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INDIAN DENTAL ACADEMY
Leader in continuing dental education
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MOMENT
TO
FORCE
RATIO
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INTRODUCTION

Understanding the biomechanics is
essential to determine the working of
an appliance system and more
importantly the undesirable changes
associated with it.
This seminar tells about the basic
concepts of biomechanics and their
importance in clinical application
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FLOW CHART OF THE PRESENTATION
DEFINITION OF THE BASIC CONCEPTS
PAE

Various
stages

EXTRA
ORAL

Head gears

COMMON SENSE MECHANICS
MOLAR CONTROL

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BEGG

Various
stages
F

O

R

C

E

DEFINED as a load applied to an object that will
tend to move it to a different position in space
. Forces may be treated as vectors and are conveniently
represented as arrows. A force vector is characterized by
four features: magnitude, point of application, line of
action, and sense.
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The parallelogram method for resolving a force into vertical
and horizontal components.
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F

O

R

. The parallelogram method of determining the resultant of
two forces with a common point of application.

C

E
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Couple force

A, Two equal and opposite, parallel, forces form a couple. B, The
translational effects of the forces cancel each other out, but the
moments of each force combine. The result is a moment with no net
force.
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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 analogus to center of mass for a restrained
body is CENTER OF RESISTANCE

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CENTER OF ROTATION

The point around which rotation
actually occurs when an object is
being moved

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Defined as the rotational tendency when force is
applied away from the center of resistance
M
O

A force acting at a distance
Mathematically given as M = f x d
Where M is the moment

M

f is the force

E

And d is the perpendicular distance of the line of
action to the center of resistance

N
T
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F

Direction of a moment

O

R

C

E

The direction of the moment of a force can be determined by
continuing the line of action around the center of resistance
towards the point of origin.
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The force in A, passing
through the center of
resistance, will result in
translation of the tooth. The
force in B, at the bracket,
will also translate the tooth
but, in addition, will cause a
rotation because of the
moment created at the
center of resistance.

Teeth move according to the forces and moments acting at the center
of resistance. Most orthodontic forces are applied to the tooth at the
bracket. Understanding the relationship between force systems at the
bracket and the center of resistance requires using the rules for
equivalent force systems.
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Force applied on a tooth
Crown moves more than root
To maintain the inclination
Of the tooth
Overcome the moment
Created by the force applied
to the crown

Counter moment
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To maintain axial inclination
Apply the force close to
the center of resisitance

Create a 2nd moment
In the direction opposite
to the first

Practical difficulty

Counter moment

Power arm

Tooth remain upright
And move bodily
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M/F (moment to force ratio) is the relationship
between the force and the counter balancing
couple that determines the type of tooth movement .
Various tooth movements
Uncontrolled tipping
Controlled tipping
Translation
Root uprighting
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Consider the moment created when force is applied Mf and the
counter balancing moment generated by the couple within the
bracket Mc
Mc/Mf = 0 –Pure tipping Crot and cres same,thus the
tooth rotates around the Cres

0 < Mc/Mf >1- Controlled tipping – Crot displaced away
from Cres – crown and root move in the same direction

Mc/Mf = 0 – Bodily movement – equal movement of crown
and root

Mc/Mf > 1 Torque – root apex moves further than the
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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
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Bracket system
P

A

A rectangular wire in
a rectangular slot

TORQUE
Generate the moment
of a couple necessary
to control root
position

E
Torque acting as the
counter moment
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Bracket system
P

TIP

In the PAE bracket system,
the tip incorporated into the
bracket acts as the counter
moment in the mesio distal
direction

A

E

This prevents the tipping
of the tooth in the mesio
distal direction

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Bracket system
P

Bracket width and interbracket span
The width of the bracket
on a tooth determines the
length of the moment arm
for the control of the
mesiodistal root position

A

E

Inter bracket span increases
Increase in the length of the wire
Increased flexibility
Decreased forces
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Principle of power arm

The line of action of the force passes through the center
of resistance. This tooth will translate, even though the
point of attachment to the tooth is at the bracket.

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A
L
I
N

Lingually malposed premolar
Aligning wire engaged
Bucally directed simple tipping
First order angular displacements
Of the adjacent teeth

G

To counteract
I
N
G

Decrease the magnitude
of the force

Broad distribution of
Responsive force

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A
L
I
N

Canine tip
When increased - during aligning there is a
tendency for the canine to be thrown forward
- tends to deepen to the bite

To counter act

G

Reduce the canine tip (MBT)
I

Placement of canine lace back

N
G

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L
E
V
E

Arch leveling

Reverse curve of Spee. The
vertical forces cancel out in the
manner shown, but moments
produced at either end of the
archwire result in torques on the
incisors and molars (anterior
lingual root torque or labial crown
torque; posterior mesial root torque
or distal crown torque).

L
I
N
G

Since intrusion is placed on the incisor segment, and
because the molars then become the reciprocal teeth, they
incur eruptive forces. Since extrusive forces acting through
the molar tubes usually result in lingual crown torque on the
molars, we have the potential for lingual crown movement
(lingual "dumping").
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L

Highly placed
canine

E

Continuous arch
wire

V
E

Intrusive force on
lateral greater than
the extrusive force
on canine

L
I
N
G

Engage a continuous
wire only after
reasonable aligning of
the anterior segment
excluding canine

Lateral intrusion rather
than canine extrusion due
to the increased root
length of canine

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Round wire with reverse curve of Spee
Lower premolars extruded
B
I
T
E
O
P
E
N
I
N
G

Tipping of the lower molar
Forward tipping of the lower incisors
To counteract
Cinched back
Roots of the lower incisor thrown forward
Forward mvt.of lower In.
Forward mvt of lower molar
To counteract
Class III Elastics
Eruptive forces on lower In. and upper molars
To counteract
Highwww.indiandentalacademy.com
pull head gear or extractions
COUNTERACTING
EFFECTS OF
LEVELING WITH
ROUND WIRE

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Banding of the second molars
B
I
T
E
O
P
E
N
I
N
G

Second molars being at a higher level

Extrusion of the first molars

Opening of the bite
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Bioprogressive Therapy
Typical variations of the mandibular utility arch.

