En masse retraction jc

A Comparison of Anchorage Loss
Wook Heoa; Dong-Seok Nahmb; Seung-Hak Baekc
www.indiandentalacademy.comwww.indiandentalacademy.com

• Introduction
• Biomechanics of retraction
• Introduction
• Common terminologies in biomechanics
• Classification of retraction mechanics
• Biomechanics of retraction
• Anchorage
• Method and material
• Result
• Conclusion
• Bibliography

Introduction
• One of the main chief complaint of patients who visited the hospital was
lip protrusion, crowded, irregular, or protruding teeth .
• Extracting the first four premolars and retracting the anterior segments
with maximum anchorage is the most common way to reduce lip
protrusion and to straighten the patient’s profile.
• Accurate prediction of the amount of anchorage loss during extraction
space closure is critical in determining both the treatment planning and
the selection of appropriate mechanics.
• Attempts to correct crowded, irregular, or protruding teeth go back to at
least 1000 BC.

• In1728, the French pioneer, Fauchard, introduced the first appliance and
noted that, to exert mechanical pressure by means of an apparatus,
sufficient resistance to the force must be exerted.
• Today, anchorage control is a major concern in the design of orthodontic
appliances.
• For minimizing anchorage loss and maximizing tooth movement
efficiency,
• Tweed emphasized anchorage preparation as the first step in
orthodontic treatment.
• Storey and Smith advocated the use of light force values, and
• Begg emphasized the advantages of differential force to produce the
maximum rate of movement of teeth.
• There have been controversies about how to achieve maximum
anchorage preservation in the first premolar extraction cases.

• Proffit and Fields recommended separate canine retraction for
maximum anchorage, stating that this approach would allow the
reaction force to be constantly dissipated over the large periodontal
ligament area in the anchor unit. They acknowledged, however, that
closing the space in two steps rather than in one would take nearly
twice as long.
• Roth also recommended separate canine retraction for maximum
anchorage extraction cases but did not recommend it for moderate ones.
• Kuhlberg described separate canine retraction as less taxing on anchorage
because the two canines are opposed by several posterior teeth in the
anchor unit www.indiandentalacademy.comwww.indiandentalacademy.com

• On the other hand,
• Staggers and Germane described anchorage as being taxed twice with a two step
retraction, as opposed to once with en masse retraction, pointing out that the
posterior segment is unaware of knowing how many teeth are being retracted
and merely responds according to the force system involved.
• Burstone also questioned whether anchorage is better controlled with separate
canine retraction.
• Storey and Smith showed that 5%to 50% of the total extraction space can be taken
up by an anchor unit made up of the first molar and the second premolar when
used to retract a canine.
• Aronsen et al showed anchorage losses of 2.4 mm in 1 monkey and 1.4 mm in
another.

• Although recent advances in orthodontic techniques, such as the
orthodontic miniscrew, allow maximum anchorage and further simplify
the procedure, it is still necessary to know the difference in anchorage
loss between en masse retraction and two step retraction of the maxillary
anterior teeth
• Despite controversies of anchorage preservation, there have been a few
studies about comparing the two paradigms. The purpose of this study
was to compare the degree of anchorage loss of the posterior teeth and
the amount of retraction of the anterior teeth between en masse
retraction and two-step retraction of the maxillary anterior teeth in Class
I malocclusion patients with lip protrusion.

• Various techniques to reinforce anchorage have been devised and used
in orthodontic practice. However, even some of the best-known intraoral
appliances—palatal or lingual bars, the Nance holding arch, and
intermaxillary elastics— have undesirable side effects, including
protrusion, extrusion, and tipping of some teeth.
• The introduction of extradental intraoral anchorage was an important
event (titanium microimplant) in the field of orthodontics.

• Orthodontic tooth movement results from application of forces to the
teeth.
• These forces are produced by appliances (wires, brackets, elastics)
• The cells of the periodontium, which respond to these forces, are
unaware of bracket design, wire shape and alloy.
• Their activity is solely based on stresses and strains occurring in their
environment, which are the mechanical stimuli.
• Orthodontic problems and their correction depends on the result of
mechanical forces
• In orthodontics, biomechanics is commonly used in discussion of the
reaction of the dental and facial structures to orthodontic force, whereas,
mechanics is reserved for the properties of the strictly mechanical
components of the appliance system.
BIOLOGY + MECHANICS = BIOMECHANICS

COMMON TERMINOLOGIES:
FORCE
MASS
CENTER OF MASS (C.M.)
CENTER OF RESISTANCE (Cres)
CENTER OF ROTATION (Crot)
MOMENT
COUPLE
MOMENT OF FORCE (MF)
MOMENT OF COUPLE (MC)

• FORCE
• “An act upon a body that changes or tends to change the state of rest or
motion of body”. R.J NIKOLAI
• Though defined in units of Newton, it is usually measured in grams or
ounces.
• In orthodontics, forces are obtained in a variety of ways.
• Deflection of wires,
• activation of springs,
• elastics and magnets are the common means of producing orthodontic force.

