Mulligan’s

Mulligan’s
Common Sense
Orthodontic
Principles in SWA

 "Common Sense Mechanics"
 Thomas F. Mulligan- series of 16 articles in JCO
(Sep. 1979 – Dec. 1980)
 Based on fact that no appliance exists which allow
an orthodontist to treat MO without adding the
necessary ingredient of "Common Sense" to the
mechanics instituted for correcting the
malocclusion.

 Refinement in appliances may ↓ the physical effort,
but will not eliminate the need for the orthodontist to
 Think
 understand
 Apply basic principles of mechanics
in a common sense manner.

 Dealing with a biologic environment (with variable
response) we must treat the patient in a practical
or realistic manner, rather than treating in a
textbook fashion.
 The textbook, may help us to determine how
equal and opposite forces are produced,
but such forces do not necessarily produce
equal and opposite responses

 Common Sense is such an important part of applying
basic mechanics that without it, even the most
sophisticated knowledge of the subject offers one
little in attaining his treatment goals.
 Common Sense approach to application of mech.
principles helps us to solve problem as well as
permits us to avoid those problems we often
introduce in trt. procedures.

 Visual inspection method
 Often confuses the orthodontist in attempting to determine
with reliability what forces are present.
 The visual method seems to be so obvious, but  faulty
conclusions.
 Not to be misled by determining forces present through the
visual inspection method

 A Simple Rule
 Different than visual inspection
 if the bend is located off center, there will be a long
segment and a short segment. When the short
segment is engaged into the bracket or tube, the
long segment will point in the direction of the force
produced on the tooth that will receive the long
segment.

 The short segment points in the opposite direction
of the force that will be produced on the tooth that
receives the short segment.

 if the bend is in the center, no long or short
segment.  No force.
 forces cancel each other upon AW engagement,
leaving pure moments.

 Determining the presence and direction of a force is
an important part of efficient mechanics, but by itself
does not describe or predict tooth movement.
 Consider other factors
 forces of occlusion
 cusp height
 habits
 if we can reliably know the force present and its
direction, we can concentrate on where we wish to
position the teeth.

 Forces and Moments
 Both are extremely important
 They produce the desirable & undesirable
movements.
 Force is nothing more than a "push" or "pull,"
and acts in a straight line

 When line of force passes through the center
of a body (in ortho, COR)— there is no
moment produced  no rotational tendency.
 When a force acts away
from the center 
moment  rotational
tendency

 Moment is the product of force times distance.
 It is the perpen. distance from this line of force to the
center that causes the moment on the tooth, resulting in
rotational tendencies
 magnitude of moment = force x perp.distance to the center

 large force might produce no moment,
 Smaller force might produce a large moment
because of the distance from the center of
resistance.

 Cue Ball Concept
 If we desired English, apply a force off center  produce left
or right English at will, simply by deciding to apply the force to
either the left or right side of center on the cue ball.

 If we only wished to "translate" the cue ball—apply
the force right through the middle of the cue ball

 The ball rotated or rolled forward due to the friction of
the table, but the response was predictable.
 Reasons behind this predictability.
 Translation
 Force through the center of the cue ball  move
forward in a st. line
 No rotation— other than the forward roll due to the
friction of the table

 Reason- there is no rotation (moment) because the
line of force has no per. distance to the center
 So a force acting through-the center of a body
produces translation without rotation.
 Rotation and Translation
 Apply force off center of cue ball  create a situation
where the line of force has a perp. distance from the COM

 Produce translation & also rotation, as a result of the
moment produced
 A force applied on a body, but not through the
center of that body, results in translation and
rotation.
 Pure Rotation (Couple)
 if two forces applied on the cue ball, equal and opposite, in
the same plane of space the ball would not translate in
any direction. Instead, it would simply maintain its position
and "spin" (rotate)

 Reason - two forces cancel each other out, but
leave a net moment (rotation) because each of
these "Lines of Force" acts at a perpendicular
distance from the center of the ball.

 Forces and Moments Acting on Teeth
 if we use a tipback bend for overbite correction,
when the short segments are placed into the molar
tubes, the long segments, prior to bracket
engagement, lie in the muco-labial fold.
 long segment points apically in the incisor area  an
incisor intrusive force while the molars have an
extrusive force present.

 When the wire is brought
down from the mucolabial
fold for insertion into the
incisor brackets the force
required acts at a perp.
distance from the center of
resistance in the molar
 Produce mesial root torque
or distal crown thrust on
each of the molars

 When the wire is engaged into the
incisor brackets, the intrusive force acts
in a straight line and usually passes
labial to COR in the incisors.
 Produces a smaller moment that on the
molar, because in spite of forces are
equal, the distances involved are
radically different.