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UTILITY ARCHES
450 TIP BEND

DISTAL UPRIGHTING

300 ROTATION
DISTO LINGUAL ROTATON
2MM BUCCAL EXPANSION
BUCCAL ROOT TORQUE
450 BUCCAL ROOT TORQUE
BUCCAL EXPANSION
50 LABIAL ROOT TORQUE ON
LOWER INCISORS
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B
U
R
S
T
O
N
E
I
N
T
R
U
S
I
O
N

Segmented approach to
simultaneous intrusion
and space closure
. Comparison of force
system developed on
molar with identical 30
gm intrusive forces. A,
Perpendicular to the
occlusal plane. B,
Parallel to the incisor
long axis and lingual to
CR. Note reduction of
the moment on the molar
in B.
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B
U
R
S
T
O
N
E
I
N
T
R
U
S
I
O
N

As the intrusive force is applied
more anteriorly to the center of
resistance of the incisors, a positive
moment is created which tends to
move the root lingually, provided the
incisor is restrained from flaring
labially.

Forces acting on the teeth from an
intrusive arch. The effect on the
molar is extrusion and a negative
rotation (crown-distal-root-mesial).
The moment (M) is equal to the
intrusive force (FA) times the
distance (L) from the incisor to the
center of resistance of the molar.

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B
U
R
S
T
O
N
E
I
N
T
R
U
S
I
O
N

Basic mechanism for intrusion; posterior anchorage
unit, anterior segment in the four incisors, and an
intrusive arch. The intrusion arch is placed in the
auxiliary tube on the first molar attachment.
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B
U
R
S
T
O
N
E
I
N
T
R
U
S
I
O
N

.
. Intrusive arch has been placed at the level of the
incisors. A double rope tie prevents arch from
being displaced into the mucobuccal fold if a tie
is accidentally lost.
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B
U
R
S
T
O
N
E
I
Force system of appliance.Note that the posterior
N
T extension allows force to be directed through the center of
R
resistance of the incisor. No incisor tipping will occur.
U
S
A long posterior extension is used to protrusive lower
I incisors to prevent flaring. The hook at the intrusive section
O
is shown.
N
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B
U
R
S
T
O
N
E
I
N
T
R
U
S
I
O
N

The extrusive force on the molar during incisor
intrusion tends to tip the crown lingually. This
can be prevented by using a lingual arch.
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T
H
R
E
E
P
I
E
C
E
A
R
C
H

A, Intrusive force through CR will intrude incisor
along line of action of this force. B, An intrusive
force perpendicular to the distal extension and
through CR will have the same effect as in A.
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T
H
R
E
E
P
I
E
C
E
A
R
C
H

Intrusive force can be directed
along long axis of anterior teeth
and applied lingual to CR. The
farther lingual the force, the
larger will be the moment acting
to tip the incisors lingually.
Direction of net intrusive force
through CR may be changed by
application of a small distal force.
The resulting intrusive force has a
direction parallel to the long axis
of the incisor and is distal to CR. .
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T
H
R
E
E
P
I
E
C
E
A
R
C
H

Diagrammatic representation of three-piece base arch.
The anterior segment extends 2 to 3 mm distal to the
center of resistance (CR) of the anterior teeth. Force
acts through center of resistance.
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T
H
R
E
E
P
I
E
C
E
A
R
C
H

Diagram of three-piece base arch and Class I elastic
stretched from maxillary first permanent molar to distal
extension of anterior segment. Class I elastics are
needed to redirect force parallel to the long axis of the
incisor.
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C
O
N
N
E
C
T
I
C
U
T
A
R
C
H

16 x 22 or 17 x 25 nickel titanium wire
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C
O
N
N
E
C
T
I
C
U
T
A
R
C
H

Intrusion force system consists of anterior intrusive
force, posterior extrusive force,and posterior tip back
moment
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C
O
N
N
E
C
T
I
C
U
T
A
R
C
H

Force system created by CTA and high-pull headgear. CTA force
system (red) consists of intrusive force on incisors, extrusive force
on molars, and moment tipping molar crowns distally. Headgear
(blue) produces intrusive force on molars and moment allowing
distal root movement. Purple arrow represents combined distal
force of CTA and headgear on molars.
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C
O
N
N
E
C
T
I
C
U
T
A
R
C
H

Force system for incisor flaring. CTA is not cinched
back, and can be ligated directly into incisor brackets for
maximum flaring.
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C
O
N
N
E
C
T
I
C
U
T

A. Force system for incisor extrusion, with CTA is inserted into
molar brackets upside down. Vertical forces shown are ideal for
A correction of minor open bites. B. Open-bite patient before
R treatment. C. Mechanics shown in A used to close bite, with highC pull headgear added to prevent forward tipping of molars and
H augment intrusive force of CTA on molars.
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K
S

19 x 25 TMA with
closed U loop 7mm long
and 2mm wide

I
R
A
R
C
H

90 degree bend placed in the arch wire at the level of the U
loop.centered V bend creates equal and opposite
moment(red) that counter tipping moment(green) produced
by activation forces www.indiandentalacademy.com
K
S
I
R
A

Off center v bend 60 degree placed 2mm distal to the loop
This bend creates an increased moment increased molar
anchorage and intrusion of the anterior teeth.

R
C
H

20 degree anti rotation
bends distal to the U loop

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S
P
A
C
E
C
L
O
S
U
R
E

INDIVIDUAL CANINE
RETRACTION

FRICTION

FRICTIONLESS

ENMASSE RETRACTION

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C
A
N
I
N
E
R
E
T
R
A
C
T
I
O
N

Individual canine retraction – friction mechanics
Initial controlled tipping of the tooth (m/f 8:1)
Force decay with time
Force level on the tooth decreases
M/f ratio is increased
Root uprighting
Walking of the canine
Do not change the power chain for 5 weeks ,let to
comlplete the root uprighting
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C
A
N
I
N
E
R
E
T
R
A
C
T
I
O
N

Lever arm adapted to
palatal vault and
bonded to lingual
surface of cuspid.
Extension soldered to
palatal bar, and
activation achieved
with buccal and
lingual Superelastic
coil springs.

Source: 1993 JCO: Modified Lingual Lever Arm Technique GERHARD KUCHER, MD, DDS, FRANK J. WEILAND, DDS,
HANS-PETER BANTLEON, MD, DDS, P.
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Schematic of force system: moments at lever arm and
bracket cancel each other out, resulting in net translation
force.

