Biomechanics of intrusion appliances final copy..

BIOMECHANICS OF INTRUSION
APPLIANCES
www.indiandentalacademy.com

MENU
1. INTRODUCTION
2. BASICS OF BIOMECHANICS
3. DEFINATION AND CLASSIFICATION OF INTRUSION.
4. PRINCIPLES OF INTRUSION
5. MORPHOLOGICAL CHARACTERISTICS OF DEEPBITE.
6. INTRUSION MECHANICS IN BEGGS.
7. INTRUSION MECHANICS IN PEA.
TRUE INTRUSION.
A. 2 X2 AND 2 X4 APPLIANCE(UTILITY ARCH)
B. TIPBACK SPRINGS ( INTRUSION SPRINGS)
C. BURSTONE’S CONTINUOUS INTRUSION ARCH.
D. BURSTONE’S THREE PIECE INTRUSION ARCH.

8. INTRUSION WITH ALPHA AND BETA MOMENTS
9. K-SIR (KALRA SIMULTANEOUS INTRUSION AND
RETRACTION.
10. CONNECTICUT INTRUSION ARCH.
APPARENT INTRUSION
A. REVERSE CURVE NiTi
B. ANTERIOR BITE PLANE.
C. INCLUDING 2ND
MOLAR IN THE STRAP-UP.
11. CONCLUSION.

INTRODUCTION
• Understanding the biomechanical principles
underlying orthodontic appliance activations is
essential for executing efficient and successful
orthodontic treatment.
• By varying the ratio of moment to force applied to
teeth, the type of tooth movement experienced can
be regulated by the orthodontist.

RE- FRESH- MENTS

BASICS
FORCE:
It is defined as an act upon a body that changes or tends to change the
state of rest or motion of the body.
Force is a vector it has both magnitude and direction.
The forces are indicated by straight arrows

Moment
• A moment is defined as tendency to rotate and
may refer to rotation, tipping, or torque in
orthodontic terminology.

F
d
MOMENT is the product of the force times the
perpendicular distance from the point of force.
M = F x d
It is measured as application to the center of
resistance in grams – millimeters.

COUPLE
Two equal and opposite, noncolinear forces are
called a couple

AdditiveAdditive
+
F1
F2
F1XDM1= M2=F2XD
D
M=F X D
If the 2 forces of the couple
act on opposite sides of the
center of resistance, their
effect is additive.

SubtractiveSubtractive
+
F1
F2
M1=F1XD1 M2=F2XD2
D1
D2
M= F X (D1-D2)
If they are on the same side of the
center of resistance, they are
subtractive.

Uncontrolled Tipping 8----Uncont-Tip.swf
A force applied to move a tooth in the desired direction,
but the crown will also tip in that direction while the apex
moves in the opposite direction.
In this case, no moment has been applied to prevent the
tipping that occurs. Only a force has applied the moment-
to-force ratio M/F applied is 0/F or 0.

CONTROLLED
TIPPING/CROWN MOVEMENT
9---Controlled-Tip.swf
The crown moves in the direction of force but the root
position remains the same or get minimally displaced.
Here Center of rotation lies at apex of the root.
MF>MC

TRANSLATION 10----transalation.swf
With an applied M/F of 10/1, the tooth will
translate in the direction of the force without
tipping. This is often referred to as pure
translation.
In pure translation, the center of rotation is
considered to be at infinity because no rotation
occurs.
MF=MC

ROOT MOVEMENT 11--root-Movement.swf
When the countermoment applied intentionally at a
bracket is more than 10 times the magnitude of the force
applied, the tooth moves in the direction of the force but
the crown tips in the opposite direction.
MC > MF

PURE ROTATION 12---pure rotation.swf
•If only a couple, and no net force is applied to a tooth, the
tooth will rotate around its center of resistance and the
tooth will not translate.
•Because the action of a couple does not depend on its
point of application, a pure moment always acts at the
center of resistance.
•The moment-to-force ratio is infinite and the center of
rotation is coincident with the center of resistance.

