Biomechanicss

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 continuous state of interaction with theircontinuous state of interaction with their
environmentenvironment
 natural laws of mechanics.natural laws of mechanics.
 Orthodontic problems are the result ofOrthodontic problems are the result of
mechanical forces, and their correction dependsmechanical forces, and their correction depends
on mechanical forces.on mechanical forces.
 The force systems in the face can form ofThe force systems in the face can form of
deform, and their conscious control is adeform, and their conscious control is a
continuing challenge in orthodontics.continuing challenge in orthodontics.
 Orthodontic therapy is a carefully planned andOrthodontic therapy is a carefully planned and
regulated interaction with those laws as theyregulated interaction with those laws as they
control the form and function of the Dentofacialcontrol the form and function of the Dentofacial
complex.complex.
 BIOLOGY + MECHANICS = BIO-MECHANICSBIOLOGY + MECHANICS = BIO-MECHANICS

BiomechanicsBiomechanics
Terminologies & LawsTerminologies & Laws
 ForcesForces
 MomentsMoments
 CouplesCouples
 Moment-to-Force RatioMoment-to-Force Ratio

FORCEFORCE
The two broad classes of mechanical forces are:The two broad classes of mechanical forces are:
 Static:Static: which deals with bodies at restwhich deals with bodies at rest
 Dynamic:Dynamic: which deals with moving bodies.which deals with moving bodies.
At any moment the oral structures can be considered to be in a stateAt any moment the oral structures can be considered to be in a state
ofof static balance.static balance.
 ForceForce is defined as an act upon a body that changes or tends tois defined as an act upon a body that changes or tends to
change the state of rest or the motion of that body.change the state of rest or the motion of that body.
Though defined in units of Newtons it is usually measured in units ofThough defined in units of Newtons it is usually measured in units of
grams or ounces.grams or ounces.
Forces are vectors, having bothForces are vectors, having both directiondirection && magnitude.magnitude. Point ofPoint of
applicationapplication of force is also important in the understanding of toothof force is also important in the understanding of tooth
movement.movement.

Force (contd.,)Force (contd.,)
 DirectionDirection
Pull and pushPull and push
 MagnitudeMagnitude
Light and HeavyLight and Heavy
 Increasing the amount of force will increase theIncreasing the amount of force will increase the
amount of a free body displacement. However,amount of a free body displacement. However,
it is unclear how force magnitude is related toit is unclear how force magnitude is related to
the rate of tooth movement, which is athe rate of tooth movement, which is a
biologically controlled phenomenonbiologically controlled phenomenon

Force (contd.,)Force (contd.,)
Point of applicationPoint of application
 Center of MassCenter of Mass
 Center of GravityCenter of Gravity
 Center of ResistanceCenter of Resistance

 Center of Mass:Center of Mass:
Each body has a point in its mass, which behaves as if the wholemassEach body has a point in its mass, which behaves as if the wholemass
is concentrated at the single point, which we callis concentrated at the single point, which we call the center of massthe center of mass
in a gravity-free environment. The same calledin a gravity-free environment. The same called center of gravitycenter of gravity inin
an environment where gravity is present.an environment where gravity is present.
Point of application of force in relation to center of Mass:Point of application of force in relation to center of Mass:
 TippingTipping – When a force is applied on this pencil below its center of– When a force is applied on this pencil below its center of
mass, it tips and moves forward. When another force is appliedmass, it tips and moves forward. When another force is applied
above the center of mass, the pencil will again tip are move forward.above the center of mass, the pencil will again tip are move forward.
 TranslationTranslation – If the force is passing through the center of mass, the– If the force is passing through the center of mass, the
whole body moves in a straight line, in a parallel fashion. Here allwhole body moves in a straight line, in a parallel fashion. Here all
the points of the body get displaced equally from the initial position.the points of the body get displaced equally from the initial position.
This is called bodily movement or translationThis is called bodily movement or translation
Therefore, same laws of mechanics apply to a tooth; for example, aTherefore, same laws of mechanics apply to a tooth; for example, a
force applied below the center of gravity of the tooth will cause theforce applied below the center of gravity of the tooth will cause the
tooth to tip.tooth to tip.