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Undesirable side effects from distal canine slide along
continuous arch: tipping, binding, lack of vertical
control and risk of anchorage loss, incisor extrusion
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C
A
N
I
N
E
R
E
T
R
A
C
T
I
O
N

Effect of pure horizontal force at the canine
bracket.
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C
A
N
I
N
E
R
E
T
R
A
C
T
I
O
N

Antitip and antirotation moment-to-force
conditions necessary for translation of
canines with average dimensions.
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C
A
N
I
N
E
R
E
T
R
A
C
T
I
O
N

PG retraction spring

Anti tip bend – 150 in
the mesial leg
Beta bend - 300 in the
distal leg

Anti rotation bend – 350

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C
A
N
I
N
E
R
E
T
R
A
C
T
I
O
N

T LOOP

The preactivated spring with the anti tip
and anti rotation is placed
Activation on insertion is 6mm
The m/f is 8:1 – controlled tipping
Now as the tooth moves the activation
reduced to 4mm – the force is reduced

M/f ratio is increased - bodily movement further
The activation is reduced to 2mm – force is
further reduced
M/f ratio increased – 12:1
Root uprighting
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C
A
N
I
N
E
R
E
T
R
A
C
T
I
O
N

T LOOP
Increasing the
gingival length of
the wire increases
the m/f ratio and
reduces the
deflection rate

Mesial leg angulated by150
Distal leg angulated by 300
Preactivation of 400
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E
N
M
A
S
S
E
F
R
I
C
T
I
O
N
L
E
S

Space closure
using a retraction
appliance.

Source: AJO-DO 1997 : Three-dimensional effects in
retraction appliance design D. W. Raboud, MSc, M. G.
Faulkner, MSc, PhD, A. W. Lipsett,..,.
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E
GROUP A ANCHORAGE
N
M
A
Distal force on anteriors
Mesial forces on posteriors
S
S Maximum potential for tooth mvt.
Miminised or counteracted
E
F
Increase moment
R
Decrease moment
I
C
Horizontal force acting on both segments are same
T
I
O
Moment to force ratio
N
L
E
Reactive unit
Anchor unit
S
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E
N
M
A
S
S
E
F
R
I
C
T
I
O
N
L
E
S

Alpha moment

Beta moment

Anteriors

posteriors
When unequal or unbalanced
Vertical forces created

Extrusion

Intrusion

alpha

alpha

beta

beta
Extrusion

Intrusion
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E
N
M
A
S
S
E
F
R
I
C
T
I
O
N
L
E
S

A. Vertical force anterior to center of resistance, producing
clockwise moment. B. Vertical force posterior to center of rotation,
producing counterclockwise moment.
Source: JCO 1990 : Vertical Force Considerations in Differential
Space Closure - BIRTE MELSEN, DO, VASSILI FOTIS, DDS,
MSD,www.indiandentalacademy.com
CHARLES J. BURSTONE,
E
N
M
A
S
S
E
F
R
I
C
T
I
O
N
L
E
S

Beta moment greater than
alpha moment, producing net
intrusive force on anterior
teeth and extrusive force on
posterior teeth. B. Alpha
moment greater than beta
moment, producing net
intrusive force on posterior
teeth and extrusive force on
anterior teeth. C. Equal alpha
and beta moments, producing
no vertical component of
force.

Source: JCO 1991 JULIE ANN
STAGGERS, DDS, MS, NICHOLAS
GERMANE, DMD

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E
N
M
A
S
S
E
F
R
I
C
T
I
O
N
L
E
S

With retraction spring, alpha moment produces distal root
movement of anterior teeth; beta moment produces mesial
root movement of posterior teeth.

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E
N
M
A
S
S
E
F
R
I
C
T
I
O
N
L
E
S

GROUP B ANCHORAGE
Distal force on anteriors

Mesial forces on posteriors

Equal potential for tooth mvt.
Alpha moment

EQUAL

Beta moment

Horizontal force acting on both segments are same

Moment to force ratio
EQUAL
RETRACTION OF ANTERIOR
PROTRACTION OF POSTERIOR

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E
N
M
A
S
S
E
F
R
I
C
T
I
O
N
L
E
S

GROUP C ANCHORAGE
Distal force on anteriors
Minimized or counteracted

Mesial forces on posteriors
Maximum potential for tooth mvt.

Increase moment

Decrease moment

Horizontal force acting on both segments are same

Moment to force ratio
Reactive unit

Anchor unit
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E
N
M
A
S
S
E
F
R
I
C
T
I
O
N
L
E
S

Burstone and koenig 1976 AJO
Three primary characteristics of retraction loops
1.moment to force ratio
2.the force at yield
3.the force to deflection rate
Factors that influence m/f
Height of the loop
Horizontal loop length
Apical length of the wire
Placement of the loop
Helix incoporation
Angulation of loop www.indiandentalacademy.com
legs
E
N
M
A
S
S
E
F
R
I
C
T
I
O
N
L
E
S

Gradual sweep versus an acute bend
Acute bend
Force concentrated on the premolar
Mesial tipping of the premolar
Undesirable
No undesirable
tipping

Gradual sweep

Force being distributed
molar and premolar

Uniform distribution of the
force and no concentration
of the force on a particular
tooth

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E
N
M
A
S
S
E

F
R
I
C
T
I
O
N

SLIDING MECHANICS

The hook is soldered at the center of resistance of the anterior
segment and active tie backs are placed from the molar hook to
the soldered hook.
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B

Conventional Begg – type of tooth movement is
uncontrolled or free tipping of the tooth

E

Amount of force required for this is less and
the moment to force ratio is also decreased

G

Uncontrolled tipping is not desirable as it hastens root
resorption and control of the tooth movement is also
difficult (source: Biomechanical principles and reacions,
Reitan1985)

G

Refined Begg – controlled
tipping
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B

E

G

G

Stage 1

Intrusion and tipping of the incisors simultaneously
Intrusive force – crown labial
root
lingual
Retractive force – crown lingual
Root labial

Moment of the intrusive force acts to counter moment the
moment of the elastic force
Moment of the intrusive force to the elastic force ratio
determine the type of tooth movement

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B

If the intrusive force is decreased
If the elastic force is increased

E

G

Moment to force ratio
Inadequate for
Controlled tipping

Thus, for controlled tipping
G

Keep the class II elastic force very light
Use adequate amount of intrusive force
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B

Anchor bend and the class II elastic force
Anchor bend

E

Distal crown
tipping of
molars

G
Retract the anterior
teeth

G

Class II elastics

Move the lower molar
forward bodily
Upright the lower
molars
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Intrusion
of anteriors
B

Torquing auxillary with spur
When spread along the wider curvature
Lingual torquing