 Differential torque
 when the archwire is tied into place and tied
back at the molar tubes, we have significantly
different (relatively) magnitudes of torque

 If we do not tie the AW to the molar tubes &if friction
does not accomplish the same by causing binding at
the tubes,
 Ant. & pos. moments may be permitted to respond
independently of each other.
 If tied back, the system behaves as a whole,
 The "tug of war" is apparent with the molar having the
obvious mechanical advantage with the larger moment.

 If the wire is round
 Extrusive force present on the molar teeth acts at the
molar tubes which lie, buccally to COR. This force times
distance results in molar lingual crown torque.

 Torque is not necessarily dependent on the use of
rectangular wire.
 If a wire were very rigidly attached to the tubes, the
applied force would pass lingual to the center of
resistance, thereby inducing buccal crown torque.

 We should be able to interpret the cause and vice
versa.
 such force systems should not be routinely
considered as undesirable side effects
 Should be prepared to prevent undesirable effects as
well as to utilize the systems effectively when
indicated.

 In entire force system
 Molar extrusive forces, incisor intrusive forces, molar
mesial root torque significantly (relatively) larger than the
incisor lingual root torque, and molar lingual crown torque.
 Lingual Root Torque
 When lingual root torque is placed into the incisor section,
a long segment & a short segment is produced as with tip
back bend.

 The long segment  molar intrusive force and &
extrusive force on the incisors.
 Torque produced on the incisors is a result of force
times distance,
 long segment has to be brought down
to the molar tube, and the
force required to bring it down acts
at a per. distance to the
incisors

 If the tipback and torque bends produce equal
angular relationships the net forces are zero.
 If unequal net forces occur. the one producing the
greater angle relative to t he level of the archwire will
determine the net force present

 if lingual root torque produces the greater angle
 net forces will be intrusive on the molar and extrusive on
the incisor.
 if we are hoping for overbite correction, but overbite will ↑
 Either ↑ the molar tipback bend, ↓ the amount of lingual
root torque on the incisor segment, or a combination of
each, in order to assure ourselves of a net intrusive force
on the incisor segment

 Static Equilibrium
 very important in orthodontic mechanics
 Teeter-totter- When a large person sat at one end and
a smaller person at the other end the board was not in
balance until the heavier end struck the ground.

 If we,, desired to convert this "dynamic" state to a state of
statics, either shift the unequal weights or the fulcrum
point on the board

 Requirements for Static Equilibrium
 Three requirements
 The sum of all the vertical forces present must equal
zero).
 we must deal with extrusive components of force
during overbite correction.

 the sum of all horizontal forces present must
equal zero
 This is why we cannot correct a unilateral crossbite with
a single horizontal force

 The sum of the moments acting around ANY point
must also equal zero
 We may produce heavy torques in a given area and little or
no torque elsewhere, but when added around any given
point, they should equal zero.


With two equal moments at either
end of the archwire, the system is
in balance.
 With two unequal moments at
either end of the archwire, the
system reaches a balance, but
seems to be unbalanced and with
the entire unit rotating
counterclockwise.

 Actually, the unequal moments create (in this case)
an extrusive force on the incisor and an intrusive
force on the molar. The sum of these forces is
zero, but the configuration causes the entire unit to
rotate clockwise.

 A full strapup with a reverse curve of Spee.
 The vertical forces cancel out but moments produced at
either end of the archwire -anterior lingual root torque or
labial crown torque; posterior mesial root torque or distal
crown torque

 Forces equal zero when the entire system is added, but do
not cancel each other at a given site, thereby allowing
predictable forces to act at these sites.
 attempting anterior intrusion ant. & pos. forces with equal
and opposite extrusive forces occurring through the bicuspid
areas.
 Intrusive forces acting through the molar tube usually produce
buccal crown torque (cue ball effect), while the intrusive force
through the incisor brackets produce labial crown torque.