Center of Resistance:Center of Resistance:
 Since the tooth is partially restrained, as itsSince the tooth is partially restrained, as its
root is embedded in bone, its center of gravityroot is embedded in bone, its center of gravity
shifts apically and is then referred to as theshifts apically and is then referred to as the
Center of resistanceCenter of resistance
 The center of resistance is a point at which theThe center of resistance is a point at which the
resistance to tooth movement is concentrated.resistance to tooth movement is concentrated.
It is determined by the nature of the externalIt is determined by the nature of the external
constraints.constraints.

MomentMoment
A moment is defined as aA moment is defined as a tendency to rotate.tendency to rotate.
 Moment of the force:Moment of the force:
When a force is applied at any point other than throughWhen a force is applied at any point other than through
the center of resistance, in addition to moving thethe center of resistance, in addition to moving the
center of resistance in the direction of the force, acenter of resistance in the direction of the force, a
moment is created. Since the tooth is embedded in themoment is created. Since the tooth is embedded in the
alveolar bone, we can never apply a force directly onalveolar bone, we can never apply a force directly on
the center of resistance. We can only apply a force onthe center of resistance. We can only apply a force on
the exposed part of the tooth, which is at a distancethe exposed part of the tooth, which is at a distance
from the center of resistance. Therefore with a singlefrom the center of resistance. Therefore with a single
force in a typical clinical situation, invariably create aforce in a typical clinical situation, invariably create a
moment, which is called asmoment, which is called as moment of force.moment of force.
 A moment may be referred as “Rotation”, “Torquing”A moment may be referred as “Rotation”, “Torquing”

Factors controlling the moment:Factors controlling the moment:
 it is the product of theit is the product of the forceforce(F) times the(F) times the
perpendicular distanceperpendicular distance from the point of forcefrom the point of force
application to the center of resistance (d).application to the center of resistance (d).
 measured in hybrid units such as grams-measured in hybrid units such as grams-
millimeters (millimeters (gm-mm).gm-mm).
 Since the value of a moment is the productSince the value of a moment is the product
of a force value (Such as grams) multiplied byof a force value (Such as grams) multiplied by
linear value (Such as millimeters) -thereforelinear value (Such as millimeters) -therefore
either increasing the magnitude of the force oreither increasing the magnitude of the force or
applying the same force even further from theapplying the same force even further from the
center of resistance will increase the tendencycenter of resistance will increase the tendency
for rotation .for rotation .

Center of Rotation:Center of Rotation:
 if we draw the long axis of the tooth in its initial andif we draw the long axis of the tooth in its initial and
final positions, we will find that both these lines intersectfinal positions, we will find that both these lines intersect
at a point. This is the point around which the toothat a point. This is the point around which the tooth
rotates and is called therotates and is called the center of rotationcenter of rotation ..
Center of Rotation and Center of Resistance:Center of Rotation and Center of Resistance:
 The center of rotation can be at the center ofThe center of rotation can be at the center of
resistance, apical to the center of resistance, at the rootresistance, apical to the center of resistance, at the root
or at infinity. Their position will determine the type ofor at infinity. Their position will determine the type of
tooth movement.tooth movement.
Uncontrolled tipping:Uncontrolled tipping:
Controlled tipping:Controlled tipping:
Translation or bodily movement:Translation or bodily movement:
 Generally speaking, the center of resistance of a toothGenerally speaking, the center of resistance of a tooth
does not change, only the center of rotation changes.does not change, only the center of rotation changes.