E

G

The larger arc of the
anterior portion of the
wire roll inwards

Vertical plane in which the
aux orients when fitted into
the incisor is changed to the
horizontal plane of the arch
wire when tied to it

The tip of spur to press in a
lingual direction against the
gingival portion of the crown

G
Inter spur span – lift in a labial
direction
Counter act
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Bracket slot
Base arch wire
MAA

B

Light couple force
acting on each tooth

E

G

Lingual crown torque
with the intrusive
couple force

II stage

Intrusive force
reduced
Additional
moment created
by the MAA

G

Prevents labial tipping of
the lower incisors

Opposite to the elastic
force
M/F 8:1
Controlled tipping

Shortens the third stage
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C
O
M
M
O
N

Common sense mechanics Thomas F mulligan JCO
1979
Off center bend
Long segment

Short segment

S Points in the direction Points in the direction
E of the force produced opposite of the force
N on the tooth
produced on tooth
S
E
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Center bend
No short or long
segment

No force produced
C
O
M
M
O
N

S
E
N
S
E
www.indiandentalacademy.com
C
O
M
M
O
N

S
E
N
S
E

Differential torque - the
molar tip back bend
produces a large distal
moment on the molar and
a small labial moment on
the anterior segment in
spite of the force being
equal as the distances
involved are radically
different.

www.indiandentalacademy.com
Round wire
C
O
M
M
O
N

S
E
N
S
E

Rectangular wire

Line of action
Buccal to center of
resistance
Lingual crown
torque

Line of action
lingual to center of
Resistance
Buccal crown
torque

Begg stage l
expansion given to
prevent lingual
rolling of molars

Beta bend to
Produce buccal
Root torque

www.indiandentalacademy.com
CUE BALL CONCEPT
C
O
M
M
O
N

S
E
N
S
E

A force off
center causes
the cue ball to
rotate as well
as move
forward in a
straight line.

No left or right When the line
of force acts
rotation is
through the
produced when
center of
the force is
resistance,
applied through
only
the center of the
translation
cue ball.
results.
www.indiandentalacademy.com

Equal and
opposite
forces
(couple)
produce
pure
rotation.
C
O
M
M
O
N

S
E
N
S
E

ROW BOAT
EFFECT

If the tipback and torque bends produce equal
angular relationships (A), the net forces are zero. If
unequal (B), net forces occur.
This explains why there is extrusion with the
increase in the alpha bend.
Thus the length of the segment and the angulation
determine the tooth movement
www.indiandentalacademy.com
C
O
M
M
O
N

DIVING BOARD
CONCEPT
When the length of the diving
board is doubled, only one-eighth
the force is required to produce the
same amount of deflection. B. The
same force acting at twice the
length will produce eight times as
much deflection.

S
E
With a constant tipback
N
S angle, the deflection doubles
E as the wire length doubles,
the force is reduced to one
www.indiandentalacademy.com
fourth
M
O
L
A
R

Bends placed in the arch wire

Variety of force systems to produce a direct
response

Off set bend
C
O
N
T
R
O
L

Step bend
Center bend

Source : Thomas Mulligan JCO 2001

www.indiandentalacademy.com
M
O
L
A
R

OFFSET BEND
Short section of the wire points in the direction of
the long arm
Vertical forces acting through the molar tube
Intrusive

Lingual crown torque
C
O
N
T
R
O
L

Extrusive

Buccal crown torque

Narrowing of the post
Arch width

Widening of the post
Arch width

Reduction in the curve
of monson

Increase in the curve
of monson

www.indiandentalacademy.com
M
O
L
A
R

Rotations first displacement second

Toe in
Rotation correction required
Toe out

C
O
N
T
R
O
L

Represent the short section of the wire of the off
center bend
Bends located just mesial to the molars
www.indiandentalacademy.com
M
O
L
A
R

Toe out corrects the distal in and/ mesial out
rotation with horizontal lingual force

C
O
N
T
R
O
L
www.indiandentalacademy.com
M
O
L
A
R

Toe in corrects the mesial in or distal out with
horizontal buccal force

C
O
N
T
R
O
L
www.indiandentalacademy.com
M
O
L
A
R

In bend for the lingual displacement

C
O
N
T
R
O
L
www.indiandentalacademy.com
M
O
L
A
R

Out bend for the buccal displacements

C
O
N
T
R
O
L
www.indiandentalacademy.com
M
Step bend for the mesio lingulal rotation
O
with a lingual displacement
L
A When 2 bends are involved and each
Increases the
R bend produces a force in the same
force
direction
magnitude

C
O
N
T
R
O
L
www.indiandentalacademy.com
M
O
L
A
R

Center bend

C
O
N
T
R
O
L
www.indiandentalacademy.com
CERVICAL PULL HEAD GEAR
H
E
A
D

LOW OUTER BOW

Head gear force line of
action mesial to the center
of resisitance
Extrusive component
Distal component

G
E
A
R
S

Large moment that
Tends to steepen the
Occlusal plane
Clockwise
Moment

www.indiandentalacademy.com
CERVICAL PULL HEAD GEAR
H
E
A
D

OUTER BOW

Head gear force line of
action passing through the
center of resisitance

At the level of the
inner bow

Extrusive component
Distal component

G
E
A
R
S

No moment that
Tends to alter the
Occlusal plane

www.indiandentalacademy.com
CERVICAL PULL HEAD GEAR
H
E
A
D

High OUTER BOW

Head gear force line of
action distal to the center
of resisitance
Extrusive component
Distal component

G
E
A
R
S

Large moment that
Tends to flatten the
Occlusal plane
Anticlockwise
Moment

www.indiandentalacademy.com
HIGH PULL HEAD GEAR
H
E
A
D

SHORT OUTER BOW

Angulated high to create
head gear force line of
action anterior to the
center of resisitance
Intrusive component
Distal component

G
E
A
R
S

Large moment that
Tends to flatten the
Occlusal plane
Anticlockwise
Moment

www.indiandentalacademy.com
HIGH PULL HEAD GEAR
H
E
A
D

OUTER BOW

Angulated such that head
gear force line of action
passes through the center
of resisitance

Equal to the inner bow

Intrusive component
Distal component

G
E
A
R
S

No moment that
Tends to alter the
Occlusal plane

www.indiandentalacademy.com
HIGH PULL HEAD GEAR
H
E
A
D

LONG OUTER BOW

Angulated to create head
gear force line of action
posterior to the center of
resisitance
Intrusive component
Distal component