• MASS AND WEIGHT:
• The mass of any body is the quantity of matter it contains.
• CENTER OF MASS (C.M.):
• The point at which the mass of a body may be
considered to be concentrated is known as
center of mass.
• It is called Centre of mass in gravity free
environment and

Centre of gravity in an environment
where gravity is present.www.indiandentalacademy.comwww.indiandentalacademy.com

• CENTER OF RESISTANCE (Cres):
• For an object in free space, the center of resistance is the same as the
center of mass.
• Since the tooth is partially restrained, as its root is partly embedded in
bone, its centre of gravity shifts apically and is then referred to as centre
of resistance.
•In a healthy tooth with an intact PDL, the centre of resistance is presumed
to be somewhere between ¼ or 1
/3 to ½ the distance from alveolar crest to
root apex.

• The center of resistance depends upon
• Root length and morphology
• Number of roots
• Level of alveolar bone support.
• The exact location of Cres for a tooth is not easily identified.
• Cres for
• Single rooted teeth with normal alveolar bone levels is about 1/3rd to ½ of the
distance from the cemento -enamel junction to the root apex.
• Multirooted teeth lies just below the furcation area i.e. 1-2 mm apical to the furcation.
• For entire teeth/segment of teeth
• Maxilla – slightly inferior to the orbitale
• Intrusive force for maxillary anterior teeth – distal to LI roots
• Although its precise location is typically unknown, it is important to
have a conceptual awareness of Cres in selecting and activating an
orthodontic appliance.
• The relationship of the force system acting on the tooth to the Cres
determines the type of tooth movement expressed. It is the point
through which pure force will produce only translationwww.indiandentalacademy.comwww.indiandentalacademy.com

• CENTER OF ROTATION (Crot):
• It is the point around which rotation actually occurs when an object is
being moved. Depending upon the force system applied, the center of
rotation may vary.
• E.g. In case of controlled tipping center of rotation will be at root apex
while in case of perfect translation it will be at infinity.

• 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
POINT OF FORCE APPLICATION

MOMENT:
A moment is defined as tendency to rotate
Moment = Force x Perpendicular distance from Cres to
point of force application
If the line of action of an applied force does not pass through the center of
resistance, the force will produce some rotation.
Thus it is measured in the unit of gm-mm.
Two factors determine MF.
1) Magnitude of force
2) Distance.

• COUPLE:
• Two forces equal in magnitude and opposite in direction produce couple.
The result of applying two forces in this way is a pure moment, since
translatory effect of the forces cancels out.
• A couple will produce pure rotation, spinning the object around its Cres.
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
This distance is called “the moment arm of the couple”.

• When the tooth is embedded in alveolar bone, we cannot apply a couple
with one force on the crown and the other force on the root.
• A force of 100 gm acting at a distance of 10 mm from the Cres of a tooth,
produces a clockwise or negative moment of 1000 gm-mm which will
cause the tooth to tip.
Tipping
10mm
100 Gms
1000gm-mm

Since tipping is undesirable, we must generate a counter balancing moment of
1000 gm-mm so that a bodily movement is obtained.
This can be achieved by twisting the anterior segment of the rectangular wire
and fitting it into a rectangular slot.
Once the wire is engaged in the bracket slot it generates an “Inherent
moment of couple”, which is nothing but the couple produced within the
wire itself. In a rectangular wire, the moment arm is the depth of the
bracket, which is very small.
Inherent couple acting at
a distance from the Cres
producing secondary
moment of a couple
Inherent
moment
of a couple

TYPES OF TOOTH MOVEMENT:
• Basic tooth movements are,
• 1.   Tipping
• 2.   Translation
• 3.   Root movement
• 4.   Rotation
• Each movement is the result of variation of the applied moment and
force (either by magnitude or point of application).
• Tipping:
• Is greater movement of the crown of the tooth than that of the root.
• Crot is apical to the Cres.
• Tipping can be further classified on the basis of the location of the center
of rotation as
• Uncontrolled tipping
• Controlled tipping.

• Uncontrolled tipping
• A horizontal force at the level of bracket will cause movements of the
root apex and crown in opposite directions.
• This is simplest type of tooth movement.
• It requires single force and no applied moment.
• Crot lies just below the Cres.
• M/F ratio = 0:1 to 5:1
• Cl II div 2,Cl III uprighted incisors
• Controlled tipping
• It is achieved by an application of force to move the crown, as done in
uncontrolled tipping and application of a moment to control or maintain
the position of the root apex. Crot lies at the root apex
• M/F ratio = 7:1
• Severely proclined incisors

• Translation: (bodily movement )
• Takes place when the root apex and crown move the same distance and
in the same direction.
• A horizontal force applied at the Cres of a tooth will result in this type of
tooth movement.
• However, the bracket where the force application takes place is at a
distance from the Cres. This force alone applied at the bracket will not
result in translation. To achieve translation at the level of the bracket, a
couple of forces are required that are equivalent to the force system
through the Cres of tooth.
Point of force application – Cres
Center of Rotation – Infinity.
M/F = 10:1

• Root movement (TORQUE):
• Root movement is achieved by keeping the crown of a tooth stationary
and applying a moment and force to move only the root.
[Placing twist in a rectangular wire, or the angle of the bracket slot with
the long axis of the tooth and the occlusal plane ]
• Point of force application – a point apical to the Cres
• Center of Rotation – at the incisal edge or bracket.
• M/F =12:1

• Pure rotation:
• This type of tooth movement occurs when tooth rotates about its center
of resistance.
• A couple is required to produce pure rotation.
• The simplest way to determine how a tooth will move is to consider the
ratio between moments created when a force is applied to the crown of a
tooth (moment of force MF) and the counter balancing moment
generated by a couple within the bracket (moment of couple Mc).