CoupleCouple
The moment of coupleThe moment of couple
 instead of single force, we applyinstead of single force, we apply two forces equal in magnitudetwo forces equal in magnitude andand
opposite in directionopposite in direction at aat a distance,distance, the movement thus created is calledthe movement thus created is called
the moment of a couplethe moment of a couple
 The two forces cancel out any tendency for the center of resistance ofThe two forces cancel out any tendency for the center of resistance of
the pencil to move, but the moment created by the two forces does notthe pencil to move, but the moment created by the two forces does not
cancel each other. The pencil therefore, rotates about its center ofcancel each other. The pencil therefore, rotates about its center of
resistance regardless of the point of application of the couple.resistance regardless of the point of application of the couple.
 If the two forces of the couple act on opposite sides of the center ofIf the two forces of the couple act on opposite sides of the center of
resistance, their effect isresistance, their effect is additive.additive. However, if they are on the same side ofHowever, if they are on the same side of
the center of resistance, their effect isthe center of resistance, their effect is subtractive.subtractive. Either way,Either way, no net forceno net force
is felt by the pencil,is felt by the pencil, only a tendency to rotate.only a tendency to rotate.
 A couple applies a pure moment to a teeth.A couple applies a pure moment to a teeth.
Moment of forceMoment of force
 The concept of couple actually encompasses all situations involvingThe concept of couple actually encompasses all situations involving
rotation. In other words any rotational tendency is related to couple. But arotation. In other words any rotational tendency is related to couple. But a
moment (rotational tendency) can be achieved with a single force. Themoment (rotational tendency) can be achieved with a single force. The
moment thus created is calledmoment thus created is called the moment of the forcethe moment of the force

AxisAxis:: An axis is any point about which rotation takes place; it isAn axis is any point about which rotation takes place; it is
dependent only on the influence of outside forces any may bedependent only on the influence of outside forces any may be
located anywhere within or outside the rotating object.located anywhere within or outside the rotating object.
FulcrumFulcrum:: A fulcrum is a physical support such as an axle or the pivotA fulcrum is a physical support such as an axle or the pivot
under a lever. A fulcrum is an actual point of application of force,under a lever. A fulcrum is an actual point of application of force,
either applied or reactive, so it is an element of input into the totaleither applied or reactive, so it is an element of input into the total
force picture.force picture.
 Because of its structural function, a fulcrum may frequently beBecause of its structural function, a fulcrum may frequently be
the location of an axis as well.the location of an axis as well.
Couple-Clinical PointCouple-Clinical Point
 When the tooth is embedded within the alveolar bone weWhen the tooth is embedded within the alveolar bone we
cannot apply a couple with one force on the crown and the othercannot apply a couple with one force on the crown and the other
force on the root. We can apply a couple only on the exposed partforce on the root. We can apply a couple only on the exposed part
of the tooth. Using this couple mechanism we can achieve variousof the tooth. Using this couple mechanism we can achieve various
tooth alignment procedures,tooth alignment procedures, irrespective of the center of theirrespective of the center of the
resistance of the tooth.resistance of the tooth.
 Depending on the place in which the couple is acting, thisDepending on the place in which the couple is acting, this
rotational tendency (moment) has been called “rotation” (first order),rotational tendency (moment) has been called “rotation” (first order),
“tipping” (second order), or “torque” (third order)“tipping” (second order), or “torque” (third order)

 Moment – to – Force RatioMoment – to – Force Ratio
 If a bracket is 10 mm from the center ofIf a bracket is 10 mm from the center of
resistance, a force applied at the bracketresistance, a force applied at the bracket
causes the tooth to tip because of a momentcauses the tooth to tip because of a moment
that is 10mm times the magnitude of the force.that is 10mm times the magnitude of the force.
To counter-act this tendency to tip, a couple isTo counter-act this tendency to tip, a couple is
applied in the magnitude of the force. Thisapplied in the magnitude of the force. This
would be an applied moment-to-force ratio ofwould be an applied moment-to-force ratio of
10:1, resulting in displacement of the tooth as if10:1, resulting in displacement of the tooth as if
the force alone had been placed through thethe force alone had been placed through the
center of resistance.center of resistance.

Tooth MovementTooth Movement
 A comprehensive way of describing tooth movement isA comprehensive way of describing tooth movement is
to express the components experienced by the tooth atto express the components experienced by the tooth at
the center of resistance, which includes both translationthe center of resistance, which includes both translation
and rotation.and rotation.
 The force at the bracket is equivalent to a force at theThe force at the bracket is equivalent to a force at the
center of resistance plus a moment that will cause thecenter of resistance plus a moment that will cause the
tooth to tip.tooth to tip.
 Whenever a force is applied at the crown of a tooth,Whenever a force is applied at the crown of a tooth,
a tendency for the tooth to rotate, tip or torque is alsoa tendency for the tooth to rotate, tip or torque is also
created (moment of force). In addition to the forcecreated (moment of force). In addition to the force
applied, a couple may also be engaged intentionally toapplied, a couple may also be engaged intentionally to
partially correct, completely correct, or over-correct thispartially correct, completely correct, or over-correct this
tendency. By changing the ratio of the moment from thetendency. By changing the ratio of the moment from the
applied coupleapplied couple (counterbalancing moment)(counterbalancing moment) to the forceto the force
applied, the center of rotation of tooth movement can beapplied, the center of rotation of tooth movement can be
varied to produce the type of tooth movement desiredvaried to produce the type of tooth movement desired