G
E
A
R
S

Large moment that
Tends to steepen the
Occlusal plane
Clockwise
Moment

www.indiandentalacademy.com
Conclusion
Newton’s third law states that every action has a
equal and opposite reaction.
Its important to keep this concept in mind working
with any appliance system and give adequate
importance to take steps to prevent the adverse
effects.
In orthodontic terms, the understanding of the
moment and the application of the necessary
counter moment to bring about the optimal tooth
movement is the key to successful treatment results
www.indiandentalacademy.com
Thank you
For more details please visit
www.indiandentalacademy.com

www.indiandentalacademy.com

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Indian Dental Academy: Moment to Force Ratio

  • 1. INDIAN DENTAL ACADEMY Leader in continuing dental education www.indiandentalacademy.com www.indiandentalacademy.com
  • 3. INTRODUCTION Understanding the biomechanics is essential to determine the working of an appliance system and more importantly the undesirable changes associated with it. This seminar tells about the basic concepts of biomechanics and their importance in clinical application www.indiandentalacademy.com
  • 4. FLOW CHART OF THE PRESENTATION DEFINITION OF THE BASIC CONCEPTS PAE Various stages EXTRA ORAL Head gears COMMON SENSE MECHANICS MOLAR CONTROL www.indiandentalacademy.com BEGG Various stages
  • 5. F O R C E DEFINED as a load applied to an object that will tend to move it to a different position in space . Forces may be treated as vectors and are conveniently represented as arrows. A force vector is characterized by four features: magnitude, point of application, line of action, and sense. www.indiandentalacademy.com
  • 6. The parallelogram method for resolving a force into vertical and horizontal components. www.indiandentalacademy.com
  • 7. F O R . The parallelogram method of determining the resultant of two forces with a common point of application. C E www.indiandentalacademy.com
  • 8. Couple force A, Two equal and opposite, parallel, forces form a couple. B, The translational effects of the forces cancel each other out, but the moments of each force combine. The result is a moment with no net force. www.indiandentalacademy.com
  • 9. 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 analogus to center of mass for a restrained body is CENTER OF RESISTANCE www.indiandentalacademy.com
  • 10. CENTER OF ROTATION The point around which rotation actually occurs when an object is being moved www.indiandentalacademy.com
  • 11. Defined as the rotational tendency when force is applied away from the center of resistance M O A force acting at a distance Mathematically given as M = f x d Where M is the moment M f is the force E And d is the perpendicular distance of the line of action to the center of resistance N T www.indiandentalacademy.com
  • 12. F Direction of a moment O R C E The direction of the moment of a force can be determined by continuing the line of action around the center of resistance towards the point of origin. www.indiandentalacademy.com
  • 13. The force in A, passing through the center of resistance, will result in translation of the tooth. The force in B, at the bracket, will also translate the tooth but, in addition, will cause a rotation because of the moment created at the center of resistance. Teeth move according to the forces and moments acting at the center of resistance. Most orthodontic forces are applied to the tooth at the bracket. Understanding the relationship between force systems at the bracket and the center of resistance requires using the rules for equivalent force systems. www.indiandentalacademy.com
  • 14. Force applied on a tooth Crown moves more than root To maintain the inclination Of the tooth Overcome the moment Created by the force applied to the crown Counter moment www.indiandentalacademy.com
  • 15. To maintain axial inclination Apply the force close to the center of resisitance Create a 2nd moment In the direction opposite to the first Practical difficulty Counter moment Power arm Tooth remain upright And move bodily www.indiandentalacademy.com
  • 16. M/F (moment to force ratio) is the relationship between the force and the counter balancing couple that determines the type of tooth movement . Various tooth movements Uncontrolled tipping Controlled tipping Translation Root uprighting www.indiandentalacademy.com
  • 17. Consider the moment created when force is applied Mf and the counter balancing moment generated by the couple within the bracket Mc Mc/Mf = 0 –Pure tipping Crot and cres same,thus the tooth rotates around the Cres 0 < Mc/Mf >1- Controlled tipping – Crot displaced away from Cres – crown and root move in the same direction Mc/Mf = 0 – Bodily movement – equal movement of crown and root Mc/Mf > 1 Torque – root apex moves further than the www.indiandentalacademy.com
  • 19. 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 www.indiandentalacademy.com
  • 20. Bracket system P A A rectangular wire in a rectangular slot TORQUE Generate the moment of a couple necessary to control root position E Torque acting as the counter moment www.indiandentalacademy.com
  • 21. Bracket system P TIP In the PAE bracket system, the tip incorporated into the bracket acts as the counter moment in the mesio distal direction A E This prevents the tipping of the tooth in the mesio distal direction www.indiandentalacademy.com
  • 22. Bracket system P Bracket width and interbracket span The width of the bracket on a tooth determines the length of the moment arm for the control of the mesiodistal root position A E Inter bracket span increases Increase in the length of the wire Increased flexibility Decreased forces www.indiandentalacademy.com
  • 23. Principle of power arm The line of action of the force passes through the center of resistance. This tooth will translate, even though the point of attachment to the tooth is at the bracket. www.indiandentalacademy.com
  • 24. A L I N Lingually malposed premolar Aligning wire engaged Bucally directed simple tipping First order angular displacements Of the adjacent teeth G To counteract I N G Decrease the magnitude of the force Broad distribution of Responsive force www.indiandentalacademy.com
  • 25. A L I N Canine tip When increased - during aligning there is a tendency for the canine to be thrown forward - tends to deepen to the bite To counter act G Reduce the canine tip (MBT) I Placement of canine lace back N G www.indiandentalacademy.com
  • 26. L E V E Arch leveling Reverse curve of Spee. The vertical forces cancel out in the manner shown, but moments produced at either end of the archwire result in torques on the incisors and molars (anterior lingual root torque or labial crown torque; posterior mesial root torque or distal crown torque). L I N G Since intrusion is placed on the incisor segment, and because the molars then become the reciprocal teeth, they incur eruptive forces. Since extrusive forces acting through the molar tubes usually result in lingual crown torque on the molars, we have the potential for lingual crown movement (lingual "dumping"). www.indiandentalacademy.com