• FORCE SYSTEMS:
• In order to achieve the described tooth movements, the proper force
system is a critical requirement. The following factors related to the
force system are potentially under the control of the clinician.
1.   Moment-to-force ratio
2.   Constancy of forces and moments.
3.   Magnitude of forces and moments
• Moment-to-force ratio:
• The proportion of rotational tendency (moment) to the force applied at
the bracket will determine the type of tooth movement. This is
represented by M/F at the bracket.
• Moment-to-force ratio plays an important role in anchorage control. By
varying the moment-to-force ratio applied to the anterior and posterior
segments during space closure after bicuspid extractions, the amount of
forward displacement of the posterior segments can be controlled.

TYPE OF TOOTH
MOVEMENT
M/F
Ratio
Translation 10/1
Controlled tipping 5/1
Uncontrolled tipping 0/1
Root movement 12/1
Force constancy:
Relatively constant force within an optimal range produces the most
desirable type of tooth movement. We will have to design the active
components of an appliance such that they have desirable spring properties
as follows.
A) Low Load deflection rate of the spring appliances,
B) Frictionless force application system.

• Load deflection rate:
• Refers to the amount of force produced for every unit of activation of
an orthodontic wire or spring. The lower the rate, the more constant is
the force as the tooth moves and the appliance is deactivated.
• Four major design parameters available to the clinician to vary the
load deflection rate are:
1. Wire cross-section.
2. Wire length.
3. Wire material.
4. Wire configuration.

• 1. Wire cross-section.
• Load deflection rate varies directly as the fourth power of the diameter
of a round wire and as the third power of the depth of a rectangular
wire.
• Therefore, reducing the cross section of the wire can significantly reduce
the load deflection characteristics of an orthodontic appliance.
• On the other hand those parts of the appliance that are concerned with
preservation of anchorage require a relatively rigid wire with a large
cross-section for more advantageous stress distribution in the
periodontal structure and to prevent the movement of the anchorage
unit.
L.D.R. α wire cross section

• 2. Wire Length:
• The wire length changes the load deflection rate inversely as the third
power.
• In continuous arch multibanded appliance, the inter-bracket distance
between adjacent teeth dictates the wire length to a great extent.
• Long wire with a longer inter-attachment distance delivers a more
constant force magnitude as well as a more constant force direction as
the teeth move to the new desired positions.
L.D.R. α Wire length

• Wire material:
• For designing appliances, stainless steel alloys are in common use today.
• In order to improve the characteristics of the stainless steel wire, multi-
stranded wires with greater flexibility (reduced load-deflection rate)
have been introduced.
• Alloys such as NiTi and Beta titanium with low modulus of elasticity
and high spring back have radically changed appliance design.
• 4. Wire configuration:
• By placing more wire at the regions where bending deflections are the
greatest and at the regions where the bending moment is large, the load
deflection rate can be optimally reducedwww.indiandentalacademy.comwww.indiandentalacademy.com

Force and moment magnitude:
• A small error in activation of spring with a high load deflection rate will
result in a larger error in the activation force. In addition to the
consideration of tissue damage, force and moment magnitude are
important in anchorage control.
• Distributing the force over more teeth can reduce the stress levels on the
anchor units
• Biomechanical considerations serve not only to explain the effect of an
orthodontic appliance but also to detect side effects of therapy and to
assist in planning strategies for the avoidance or therapeutic exploitation
of these side effects.
• Efficient orthodontic treatment requires that sound treatment plans bewww.indiandentalacademy.comwww.indiandentalacademy.com

CLASSIFICATION OF RETRACTION MECHANICS
• A] Based on wire configuration
• Continuous arch mechanics
• Segmented arch mechanics
• B] Based on friction
• Friction mechanics {Sliding Mechanics}
Canine retraction with coil springs
Continuous anterior retraction i.e. as in MBT
Retraction with J- Hook headgear
• Frictionless mechanics
Use of loops or specialized springs
T-loop, Omega loop ,PG retraction spring etc
• C] Based on type of tooth movement
• Tipping followed by uprighting – Begg and Tip-Edge systems
• Translation – Standard Edgewise and Pre-Adjusted Edgewise
• D] Based on mode of retraction
• Cuspid retraction (Two step)
• En masse retraction
• E] Based on Anchorage
• Type A – Maximum Anchorage
• Type B – Moderate Anchorage
• Type C – Minimum Anchorage

• Once a decision to extract the teeth has been made, the orthodontist
has to plan how to close the space.
• There are two schools of thought of Retraction Mechanics
1.Seperate canine and incisor retraction
2.En masse retraction
1. Canines and incisors retracted separately to conserve anchorage when
using sliding mechanics
• - The principle is that by retracting fewer teeth at a time, less strain is
placed on the posterior anchorage
• - However it is time consuming and moreover the anchorage is taxed
twice

2. In En masse Retraction
• Where the canines and incisors are retracted together
• Here the anchorage is based on type of tooth movement of anterior
and posterior segment i.e. translation or root torquing in the posterior
teeth Vs. controlled tipping in the anterior segment.