 Arch Leveling
 When leveling an arch,
 in a full strap up, intrusive forces act through the molar
tubes, producing buccal crown torque on the molars.
 When a 2×4 (incisors and molars) strap up is utilized for
overbite correction, As intrusion is placed on the incisor
segment, and because the molars then become the
reciprocal teeth, they incur eruptive forces

 Extrusive forces acting through the molar tubes
usually result in lingual crown torque on the molars
(lingual "dumping").
 Undesirable responses that often occur
unexpectedly
 when these occurrences are predictable beforehand 
avoidable
 The recognition of causes permits us to utilize as

 Crossbites
 If an individual molar, or an entire buccal segment in
crossbite—
 we would like to apply a force in the necessary direction
for correction on those teeth only.
 when we observe a buccal segment in crossbite, it may be
a unilateral crossbite, or in most of cases a bilateral
crossbite with a lateral mandibular shift.

 there will be equal and opposite horizontal forces present
(whose sum = zero), as both sides will require the force.
Overlays
 Refer to a heavy wire overlaying
the main AW. It can either be
inserted into the headgear tube
or be designed with terminal
hooks to engage AW

 .045 headgear tube - .036
 The force provided will be equal and opposite— not unilateral
in direction as might appear to be the case when the overlay
is inserted into one tube and observed

 upon insertion into both molar tubes, there exists a buccal
force on both the left and right
 By the time overcorrection of the side in crossbite is obtained,
the "normal" side is in buccoversion but readily "relapses" to
its normal position
 the side originally in crossbite relapses to the point of
improved function.
 If not, the overlay is reinserted.

 Cosmetic Overlays
 In late mixed dentition where only a single tooth is in crossbite
with mild overbite The crossbite could be treated simply by
use of an .036 overlay and two molar bands
 The overlay is referred to as "cosmetic" because it is
designed not to show when the patient smiles.

 Bodily Movement
 If bodily movement is desired, a rectangular wire may be
placed to provide the necessary torque at the root level.
 "bodily expand", - buccal root torque  crowns to initially
move lingually.
 The overlay overcomes this initial reaction by providing the
necessary force at the crown level.

Reduction of Posterior Arch Width
 The same overlays as used for expansion are
utilized. Instead of the overlay being expanded, it is
constricted.

 Controlling Vertical Forces Intraorally
 By controlling magnitudes of force intraorally
 The force MAGNITUDES are controlled so that posterior teeth
are only allowed to erupt to the extent of vertical growth within
a given patient, rather than actually intruding posterior
segments.

 The Diving Board Concept
 Used to tell the advantages of utilizing the factor of "length"
in AW.
 Stiffness or load/deflection rate α 1/ L3
 Formulas -confusing & little use to the orthodontist, as well
as difficult to remember.

 To make all of this useful and a little easier
 Stiffness is the amount of deflection we get from a given
force.
 The formula tells us that if with a cantilever (such as a
diving board), 2L 1/8 force will be required to produce
the same deflection or the same force acting at 2L  8
times deflection

 Load on diving board produces bending moments along the
board, with the maximum moment being located closest to the
point of attachment.
 In orthodontics, we often refer to this moment as the "critical
moment", as it is the largest moment involved and is often
responsible for breakage in an
archwire at that particular
point.

 The moment keeps decreasing along the diving
board and finally reaches zero directly underneath
the individual (load) standing on the board as no
distance left in relation to applied force.

 Cantilever Principle
 In Cantilever system - a pure force acting at one end, & an
equal and opposite force at the other end accompanied by
a moment.
 The pure force can be used for overbite correction while
the differential torque can be utilized for intraoral
anchorage control.

 Constant Load versus Constant Deflection
 To maintain the same force requires variation in
archwire deflection.
 For a given bend
determine angle necessary to
produce the desired force.
& to know length of wire
between brackets and tubes.

 Constant deflection (bends)
creates variable loads.
 Problem - some of these loads
might not be be biologically and
physiologically acceptable,
 Particularly those cases
involving vertical dimension
problems.

 Constant bends (angular) are pref.
 easy to do
 readily reproducible
 intraorally activated (light wires only)
 offer low force ranges ( the "by-pass" approach to force
control).

 Clinical Application of the Diving Board Concept
 Diving Board Concept- length affects load (force).
2L ↓ force per unit of deflection to 1/8
 if we bypass PM and cuspids during overbite correction,
and use a wire with tipback bends at the molars, effect
created a "diving board“.

 With a constant tipback angle, the deflection doubles as
the wire length doubles.
 load per unit of deflection is ↓ to 1/8 ,the unit of
deflection is doubled, resulting in a net force of one-
fourth (2 × 1/8 = ¼).

 Affect on Forces and Moments
 AP arch length varies from pt. to pt, when PM & cuspids
bypassed & magnitudes of the intrusive and extrusive
forces at each end of the archwire,
 Entire range of force is so low that low magnitudes of force
may pose a greater problem than attaining higher levels of
force.
 use AW of greater diameter to produce a required force.
 Not use too large a tipback bend, as this in combination
with duration  in excessive tipback of the molar teeth.