  • 27. L Highly placed canine E Continuous arch wire V E Intrusive force on lateral greater than the extrusive force on canine L I N G Engage a continuous wire only after reasonable aligning of the anterior segment excluding canine Lateral intrusion rather than canine extrusion due to the increased root length of canine www.indiandentalacademy.com
  • 28. Round wire with reverse curve of Spee Lower premolars extruded B I T E O P E N I N G Tipping of the lower molar Forward tipping of the lower incisors To counteract Cinched back Roots of the lower incisor thrown forward Forward mvt.of lower In. Forward mvt of lower molar To counteract Class III Elastics Eruptive forces on lower In. and upper molars To counteract Highwww.indiandentalacademy.com pull head gear or extractions
  • 29. COUNTERACTING EFFECTS OF LEVELING WITH ROUND WIRE www.indiandentalacademy.com
  • 30. Banding of the second molars B I T E O P E N I N G Second molars being at a higher level Extrusion of the first molars Opening of the bite www.indiandentalacademy.com
  • 31. Bioprogressive Therapy Typical variations of the mandibular utility arch. www.indiandentalacademy.com
  • 32. UTILITY ARCHES 450 TIP BEND DISTAL UPRIGHTING 300 ROTATION DISTO LINGUAL ROTATON 2MM BUCCAL EXPANSION BUCCAL ROOT TORQUE 450 BUCCAL ROOT TORQUE BUCCAL EXPANSION 50 LABIAL ROOT TORQUE ON LOWER INCISORS www.indiandentalacademy.com
  • 33. B U R S T O N E I N T R U S I O N Segmented approach to simultaneous intrusion and space closure . Comparison of force system developed on molar with identical 30 gm intrusive forces. A, Perpendicular to the occlusal plane. B, Parallel to the incisor long axis and lingual to CR. Note reduction of the moment on the molar in B. www.indiandentalacademy.com
  • 34. B U R S T O N E I N T R U S I O N As the intrusive force is applied more anteriorly to the center of resistance of the incisors, a positive moment is created which tends to move the root lingually, provided the incisor is restrained from flaring labially. Forces acting on the teeth from an intrusive arch. The effect on the molar is extrusion and a negative rotation (crown-distal-root-mesial). The moment (M) is equal to the intrusive force (FA) times the distance (L) from the incisor to the center of resistance of the molar. www.indiandentalacademy.com
  • 35. B U R S T O N E I N T R U S I O N Basic mechanism for intrusion; posterior anchorage unit, anterior segment in the four incisors, and an intrusive arch. The intrusion arch is placed in the auxiliary tube on the first molar attachment. www.indiandentalacademy.com
  • 36. B U R S T O N E I N T R U S I O N . . Intrusive arch has been placed at the level of the incisors. A double rope tie prevents arch from being displaced into the mucobuccal fold if a tie is accidentally lost. www.indiandentalacademy.com
  • 37. B U R S T O N E I Force system of appliance.Note that the posterior N T extension allows force to be directed through the center of R resistance of the incisor. No incisor tipping will occur. U S A long posterior extension is used to protrusive lower I incisors to prevent flaring. The hook at the intrusive section O is shown. N www.indiandentalacademy.com
  • 38. B U R S T O N E I N T R U S I O N The extrusive force on the molar during incisor intrusion tends to tip the crown lingually. This can be prevented by using a lingual arch. www.indiandentalacademy.com
  • 39. T H R E E P I E C E A R C H A, Intrusive force through CR will intrude incisor along line of action of this force. B, An intrusive force perpendicular to the distal extension and through CR will have the same effect as in A. www.indiandentalacademy.com
  • 40. T H R E E P I E C E A R C H Intrusive force can be directed along long axis of anterior teeth and applied lingual to CR. The farther lingual the force, the larger will be the moment acting to tip the incisors lingually. Direction of net intrusive force through CR may be changed by application of a small distal force. The resulting intrusive force has a direction parallel to the long axis of the incisor and is distal to CR. . www.indiandentalacademy.com
  • 41. T H R E E P I E C E A R C H Diagrammatic representation of three-piece base arch. The anterior segment extends 2 to 3 mm distal to the center of resistance (CR) of the anterior teeth. Force acts through center of resistance. www.indiandentalacademy.com
  • 42. T H R E E P I E C E A R C H Diagram of three-piece base arch and Class I elastic stretched from maxillary first permanent molar to distal extension of anterior segment. Class I elastics are needed to redirect force parallel to the long axis of the incisor. www.indiandentalacademy.com
  • 43. C O N N E C T I C U T A R C H 16 x 22 or 17 x 25 nickel titanium wire www.indiandentalacademy.com
  • 44. C O N N E C T I C U T A R C H Intrusion force system consists of anterior intrusive force, posterior extrusive force,and posterior tip back moment www.indiandentalacademy.com
  • 45. C O N N E C T I C U T A R C H Force system created by CTA and high-pull headgear. CTA force system (red) consists of intrusive force on incisors, extrusive force on molars, and moment tipping molar crowns distally. Headgear (blue) produces intrusive force on molars and moment allowing distal root movement. Purple arrow represents combined distal force of CTA and headgear on molars. www.indiandentalacademy.com
  • 46. C O N N E C T I C U T A R C H Force system for incisor flaring. CTA is not cinched back, and can be ligated directly into incisor brackets for maximum flaring. www.indiandentalacademy.com
  • 47. C O N N E C T I C U T A. Force system for incisor extrusion, with CTA is inserted into molar brackets upside down. Vertical forces shown are ideal for A correction of minor open bites. B. Open-bite patient before R treatment. C. Mechanics shown in A used to close bite, with highC pull headgear added to prevent forward tipping of molars and H augment intrusive force of CTA on molars. www.indiandentalacademy.com
  • 48. K S 19 x 25 TMA with closed U loop 7mm long and 2mm wide I R A R C H 90 degree bend placed in the arch wire at the level of the U loop.centered V bend creates equal and opposite moment(red) that counter tipping moment(green) produced by activation forces www.indiandentalacademy.com
  • 49. K S I R A Off center v bend 60 degree placed 2mm distal to the loop This bend creates an increased moment increased molar anchorage and intrusion of the anterior teeth. R C H 20 degree anti rotation bends distal to the U loop www.indiandentalacademy.com