• Retraction mechanics can be divided into two
categories
•Sliding mechanics ( Friction mechanics )
•Frictionless mechanics
Sliding
Mechanics
Separate
Canine
Retraction
Frictionless
Mechanics
En masse
Space closure

BIOMECHANICS OF SLIDING MECHANICS
• It involves either moving the brackets along the archwire or sliding the
archwire through brackets and tubes
• Friction plays an important role in sliding space closure, hence the term
‘Friction mechanics’.

What is friction mechanics?
Tooth is retracted or slides through the arch wire.
It is used for both 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 alloys4. J hook head gear
5. Mulligan V bend sliding mechanics
6. Employing tip-Edge brackets on canines.www.indiandentalacademy.comwww.indiandentalacademy.com

• In sliding mechanics an e-link is attached between the teeth
and a continuous archwire is placed.
• E-link is the force component of the retraction assembly and
moment is produced by the Archwire-bracket assembly
Force
component
Moment

• One moment rotates the tooth mesial out and other causes the distal
tipping of the crown.
• The mesial out moment is an undesirable side effect causing rotation of
the tooth.
•However the distal tipping contributes to the retraction by causing
binding of the arch wire, which in turn produces moment that results in
distal root movement.

WALKING MOVEMENT OF THE CANINE
Binding
•As the tooth uprights, the moment decreases until the wire no longer
binds.
•The crown then slides along the archwire again distal crown tipping again
causes binding.
•This process is repeated until the tooth is retracted or the elastic force is
dissipated. www.indiandentalacademy.comwww.indiandentalacademy.com

• FACTORS AFFECTING MAGNITUDE OF MOMENT
• The magnitude of moment, which causes distal root movement, depends
upon the size, shape and material of the archwire and width of the
bracket
• Hence wires with greater load deflection rates (i.e. SS in comparison
with NiTi an TMA ) produce greater force when they are deflected and
hence produce greater moments (i.e. Stiffer wires produce greater
moments)
• Also, the wider the bracket, the greater the moment, that the distance at
which the wire binds with the bracket increases.
• Rectangular wires produce more friction than round wires.
• Round wires can get distorted easily and do not offer control in three
planes of space www.indiandentalacademy.comwww.indiandentalacademy.com

• Therefore, a .016/.022 wire in an .018 slot and .019/.025 wire in an .022
slot are ideal for sliding mechanics.
• Co-Cr, TMA & NiTi wires produce more friction than SS wires due to
surface topography of the wires.
• Ceramic brackets offer more resistance than SS brackets

• MOMENT TO FORCE RATIO DURING RETRACTION
• The moment to force ratio of the retraction assembly is at its lowest
during the first few days after placement of E- chain because the
magnitude of force is at highest level.
• As the teeth are retracted the moment to force ratio improves because
the elastic force dissipates and the archwire bracket interaction due to
crown tipping produces a moment.
• To optimize the use of sliding mechanics, sufficient time must be
allowed for the distal root movement to occur.
• A common mistake is to change the elastic chain too often, thus
maintaining the high force levels and moment to force ratio that
produces distal tipping only.

• ADVANTAGES OF FRICTION MECHANICS
• Complicated wire configuration is not required
• Initial wire placement is less time consuming.
• Enhances patient comfort.
• DISADVANTAGES OF FRICTION MECHANICS
• Confusion concerning higher force levels.
• Tendency to over activate elastic and spring forces, which causes initial
tipping but gives inadequate rebound time for the tooth to upright.

• STEPS BEFORE RETRACTION
• Selection of the best bracket system
• Proper bracket placement
• Proper alignment of the teeth
• Anchorage control
• Retraction control
• CANINE RETRACTION
• Often in extraction cases space for the alignment is obtained by
distalization of the canines.
• Also, in maximum anchorage situations it would be ideal to retract the
canines separately, consolidate the anterior segment and then retract the
incisors.
• Major cuspid retraction consists of controlled tipping or translation of
the canine when more than 3mm of arch length per side is required.
• Minor cuspid retraction consists of uncontrolled tipping of the canine
when 1-2 mm of arch length per side is required.
• It can be carried out with the help of lacebacks

Minor cuspid retraction with
lacebacks
As the canine is retracted the anterior crowding unravels.
The lateral incisors tend to move distally due to the pull of transeptal fibres.

For the major cuspid retraction the E-link must be attached to the Power-
arm of the cuspid bracket.
•If the cuspid bracket does not have power arm a ‘Kobayashi hook’ may be used.
•The idea is to pass the force as close to the centre of resistance as possible.
•One moment rotates the tooth mesial out and other causes the distal tipping of the
crown.
•The mesial out moment is an undesirable side effect causing rotation of the tooth.
•However the distal tipping contributes to the retraction by causing binding of the arch
wire, which in turn produces moment that results in distal root movement.
•As the tooth uprights, the moment decreases until the wire no longer binds.
•The crown then slides along the archwire again distal crown tipping again causes
binding.
•This process is repeated until the tooth is retracted or the elastic force is dissipated.

