Retraction mechanics

RETRACTION MECHANICS
Good morning
DR TONY PIOUS

CONTENTS
 Introduction
 Definitions & Concepts
-force
-Center of resistance
-Moment
-Center of rotation
-moment to force
 Anchorage
-Defination
-Classification
-Anchorage control

 Bends
-V-bend
-step bend
 Retraction in Beggs Mechanotherepy
 Retraction in Fixed Mechano therepy
Frictional mechanics- friction
a) mechanism of action in friction mechanics
b) force delivery system
c) variables affecting frictional resistance
during sliding tooth movement

 Frictionless mechanics-
loop
 Open vertical loop
 Closed vertical loop
 Bull loop
 Vertical open loop with helix
 Omega loop
 Delta loop
 Opus loop
 T loop
 Asymmetrical T loop
 Mashroom loop
 Canine retraction
springs
 Ricketts maxillary canine
retraction
 Poul gjessing spring
 NiTi canine retraction
spring
 Canine retraction with J
hook headgear
 Rapid canine distraction

 K sir arch
 Statically
determinate
retraction system
 Retraction utility
arch
 Three piece
intrusion arch
 Translation arch
 Retraction by
Magnets
 The Hycon Device
 Retraction by implants
 Conlcusion

INTRODUCTION
 Antero-posterior therapy procedures to close spaces correct
procumbency, reduce overjet, and eliminate extraction sites is
generally categorized as Retraction mechanics
It involves carefully designed treatment strategy as to lose or
not to lose the anchorage.
Whether anterior retraction or posterior protraction or a
combination of both is used the same basic principles of
retraction mechanics apply.

FORCE
Defined - An act upon a body that changes or tends to change
the state of rest or the motion of that body.
Measured in Newton
Force is a vectors quantity thus has a –
magnitude,
point of application,
line of action,
and sense.

CENTER OF RESISTANCE
Center of mass is a point through which an applied force must
pass for a free object to move linearly without any rotation.
The center of a mass is for a generic free body.
Tooth – not generic free- periodontal support.
The analogous to center of mass for a restrained body is
CENTER OF RESISTANCE

Burstone C.J in AJO 1980
stated that
The center of
resistance for a tooth is
approximately the 1/3 to
½ apical to CEJ in single
rooted teeth along the
long axis

For multi rooted teeth it lies
1 to 2 mm apical to furcation

MOMENT
Defined- as the rotational tendency when force is applied away
from the center of resistance
Mathematically given as M = f x d
Where M -is the moment
f -is the force
d -is the perpendicular
distance from the line of
action to the center of resistance

CENTER OF ROTATION
 It is the point around which the body seems to
have rotated.
 The center of rotation is not a fixed point and
can be changed by the manner of force
application

 Translation - infinity
 Controlled tipping - apex
 Uncontrolled tipping - slightly
apical to center of
resistance.
 Root movement - incisal
edge

COUPLE
Two equal and
opposite non-
collinear forces are
called a couple

MOMENT OF A COUPLE
 The two forces since they are equal and
opposite cancel out but
 Moments created by the two forces do not
cancel out and a pure rotation is produced.
Measured as F x d
F=magnitude of one of the forces
d=distance b/w the forces

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 DETERMINING THE TOOTH
MOVEMENT REQUIRED DURING SPACE CLOSURE
 Amount of crowding
 Anchorage
 Axial inclination
 Midline discrepancies and left or right
asymmetries
 Vertical dimension

Amount of crowding:
 in cases of severe crowding, anchorage control is very
important to maintain the extraction space for relieving the
anterior crowding
Anchorage
 using the same mechanics for different anchorage needs is
very important. Traditional anchorage methods like lip
bumpers, headgears, transpalatal arches may be utilized
but non compliance methods for anchorage control based
on biomechanics can also be used.
NANDA& KULHBERG

Axial inclination of canines
the same force /and or moment applied to teeth with different
axial inclinations will result in different types of tooth movement.

Midline discrepancies and left right symmetry.
 Midline discrepancies should be corrected as early as
possible in treatment as it allows the remaining space
closure to be completed symmetrically. Using asymmetric
mechanics can cause in unilateral anchorage loss, skewing
of the dental arches, or unilateral vertical forces.
Vertical dimension
 Control of vertical dimension is essential in space
closure. Undesired vertical extrusive forces on the
posterior teeth can result in increased LAFH, increased
interlabial gap, and excessive gingival display. Class II
elastics may potentate this problem.

ANCHORAGE
 Anchorage is an important aspect of orthodontic
space closure
 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”
By: T.M.Graber
 “amount of movement of the posterior
teeth(molars,Premolars) to close the extraction
space in order to achieve selected treatment goal”
By: Ravindra Nanda

ANCHORAGE CLASSIFICATION
 According to Ravindra Nanda
 GROUP A
 GROUP B
 GROUP C
BIOMECHANICS IN CLINICAL
ORTHODONTICS -RAVINDRA NANDA

Maximum anchorage cases
retractive forces to the anterior teeth and no forces
to the posteriors.
Two ways of achieving this-
altering the forces
altering the moments
both the above ways aiming to increase the
m/f ratio of the post and decreasing the m/f of the ant

1. Altering the forces -a. ant segment.
moment should be a constant- the only option increase
in force should not be associated with a reactionary increase
a.class II elastics
b.j-hook from headgear
b.Post segment.
moment should be constant- the only option force
opposite to that acting on the post segments
headgear-distal

2. Altering the moments
force constant- increasing the post moment- β and
decreasing the ant moment-α
3. Position of the loop
mesio distal positioning- important
midway-equal and opp activation moments
off centered to distal- tip back moment and
intrusive force-maximum anchorage cases.
mesially off centered- increases the ant moment-
minimum anchorage cases

ANCHORAGE CONTROL
Anchorage control is done in three planes
1.Horizontal
2.Vertical
3.Transverse