  • 51. C A N I N E R E T R A C T I O N Individual canine retraction – friction mechanics Initial controlled tipping of the tooth (m/f 8:1) Force decay with time Force level on the tooth decreases M/f ratio is increased Root uprighting Walking of the canine Do not change the power chain for 5 weeks ,let to comlplete the root uprighting www.indiandentalacademy.com
  • 52. C A N I N E R E T R A C T I O N Lever arm adapted to palatal vault and bonded to lingual surface of cuspid. Extension soldered to palatal bar, and activation achieved with buccal and lingual Superelastic coil springs. Source: 1993 JCO: Modified Lingual Lever Arm Technique GERHARD KUCHER, MD, DDS, FRANK J. WEILAND, DDS, HANS-PETER BANTLEON, MD, DDS, P. www.indiandentalacademy.com
  • 53. Schematic of force system: moments at lever arm and bracket cancel each other out, resulting in net translation force. www.indiandentalacademy.com
  • 54. Undesirable side effects from distal canine slide along continuous arch: tipping, binding, lack of vertical control and risk of anchorage loss, incisor extrusion www.indiandentalacademy.com
  • 55. C A N I N E R E T R A C T I O N Effect of pure horizontal force at the canine bracket. www.indiandentalacademy.com
  • 56. C A N I N E R E T R A C T I O N Antitip and antirotation moment-to-force conditions necessary for translation of canines with average dimensions. www.indiandentalacademy.com
  • 57. C A N I N E R E T R A C T I O N PG retraction spring Anti tip bend – 150 in the mesial leg Beta bend - 300 in the distal leg Anti rotation bend – 350 www.indiandentalacademy.com
  • 58. C A N I N E R E T R A C T I O N T LOOP The preactivated spring with the anti tip and anti rotation is placed Activation on insertion is 6mm The m/f is 8:1 – controlled tipping Now as the tooth moves the activation reduced to 4mm – the force is reduced M/f ratio is increased - bodily movement further The activation is reduced to 2mm – force is further reduced M/f ratio increased – 12:1 Root uprighting www.indiandentalacademy.com
  • 59. C A N I N E R E T R A C T I O N T LOOP Increasing the gingival length of the wire increases the m/f ratio and reduces the deflection rate Mesial leg angulated by150 Distal leg angulated by 300 Preactivation of 400 www.indiandentalacademy.com
  • 60. E N M A S S E F R I C T I O N L E S Space closure using a retraction appliance. Source: AJO-DO 1997 : Three-dimensional effects in retraction appliance design D. W. Raboud, MSc, M. G. Faulkner, MSc, PhD, A. W. Lipsett,..,. www.indiandentalacademy.com
  • 61. E GROUP A ANCHORAGE N M A Distal force on anteriors Mesial forces on posteriors S S Maximum potential for tooth mvt. Miminised or counteracted E F Increase moment R Decrease moment I C Horizontal force acting on both segments are same T I O Moment to force ratio N L E Reactive unit Anchor unit S www.indiandentalacademy.com
  • 62. E N M A S S E F R I C T I O N L E S Alpha moment Beta moment Anteriors posteriors When unequal or unbalanced Vertical forces created Extrusion Intrusion alpha alpha beta beta Extrusion Intrusion www.indiandentalacademy.com
  • 63. E N M A S S E F R I C T I O N L E S A. Vertical force anterior to center of resistance, producing clockwise moment. B. Vertical force posterior to center of rotation, producing counterclockwise moment. Source: JCO 1990 : Vertical Force Considerations in Differential Space Closure - BIRTE MELSEN, DO, VASSILI FOTIS, DDS, MSD,www.indiandentalacademy.com CHARLES J. BURSTONE,
  • 64. E N M A S S E F R I C T I O N L E S Beta moment greater than alpha moment, producing net intrusive force on anterior teeth and extrusive force on posterior teeth. B. Alpha moment greater than beta moment, producing net intrusive force on posterior teeth and extrusive force on anterior teeth. C. Equal alpha and beta moments, producing no vertical component of force. Source: JCO 1991 JULIE ANN STAGGERS, DDS, MS, NICHOLAS GERMANE, DMD www.indiandentalacademy.com
  • 65. E N M A S S E F R I C T I O N L E S With retraction spring, alpha moment produces distal root movement of anterior teeth; beta moment produces mesial root movement of posterior teeth. www.indiandentalacademy.com
  • 66. E N M A S S E F R I C T I O N L E S GROUP B ANCHORAGE Distal force on anteriors Mesial forces on posteriors Equal potential for tooth mvt. Alpha moment EQUAL Beta moment Horizontal force acting on both segments are same Moment to force ratio EQUAL RETRACTION OF ANTERIOR PROTRACTION OF POSTERIOR www.indiandentalacademy.com
  • 67. E N M A S S E F R I C T I O N L E S GROUP C ANCHORAGE Distal force on anteriors Minimized or counteracted Mesial forces on posteriors Maximum potential for tooth mvt. Increase moment Decrease moment Horizontal force acting on both segments are same Moment to force ratio Reactive unit Anchor unit www.indiandentalacademy.com
  • 68. E N M A S S E F R I C T I O N L E S Burstone and koenig 1976 AJO Three primary characteristics of retraction loops 1.moment to force ratio 2.the force at yield 3.the force to deflection rate Factors that influence m/f Height of the loop Horizontal loop length Apical length of the wire Placement of the loop Helix incoporation Angulation of loop www.indiandentalacademy.com legs
  • 69. E N M A S S E F R I C T I O N L E S Gradual sweep versus an acute bend Acute bend Force concentrated on the premolar Mesial tipping of the premolar Undesirable No undesirable tipping Gradual sweep Force being distributed molar and premolar Uniform distribution of the force and no concentration of the force on a particular tooth www.indiandentalacademy.com
  • 70. E N M A S S E F R I C T I O N SLIDING MECHANICS The hook is soldered at the center of resistance of the anterior segment and active tie backs are placed from the molar hook to the soldered hook. www.indiandentalacademy.com
  • 71. B Conventional Begg – type of tooth movement is uncontrolled or free tipping of the tooth E Amount of force required for this is less and the moment to force ratio is also decreased G Uncontrolled tipping is not desirable as it hastens root resorption and control of the tooth movement is also difficult (source: Biomechanical principles and reacions, Reitan1985) G Refined Begg – controlled tipping www.indiandentalacademy.com
  • 72. B E G G Stage 1 Intrusion and tipping of the incisors simultaneously Intrusive force – crown labial root lingual Retractive force – crown lingual Root labial Moment of the intrusive force acts to counter moment the moment of the elastic force Moment of the intrusive force to the elastic force ratio determine the type of tooth movement www.indiandentalacademy.com
  • 73. B If the intrusive force is decreased If the elastic force is increased E G Moment to force ratio Inadequate for Controlled tipping Thus, for controlled tipping G Keep the class II elastic force very light Use adequate amount of intrusive force www.indiandentalacademy.com