 Pure Force
 A pure force will not occur if the design of the AWs is
improper.
 For pure and known intrusive force, a wire segment can be
placed into the incisor brackets and the archwire then used
as an "overlay"

 The bypassing allows
 light forces,
 erupting teeth to adjust to their environment without direct
interference from an appliance.
 There is a large moment produced on the molar
teeth from the tipback bend.
 When the archwire is tied securely to the molar tubes, this
moment tends to tip all of the teeth distally

 This "distalization" tendency -easy to check simply by
observing the unbanded cuspids and their change in axial
inclination.
 The cuspid crowns tip distally as they are forced back as a
result of the thrust being received at the crown level.
 Distalization With Differential Torque
 Tipback bend is an off-center bend and that the long
segment and short segment indicate the direction in which
the forces act.

 Moments involved are unequal, thus
resulting in "differential torque".
 "rowboat effect“- tendency for the
maxillary teeth to move forward during
anterior lingual root torque
 Reverse the conditions and create the
opposite tendency, distalization

 when anterior lingual root torque is applied,
crown movement tends to precede root
movement.
 When the archwire is tied to the molar
tubes, this "rowboat effect" is transmitted to
all of the teeth.
 When a rectangular wire with anterior
lingual root torque is engaged into the molar
tubes, anterior lingual root torque is
produced
 produce the opposite tendency for tooth
movement by placing mesial root torque on
the molars using a tipback bend in a round
wire

 if the 2nd
PM is engaged, the bend is no longer an off-center
bend and will result in, basically, equal and opposite torque on
the molars and bicuspids.
 When wire with tipbacks is inserted into the molar tubes and
then engaged into the incisor brackets, mesial root torque will
be produced on the molars.
 but crown movement tends to precede root movement
distal crown movement.
 If the archwire is tied to the molar tubes, there is a
distalization tendency for the entire upper arch

 If overbite interferes, at the time, with the distal crown
movement (tendency), mesial root movement of the molars
will occur.
 Level of unerupted second molars does not pose the threat of
impaction with the use of a tipback bend except with
techniques that use excessively high vertical force levels.
 If the teeth are not permitted to extrude, they will tip back and
literally push the unerupted second molar even further back.

 Class II Correction Without Headgear or Elastics
 Class II correction is coincidental during overbite correction
using tipback bends esp. in U/arch..
 This is not a means of eliminating headgear or elastics. but
the amount of headgear treatment originally planned is
either reduced, sometimes even eliminated.
 Tipping back of incisor crowns with this force system, as
opposed to the labial flaring seen in the traditional full
strapup with the use of an archwire containing a reverse
curve of Spee.

 With a reverse curve of Spee, the incisors do flare,
 There is no differential torque and, thus, the intrusive force
acting through the incisor brackets produces labial crown
torque on the incisor segment with resultant flaring.
 With the tipback
 this anterior torque is "overwhelmed" by the molar
moment, and the molars are favorites to win the "Tug of
War"
 Class II elastics tip an occlusal plane downward, use of a
tipback in an upper arch only, does just the opposite, and can
permit the use of Class II elastics in such cases without
affecting the upper occlusal plane.

 Wire/Bracket Relationships
 The relationship of the archwire to
the brackets and tubes, prior to
engagement, offers valuable and
interesting information
 If a straight wire is placed over
angulated brackets, a certain
angular relationship develops
between the wire and the plane
of the bracket slot

 The same wire/bracket
relationship can be
created by a bend in the
wire or a straight wire in
relation to a
malocclusion.

 Center Bend Force System
Applying the requirements for static equilibrium.
 If all four forces (activational) are equal- first requirement for
static equilibrium is fulfilled.
 No horizontal forces necessary to engage the wire into the
brackets, the second requirement is also fulfilled.

 Forces A & B In produce a
clockwise moment
 Forces C & D produce a
counterclockwise moment.
 Tooth movement resulting from
deactivation of the force systems is
counterclockwise from Forces A &
B and clockwise from Forces C &D.

 Step Bend Force System
Applying the requirements for static equilibrium.
 If all four forces (activational) are equal- first requirement
for static equilibrium is fulfilled.
 No horizontal forces necessary to engage the wire into the
brackets, the second requirement is also fulfilled.

 Force A & Force D produce equal clockwise moments
 Moments produced by Forces B and C are equal to each
other and counterclockwise, they are smaller in magnitude
than Forces A and D, because they are produced at smaller
distances.
 Therefore, the sum of the moments does not equal zero.
 Step bend force system with Forces A and D less than Forces
B and C doff satisfy the requirements of static equilibrium.