HORIZONTAL ANCHORAGE CONTROL
(ANTERIO POSTERIOR )
 Limiting the mesial movement of the posterior segment while
encouraging distal movement of the anterior segment or vice-
versa.
 It is done by:
CONTROL OF POSTERIOR SEGMENT
Upper arch
a) Headgear
b) Palatal bar(trancepalatal arch)
c) Nance holding arch
Lingual arch
a) Lip bumper
b) Class III elastics and headgear

VERTICAL ANCHORAGE CONTROL
MOLAR CONTROL
a) Upper scond molar banding should avoided
initially (in high angle case)
b) Expansion if required should be achieved by
bodily moment of the posterior teeth(in high
angle case)
c) Transpalatal arch should be 2-3mm away from
the palate and with the U loop facing forward
d) High pull or combi pull headgear to be used
e) Posterior bite planes or bite blocks

TRANSVERSE PLANE OR LATERAL
b) Correction of molar cross bite
1. Rapid palatal expansion
2. Quad helix
3. Transpalatal arch

BENDS
An infinite number of shapes or bends can be placed
on the wire. Two commonly used basic bends are:
1) V-bend 2) step bend
Creative wire bending –The force system from step
bends & V-bends, Burstone & Koening, AJODO
1988, 93:59-67

V-bend principle
 The force & moments from a V-bend change
according to the position of the bend.
 α moment –produced anteriorly
 Β moment - produced at molar

Centre bend
 Also called as
symmetric bend
 Equal & opposite
moments are created
 No forces are
produced

Off centre bend or asymmetric bend

OFF CENTRE BEND
 Position b/w 1/2 to 1/3 of distance
 Greater moment is generated in the bracket
closer to the V-bend.
 Opposite moments are generated at both ends.

 Opposite vertical forces

OFF CENTRE BEND
 At 1/3
 Greater moments at shorter arm.
 No moment at longer arm.
 Equal & Opposite vertical forces
 Represents cantilever system.

OFF CENTRE BEND
 At < 1/3 of distance
 Opposite vertical forces of greater magnitude
 Moments in same direction.
 Greater moment on shorter arm.

Step bend
 Equal & opposite
vertical forces
 Equal unidirectional
couple
 As the height of the
step increases the
vertical forces &
moments increase

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

RETRACTION IN BEGGS
 The Begg technique advocates a two-stage retraction
and it is not the only technique that uses this kind of
two-stage retraction
 the first stage involving distal tipping of the anterior
crowns with elastomerics and/or interarch elastics.
 Begg brackets permit only a point contact between
bracket and archwire, no moment is produced by wire
bracket interaction.
 As a result, only uncontrolled tipping of the anterior
teeth (center of rotation between the apex and the
center of resistance) occurs during the first stage of
retraction.

 The second stage involves
lingual torquing of the
anterior roots, usually by
means of a torquing auxiliary.
 A moment-to-force ratio of
about 12:1 is required for
such movement and such a
high ratio is technically
difficult to achieve. For this
reason, two-stage retraction
with initially uncontrolled
tipping is not the most
efficient retraction method.
 (JCO 1991 Jun(364 - 369):
Clinical Considerations in the
Use of Retraction Mechanics -
JULIE ANN STAGGERS, &
NICHOLAS GERMANE)

RETRACTION MECHANICS IN EDGEWISE
 Friction mechanics or sliding mechanics
 Friction less or loop mechanics

FRICTION
 Friction-a function of the relative roughness of
two surfaces in contact. It is the force that resists
the movement of one surface past another and
acts in a direction opposite the direction of
motion.

Resolved in 2 components –
 Frictional component - parallel but opposing the
motion
 Normal component – perpendicular to contacting
surfaces and to frictional component
F = µ N
 F is frictional force
 µ is coefficient of friction.
 N is normal force

 Friction is of two types-
 Static friction – is the smallest force needed to start
the motion of solid surfaces that were previously at
rest.
F = µs N
where µs is coefficient of static friction
 Kinetic friction- is the force that resist the sliding
motion of one solid object over another at constant
speed (acts during the period of motion itself)
F= µk N
where µk is coefficient of kinetic friction
 Static friction is considered to have a greater effect
on preadjusted mechanics than dynamic friction

Friction mechanics or sliding mechanics
 sliding mechanics involves either moving the bracket along an
arch wire or sliding the archwire though brackets and tubes
 Advantages
 Minimal wire bending time
 More efficient sliding of arch wire through post. Bracket slots
 No running out of space for activation
 Patient comfort
 Less time consumption for placement
 Disadvantages
 Confusion regarding ideal force level
 Tendency of overactive elastic & spring force  initial tipping
& inadequate rebound time for uprighting if forces are
activated too frequently
 Generally slower than loop mechanics due to friction

MECHANISM OF ACTION OF FRICTION MECHANICS

MECHANISM OF ACTION OF FRICTION MECHANICS
 To move a tooth
bodily, the force
should pass through
centre of resistance
of tooth.
 When force is applied
on crown, tooth
experiences both
moment (in 2 planes)
& force
 One moment tends to
rotate the tooth
mesial- out & other
distal tipping.