• WALKING OF THE CANINE
• Due to the force of the E- link the canine tooth initially tips distally,
followed by period of rebound due to the leveling effect of archwire
bracket interaction, which causes distal uprighting of the root
• This initial tipping followed by subsequent uprighting of the canine, in a
repeated succession, resulting in its distal movement is referred to as
“Walking of the Canine”.
• This is possible because of the limited amount of play between the
bracket and the archwire

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
• 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 close to center of resistance of tooth

• EN MASSE SPACE CLOSURE WITH SLIDING MECHANICS
• In 1990s, a method of controlled space closure was described using
sliding mechanics.
• The MBT technique recommends following
ARCHWIRES
• Rectangular .019/.025 steel wires (working wires) are recommended
with the .022” slot.
• This wire size has good overbite control while allowing free sliding
through the buccal segment
• Thicker wires sometimes restricts free sliding of molars and premolars.
• Thinner wires have less control.
• Thinner wires along with the heavy forces of E-chain can give rise to
Roller-Costar kind of effect

Clinical example of Roller Costar Effect
SOLDERED HOOKS
0.7 brass hooks are preferred.
Soft SS 0.6 soldered hooks can be a useful alternative.
The most common hook positions are 36-38mm in Upper and 26mm in
the Lower.

• ACTIVE TIEBACKS USING LASTOMERIC MODULES
• In day to day clinical practice these are simple, economical and reliable.
• Placement is not difficult and can be done routinely.
• Active tiebacks using elastomeric modules are preferred for space
closure, even though NiTi springs have been shown to be more reliable
and effective.
NiTi CLOSED COIL SPRINGSACTIVE TIEBACKS

• ACTIVE TIEBACKS
• ADVANTAGES
• Convenient means of force application
• DISADVANTAGES
• Variation of efficiency of force delivery
• High initial force levels
• Degradation of force levels over a period of time
• Tendency to absorb moisture and accumulate food debris and
bacteria
• NiTi COIL SPRINGS
• ADVANTAGES
• Efficient and relatively quick to close extraction space owing to their
continuous force
• No frequent activation required
• DISADVANTAGES
• Expensive
• MBT recommends use of elastomeric modules for space closure in
most cases.
• If spaces are closed too rapidly, incisor torque can be lost which then
requires several months to regain at the end of space closure.

• FORCE LEVELS
• Active tiebacks are stretched their original size during activation.
• Without pre-stretching the force levels range in between 200-300 gms.
• If large spaces are to be closed NiTi coil spring are used instead of
Elastomeric module.
• The force decay in the NiTi coil springs is very much less as compared to
elastomeric modules.

• INHIBITORS OF SLIDING MECHANICS
• Inadequate leveling results in archwire binding
• When torque is being manifested in the posterior segment sliding cannot
occur simultaneously
• The ligature wire around the molar tube can block the distal end of the
wire
• Any damage or compressed bracket binds with the archwire and
prevents sliding.
• Soft tissue resistance due to its overgrowth in extraction space

• WIRE SELECTION IN SLIDING MECHANICS
• Sliding mechanics requires wire that produces less friction with the
brackets
• The friction between archwire and bracket slows down the movement of
teeth along the archwire.
• A large number of variables can directly or indirectly contribute to
frictional force levels between bracket and the archwire.
• PHYSICAL FACTORS
1. ARCH WIRE
• Material
• Cross sectional shape and size
• Surface texture
• Stiffness
2. LIGATION OF ARCHWIRE TO BRACKET
• Ligature wires
• Elastomerics
• Method of ligation www.indiandentalacademy.comwww.indiandentalacademy.com

3. BRACKET
• Material
• Manufacturing process (cast or sintered SS)
• Slot width & depth
• Design of the bracket – Single / Double width
• 1st order ( in-out), 2nd order (angulations), 3rd order (inclinations)
specifications.
4. ORTHODONTIC APPLIANCE
• Inter-bracket distance
• Force levels
• Level of bracket slot between adjacent teeth
• BIOLOGICAL FACTORS
• Saliva
• Plaque
• Corrosion

• CLINICAL SIGNIFICANCE OF FRICTION
• With best of archwire-bracket combination, at least 50Gms of friction
must be included in the force applied to tooth to initiate movement.
• High levels of friction may result in binding of the bracket with little or
no movement.
• The ideal situation is the one in which there is no friction between the
wire and the bracket.
• Since this situation does not exist with the friction mechanics, the
orthodontist must be aware of the magnitude of friction in the appliance
system
• Friction can be compensated for in the applied force and it is “hoped”
that the optimal force value can be achieved!!!

• Disadvantages of sliding mechanics
• It gives variable force.
• E-chain absorbs water and saliva when exposed to oral environment
causing degradation of force by 50%-70% by 1st day
• Excess Stretching of E-chain causes breakdown of internal bond leading
permanent deformation.
• Permanent staining of E-chain
• Dependent on patient cooperation in case of elastic bands
• 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.