APPETIZERS

When the apex of the V bend is half way between
the brackets, the wire exerts equal and opposite
couples at the both attachments and no forces
V BEND PRINCIPLE

The V bend is moved off center, the couple
nearer the bend increases and couple further
from the bend decreases, forces result to
maintain appliance equilibrium

When the V bend is at 1/3rd
the distance between the
brackets, a couple is only present at the bracket
nearer the bend. No couple is experienced at the
bracket further from the bend and forces result to
maintain equilibriumwww.indiandentalacademy.com

When V bend is very close to one bracket, couple in
the same direction is experienced at both bracket,
with larger couple at the bracket closer to the bend.
Forces increase, as the bend is moved further off
center

A step bend, regardless of where it is placed, results
in equal couples in the same direction at both
attachments. Forces are at maximum.

ONE COUPLE SYSTEM
One Couple Appliances—Statically Determinate
Systems
A 1-couple orthodontic appliance is inserted into a
bracket or tube at 1 end and is tied as a point
contact at the other.
The bracket end or tube experiences couple whereas
the tied end experiences force.

Begg appliance is a good example of single
couple system.
Stage I arch wire
20mm
50 gm
50 gm
1000 gm

TWO COUPLE SYSTEM
• Two-Couple Appliances—Statically Indeterminate
Systems
• A 2-couple appliance is one that is engaged into
attachments at both ends. A couple, therefore, may
be generated by the wire at either or both
attachment sites.

.
INTRUSION
Intrusion refers to the apical movement of the
geometric center of the root (centroid) in respect
to the occlusal plane or plane based on the long
axis of the tooth.

True intrusion is achieved by moving the root apices
of the anteriors closer to the bony base.
Relative intrusion is achieved by keeping them
where they are, while the mandible grows and the
posterior teeth erupt.
Apparent intrusion is achieved by extrusion of the
posterior teeth

ABSOLUTE INTRUSION
RELATIVE INTRUSION
APPARENT INTRUSION

• The difference between relative and apparent is
that when the vertical growth of the ramus
compensates for the increase in molar height ; that
is when the mandibular plane angle is maintained,
it is relative intrusion
• If mandibular plane angle increases and if the
mandible rotates backwards and downwards, it is
called apparent intrusion.

MORPHOLOGIC CHARACTERISTICS
OF DEEP OVERBITE
Dentoalveolar Deep Overbite
The dental alveolar deep overbite is of two types :
1. True deep bite- caused by infra-occlusion of the
molars.
2. Pseudo deep bite - caused by supra eruption of the
incisors.

• According to Proffit the optimum force for intrusion
is 15-25 gm.
• Values depend in part on the size of the tooth.
Smaller values appropriate for incisors. Higher
values are for multirooted posterior teeth.

According to Burstone the average force
values for intrusions are :
•Moment values are based on 30 mm distance from incisors to the
center of resistance of posterior segment.
Teeth Force /Side Total force in
midline
Moment/side
(gm- mm)
Upper
Central incisors.
Central & lateral incisors.
Central & lateral incisors &
canine.
25
50
100
50
100
200
750
1,500
3,000
Lower
Central & lateral incisors.
Central & lateral incisors &
canines.
20
80
40
160
600
2,400

1. Controlling force magnitude and constancy.
The lowest magnitude of force capable of intruding must be
used.
Heavier force cause
a) root resorption
b) side-effects of extrusion on anchor unit.
Constant force by low load-deflection spring.
Low load deflection springs are more accurate and need
less force per millimeter deactivation than high load-
deflection spring.
PRINCIPLES OF INTRUSION

2. Anterior single point contact
• The intrusion arch is not placed directly into the
brackets of the teeth to be intruded. It is tied to the
anterior segment usually forming two point
contact.

• If placed in bracket it may introduce torque. If
labial torque is placed then there will be increase
in intrusive force thereby increase side-effect on
anchorage.
• If lingual root torque is present there is decrease in
intrusive force but may actually extrude the teeth.

3. Point of force application
• Intrusive force through the center of resistance of any
tooth will intrude the tooth without producing any labial
or lingual rotation of the tooth being intruded.
• If intrusive force is labial to CORe a greater moment is
created which will flare the tooth.

• To overcome,
• 1. if tooth is forwardly placed, retrude and then
intrude.
• 2. and to apply the vertical force lingual to the

Control of force vector
Normal axial
inclination
Proclined
incisors.
Retroclined
incisors

4. Selective intrusion
• Leveling with a continuous arch or with a
sectional wire can produce undesirable side
effects.
• Many times the overbite is corrected not because
of intrusion but by extrusion.