 Mesial out rotation is undesirable side effect
 Distal tipping  retraction, by binding the arch
wire which in turn produces moment results in
distal root movement hence uprighting of tooth.
 As tooth uprights moment es until wire no↓
longer binds.
 Again canine retracts along arch wire till tipping
again causes binding

ROLE OF FRICTION IN ELICITING BIOLOGICAL RESPONSE
 Both static and kinetic sliding friction arise in an arch wire through a bracket
or a bracket along an arch wire.
 Initially, upon appliance activation, the delivered force is sufficient to
''overcome" friction (to exceed the maximum static frictional force in
magnitude) and the tooth/teeth are displaced.
 This movement continues until the resistance of the deformed periodontal
support structure builds to a value which, when added to the kinetic frictional
force, offsets the delivered force and tooth motion temporarily ceases.
 As time proceeds, periodontal remodeling affects resistance potential, and
occlusion, wire resiliency, and masticatory action alter the mean resultant
normal force between bracket and wire, so that the "friction lock" is broken
and reset over and over again.
 Hence, in the presence of appliance friction, tooth movement apparently
occurs as a sequence of very short steps or jumps rather than as a smooth,
continuous motion.
 Frictional resistances between orthodontic bracket and arch wire -
Frank AJO-DO Volume 1980 Dec (593 - 609):

FORCE DELIVERY SYSTEM :
1. ELASTOMERICS
 1. ELASTIC MODULES WITH LIGATURE :
( Active tie backs)
 This method was popularized by BENETT & MCLAUGHLIN
(controlled space closure with preadjusted appliance
system) JCO 1990 April.

 An elastic module is stretched by 2-3mm(ie) twice
its normal length
 it usually delivers 0.5 - 1.5mm of space closure
per month.
 Tie backs are replaced every 4-6 weeks. Modules
generate 50-100 gm of force if module was pre
stretched before use.
 If used directly from manufacture without pre-
stretching force delivered is greater.

 Alternate systems found to be disadv. to this
in following aspects
 Power chain- variable force, difficult to keep
clean, some times falls off
 Elastic bands- Applied by patient,
inconsistent results due to cooperation factor
 Stainless steel coil spring- deliver excessive
force, unhygenic

 Elastomeric Chains
 Introduce in 1960’s
 Can be used for canine retraction, diastema closure,
rotation correction.
 Advantages.
 Inexpansive
 Relatively hygienic
 Easily applied without arch wire removal
 Not depend on pt. cooperation
 Disadvantages
 Absorb water & saliva
 Permanent staining after few days in oral cavity
 Stretching - breakdown of internal bonds –permanent
deformation
 Force degradation- variable force levels- effectiveness↓
 Can untie or break if not placed with care

 Configurations
 Closed loop chain
 Short filament chain
 Long filament chain
 Clinical considerations
 M/F is lowest at initial placement of E-chain distal crown
tipping of canine
 As tooth retracted M/F es due to dissipation of E force &↑ by
binding the arch wire produces moment results in uprighting of
tooth.
 For optimize tooth movement sufficient time should be allowed
for distal root movement
 A common mistake to change elastic chain too often-
maintaining high force & M/F which produce distal tipping only
 Even if extraction spaces are closed by tipping canines
distally, maintaining the space closure will be difficult
without also moving the roots distally.
 Hyalinization around canine & direct resorption of pos.  anchor
loss
 E-chain or module should be changed at interval of 4-6 weeks.

 Maxillary canine retraction with retraction spring
and sliding mechanics - Ziegler and Ingervall
AJO-DO Volume 1989 Feb (99 - 106):
 The efficiency of maxillary canine retraction by
means of sliding mechanics along an 0.018-inch
labial arch and an AlastiK chain was compared
with that using the canine retraction spring
designed by Gjessing.
 The canine was retracted faster and with less
distal tipping with the spring than with the sliding
mechanics. The canine retraction spring was not
Superior to the sliding mechanics in controlling
canine rotation during the retraction.
 the correction of rotation after the retraction is
less time-consuming than the uprighting of a
tipped canine and places much less demand on
the anchorage.

Closed coil springs
 Coil springs were introduced to the orthodontic
world as early as 1931.
 Nagamoto suggested that the "pulling action"
delivered by closed coil springs is more delicate, and
such a force is desirable during the course of
orthodontic treatment.
 The various materials that have been used for
making springs are
 Stainless steel
 NiTi
 Co-Cr Ni alloy

 Stainless steel coil spring
 Apply more predictable level of force than force elastics
 Easy to apply
 But have high LDR as compare to NiTi, so as space closes,
some force degradation due to lessening activation
 NiTi close coil spring
 The concept of Nickel titanium coil springs was introduced in
1979.
 The force degradation is very less due to the low load
deflection rate. Produce more consistent space closure than
elastics
 Indicated if large spaces need to close or infrequent
adjustment opportunities

 Two sizes avaliable – 9 mm & 12 mm
 Springs should not be extending beyond
manufacture Recommend (22mm for 9 mm
spring, 36 mm for 12 mm springs)
advantages of NiTi coil springs
 Can be easily placed and removed without
archwire removal
 Do not need to be reactivated at each
appointment
 Patient co-ordination not required.

 Nickel-titanium spring properties in a simulated
oral environment
Sangkyu Han, Donald C. Quick. Angle
Orthodontist 1993 No. 1, 67 - 72:
 A study of nickel-titanium springs was undertaken
to determine whether their mechanical properties
are affected by prolonged exposure to a static,
simulated oral environment. Stainless steel
springs and polyurethane elastic chains were also
studied for comparison
 Nickel-titanium springs suffered no degradation of
their spring properties in the simulated oral
environment. In contrast, stainless steel springs
became slightly more compliant to stretching, and
polyurethane elastics lost a large portion of their
force-generating capacity.

Force degradation of closed coil springs - Angolkar,
Arnold, Nanda, and Duncanson AJO-DO Volume 1992
Aug
 examines the force degradation coil spring of SS
Co-Cr-Ni and NiTi coil springs they concluded that
 All springs showed force loss over time
 The major force loss was found to occur in the first
24 hours for most springs.
 coil springs showed a 8% to 20% force loss at the
end of 28 days, which is relatively lower than the
force loss shown by latex elastics and synthetic
elastic modules.