• WHAT IS FRICTIONLESS MECHANICS
• In frictionless mechanics, teeth are moved without the brackets sliding
over the archwire.
• Retraction is accomplished with the help of loops or springs.
• Frictionless space closure involves bending loops of various
configurations-
• -Sectionally (To deliver the desired force to an individual tooth
• OR -In a continuous archwire (To deliver the desired force levels to
several teeth)
• When activated, the loop distorts from the original configuration
• As the tooth moves the loop gradually returns to its original
preactivated position – delivering energy stored at the time of activation.
Loops

Theoretically, with closing loops for space closure, more accurately defined
force systems can be applied to groups of teeth.
Precise anchorage control, anteroposterior and vertical control can be
obtained.

BIOMECHANICS FOR FRICTIONLESS MECHANICS
• 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.
• 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
MESIAL LEGDISTAL LEG

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.
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 .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.
FACTORS THAT INFLUENCE M:F RATIO
Height of the loop
Horizontal loop length
Apical length of the wire
Placement of the loop
Helix incorporation
Angulations of loop legs
BURSTONE and KOEING

• Definition
• Webster’s International Dictionary defines anchorage as “ a secure hold
sufficient to resist a heavy pull.”
• “Refers to the nature and degree of resistance to displacement offered by an
anatomic unit when used for the purpose of effecting tooth movement” :
T.M.Graber
• “Amount of movement of the posterior teeth(molars,Premolars) to close the
extraction space in order to achieve selected treatment goal” :
Ravindra Nanda
• Define anchorage control during leveling and aligning as "the maneuvers used to
restrict undesirable changes during the initial phase of treatment, so that leveling
and aligning is achieved without key features of the malocclusion becoming worse”.
Richard P. Mclaughlin, JOHN C. Bennet
ANCHORAGE

• ANCHORAGE CLASSIFICATION
• According to Ravindra Nanda
• Group A Anchorage: - 75% or more of extraction space is required for
anterior retraction
• Group B Anchorage: -relatively symmetric space closure
• Group C Anchorage: - “Noncritical anchorage”- 75% or more extraction
space is closed by mesial movement of molars.

• According to Moyers
• Manner of force application
• Simple
• Stationary
• Reciprocal
• Jaw involved
• Intra and intermaxillary
• Site of anchorage
• Intraoral
• Extraoral-cervical, occipital, cranial, facial
• Muscular
• No. of anchorage units
• Single/primary
• Compound
• Reinforced

A
B
C

FACTORS DETERMINING 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
movement example in case of unfavorable positioned canine (root mesial
crown distal)

MIDLINE DISCREPANCIES AND LEFT OR RIGHT ASYMMETRIES
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
ENMASSE STAGED
SLIDINGFRICTIONLESS
TIP AND UPRIGHT
SIMULTANEOUS
INTRUSION
AND RETRACTION
STAGE 1 STAGE 2
CANINE ANTERIORS
FRICTIONLESS
SLIDING
FRICTIONLESS
SLIDING

INDIVIDUAL CANINE RETRACTION
• The canines are key stones of occlusion.
• Correct positioning of the canine after retraction is imperative for
function, stability and esthetic
• 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 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

VARIOUS CANINE RETRACTION SPRINGS
• CUSPID RETRACTOR(RICKETT’S/AJO/76)
• T-LOOP SPRING(BURSTONE/AJO/1976)
• P.G SPRING (P.GJESSING/AJO/1985)
• CUSPID RETRACTOR (R.HASKELL/AJO/1990
• NICKEL TITANIUN CANINE RETRACTION SPRING(/JCO/2002/YASOO
WATANABE)

T-LOOP SPRING (BURSTONE/AJO/1976)

MATERIALS AND METHODS
• The initial sample consisted of 120 adult female patients with Class I
malocclusion and lip protrusion who needed maximum posterior
anchorage. According to the following criteria, samples were selected :
• women older than 17 years to eliminate potential influence of sex and
growth;
• Class I malocclusion (00
<ANB <50
) with normodivergent pattern (220
<
FMA < 310
), lip protrusion (Ricketts’ lower lip to esthetic line 2 mm),
labioversed upper incisor (U1 to palatal plane 1050
), and less than 4 mm
crowding in each arch;
• four first premolars extraction cases; and
• use of a 0.022-inch straight wire appliance with Roth setup (fully bonded
to second molars).

• Group 1 (n 15, mean age 21.4 years, en masse retraction, using sliding
mechanics, as described by Bennett and McLaughlin) and
• Group 2 (n 15, mean age 24.6 years, two-step retraction, with sliding
mechanics for canine retraction and loop mechanics for the upper incisor
retraction) after matching gender, age, skeletal, dental, and soft tissue
relationships and treatment appliance.
• The open-type vertical loops made of 0.019-inch X 0.025-inch stainless
steel wire with 8 mm height and 45 gable bends were used for the
second stage of retraction of the upper four incisors. The loops were
activated by 1 mm to produce a force of 150 g/side. Once the loops were
deactivated, they were reactivated by 1 mm.