 Forces A and B in produce a clockwise moment;
Forces C and D also produce a clockwise
moment.
 Clockwise moments result in counterclockwise
tooth movement.

 Extraction Mechanics
 A wire with a off center bend  net forces at the
bracket
 A center bend involves no net forces, but only equal
and opposite moments in any plane of space.

 Depending on the angle at which
the wire with an off-center bend
crosses the bracket, and the
length of the long segment
 moment produced by the longer
segment can be
 clockwise
 counterclockwise
 nonexistent
In all three instances, the net effect is
counterclockwise, dominated by the
short segment

 The resilient characteristics of the wire can
complicate our interpretations,
 archwire activation often produces a different
wire/bracket relationship, initially, than might be
anticipated

 Practical Interpretation of Forces and Moments
 Most examples used for center and off-center bends have
involved only two teeth or two units of teeth.
 But we are going to be dealing with many teeth during the
treatment of various malocclusions
 Techniques that create a "single tooth" by segmenting a
number of individual teeth. Four incisors as a single unit by
the placement of an anterior segment of wire, and then an
overlay archwire was used to apply the desired force.

 Mulligan treated the two teeth on either side of the
bend, but by using a continuous archwire and
multiple banding described "segmented tooth
movement", but on a continuous archwire.
 When dealing with multiple teeth - the force system
acts on the adjacent teeth most effectively.

 Cuspid Retraction
 The typical extraction strap up involves the banding /
bonding of cuspids, 2nd
PM, and first molars
 Band second molars to increase anchorage However, not
always reliable. Sometimes, the anchor unit serves well,
while at other times it readily seems to move forward.

 Since the forces during retraction are equal and opposite
on anchor unit and non-anchor unit — the multi banded
unit actually receives the lesser stress along the
periodontal membrane while cuspid receives the greater.
This could be one of the causative factors in the variations
that occurs.
 Anti-rotational ties are placed next to the extraction sites,
unless such rotations are indicated.

 The malocclusion usually results in initial archwire
activation, due to the fact the brackets are not yet aligned.
 Toe-in bends should be placed early, to prevent ML
rotation of the molars when retraction is begun.
 Placement of bends intraorally.
 If bends are placed IO, cannot .be placed against the
brackets completely, - ↓ differential torque

 smaller interbracket distances result in bends being
relatively close to center.
 2nd
PM are sometimes temporarily not banded to increase
the distance and therefore the differential torque.
 Power chains can be used for retraction - cuspid directly
tied to the molar, while the second bicuspid is tied
individually with an "O" Ring. This allows a greater range of
force.

 The anchor unit should remain relatively upright,
 the non-anchor unit should undergo tipping until archwire
binding occurs.
 Once binding occurs, the roots will respond to the moments
produced by the archwire, until binding stops and crown
movement is resumed.
 As cuspids continue to move distally- when the extraction
sites are closed, the bend is centered.

 Differential torque begins to gradually disappear, and
becomes equal and opposite torque (for roots IIing)
when the bend is finally centered.
 center of the wire lying between the bicuspid and
cuspid brackets.

 if the second bicuspid is not banded
 once the spaces are closed, a centered bend will not
be present, as the bend has been placed against the
molar.
 to produce equal and opposite moments, a bend can
be placed immediately distal to the cuspid bracket

 Bicuspid Retraction
 Since differential torque considers the effectiveness of a
net moment, total root area in the anchor unit is not the
primary consideration.
 As a result, bicuspid can be retraction in the same way as
cuspid retraction.
 Molar Protraction
 protraction is accomplished in the same manner— by
locating the bend off center.

 However, protraction will simply utilize the non-anchor
side of the bend.
 the bend is moved "away" from the teeth to be
protracted (anteriorly)
 To counteract ML rotation of molar, a sharp toe-
in bend must not be placed – Place a gentle
curve

 Simultaneous Cuspid and Bicuspid Retraction
 accomplished in the same manner— by locating the bend
off center.
 if desired, the bend can be placed in the archwire outside
of the mouth, - closer to the molar tubes and thus a greater
distance from the center of the wire lying across the
extraction sites.
 the elastics are attached from the molars to the
cuspids.

Conclusion
 Acc. to Mulligan there is nothing wrong with the
so-called "cookbook" approaches to orthodontic.
treatment, but it can become quite routine and
even boring at times.
 Being able to vary procedures according to the
time available and the tooth movement desired -
more excitement & ease of manipulation on the
part of the operator.

Mulligan’s

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