5. Control of the reactive unit
• The largest effect upon the anchorage unit will be
a result of the moment produced by the intrusive
force which is large because of the long moment
arm.
• So add more teeth for anchorage.
• Keep intrusion forces as low as possible.

• Do as much retraction as possible to decrease the
length of moment arm.
• Also, moment on the molar will tip molar crown
lingually and root buccally, which can be
prevented by lingual arch or TPA.

6. Avoiding extrusive mechanics
• Extrusive mechanics such as employing class II or
class III elastics should be avoided in patient who
need genuine intrusion.

MAIN COURSE

INTRUSION MECHANICS IN BEGG
• In the use of the standard, or pure Begg technique,
increased anterior overbites are reduced by the
combined mechanical effects of the anchor bends
and the vertical component of force of the
intermaxillary elastics.
• Once pinned into the bracket slots of the incisors,
intrusive forces are applied to the incisors and an
extrusion force applied to the molars

DIFFERENTIAL MOMENT
• When wire is engaged
in bracket slot and anti-
clockwise moment is
generated in anterior as
the force is labial to the
center of resistance and
reciprocal clockwise
moment of greater
magnitude on molar.
This is referred to as
differential moment.

TRADITIONAL BEGGS
• We apply forces from the
archwire and the class II
elastics. Thus we have two
vectors of force acting at a
point. The resultant of
these forces will be applied
on the tooth or the
direction in which the
tooth will move.
• As the force is passing
behind the COR thereby,
causing a moment
resulting in uncontrolled
tipping.www.indiandentalacademy.com

Power arm with
class I elastics.
• Now at present we
switch from class II to
class I elastics,
keeping the force
constant, the resultant
passes close to the
Consequently, the
moment is reduced
and rotational effect is
decreased.
REFINED
BEGGS

• If we use power arm
and engage class I
elastics, the resultant
force passes even
closer to center of
resistance of the tooth,
resulting in controlled
tipping and intrusion.

• The Begg appliance works
to our satisfaction in cases
of bidental protrusion.
This is because in most of
cases the bite is shallow
and class I or horizontal
force is delivered right
from the beginning. This
causes the resultant to
pass close to the CORe of
the teeth, leading to
controlled tipping of the
upper and lower anteriors.

• Buccolingual control, a
round archwire in a round
tube cannot control the
molars buccolingually and
the anchor bends which
we incorporate in the
archwire produce a
number of side effects.
• There is extrusion as the
force is buccal to the
CORe of molar, the
molars tend to roll
lingually.
• This can be overcome by
TPA or lingual arch.

• The intrusive force
generated by the
archwire converges the
teeth more because it is
passing mesial to the
center of resistance. So
the net intrusive effect is
almost nil.
converging incisors.swf

• The intrusive force passes
distal to the center of
resistance. The moment
created causes the teeth to
tip further distally.
Flash Player Movie

• Therefore, the intrusive
force generated by the
archwire used in Begg is
effective only where the
anterior teeth are upright
mesiodistally, as the force
will pass through the

PEA

INTRUSION IN PEA
INTRUSION ARCH WIRES
Intrusion can be accomplished in two ways with
intrusion arches.
1. With continuous archwire that bypasses the
premolars and canine teeth.
2. With segmented base archwire. So that there is no
connection along the arch between the anterior
and posterior segments and an auxiliary
depressing arch.

UTILITY ARCH (2X4 APPLIANCE)
• This auxiliary archwire was developed and refined
by Ricketts for bioprogressive therapy.
• The utility arch engages only two molars and the
four incisors. It is commonly known as a 2 X 4
appliance.

Incisal
segment
Posterior
vertical
segment
Vestibular segment
Molar
segment
Anterior
vertical
segment
PARTS OF UTILITY ARCHwww.indiandentalacademy.com

Gable bend
Cinching
distally
Tip-back bend

MATERIAL FOR UTILITY ARCH
Blue elgiloy of 0.016" x 0.016"
0.016" x 0.022”
Dimension in an 0.022" slot.
A utility arch can even be made with 0.014" or
0.018" round wires.

• It produces 60-100 gms on the lower incisors for
intrusion.
• The overall effect is intrusion and possible
torquing of the lower incisors as well as tipping
back of the molars.
• 5 mm space between the anterior border of the
auxiliary tube and the posterior vertical segment
of the utility arch allows tying back the utility
arch.