A clinical study of space closure with nickel-titanium
closed coil springs and an elastic module R. H. A.
Samuels, AJO-DO 1998 Jul (73 – 79)
 1.Sentalloy nickel-titanium closed coil springs
produce more consistent space closure than an
elastic module.
 2. 150- and 200-gram springs produce a faster rate
of space closure than either the elastic module or
the 100-gram spring.
 3. No significant difference was found in the rates of
space closure caused by the 150-gram and 200-
gram springs.

EFFECT OF ENVIRONMENTAL FACTORS ON E- CHAIN & NITI-COIL
SPRINGS. Claire Nattrass (EJO-1998-vol20/169-176)
 Temp variations affected both E-chain and NITI coil
springs
 E-chains – Effect of temp was more profound. Force loss
greater at higher temp.
 NITI springs- overall effect of temp was smaller. Force
loss greater at lower temp.
 This is due to modifications in the crystal structure of
the alloy
 E-Chains are also affected by other environmental
factors such as food. The gross colour change is a
common clinical finding in patients who consume spicy
foods.
 Force decay of E-chain was more in carbonated drinks
than in water which may be due to low PH

 Dixon et al (JO 2002) compared the rates of
orthodontic space closure using active ligatures,
polyurethane power chains and NiTi springs.
 Mean rates of space closure were 0.35 mm with
active ligatures, 0.58 mm with powerchains and 0.81
mm with Ni Ti springs.
 The difference between the rate of closure between
NiTi spring and active ligatures was significant.
 The authors concluded that NiTi springs are the
most rapid, and are the treatment of choice, but
power chains offer a cheaper option.

Problems During Space Closure
 4. DIRECT HEADGEAR RETRACTION
 J hook headgear, either of the straight pull or high pull
type is clipped on the archwire mesial to the canines to slide
them distally.
 Straight pull headgear allows swifter canine retraction
than the high pull type. However, this may cause anterior
extrusion (Perej et al 1980; Hickham 1974) and
unfavourable occlusal plane rotations (Bowden 1978). This
might specially be a problem in high maxillomandibular
angle cases.
 High pull headgear may cause more bodily retraction.
However, it is not as efficient for distal movement, needing
prolonged periods of wear for modest results.

 Mulligan’s V bend sliding mechanics
 V bend is placed towards the molars thus more moment for
anchorage
 Canine is at long segment initially tips as less moment
 But as the space closes moment increases and cause its
translation
 Finally V bend will become centre bend and root paralleling takes
place

 Employing tip edge bracket on canines
 In case of upright or distally tipped canine
(deepening of bite & lateral open bite) Tip edge
bracket
 Prevent binding between AW & slot during initial
stages when major movements
 After retraction is comp.- uprighting spring to
correct angulation without ant. Extrusion
 Full size rectangular wire can be placed for
desired tip/torque specifications.

Effects of Overly Rapid Space Closure
• Space closure typically occurs
more easily in high-angle
patterns with weak
musculature than in low-angle
patterns with stronger
musculature.
• The rate of closure can be
increased, particularly in high-
angle cases, by slightly raising
the force level or using thinner
archwires. However, more
rapid space closure can lead to
loss of control of torque,
rotation, and tip.

• Loss of torque control results in
upper incisors being too upright at
the end of space closure with spaces
distal to the canines and a
consequent unaesthetic appearance.
• The lost torque is difficult to regain.
• Also, rapid mesial movement of the
upper molars can allow the palatal
cusps to hang down, resulting in
functional interferences, and rapid
movement of the lower molars
causes "rolling in"

 Reduced rotation control
can be seen mainly in the
teeth adjacent to
extraction sites, which also
tend to roll in if spaces are
closed too rapidly
 Reduced tip control
produces unwanted
movement of canines,
premolars, and molars,
along with a tendency for
lateral open bite.
 In high-angle cases,
where lower molars tip
most freely, the elevated
distal cusps create the
possibility of a molar
fulcrum effect


 In some instances,
excessive soft-tissue
hyperplasia occurs at
the extraction sites
 this is not only
unhygienic, but it can
prevent full space
closure or allow
spaces to reopen after
treatment.
 Local gingival surgery
may be necessary in
such cases.

Inhibitors to Sliding Mechanics
• Proper alignment of bracket slots is
essential to eliminate frictional
resistance to sliding mechanics.
• The common procedure is to use .
018" or .020 " round wire for at
least one month before placing .
019"´.025" rectangular wires.
• Leveling and aligning continues for
at least a month after insertion of
the rectangular wires, and that
space closure cannot proceed
during that period.

 Therefore the rectangular wires are tied passively
for at least the first month, until leveling and
aligning is complete and the archwires are passively
engaged in all brackets and tubes
 Conventional elastic tiebacks are than placed ,In
some cases, this phase takes three months.

VARIABLES AFFECTING FRICTIONAL RESISTANCE
DURING TOOTH MOVEMENT
 PHYSICAL
 ARCHWIRE
 LIGATION
 BRACKET
 ORTHODONTIC
APPLIANCE
 BIOLOGICAL
 SALIVA
 PLAQUE
 ACQUIRED PELLICLE
 CORROSSION
NANDA& KULHBERG

 PHYSICAL HYSICAL
 ARCHWIRE
 crossectional size/shape
 material
 surface texture
 stiffness
 LIGATION
 ligature wires
 elastomerics
 self ligating brackets
 BRACKET
 material
 manufacturing process
 slot width and depth
 first/second/third order bends
 ORTHODONTIC APPLIANCE
 interbracket distance
 level of bracket slots between
adjacent teeth
 forces applied for retraction
 Saliva
 Plaque
 Acquired pellicle
 Corrosion
BIOLOGICAL