• In the mandibular arch, six anterior teeth were retracted by en masse
retraction with sliding mechanics in both groups. Space closure of the
mandibular arch was performed simultaneously with that of the
maxillary arch.
• Lateral cephalometric radiographs were taken before (T1) and after
treatment (T2).
• All lateral cephalograms were traced by one investigator.
• All traces were digitized by means of a graphic tablet (Wacom Co Ltd,
Vancouver, BC, Canada) using a program developed for this study with
an IBM-compatible computer.
• Linear measurements were in increments of 0.01 mm, and angular
measurements were in increments of 0.010
.

•9 skeletal and 10 anchorage variables were measured.

• Error determination of cephalometric landmark location and
measurement was done.
• Six randomly selected sets of cephalograms were retraced and
redigitized after the first set of recordings was obtained.
• The linear measurement error was found to be less than 0.43 mm, while
the angular measurement error was less than 1.29. Therefore, the first
measurement was used for this study.
• Comparison of skeletal variables between groups 1 and 2 at T1, the time
of retraction between groups 1 and 2, anchorage variables between
groups 1 and 2 at T1 and T2, and changes of anchorage variables during
T2 and T1 were evaluated by independent t tests

• Result
• Although there was no significant difference in skeletal horizontal
variables between group 1 and group 2at T1, skeletal vertical variables
such as the Bjork sum (P .05), facial height ratio (P .05), and FMA (P .05)
in group 2 showed a relatively more hypodivergent pattern than in
group 1 .
• Although the mean time of retraction in group 2 was longer than in
group 1, there was no significant difference in the time of retraction
between groups 1 and 2
• The anchorage variables at T1 showed no significant differences between
group 1 and group 2 . At T2, there were also no significant differences
between the two groups except U1A-Hor .

• U1A-Hor showed that the upper incisor root apex in group 2 was farther
from the PTV than in group 1 (P .05;).
• Since there was mild labial movement of the root apices of the upper
incisors in group 2 at T2, the amount of change in inclination of the
upper incisor (U1 to P; P .05) and the horizontal position of the upper
incisor apex (U1A-Hor) showed a significant difference from group 1 at
P .001
• Although there was no significant difference in the amount of change in
the horizontal position of the upper incisal edge (U1E-Hor) between the
two groups, the amount of change in the vertical position of the upper
incisal edge (U1E-Ver) showed a significant difference (P .05;). The
reason could be due to downward movement of the upper incisal edge
of group 2, which was originally positioned more superiorly.
• However, the vertical position of the upper incisal edge of group 1 was
well maintained. www.indiandentalacademy.comwww.indiandentalacademy.com

• There were no significant differences in the amount of changes in the
upper molar such as U6 to PP, U6MHor, U6A-Hor, U6C-Ver, and U6F-
Ver between groups 1 and 2 .
• Bodily and mesial movements of the upper molars were found in both
groups.
• Approximately 4 mm of the retraction of the upper incisal edges resulted
from 1 mm of anchorage loss in the upper molars in both groups .

• This study was performed to determine whether two-step retraction
provides better anchorage preservation than en masse retraction. To
exclude the influence of skeletal and dental factors, patient records with
Class I malocclusion, lip protrusion, normodivergent skeletal patterns,
labioversion of the upper incisors, and less than 4 mm crowding in each
arch were adopted.
• Although there was no significant difference in skeletal horizontal
variables between two groups at T1, there were significant differences in
skeletal vertical variables (Bjork sum, facial height ratio, FMA, P .05) by
chance.
• This means that group 2 showed a relatively greater hypodivergent
pattern within the normodivergent skeletal pattern compared to group1.

• Since it is known that patients with a hypodivergent facial type have
stronger natural anchorage than those with a hyperdivergent one, group
2 might have a better tendency of natural anchorage preservation than
group 1.
• However, the fact that there was no difference in anchorage loss of the
upper molar suggests that two-step retraction takes only more time to
close the extraction space without advantage of anchorage preservation
• During retraction, both groups showed bodily and mesial movement of
the upper molars (U6 to PP,U6M-Hor, U6A-Hor;).

• Since maximum posterior anchorage includes 100% anterior retraction
(no posterior anchorage loss) to 75% anterior retraction (25% of space
closure from posterior anchorage movement), the amounts of anchorage
loss were 2.0 mm in group 1 and 1.9 mm in group 2.
• These values are less than 25% when considering the premolar
extraction
space as 8.3 to 8.4 mm. Therefore, it seemed to be acceptable as
maximum posterior anchorage.
• The upper incisors were retracted in group 1 with a combination of
tipping and bodily movement .
• However, the upper incisor in group 2 moved in a relatively
uncontrolled tipping manner (U1 to PP, P .05; U1A-Hor, P .001;) and
showed a resultant downward movement of the upper incisal edge
(U1E-Ver, P .05; Table 3). It is known that a tipping movement of the
upper anterior teeth is easier and requires less anchorage of the upper
posterior teeth than bodily movement.