Uncontrolled tipping:Uncontrolled tipping:
 When only a force is applied at the bracket toWhen only a force is applied at the bracket to
move a tooth, the equivalent force system at the centermove a tooth, the equivalent force system at the center
of resistance is the force plus a moment that will tip theof resistance is the force plus a moment that will tip the
crown in the direction of force. Without a moment tocrown in the direction of force. Without a moment to
counteract the tendency of the tooth to tip in thecounteract the tendency of the tooth to tip in the
direction of the force, the center of resistance of toothdirection of the force, the center of resistance of tooth
moves in the direction of the force, the crown movesmoves in the direction of the force, the crown moves
further than the center of resistance, and the apexfurther than the center of resistance, and the apex
actually moves in a direction opposite to the force.actually moves in a direction opposite to the force.
Therefore theTherefore the center of rotationcenter of rotation when the moment –towhen the moment –to
–force ratio is–force ratio is zerozero isis just apical to the center ofjust apical to the center of
resistance.resistance.

Controlled tipping:Controlled tipping:
 To counteract the tendency for tipping, a coupleTo counteract the tendency for tipping, a couple
can be applied intentionally at the bracket to produce acan be applied intentionally at the bracket to produce a
moment ofmoment of lessless magnitude in the opposite directionmagnitude in the opposite direction
(counterbalancing-moment). When a moment to force(counterbalancing-moment). When a moment to force
ratio of 7:1 is applied at the bracket, the equivalentratio of 7:1 is applied at the bracket, the equivalent
force system at the center of resistances is a force toforce system at the center of resistances is a force to
move the tooth plus a small net tendency for the crownmove the tooth plus a small net tendency for the crown
to tip in the direction of the force. Therefore theto tip in the direction of the force. Therefore the centercenter
of rotationof rotation when the moment-to-force ratio iswhen the moment-to-force ratio is 7:17:1 is atis at
the apex of the tooth,the apex of the tooth, and only crown movementand only crown movement
occurs.occurs.

Translation:Translation:
 To counteract the tendency for tipping, aTo counteract the tendency for tipping, a
couple can be applied intentionally to producecouple can be applied intentionally to produce
a moment ofa moment of equalequal magnitude in the oppositemagnitude in the opposite
direction (counterbalancing-moment). When adirection (counterbalancing-moment). When a
moment to force ration ofmoment to force ration of 10:110:1 is applied at theis applied at the
bracket, the equivalent force system at thebracket, the equivalent force system at the
center of resistance is a single force with nocenter of resistance is a single force with no
net moment. In the pure translation, thenet moment. In the pure translation, the
center of rotationcenter of rotation is considered to beis considered to be atat
infinityinfinity because no rotation occurs.because no rotation occurs.

Root movement:Root movement:
 When the counter-moment applied intentionally atWhen the counter-moment applied intentionally at
a bracket isa bracket is more thanmore than the moment of force, the tooththe moment of force, the tooth
moves in the direction of the force but the crown tips inmoves in the direction of the force but the crown tips in
the opposite direction. When a moment to force ratiothe opposite direction. When a moment to force ratio
of 13:1 is applied at the bracket, the equivalent forceof 13:1 is applied at the bracket, the equivalent force
system at the center of resistance is a force to movesystem at the center of resistance is a force to move
the tooth plus a small net tendency for the tooth to tipthe tooth plus a small net tendency for the tooth to tip
in the direction of the force. Thein the direction of the force. The center of rotationcenter of rotation
when the moment to force ratio is 13:1 iswhen the moment to force ratio is 13:1 is at the crownat the crown
of the toothof the tooth and only root movement occurs.and only root movement occurs.