ACTIVATION
Two types of forces can be produced using the
design which are retraction and intrusion.
Retraction can be achieved by grasping the end of
the molar segment with a Weingart plier distal to
the molar tube and then turning this segment
gingivally after pulling the wire posteriorly
through the tube. This type of activation prevents
proclination of the lower incisors during intrusion

• Intrusion of the anterior teeth can be produced in
one of the two ways:
• 1. After ligating the utility arch into the anterior
brackets, an intrusive force can be produced by
placing an occlusally directed gable bend in the
posterior portion of the vestibular segment of the
archwire

2. Other type of activation involves placing a tip
back bend in the molar segment. The tip back
bend causes the incisal segment of the archwire to
lie in the vestibular sulcus. The intrusive force is
created by placing the incisal segment of the
utility arch into the bracket of the incisors. This
activation creates a moment that allows for the
long action of the lever arm of the utility arch to
intrude the incisors.

• The tip back bend in
the molar segment
leads to posterior
tipping of the first
molars.
• Which can be avoided
by placing a gable
bend in the posterior
aspect of the
vestibular segment
or a
transpalatal arch can
be used.www.indiandentalacademy.com

• Bench also recommends the placement of buccal
root torque in the lower molar region to anchor the
roots of the molars in cortical bone. This type of
force also produces lingual crown torque which is
counter balanced by placing 10 mm expansion in
the utility arch in the molar region during
fabrication

Retraction Utility Arch
• Retraction and intrusion of the
incisors by incorporating loops in
the archwire anterior to the
anterior vestibular segment.
• Retraction and intrusion can be
produced by activating the
retraction arch in a similar fashion
previously described of the
intrusion utility arch.
• The incorporation of the loop into
the design allows for a longer
range of activation.

ACTIVATION
• 1. To grasp the extension posterior to the auxillary
tube. The wire is pulled 3-5 mm posteriorly and
them bent upward at an angle.
• 2. An occlusally directed gable bend in the
vestibular segment is used to produce intrusion.

BURSTONE’S INTRUSION
SPRING

• By Burstone,
• These springs are made of 0.017”x 0.025” TMA
wire. The upper and lower arches have to be
leveled and aligned and a rigid stainless steel wire,
preferably 0.017”x 0.025” dimension is engaged.
• Anchor is reinforced by TPA and lingual holding
arch.

• The intrusion springs can be made with or without
helix. The wire is bent gingivally mesial to the
molar tube and then helix is formed. The mesial
end is bent in hook and is engaged onto the main
archwire distal to the lateral incisors.
• The mesial end of the spring lies passively at the
height of the mucobuccal fold and the spring is
activated by pulling the hook down and engaging
in onto the archwire.

Continuous intrusion arch
The basic mechanism for intrusion consists of three parts:
1. The posterior anchorage unit.
2. The anterior segment.
3. The intrusion arch itself.
Initial alignment of anterior teeth is not necessary when
performing intrusion.
The intrusion arch itself is fabricated from 0.017" x 0.025"
TMA or 0.016" x 0.022" TMA.

Continuous intrusion arch

DESSERTS

Burstone’s Three piece
Intrusion Arch
• The basic mechanism for intrusion consists of
three parts:
• 1. The posterior anchorage unit.
• 2. The anterior segment.
• 3. The intrusion spring itself.

Intrusion
cantilever
Posterior
anchorage unit
Anterior
segment
with
posterior
extension

• The anterior segment is bent gingivally distal to
the laterals and then bent horizontally creating a
step of approximately 3mm.
• The distal part extends posteriorly to the distal end
of the canine bracket where it is formed into a
hook.
• The anterior segment should be made of
0.021”x0.025” stainless steel wire to prevent side
effects created by bending of the wire during force
application.

• The intrusion cantilevers are made from 0.017" X
0.025" TMA wire.
• The wire is first bent gingivally mesial to the molar
tube and then a helix is formed. On the mesial end
the cantilever, hook is bent through which the
intrusion force can be applied to the anterior
segment.
• The cantilever is then activated by the making a
bend mesial to the helix at the molar tube, and then
cinched back.