Clinical Considerations in the Use of Retraction
Mechanics - JULIE ANN STAGGERS, DDS, MS, NICHOLAS
GERMANE, DMD, JCO Volume 1991 Jun(364 - 369)
 Wire selection
 Cobalt chromium, beta titanium, and nickel
titanium wires produce more friction than
stainless steel wires.
 Rectangular wires produce more friction than
round wires
 larger wires more than smaller wires
 0.016” s.s lowest friction not ideal wire (not
offer control) in three planes
 0.016X 0.022ss for 0.018 slot
 0.017x 0.022 or .019x .025 for 0.022 slot

 a. Wire material:
 Most studies have found stainless steel wires to be
associated with the least amount of friction.
 This is further backed up by specular reflectance
studies which show that stainless steel wires have
the smoothest surface, followed by Co-Cr, β-Ti,
and NiTi in order of increasing surface roughness.
 Kusy & Whitney (1990) found Stainless steel to
have least coefficient of friction & the smoothest
surface. However B titanium showed greater
friction compared to Ni Ti

 B. Wire Size: -
 Several studies have found an increase in wire size
to be associated with increased bracket-wire friction.
 In general, at non-binding angulations, rectangular
wires produce more friction than round wires.
However, at binding angulations, the bracket slot can
bite into the wire at one point, causing an indentation
in the wire.

C. Wire stiffness: Drescher et al (AJO-DO 1989)
stated that friction depends primarily on the vertical
dimension of the wire.
An 016” stainless steel round wire and an 016 x
022” stainless steel rectangular wire showed
virtually the same amount of friction. This was
however lower than that for 018 X 025” wires.
The authors stated however, that for mesiodistal
tooth movement, rectangular wire is preferred
because of its additional feature of buccolingual
root control.

2. Ligation method
 Various methods of ligation are available: - stainless
steel ligatures, elastomeric modules, polymeric coated
modules and finally the self ligating brackets, which may
be having a spring clip (Hanson SPEED and Adenta
Time) which pushes the wire into place, or it may have a
passive clip which does not press on the wire (Activa
and Danson II brackets.)
 Elastomeric ligatures are adversely affected by the oral
environment, and demonstrate stress relaxation with
time and great individual variation in properties.
 Stainless steel ligatures can be tied too tight or too loose
depending on the clinicians technique.

 Self ligating brackets with a passive clip have been
shown to generate negligible friction.
 Henao & Kusy (Angle Orthod. 2004) compared the
frictional resistance of conventional & self ligating
brackets using various archwire sizes.
 They reported that self ligating brackets exhibited
superior performance when coupled with smaller
wires used in early stages of orthodontic treatment.
 However when larger 016 x 022” and 019 x 025”
AW were tested, the differences between self-
ligating & conventional brackets were not so
evident.

3. Bracket
a. Bracket Material:
 For most wire sizes, sintered stainless steel brackets
produce significantly lower friction than cast SS
brackets. (upto 38-44% less friction.) This difference in
frictional forces could be attributed to smoother
surface texture of sintered SS material.
 Ceramic brackets, in spite of their superior esthetics,
have frictional properties far inferior to stainless steel.
Highly magnified views have revealed numerous
generalized small indentations in the ceramic bracket
slot, while SS brackets appear relatively smooth

 Since ceramic brackets on anterior teeth are often
used in combination with stainless steel brackets
and tubes on premolar and molar teeth, retracting
canines along an archwire may result in greater
loss of anchorage because of higher frictional
force associated with ceramic than steel brackets.
Greater caution in preserving anchorage must be
exerted in such situation.

 Titanium brackets are comparable to SS brackets
in the active configuration & are a suitable
substitute for SS in sliding mechanics.

 EFFECTS OF SALIVA ON KINETIC FRICTION
 SALIVA or saliva substitute serves as an excellent
lubricant in sliding of the bracket along the archwire.
 Kusy found that saliva had a lubricous as well as an
adhesive behaviour depending behaviour on the
archwire bracket combination.
 SS showed an adhesive behaviour with saliva and
there was a resultant increases in coefficient of friction
in the wet state

FRICTIONLESS MECHANICS
CANNE RETRACTION SPRINGS
EN MASS RETRACTION SPRINGS

frictionless mechanics
 In frictionless mechanics, teeth are moved without the
brackets sliding along the archwire.
 Retraction is accomplished with loops or springs,
which offer more controlled tooth movement than
sliding mechanics
frictionless system
 Disadvantages
 the complexity of loop forming
 the presence of unknown factors
 minor errors can result in major differences in
tooth movement
 some patients find the loop uncomfortable

 EVOLUTION OF LOOPS
 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 mechanics
 On the other hand Dr.P.R.Begg (1952) advocated their usage
in the initial phase of Begg treatment
 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.Poul Gjessing –
P.G.RETRACTION SPRING/AJO/1985,92
 Dr.Raymond Siatkowski- OPUS LOOP/AJO/1997

 General properties of the loops:
David lane (Angle orthodontist 1980)
 No loop exerts a truly continous force.
 Loops may be contoured to open or close up on
activation.
 The use of any loop will result in reduced stiffness and
greater range of activation because of increased
length of wire between brackets.

 Loop stiffness may be decreased by incorporating
helices in the loop or reducing cross sectional
dimensions of the wire of the loop.
 Elastic range of loop is increased if the loop is
activated in the same direction as it is formed.
(Bauschinger effect)

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 4 major
Characteristics
1. Spring properties
2. Moment it generates
3. Its location
4. Additional design principle
(WILLIAM.R.PROFFIT,II EDITION)

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 incorporated in the loop is
also important

FROM
WILLIAM.R.PROFFIT
II 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
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

• 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.

3.Its location
Its location is very important for its performance in closing space.
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
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
Controlled force designed to produce desire tooth movement at the
rate of appr. 1mm per month should not exceed 2mm per month
So movement would stop if patient missed appointment
Design should be as simple as possible
During activation of loop it is considered more effective when it is
closed rather than opened

OPEN VERTICAL LOOP
Dr.Robert.W.Strang
(1933).
 It was used for
retraction of
anterior teeth.
 Height of the loop
was 8mm.