Pure rotation:Pure rotation:
 If only a couple, and no force is applied to a tooth,If only a couple, and no force is applied to a tooth,
the tooth will rotate around its center of resistance andthe tooth will rotate around its center of resistance and
the tooth will not translate.the tooth will not translate. Because the action of aBecause the action of a
couplecouple does not dependdoes not depend on its point of application, aon its point of application, a
pure moment always acts at the center ofpure moment always acts at the center of
 The forces of couples cancel out any tendency forThe forces of couples cancel out any tendency for
the center of resistance of the tooth to move, but thethe center of resistance of the tooth to move, but the
moment produced by the couple causes the tooth tomoment produced by the couple causes the tooth to
rotate. The moment to force ratio is infinite and therotate. The moment to force ratio is infinite and the
center of rotationcenter of rotation isis coincident with the center ofcoincident with the center of

Predicting the force systems:Predicting the force systems:
 Understanding the physics that determine the force systemUnderstanding the physics that determine the force system
generated by activating orthodontic appliances discloses the forcegenerated by activating orthodontic appliances discloses the force
and moment that are applied to teeth at their point of attachment,and moment that are applied to teeth at their point of attachment,
usually at the brackets.usually at the brackets.
To deduce how each tooth will be displaced as a result of activation,To deduce how each tooth will be displaced as a result of activation,
the equivalent force systems acting at the centers of resistancesthe equivalent force systems acting at the centers of resistances
must be accessed subsequently.must be accessed subsequently.
Visual inspection method:Visual inspection method:
 In determining what forces are present, the arch wire is fullyIn determining what forces are present, the arch wire is fully
engaged into a bracket or tube and possible force system isengaged into a bracket or tube and possible force system is
evaluated by the eyeballing. This method is based on laws ofevaluated by the eyeballing. This method is based on laws of
static equilibrium and if not understood correctly can confusestatic equilibrium and if not understood correctly can confuse
further.further.

Static equilibrium:Static equilibrium:
 According to Newton’s third law, every action has anAccording to Newton’s third law, every action has an
equal and opposite reaction.equal and opposite reaction.
Requirement for static equilibrium:Requirement for static equilibrium:
Three requirements are accomplished automaticallyThree requirements are accomplished automatically
whenever static equilibrium is established. They are:whenever static equilibrium is established. They are:
 The sum of all forces present must equal zero.The sum of all forces present must equal zero.
 The sum of all moments present must equal zeroThe sum of all moments present must equal zero
 The sum of all forces and moments present must equalThe sum of all forces and moments present must equal
zero.zero.

 When an arch wire is fully engaged, we are generatingWhen an arch wire is fully engaged, we are generating
unequal moments. Forces are also generated to keepunequal moments. Forces are also generated to keep
the system balanced. Therefore, all the moments andthe system balanced. Therefore, all the moments and
forces will sum up to zero (i.e. always results in staticforces will sum up to zero (i.e. always results in static
equilibrium).equilibrium).
 This application is theThis application is the for every appliance,for every appliance, but notbut not
necessarily for every tooth to which it is attached,necessarily for every tooth to which it is attached, thethe
sum of the forces and the sum of the momentssum of the forces and the sum of the moments
must equal to zero.must equal to zero. That is because the orthodonticThat is because the orthodontic
appliance itself does not move instantaneously once itappliance itself does not move instantaneously once it
is placed (e.g. an arch wire fully engaged will not moveis placed (e.g. an arch wire fully engaged will not move
the teeth instantaneously).the teeth instantaneously).