• The anterior segment which is extended till the
distal end of the canine bracket, i.e., 2-3 mm distal
to the center of resistance of the anterior segment
of teeth allows distal placement of the intrusive
force, which is desired in a case of flared incisors.
• A small distal force can be added by placing an
elastomeric chain extending form the molars to the
anterior segment of wire on each side.
• This force facilitate simultaneous intrusion and
retraction by redirecting the force parallel to the
incisor long axis.

• The center of resistance of the four incisors is usually
estimated to be halfway between the crest of the
alveolar bone and the apex of the lateral incisors root in
the sagittal plane.
• An intrusive force through the centre of resistance of
the four incisors will cause pure intrusion of these
incisors along the line of action of the force. This same
effect can be produced in a three piece intrusion arch
with force passing perpendicular to the distal extension
of the anterior segment and through the center of
resistance.

• It is possible to change the direction of the net
intrusive force by applying a small distal force. Thus,
if intrusion along the long axis of the incisors in
indicated, the point of intrusive force. can be moved
anteriorly and a small distal force will help to direct
the intrusive force along the long axis of the incisors.
• If the intrusive force is placed distal to the centre of
resistance and an appropriate small distal force is
applied, intrusion and simultaneous retraction of the
anterior teeth occurs. This is because of the
clockwise moment created around the centre of
resistance of the anterior segment.

The overall force system includes an anterior
intrusive force and a posterior extrusive force and
a tip back moment.
But, when a small force is added between the
anterior and posterior segments with an
elastomeric chain a posterior tip forward moment
is formed. This added force which produces a top
forward moment on the posterior, reduces the tip
back moment on posteriors and thus occlusal
plane to tip.

LOOP MECHANICS
When a offset bend is placed in the wire like
anchor bend in Begg, a differential moment is
created, with a greater clockwise moment in the
posterior and anticlockwise moment in the anterior
segment. The side with the greater moment
shows extrusion and there is intrusion on the side
with the lesser moment.www.indiandentalacademy.com

• The force system of an orthodontic appliance
determine the type of tooth movement expressed.
• The force act in all three planes of space (first ,
second and third order) creating moments.

• Alpha moment:- this is the moment acting on the
anterior teeth (often termed anterior torque).

• Beta moment:- this is the moment acting on the
posterior teeth. Tip-back bends placed mesial to
the molars produce an increased moment.

• Horizontal forces:- these are the mesio-distal
forces acting on the teeth.

• Vertical forces:- These are intrusive – extrusive
forces acting on the anterior or posterior teeth. These
forces generally result from unequal alpha and beta
moments.

Alpha and beta bends.
150
250
If the beta moment is greater than the alpha moment, anchorage is
enhanced by the mesial root movement of the posterior segment, and
there is a net intrusive force on the anterior teeth.

• The K-SIR (Kalra
Simultaneous Intrusion and
Retraction) archwire is a
modification of the segmented
loop mechanics of Burstone
and Nanda
• K-SIR archwire: .019“x.025"
TMA archwire with closed U-
loops 7mm long and 2mm
wide.
K- SIR APPLIANCE

• 90° bends placed in archwire at level of U-loops.
• Centered 90° V-bend creates two equal and opposite
moments (red) that counter tipping moments (green)
produced by activation forces.

• Archwire with off-center 60° V-bend placed about 2mm distal
to U-loop.
• Off-center V-bend creates greater moment on molar,
increasing molar anchorage and intrusion of anterior teeth.

• 20° antirotation bends placed in archwire just distal to U-
loops.

• Trial activation performed on each loop.
• Archwire after trial activation.

Neutral position of loop determined with mesial and distal
legs extended horizontally. In neutral position, loop is
3.5mm rather than 2mm wide.

K-SIR archwire in place prior to cinching back. First molar
and second premolar are connected by segment of .019"x .
025" TMA wire.
Archwire cinched back to activate loop about 3mm, so that
mesial and distal legs are barely separated.

THE CONNECTICUT INTRUSION ARCH
• The CTA is fabricated from a nickel titanium alloy. It
incorporates the characteristics of utility arch as well as
those of the conventional intrusion arch.
• Two wire size are available 0.016” x 0.022” and 0.17” x
0.25”.

• The maxillary and mandibular versions have anterior
dimensions of 34mm and 28mm, respectively.
• In most cases, the wire is not directly ligated into the bracket
slots, the anterior wire dimension is adequate to allow for it.
• The bypass, located distal to the lateral incisors, is available in
two different lengths to accommodate for extraction,
nonextraction, and mixed dentition cases.