CLOSED VERTICAL LOOP
 Only being
difference is
horizontal
overlapping

BULL LOOP
 Dr. Harry bull
(1951)
 variation of
standard vertical
loop
 Loops legs were in
contact with each
other
 .021x .
025stainless steel

VERTICAL OPEN LOOP WITH HELIX
 Dr Morris Stones
 Main purpose is to
increase the working
range
1975

OMEGA LOOP
 As mentioned by Dr
Morris Steiner this
loop is named so
because of the
resemblance to the
Greek letter omega.
The loop is believed to
distribute the stresses
more evenly

CLOSED VERTICAL LOOP WITH
HELIX (MORRIS STONER/1975)

DELTA LOOP
 It was described by Dr
Proffit.
 16 x 22-0.018 slot
 18 x 25-0.022 slot
 Approximately 20
degree angulation on
either side

OPUS LOOP
RAYMOND.E.SIATOWSKI AJODO 1997
 Opus loop, capable of
delivering a nonvarying
target M/F within the
range of 8.0 to 9.1 mm
inherently, without adding
residual moments via twist
or bends (commonly gable
bends) anywhere in the
arch wire or loop before
insertion

As the tooth moves the appld force decreases-
moment can ↑ or ↓
M/f changes as tooth moves and the tooth responds –
Controlled tipping-translation-root movement
Factors affecting the m/f of the opus loop
1. Wire size and young's modulus have little effect on
inherent m/f.[but a major impact on LDR]
2. The greatest effect on m/f-height of the loop

3. Increasing the number of apical helixes-lesser effect on m/f
4. Varying the loop diameter does not significantly affect the
m/f. It is maximized –loop dia 3.5mm
Position of the opus loop
it is always placed close to the ant end-1.5mm

Angulation of the vertical le-70 degrees to the plane of the
bracket
The experimental results with the opus loop show that the
opus loop has to be bent with great accuracy to achieve
the design potential

 Opus loop can be fabricated from 16×22, 18×25, or
17×25 TMA wire. The design of the loops calls for an
off center positioning with the loop 1.5 mm from the
mesial canine bracket. It is activated by tightening it
distally behind the molar tube and can be adjusted to
produce maximal, moderate or minimal incisor
retraction. (Siatkowski 2001).

T-LOOP
 T-LOOP is one of the most versatile space
closure devices available.
 This was developed by Charles Burstone in 1962.
 USES:
1. Segmental space closure:
a. Anterior retraction
b.Symmetric space closure
c.Posterior protraction
2. En-masse space closure

 ADVANTAGES:
The advantages of T-Loop over a
vertical loop :
1. Produces higher M/F ratio
2.Lower load deflection rate
3.Delivers more constant forces
Differential force system:
The force system produced by a segmented
T-loop consist of several components:
1. Alpha moment
2.Beta moment
3.Horizontal forces
4.Vertical forces

 Alpha moment : Produced by placing a bend on the mesial
leg of T-loop.It produces distal root movement of anterior
teeth.
 Beta moment : This is the moment acting on the posterior
teeth.It produces mesial root movement of posterior teeth.
 Horizontal forces: These are the mesio-distal forces acting
on the teeth. The distal forces acting on the anterior teeth
always equal the mesial forces acting on the posterior teeth.
 Vertical forces :These are intrusive-extrusive forces acting on
the anterior or posterior teeth. These forces results from
unequal alpha and beta moments.
10 mm
5 mm
2 mm
4 mm
ALPHA
(ANTERIOR) SEGMENT
BETA
(POSTERIOR) SEGMENT

 Fabrication:
- Made by .017 .025” TMA wire(Titanium-
molybdenum alloy).
Advantages of TMA over S.S wire
-Low modulus of elasticity
-Generate low force
-High range of action

 Preactivation Bends:
-To increase the moment- force
ratio by decreasing the force.
1
β α
2
3 4
65

The center position of the spring can be found by:
distance = (interbracket distance –activation)/ 2
where distance = length of the anterior and posterior arms (distance from
the center of the T loop to either the anterior or posterior tubes)
interbracket distance =distance between the canine and molar brackets.
Activation = millimeters of activation of the spring
Passive position
Neutral position Spring activated
T-loop position and anchorage control AJODO 1997

 Space closure should be monitored periodically. To
check the remaining activation, the spring is removed
from the canine bracket and the remaining activation
at the neutral position is measured
 Control of side effects:
 Tipping of the anterior and posterior segments into
extraction spaces.
 Flaring of the anterior teeth.
 Mesial in rotation of the buccal segments
 Excessive lingual tipping of anterior teeth.

MUSHROOM LOOP
 In this loop -apical addition of the wire in archial
configuration decreases the load deflection rate
and there for produces more lower and
continuous forces
Archial shape has added adv-increases the added
moment when the spring is activated

 0.017xo.o25 TMA
 Bypass premolars and directly engaged the molar
auxillary tube –allows force/moment delivery to
the active and reactive teeth directly
 Increase interbracket distance has the effect of
reducing the errors in the loop placement and
Maintains force cosistency
 Stabilize the posterior teeth with a transpalatal
arch and buccal segment
 Care taken –make a trial activation ,correct any
distortion that may occur under initial loading
 Loop activated up to 5 mm
 Reactivation done approximately every 6-8 weeks

Ricketts maxillary canine retraction
 Combination of
double closed helix
and an extended
crossed T
 In critical anchorage
case, 45° gable
bends and 0-5g/mm
of activation (Ricketts
1974)

Rapid canine retraction through Distraction of PDL
Eric JW Liou, DDS, MS, and C. Shing Huang,
D..AJODO .1998 oct
 procesure
 At the time of first premolar extraction, the interseptal
bone distal to the canine was undermined with a bone
bur, grooving vertically inside the extraction socket
along the buccal and lingual sides and extending
obliquely toward the socket base.
 Then, a tooth-borne, custom-made, intraoral
distraction device was placed to distract the canine
distally into the extraction space.
 It was activated 0.5 to 1.0 mm/day immediately after
the extraction. The anchor units were the second
premolar and first molar