PEAPEA

ANCHORAGE CONTROLANCHORAGE CONTROL
in PEAin PEA

 Bennett and McLaughlin emphasize the need to considerBennett and McLaughlin emphasize the need to consider
anchorage in all the three planes of space, i.e.,anchorage in all the three planes of space, i.e.,
horizontal, vertical and transverse (lateral).horizontal, vertical and transverse (lateral).
 Horizontal anchorage control means limiting theHorizontal anchorage control means limiting the
mesial movement of the posterior segment whilemesial movement of the posterior segment while
encouraging distal movement of the anterior segment.encouraging distal movement of the anterior segment.
When the posterior mesialize and the anteriors procline,When the posterior mesialize and the anteriors procline,
anchorage is being lost in the horizontal plane.anchorage is being lost in the horizontal plane.
 Vertical anchorage control involves the limitation ofVertical anchorage control involves the limitation of
the vertical skeletal and dental development in thethe vertical skeletal and dental development in the
posterior segments and limitation of the vertical eruptionposterior segments and limitation of the vertical eruption
of, or even intrusion of the anterior segments.of, or even intrusion of the anterior segments.
 In the transverse plane it comprises theIn the transverse plane it comprises the
maintenance of expansion procedures, primarily in themaintenance of expansion procedures, primarily in the
upper arch, and the avoidance of tipping or extrusion ofupper arch, and the avoidance of tipping or extrusion of
the posterior teeth during expansion.the posterior teeth during expansion.

The various adjuncts used to gain orThe various adjuncts used to gain or
preserve anchorage in all threepreserve anchorage in all three
dimensions of space.dimensions of space.
They can best be classified as extraoral andThey can best be classified as extraoral and
intraoral .intraoral .
 Extraoral adjuncts include headgearsExtraoral adjuncts include headgears
and facemasks.and facemasks.
 Intraoral adjuncts include lacebacks,Intraoral adjuncts include lacebacks,
transpalatal arches, holding arches, liptranspalatal arches, holding arches, lip
bumpers, etc.bumpers, etc.

Head gearHead gear
 Head gear can accomplishHead gear can accomplish
 Retraction of posterior teeth or all teeth in the archRetraction of posterior teeth or all teeth in the arch
 Restriction of mesial drift associated with growth,Restriction of mesial drift associated with growth,
premature loss of deciduous teethpremature loss of deciduous teeth
 reduction of slippage of posterior teeth in extractionreduction of slippage of posterior teeth in extraction
cases, eruption of teeth in intermaxillary growth spacecases, eruption of teeth in intermaxillary growth space
 Increase of vertical anchorage during treatment ofIncrease of vertical anchorage during treatment of
overbite or openbiteoverbite or openbite
 Protraction of teeth intra or intersegmentally, or evenProtraction of teeth intra or intersegmentally, or even
intermaxillarilyintermaxillarily

Head GearHead Gear
 The force system of each headgear is determined byThe force system of each headgear is determined by
the point of attachment of the strap (or rubberband) ofthe point of attachment of the strap (or rubberband) of
the headgear (also called the pull of the headgear) inthe headgear (also called the pull of the headgear) in
relation to the centre of resistance of the tooth, therelation to the centre of resistance of the tooth, the
segment or the entire jaw.segment or the entire jaw.
There are basically two ways of altering this attachmentThere are basically two ways of altering this attachment
relationship.relationship.
 Changing the orientation of the outer bow on an inner –Changing the orientation of the outer bow on an inner –
outer bow type of headgear i.e. bending it either up orouter bow type of headgear i.e. bending it either up or
down.down.
 Changing the length of the outer bow.Changing the length of the outer bow.
(Inner bow always lies passive in the molar tubes.)(Inner bow always lies passive in the molar tubes.)

The headgear can be classified, according to the point of origin, asThe headgear can be classified, according to the point of origin, as
follows:follows:
1. Cervical – anchorage obtained from the nape of the neck.1. Cervical – anchorage obtained from the nape of the neck.
2.Occipital – anchorage obtained from the back of the head.2.Occipital – anchorage obtained from the back of the head.
3. Parietal – anchorage obtained from upper part of the head.3. Parietal – anchorage obtained from upper part of the head.
B.B.
1. High – pull1. High – pull
Anchorage is obtained from the upper part of the head and theAnchorage is obtained from the upper part of the head and the
line of traction is above the centres of resistance of the maxillaline of traction is above the centres of resistance of the maxilla
and the maxillary dentition.and the maxillary dentition.
 2. Combi – pull2. Combi – pull
The line of traction is between high pull and cervical pull.The line of traction is between high pull and cervical pull.
 3. Cervical –pull3. Cervical –pull
Anchorage is obtained from the nape of the neck and the line ofAnchorage is obtained from the nape of the neck and the line of
traction is below the centre of resistance of the dentition.traction is below the centre of resistance of the dentition.