Dimensions of preformed CONNECTICUT INTRUSION ARCHES
• ) Maxillary CTA Mandibular CTA
Anterior dimension 34mm 28mm
Posterior dimension: long
(non-extraction
22mm 22mm
Posterior dimension: short
(extraction and mixed
dentition)
15mm 15mm

MECHANICS
• The CTA’s basic mechanism for force delivery is a V
bend lies just anterior to the molar brackets.
• When the arch is activated, a simple force system results,
consisting of a vertical force in the anterior region and a
moment in the posterior region.

• Incisor intrusion requires 50g of force directed apically
along the center of resistance.
• The moment created at the molar will also vary, according
to the amount of force at the incisor multiplied by the
distance at the molars. These minor changes can be made
to ensure proper force delivery.

• A pure intrusion arch would have a point contact at the
incisors.
• Insertion of the wire into the incisor brackets, however, will
tend to flare the incisors, which may or may not be
desirable.
• The CTA’s point of force application is anterior to the
center of resistance, which will flare the incisors.
• A tight cinch-back—a sharp bend distal to the molar tube,
preventing forward slippage of the wire—will prevent
incisor flaring during intrusion and produce some retraction
of the incisors during molar tipback.

ANTERIOR BITE PLANE

ANTERIOR BITE PLANE
• In growing patient an efficient method of overbite
reduction is the use of an anterior bite plane.
• Anterior plane inhibits the vertical development of the
lower incisors and allows differential eruption of the
posterior teeth to take place. The lower incisors are not
intruded.
• The anterior bite plane should be just thick enough to
disengage the posterior teeth by 2-3 mm.

• Motivate the patients to wear the appliance 24 hours
especially during eating so that the efficiency of the
appliance is enhanced. Within about two months the
posterior teeth will be in occlusion and the overbite will be
reduced
• Maintenance of overbite reduction will require a lower
fixed appliance before the bite plane is removed; the lower
arch should be fully bonded and an archwire should be
fitted with sufficient dimension to maintain control of the
vertical positions of the incisors.

REVERSE CURVE NITI

• When a reverse curve NiTi wire is introduced with the
concept that two equal and opposite moments will be
produced as it is two couple system.
• If the moments are not equal, as the system to come into
equilibrium vertical forces are created.
• Extrusion in the posteriors and intrusion in the anterior
will take place

Inclusion of second molars
Extrusion of second molars brings about a greater bite
opening in the incisor region.
Second molars are extruded by keeping molar tube more
gingivally.
One mm of extrusion of both upper and lower molars will
be lead to backward rotation of the mandible.

CONCLUSION
• This seminar provides an overview of the appliances and
the biomechanical principles of the same.
• Rather than knowing the nitty-gritty of individual
appliances it is more important to grasp the fundamentals.
• This enables an operator to employ his creative and
intellectual ability to get the best out of an appliance
system.

RECIPES
• Steven J. Lindauer, “Basics of mechanics” semin orthod,
7, 2001: 1-15
• Charles J. Burstone “ Biomechanics of deep overbite
correction” semin orthod 2001: 7: 26-33
• Bhavana Shroff, Steven J Lindauer , Charles J
Burstone “ Segmented approach to simultaneous intrusion
and space closure: biomechanics of three piece base arch
appliance” Am J Orthod dentofac Orthop 1995:107: 136-
43.
• Jayade “ Refined beggs”
• Richard J. Smith, Charles J. Burstone, “ Mechanics of
tooth movement” vol 85, 294-307
• Mcnamara A J and Brudon WL, Orthodontic and
dentofacial orthopedics. Needham press, 2001.

• Charles J. Burstone, Modern edgewise mechanics and the
segmented arch technique” ed. Ormco 1995.
• Marcotte MR: Biomechanics In orthodontics. B.C. Decker
Inc., 1990.
• Nanda: Biomechanics in clinical orthodontics. W.B.
Saunders Company 1975.
• Varun Kalra, “simultaneous intrusion and retraction of the
anterior teeth” JCO 1998 p535-540.
• Nanda R, Marzban R, Kulberg, “The Connecticut Intrusion
Arch” JCO1998 p 708 – 715

THANK
YOU

Biomechanics of intrusion appliances final copy..

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