• In view of that, group 2 might have an advantage over group 1 in terms
of anchorage preservation. However, the result that there was no
difference in anchorage loss of the upper molar suggests that the
anchorage loss in group 2 continuously occurred during separate canine
retraction and following incisor retraction with a forfeit of the advantage
of anchorage preservation.
• The fact that approximately 4 mm of the retraction of upper incisal edges
resulted from 1 mm of anchorage loss of the upper molars in both
groups may be helpful when diagnosing lip protrusion patients and
estimating soft tissue change for them.
• If, in lip protrusion cases, more retraction of the anterior teeth is needed
than the predicted amounts, additional anchorage reinforcement with
headgear or orthodontic miniscrews would be necessary.

• CONCLUSIONS
• No significant differences existed in the degree of anchorage loss of the
upper posterior teeth and the amount of retraction of the upper anterior
teeth associated with en masse retraction and two-step retraction of the
anterior teeth.
• When choosing retraction mechanics, it is necessary to consider
additional aspects such as the inclination and vertical position of the
anterior teeth rather than anchorage loss.

• Anchorage control is one of the most important aspects of orthodontic
treatment.
• Moderate anchorage is relatively easy to manage using some intraoral
appliances and biomechanical procedures.
• Cases that require maximum anchorage require extraoral support to
reinforce the anchorage.
• In some instances, 100% anchorage has to be maintained, and such an
anchorage can be termed as absolute anchorage.
• It is difficult and often impossible to obtain absolute anchorage by
conventional methods such as extraoral force application.

• The term ‘‘skeletal anchorage’’ became popular after titanium miniplates
and microscrews began to be used for anchorage purposes.
• To treat skeletal open bite, Erverdi et al and Sherwood et al used
titanium miniplates, as anchorage which were placed in the zygomatic
area.
• De Clerck et al used zygomatic anchorage during retraction of maxillary
anterior teeth.
• Their reports suggest that the zygomatic buttress serves as a useful site
for obtaining absolute orthodontic anchorage.

• Nowadays, clinicians seek alternative anchorage protocols, which will
not incorporate extraoral appliances and which will not require patient
cooperation.
• Recent developments in the field of osseointegration have made possible
the use of implants for orthodontic anchorage.
• Wehrbein et al, Bernhart et al, Triaca et al, Tosun et al, and Keles et al, all
used implants to achieve absolute anchorage and reported successful
results.
• The en masse retraction of upper anterior teeth has always been a
popular option in the treatment of maxillary protrusion cases, with the
shortened treatment time being its main advantage.www.indiandentalacademy.comwww.indiandentalacademy.com

• Bodily movement of the anterior segment during retraction creates a
more favorable tissue response compared with the alternative tipping
and uprighting technique, and it allows the extraction space to be closed
in a single step.
• However, the anchorage requirement for bodily retraction is much
greater than that for tipping.
• Bodily movement during retraction can be achieved by applying a force
and a couple at the bracket level or by carrying the point of force
application to the level of center of resistance of the anterior segment.
• The center of resistance of the anterior segment, including the canines,
has been shown to be about 3.5 mm apical to the palatal bone level at the
incisor region

BIBILOGRAPHY
1. Strang RHW. Orthodontic anchorage. Angle Orthod. 1941;11:173–186
2. Bills DA, Handelman CS, BeGole EA. Bimaxillary dentoalveolar
3. protrusion: traits and orthodontic correction. Angle Orthodontist
2005;75:333–339.
4. Nejat Erverdia; Ahu Acarb: Zygomatic Anchorage for En Masse
Retraction in the`Treatment of Severe Class II D; Angle Orthodontist
2005;75:483–490.
5. McLaughlin RP, Bennett JC. The transition from standard edgewise to
preadjusted appliance systems. J Clin Orthod. 1989;23:142–153.
6. Bennett JC, McLaughlin RP. Controlled space closure with a
preadjusted appliance system. J Clin Orthod. 1990;24:251–260
7. Staggers JA, Germane N. Clinical considerations in the use of
retraction mechanics. J Clin Orthod. 1991;25:364–369

8. McLaughlin RP, Bennett JC. Anchorage control during leveling and
aligning with a preadjusted appliance system. J Clin Orthod.
1991;25:687–696.
9. Park HS, Bae SM, Kyung HM, Sung JH. Micro-implant anchorage for
treatment of skeletal Class I bialveolar protrusion. J Clin Orthod.
2001;35:417–422
10. Bae SM, Park HS, Kyung HM, Kwon OW, Sung JH. Clinical
application of micro-implant anchorage. J Clin Orthod. 2002; 36:298–
302.
11. Thiruvenkatachari B, Pavithranand A, Rajasigamani K, Kyung HM.
Comparison and measurement of the amount of anchorage loss of the
molars with and without the use of implant anchorage during canine
retraction. Am J Orthod Dentofacial Orthop. 2006;129:551–554.www.indiandentalacademy.comwww.indiandentalacademy.com

12. Nanda R. Biomechanics in Clinical Orthodontics
13. Proffit WR, Fields HW Jr. Contemporary orthodontics. 3rd
ed. St Louis,
Mo: CV Mosby; 2000:348.
14. Graber TM, Vanarssall RL, Katherine WL. Orthodontics, Current
Principles and Techniques.
15. Kuhlberg AJ. Steps in orthodontic treatment: Bishara SE, Textbook of
Orthodontics.
16. Richard P McLaughlin, John C Bennett, Hugo J Trevisi. Systemized
orthodontic treatment mechanics

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