 With this technique, anchorage teeth can withstand
the retraction forces with no anchorage loss and
without clinical or radiographic evidence of
complications, such as root fracture, root resorption,
ankylosis, periodontal problems, and soft tissue
dehiscence.
 technique reduces orthodontic treatment duration by
6 to 9 months in patients who need extraction, with
no need for an extraoral or intraoral anchorage
devices and with not unfavorable short-term effects in
the periodontal tissues and surrounding structures

NITI CANINE RETRACTION
SPRING JCO/JULY 2002
YASOO WATANABE, DDS, PHD
KEISUKE MIYAMOTO, DDS, PHD

Simple closing vertical loop with antitip &antirotation bend.
The major advantage of the spring is the ability to use it
without a preliminary leveling stage ,because it can
simultaneously retract the canine and level the posterior
teeth.

.016 * .022 titanal wire .10 mm loop is made
the vertical closing loop and the antitip and antirotation
bends were memorized by heat-treating the wire in an electric oven.
•Light continous force produced even large activation
Without the need for reactivation of the closing loops,
patient discomfort, chairtime, and appointment frequency can all be
reduced.
•A 2 × 4 appliance and a lingual arch and/or
transpalatal arch were used for-anchorage reinfocement

Retraction utility arch
 The retrusion arch originates in the auxiliary
tube on the molar, and 5-8mm of wire should
protrude anteriorly before a posterior vertical
step of 3-4mm is placed.
 The vestibular segment extends anteriorly to
the interproximal region between the lateral
incisor and the canine. At this point, a 90° bend
is placed

Activation
 Gable bend for intrusion
 The wire is pulled 2-3mm posteriorly and
then bent upward at a 90° angle for
retraction .

Canine retraction with j hook headgear
By Ayala AJO-DO 1980 Nov (538-547):

 The hook is attach mesial to the canines
 Head gear exert a force over them so that they will
slide along the wire
 Since this incorporates extraoral anchorage in canine
retraction, it should be effective in maximum
anchorage cases.
 Three different vectors of force, representing high,
medium, and low pull headgear, were applied.
 The high-pull force vector was placed at an angle of 40
degrees above the occlusal plane, the medium-pull at
20 degrees above, and the low-pull parallel to the
occlusal plane
 high-pull headgear produced the least tipping effect
during maxillary canine retraction

 PG retraction spring
 Poul Gjessing of denmark 1985

 Spring design
 made from 0.016 by 0.022 inch stainless steel wire.
 The predominant active element is the ovoid double helix loop
extending 10 mm apically.
 It is included in order to reduce the load/deflection of the spring
and is placed gingivally so that 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 tooth.
 The smaller loop occlusally is incorporated to lower levels of
activation on insertion in the brackets in the short arm (couple)

Clinical Application
 1. Alignment of the buccal teeth. The spring is
constructed to resist tendencies for tipping and
rotation during canine retraction
 .2 Adjustment of faciolingual loop inclination. The
correct faciolingual position of the spring
 3. Bracket engagement. The anterior extension of
the spring is engaged in the canine bracket. The
posterior extension must be engaged in both the
premolar and the molar
 4. Activation. The spring is activated by pulling
distal to the molar tube until the two loops
separate. The wire is secured with a gingival bend
in the posterior extension. Reactivation to the
initial spring configuration should be done every
four to six weeks.
 1.2mm of space closer takes place in 4 weeks

 A study was conducted (Divakar Karanth and V.
Surendra Shetty. JIOS 2002) to analyze the horizontal
force exerted and the load deflection characteristics of
the T-loop retraction spring and PG retraction spring
which were fabricated from different dimensions of
stainless steel, cobalt chromium, beta titanium and
titanium niobium wires and to compare them.
 The springs were fabricated on a template for
standardization purpose and horizontal forces exerted
by these springs were measured for every millimeter of
activation till 6 mm.
 The results of the study revealed that PG springs
exerted relatively low magnitude of force and relatively
constant load deflection rate when compared to T
spring.
 Beta titanium and titanium niobium springs showed
force values closer to the optimum force required for
translation of canines.

K-SIR ARCH
 By Dr VARUN
KALARA (JCO 98)

Fabrication
 19x25 TMA wire
 Closed 2x7 mm loop at the extraction site
 Indication
 Retraction of anterior teeth in the first PM extraction
with deep overbite and excessive overjet-require both
intrusion and maximum anchorage

A 90 bend is placed on the arch wire at the
level of loop that creates two equal and
opposite moments that counters tipping
moments produced by activation forces.

 An additional 60˚ v bend is placed at 2mm distal to u
loop. This is a off centered bend that creates greater
moments at molars to-
 Increase molar anchorage
 To intrude anterior teeth

 A 20 anti rotational bend is placed distal to
u loop to prevent buccal segment rolling
mesio -lingually

A trail activation is performed outside mouth
It releases stresses build up in wire bending
arch wire after trail activation with reduction in
severity of bends

Neutral position is determined with legs
extended horizontally
In neutral position loops are 3.5mm apart than 2
mm

Arch wire is placed and activated by 3mm and
cinched back
2nd
premolar is bypassed to increase inter bracket
distance

 Initially there is tipping but as loop starts
deactivating it produces bodily movement
than root movement
 Thus arch wire not to be reactivated at short
intervals but after 8 weeks.
 It produces 125 gm of intrusive force on the
anteriors.
 Adv- simultaneous retraction and intrusion
 Shortens treatment time

Statically determinate retraction
system
 This novel system consisted of a single-force
cantilever arm
 Made of 0.017 x 0.025 TMA wire for active
retraction
 active component for space closure is a cantilever,
it is simple to measure the force system
of the spring with a force gauge

The system consists of passive rigid stabilizing units and
active retraction springs.
Rigid stainless steel wire is used for the buccal
stabilizing units and an anterior stabilizing unit.
The buccal stabilizing units are connected with a
transpalatalarch to the contralateral side.
The anterior stabilizing arch has a distal extension with a
hook about six mm superior to the canine bracket slot.
The SDRS spring is made with 0.017 3 0.025–inch
titanium molybdenum alloy wire. A turn of helix is placed
in front of the auxiliary tube for the molar and ended with
a hook at the anterior end. A 90 bend is placed in the
middle of the spring. The spring is activated 90 at the
helix as well. The hook from the SDRS spring and the
extension hook of the anterior segment are connected
with a ligature.