  • 74. B Anchor bend and the class II elastic force Anchor bend E Distal crown tipping of molars G Retract the anterior teeth G Class II elastics Move the lower molar forward bodily Upright the lower molars www.indiandentalacademy.com Intrusion of anteriors
  • 75. B Torquing auxillary with spur When spread along the wider curvature Lingual torquing E G The larger arc of the anterior portion of the wire roll inwards Vertical plane in which the aux orients when fitted into the incisor is changed to the horizontal plane of the arch wire when tied to it The tip of spur to press in a lingual direction against the gingival portion of the crown G Inter spur span – lift in a labial direction Counter act www.indiandentalacademy.com Bracket slot Base arch wire
  • 76. MAA B Light couple force acting on each tooth E G Lingual crown torque with the intrusive couple force II stage Intrusive force reduced Additional moment created by the MAA G Prevents labial tipping of the lower incisors Opposite to the elastic force M/F 8:1 Controlled tipping Shortens the third stage www.indiandentalacademy.com
  • 77. C O M M O N Common sense mechanics Thomas F mulligan JCO 1979 Off center bend Long segment Short segment S Points in the direction Points in the direction E of the force produced opposite of the force N on the tooth produced on tooth S E www.indiandentalacademy.com Center bend No short or long segment No force produced
  • 79. C O M M O N S E N S E Differential torque - the molar tip back bend produces a large distal moment on the molar and a small labial moment on the anterior segment in spite of the force being equal as the distances involved are radically different. www.indiandentalacademy.com
  • 80. Round wire C O M M O N S E N S E Rectangular wire Line of action Buccal to center of resistance Lingual crown torque Line of action lingual to center of Resistance Buccal crown torque Begg stage l expansion given to prevent lingual rolling of molars Beta bend to Produce buccal Root torque www.indiandentalacademy.com
  • 81. CUE BALL CONCEPT C O M M O N S E N S E A force off center causes the cue ball to rotate as well as move forward in a straight line. No left or right When the line of force acts rotation is through the produced when center of the force is resistance, applied through only the center of the translation cue ball. results. www.indiandentalacademy.com Equal and opposite forces (couple) produce pure rotation.
  • 82. C O M M O N S E N S E ROW BOAT EFFECT If the tipback and torque bends produce equal angular relationships (A), the net forces are zero. If unequal (B), net forces occur. This explains why there is extrusion with the increase in the alpha bend. Thus the length of the segment and the angulation determine the tooth movement www.indiandentalacademy.com
  • 83. C O M M O N DIVING BOARD CONCEPT When the length of the diving board is doubled, only one-eighth the force is required to produce the same amount of deflection. B. The same force acting at twice the length will produce eight times as much deflection. S E With a constant tipback N S angle, the deflection doubles E as the wire length doubles, the force is reduced to one www.indiandentalacademy.com fourth
  • 84. M O L A R Bends placed in the arch wire Variety of force systems to produce a direct response Off set bend C O N T R O L Step bend Center bend Source : Thomas Mulligan JCO 2001 www.indiandentalacademy.com
  • 85. M O L A R OFFSET BEND Short section of the wire points in the direction of the long arm Vertical forces acting through the molar tube Intrusive Lingual crown torque C O N T R O L Extrusive Buccal crown torque Narrowing of the post Arch width Widening of the post Arch width Reduction in the curve of monson Increase in the curve of monson www.indiandentalacademy.com
  • 86. M O L A R Rotations first displacement second Toe in Rotation correction required Toe out C O N T R O L Represent the short section of the wire of the off center bend Bends located just mesial to the molars www.indiandentalacademy.com
  • 87. M O L A R Toe out corrects the distal in and/ mesial out rotation with horizontal lingual force C O N T R O L www.indiandentalacademy.com
  • 88. M O L A R Toe in corrects the mesial in or distal out with horizontal buccal force C O N T R O L www.indiandentalacademy.com
  • 89. M O L A R In bend for the lingual displacement C O N T R O L www.indiandentalacademy.com
  • 90. M O L A R Out bend for the buccal displacements C O N T R O L www.indiandentalacademy.com
  • 91. M Step bend for the mesio lingulal rotation O with a lingual displacement L A When 2 bends are involved and each Increases the R bend produces a force in the same force direction magnitude C O N T R O L www.indiandentalacademy.com
  • 93. CERVICAL PULL HEAD GEAR H E A D LOW OUTER BOW Head gear force line of action mesial to the center of resisitance Extrusive component Distal component G E A R S Large moment that Tends to steepen the Occlusal plane Clockwise Moment www.indiandentalacademy.com
  • 94. CERVICAL PULL HEAD GEAR H E A D OUTER BOW Head gear force line of action passing through the center of resisitance At the level of the inner bow Extrusive component Distal component G E A R S No moment that Tends to alter the Occlusal plane www.indiandentalacademy.com
  • 95. CERVICAL PULL HEAD GEAR H E A D High OUTER BOW Head gear force line of action distal to the center of resisitance Extrusive component Distal component G E A R S Large moment that Tends to flatten the Occlusal plane Anticlockwise Moment www.indiandentalacademy.com
  • 96. HIGH PULL HEAD GEAR H E A D SHORT OUTER BOW Angulated high to create head gear force line of action anterior to the center of resisitance Intrusive component Distal component G E A R S Large moment that Tends to flatten the Occlusal plane Anticlockwise Moment www.indiandentalacademy.com
  • 97. HIGH PULL HEAD GEAR H E A D OUTER BOW Angulated such that head gear force line of action passes through the center of resisitance Equal to the inner bow Intrusive component Distal component G E A R S No moment that Tends to alter the Occlusal plane www.indiandentalacademy.com
  • 98. HIGH PULL HEAD GEAR H E A D LONG OUTER BOW Angulated to create head gear force line of action posterior to the center of resisitance Intrusive component Distal component G E A R S Large moment that Tends to steepen the Occlusal plane Clockwise Moment www.indiandentalacademy.com
  • 99. Conclusion Newton’s third law states that every action has a equal and opposite reaction. Its important to keep this concept in mind working with any appliance system and give adequate importance to take steps to prevent the adverse effects. In orthodontic terms, the understanding of the moment and the application of the necessary counter moment to bring about the optimal tooth movement is the key to successful treatment results www.indiandentalacademy.com
  • 100. Thank you For more details please visit www.indiandentalacademy.com www.indiandentalacademy.com