fashion.


Major cuspid retraction
 Controlled tipping or translation of more

than 3 mm of arch length per side is
required.
 Where the canine’s axial inclination is ideal,
it is preferable to translate the tooth.
 As the canine is retracted, the anterior
crowding unravels. The lateral incisors
tends to move distally due to pull of the
trans-septal fibers.

MOMENT


MOMENT

COUNTER MOMENT

MOMENT


MOMENT

COUNTER MOMENT

Process is repeated until tooth is
retracted or the elastic force is
dissipated


INCISOR RETRACTION
MECHANICS


INCISOR RETRACTION (SLIDING
MECHANICS)
 In friction or sliding mechanics an elastic

chain or thread is attached to the tooth
and a continuous archwire is placed.
 The elastic chain is the force component of
the retraction.
 The wire-bracket interaction produces the
moment


Advantages of Friction
Mechanics

 The complicated wire bending is not





required, making initial wire placement
less time-consuming.
This can enhance patient comfort.
No running out of space for activation.
Fail safe
Vertical force consideration can be
avoided, so there will not be any first
order or third order side effects.

Disadvantages Of Friction
Mechanics
 Any thing that adds the friction slows
the movement of teeth along the
archwire.
 Unpredictable
 Chances of loosing anterior torque is
higher as no time given for uprighting


Force applied by loops or
springs
Preactivation bends given


Loop anatomy:


Types of loops:
1. open loops
2. closed loops


Loops and springs used for
retraction:
•T loop
•Omega loop
•Tear drop loop
•PG spring


 Alpha moment:- this is the moment
acting on the anterior teeth(often
termed anterior torque).


 Beta moment:- this is the moment acting
on the posterior teeth. Tip-back bends
placed mesial to the molars produce an
increased moment.


 Horizontal forces:- these are the

mesio-distal forces acting on the teeth.


 Vertical forces:- These are intrusive –

extrusive forces acting on the anterior
or posterior teeth. These forces
generally result from unequal alpha and
beta moments.


CANINE RETRACTION BY
FRICTIONLESS MECHANICS


FIRST LET US SEE IN
THE ANTERIOR
SEGMENT


Alpha and beta bends.


NOW LET US SEE IN
THE POSTERIOR
SEGMENT


T loop


 The use of the T-loop for major

cuspid retraction is recommended.
It fulfills all the requirements of a
retraction assembly.
It is easily fabricated at the chair.
It is inexpensive.
It is resistant to deformation.
It is easily contoured for comfort.
It has a adequate M/F ratio for controlled
tipping or translation.
 Its M/F ration can be easily adjusted.








CRITERIA FOR OPTIMAL
SPRING
 It should possess low load deflection





rate.
It should deliver optimal force.
It should deliver proper M/F ratio
which determines proper C.rot.
Less bulky
Hygienic

 It is made form 0.017 x 0.025 inch

TMA.
 The spring is first made passive from
the auxiliary tube of the first molar to
the cuspid slot, it must be remembered
that the canine slot is slightly occlusal
to the auxiliary tube of the first molar
bracket that is why distal vertical leg of
T-loop is kept 1 mm short.

CONFIGURATION FOR THE
BASIC
T-LOOP SPRING
10mm

2mm
4mm

5mm
1mm

?mm

2mm

?mm

Pre-activation bends

PRE-ACTIVATION BENDS

1st bend

2nd bend


3rd bend

4th bend

6th bend

5 bend
th


Antirotation bends


Neutral position:


Trial activation:


Position of the loop


EN MASS RETRACTION
WITH FRICTIONLESS
MECHANICS


CONCLUSION
“Well begun is half work done” so
taking this guideline, meticulous
attention has to be given to
biomechanics.
COZ IF YOU DON’T…………..

THINK BEFORE YOU ACT!!!!

ANCHORAGE :






Relation of contiguous teeth
Forces of occlusion
Age of the patient
Individual tissue response


T H A N K Y OU


Retraction mechanics in swa 2 /certified fixed orthodontic courses by Indian dental academy

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