(A) The statically determinate
retraction system (SDRS)
before activation.
Activated shape of the SDRS
Note the indicated
locations of the center of
resistance for the anterior
and posterior
segments and the line of
action

Advantages
 SDRS uses frictionless mechanics
 The cantilever spring has a low load-deflection
rate, thus constant force
 The force direction changes minimally and
remains constant during space closure
 Its force system can easily be visualized &
measured and can be modified by the clinician.

Three piece intrusion and retraction
Bhavna Shroff, Won M. Yoon, Steven J. Lindauer
Angle Orthodontist 1997 No. 6, 455 - 461

Principle
 Applying an intrusive force parallel to the long
axis of the incisors and lingual to the center of
resistance of the anterior segment of teeth is
a more efficient means of achieving
simultaneous intrusion and retraction of these
teeth

Design
 Arch consists ofA rigid anterior segment of wire
(0.021" x 0.025" or larger stainless steel) is placed into
the brackets of the four incisors and extended distally
to the mesial aspect of the canines.
 This anterior wire is stepped up around the canines to
avoid any interferences with the brackets. Typically,
this anterior segment extends 2 or 3 mm distal to the
center of resistance of the anterior segment of teeth
 Bilateral tipback springs of 0.017" x 0.025" TMA the
wire is bent gingivally mesial to the molar tube and the
helix is formed .the mesial end of the cantilever is bent
in to a hook .the cantilever than activated by making
bend mesial to the helix at the molar tube, such that
anterior end lies passively in the vestibule

 Intrusive force- 60 g at the midline (30 g per
side).
 Distal force is added by placing an
elastomeric chain or elastic extending from
the molars to the anterior segment of wire on
each side

TRANSLATION ARCH JCO/1997
MARTINA

 016" × .022" TMA for .018" bracket slots.
 The anterior segment of the Translation Arch is
inserted into the incisor brackets, and the two buccal
segments into the gingival first molar tubes
 Two loops, extended as far vertically as possible,
connect the anterior and posterior segments. The
bends in the TMA wire should be rounded to avoid
fracturing the wire.
 Translation Arch is easy to manage clinically.
 The system of forces and moments required for bodily
incisor retraction is quite complex

Magnets
 Magnetic force systems in
orthodontics - Blechman AJO-DO
Volume 1985 Mar (201 - 210)

 The use of operator-controlled, small,
permanent magnets for inter-maxillary and
intra maxillary mechanics.

 Upper and lower magnetic poles in attraction must
face each other in order to generate the force
necessary to move the upper canine distally along
the base arch wire and the lower buccal segments
mesially along the base wire
 The force that is developed is determined solely by
the distance that is set between the magnetic
poles, that is, the air gap.
F ∞ 1∕distance²

 Upper canine retraction can be enhanced, if needed, by
the addition of a third magnet attached to the lower
sectional arch and positioned mesially to repel the upper
magnet.
 Anchorage for the lower arch is protected by a full heavy
arch wire.

 Intramaxillary magnetic forces to close
spaces.

The Hycon Device
 The Hycon Device for extraction space closure was
developed in Germany orthodontist Dr. winfried
schutz in 1980s.
 This system uses a screw mechanism that is
attached posteriorly to the molar tube and
anteriorly to the anterior segment to be retracted.
 The nut and bolt assembly can be turned by the
patient for space closure.
 It is compatible with all common fixed appliances.

Use of implants to facilitate retraction
mechanics
 In recent years, with the introduction of miniscrews,
palatal implants and miniplates, absolute
anchorage or skeletal anchorage has become a
reality.
 In case of direct anchorage, a miniscrew or
miniplate is inserted near the upper first molar
during retraction of anterior segment.
 Nickel titanium coil springs or elastics are used to
connect this bone anchor with the anterior
segment.
 In many cases, incisors and canines can be
distalized simultaneously with sliding mechanics.

A comparison between friction and frictionless
mechanics with a new typodont simulation system
Joon-No Rhee, DDS, MSD,a Youn-Sic Chun DDS, MSD, PhD,b and Joon
Row, DDS, MSD, PhDc (Am J Orthod Dentofacial Orthop 2001;119:292-9)
 This study was designed to explore the differences
between friction and frictionless mechanics for
maxillary canine retraction with the use of a new
typodont simulation system, the Calorific machine
system.this study concluded that
 Friction mechanics were superior to frictionless
mechanics for rotational control and arch dimensional
maintenance. Frictionless mechanics were more
effective than friction mechanics at reducing the tipping
and extrusion.
 There was no significant difference in anchorage loss
between the 2 methods.
 This study could not establish the superiority of 1 of
the 2 methods over the other.

conclusion
 Today's orthodontist needs a working
knowledge of both friction and frictionless
mechanics. There are indications for both,
and therefore a practitioner should not be
limited to one or the other.

Retraction mechanics

More Related Content

What's hot

Viewers also liked

Similar to Retraction mechanics

More from Tony Pious

Recently uploaded

Retraction mechanics