 Another variable of the headgear is the outerAnother variable of the headgear is the outer
bow of the facebow.bow of the facebow.
The outer bow can beThe outer bow can be
 Long.Long.
 MediumMedium
 Short.Short.
The line of traction or direction of pull can beThe line of traction or direction of pull can be
changed by varying either the length of thechanged by varying either the length of the
outer bow or the angulation between the outerouter bow or the angulation between the outer
and inner bows.and inner bows.

 Cervical – pull headgearCervical – pull headgear
 With cervical – pull headgear, when the inner andWith cervical – pull headgear, when the inner and
outer bows are in the same plane, there is clockwiseouter bows are in the same plane, there is clockwise
rotation of both the maxilla and the maxillary dentition.rotation of both the maxilla and the maxillary dentition.
The incisor region will move inferiorly to a greater extentThe incisor region will move inferiorly to a greater extent
than the molar region. The occlusal plane will also rotatethan the molar region. The occlusal plane will also rotate
in a clockwise direction.in a clockwise direction.
 If the outer bow is bent upwards so that the directionIf the outer bow is bent upwards so that the direction
of traction is between the centres of resistance of theof traction is between the centres of resistance of the
maxilla and the maxillary dentition, the maxilla will rotatemaxilla and the maxillary dentition, the maxilla will rotate
in a clockwise direction and the dentition will rotate in anin a clockwise direction and the dentition will rotate in an
anti-clockwise direction. Hence, the molars willanti-clockwise direction. Hence, the molars will
experience more downward influence than the incisorsexperience more downward influence than the incisors
and the occlusal plane will rotate in an anti –clockwiseand the occlusal plane will rotate in an anti –clockwise
direction.direction.
 cervical –pull headgear causes extrusion of thecervical –pull headgear causes extrusion of the
posteriors leading to an increase in the lower anteriorposteriors leading to an increase in the lower anterior
face height.face height. www.indiandentalacademy.comwww.indiandentalacademy.com

High cervical headHigh cervical head
geargear

High – pull headgearHigh – pull headgear
 When the direction of pull is placed behind theWhen the direction of pull is placed behind the
centres of resistance of the maxilla and the maxillarycentres of resistance of the maxilla and the maxillary
dentition, a clockwise rotation of the maxilla and thedentition, a clockwise rotation of the maxilla and the
maxillary dentition is observed. The molars will intrudemaxillary dentition is observed. The molars will intrude
and the incisors extrude. The net effect is a clockwiseand the incisors extrude. The net effect is a clockwise
rotation of the occlusal plane.rotation of the occlusal plane.
 When the direction of pull is in the front of theWhen the direction of pull is in the front of the
centres of resistance of both the maxilla and thecentres of resistance of both the maxilla and the
maxillary dentition, an anti-clockwise rotation ismaxillary dentition, an anti-clockwise rotation is
observed. The molars tend to extrude and the incisorsobserved. The molars tend to extrude and the incisors
intrude. The occlusal plane also rotates in an anti-intrude. The occlusal plane also rotates in an anti-
clockwise direction.clockwise direction.
 The best vertical and rotational control is seen whenThe best vertical and rotational control is seen when
the force passes through the centres of resistance ofthe force passes through the centres of resistance of
both the maxilla and the maxillary dentition. This isboth the maxilla and the maxillary dentition. This is
therefore the ideal set-up for vertical control and thetherefore the ideal set-up for vertical control and the
most desirable situation.most desirable situation.

Combee type headCombee type head
geargear

Combi-pullCombi-pull
 This type of headgear allows a distal force toThis type of headgear allows a distal force to
pass straight through the centre of resistancepass straight through the centre of resistance
of the maxillary dentition.of the maxillary dentition.
 In order to achieve this the outer bow of theIn order to achieve this the outer bow of the
facebow is angled upward by about 15facebow is angled upward by about 15
degrees.degrees.
 This allows for a more distalization of the molarThis allows for a more distalization of the molar
with minimal rotation.with minimal rotation.

Interlandi head gearInterlandi head gear

High pull and combeeHigh pull and combee
pullpull

Occipital head gearOccipital head gear

Occipital HG withOccipital HG with
short OBshort OB

Occipital HG straightOccipital HG straight
upwardupward

Occipital pull headOccipital pull head
geargear

Force and duration ofForce and duration of
wearwear
 Most authors believe that headgear forces of 400-800Most authors believe that headgear forces of 400-800
gm are adequate.gm are adequate.
 Light continuous force seem to produce moreLight continuous force seem to produce more
dental changes than skeletal, while heavy forces anddental changes than skeletal, while heavy forces and
intermittent wear are found to produce more skeletalintermittent wear are found to produce more skeletal
changes.changes.
 Marcotte suggests force values of 200 gm per side inMarcotte suggests force values of 200 gm per side in
the mixed dentition and 500 gm per side in thethe mixed dentition and 500 gm per side in the
permanent dentition, for 18-20 hours per day.permanent dentition, for 18-20 hours per day.
 Bennett and McLaughlin advocate a force of 150-250Bennett and McLaughlin advocate a force of 150-250
gm for occipital-pull and 100-150 gm for cervical-pull.gm for occipital-pull and 100-150 gm for cervical-pull.

 Extrusion of teeth and steepening of OPExtrusion of teeth and steepening of OP
-cervical gear with OB even or low-cervical gear with OB even or low
 Extrusion of teeth and flattening of OPExtrusion of teeth and flattening of OP
CG with OB very highCG with OB very high
 Intrusion of teeth and steepening of OPIntrusion of teeth and steepening of OP
OG with OB post to CresOG with OB post to Cres
 Intrusion of teeth and flattening of OPIntrusion of teeth and flattening of OP
OG with OB ant to CresOG with OB ant to Cres

Good distal force and flattening of OPGood distal force and flattening of OP
 Combee gear above CresCombee gear above Cres
Good distal force and steepening of OPGood distal force and steepening of OP
 Combee gear below CresCombee gear below Cres
Good distal force and no change in OPGood distal force and no change in OP
 Combee gear with OB through CresCombee gear with OB through Cres

Delaire facial maskDelaire facial mask

Delaire face maskDelaire face mask

Petit face maskPetit face mask

Hickham chin cupHickham chin cup

Anchorage controlAnchorage control
1. Horizontal plane (anteroposterior)1. Horizontal plane (anteroposterior)
 a.a. Control of anterior segmentsControl of anterior segments
LacebacksLacebacks
BendbacksBendbacks
 b.b. Control of posterior segmentsControl of posterior segments
Upper arch: Headgears, Transpalatal arch,Upper arch: Headgears, Transpalatal arch,
Nance holding archNance holding arch
Lower arch: Lingual arch, Class III elastics,Lower arch: Lingual arch, Class III elastics,
Lip bumberLip bumber

Bend backBend back

Anchorage control inAnchorage control in
anterior segmentsanterior segments

Anchorage control inAnchorage control in
vertical planevertical plane

Anchorage in verticalAnchorage in vertical
planeplane

Vertical molar controlVertical molar control

2. Vertical plane2. Vertical plane
a.a. Incisor controlIncisor control
 Utility archesUtility arches
 Avoid engaging the incisors when the canines have aAvoid engaging the incisors when the canines have a
negative angulation.negative angulation.
b. Molar controlb. Molar control
 Upper second molar banding to be avoided initially (inUpper second molar banding to be avoided initially (in
high angle cases).high angle cases).
 Expansion if required should be achieved by bodilyExpansion if required should be achieved by bodily
movement of the posterior teeth (in high angle cases).movement of the posterior teeth (in high angle cases).
 Transpalatal arch should be 2-3 mm away from theTranspalatal arch should be 2-3 mm away from the
palatepalate
 High pull or combi pull headgear to be usedHigh pull or combi pull headgear to be used
 Posterior bite planes or bite blocks.Posterior bite planes or bite blocks.

3. Lateral or transverse plane3. Lateral or transverse plane
 a. Maintenance of upper and lowera. Maintenance of upper and lower
intercanine widthintercanine width
 b. Correction of molar crossbite withb. Correction of molar crossbite with
Rapid maxillary expander, Quad helix orRapid maxillary expander, Quad helix or
Transpalatal arch.Transpalatal arch.

Transpalatal archTranspalatal arch

TPA ArchTPA Arch

Nance palatal buttonNance palatal button

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