intrusion

Intrusion
www.indiandentalacademy.com

Introduction
• Intrusion has always been a challenge to the
orthodontist,while some authors claim it is
possible to achieve intrusion some others
claim that it is impossible to achieve true
intrusion. The biomechanical and
histological basis of this tooth movement
has been a difficult problem for evaluation
and understanding.

Definitions
•Intrusion is defined as the apical movement of
the geometric center of the root in respect to the
occlusal plane or a plane based on the long axis of
the tooth
•Pseudointrusion refers to the labial tipping of
the incisor around the centroid
•Relative intrusion, deep bite correction by the
extrusion of the posterior teeth rather than the true
intrusion of the anterior teeth

Planning for intrusion
• Natural plane of occlusion – original axial
inclination and alignment of the posterior
teeth
• Anterior aesthetics – the relationship of the
incisor to the upper lip
• The amount of attached gingiva present in the
mandibular incisor region
• A – B discrepancy

Deep bite
correction
Intrusion of anteriors
Extrusion of posteriors

Correction by extrusion
Extrusion of the
posteriors
Increases lower
facial height
Steepening of the
occlusal plane
Worsening of
Class II Profile
Downward and
backward rotation
of the mandible

Intrusion of the
anteriors
Control of the
vertical dimension
Forward rotation
of the mandible
Improves the
Class II Profile
Correction by Intrusion

Intrusion
IntrusionIntrusion
Bio MechanicalBio Mechanical HistologicalHistological

Factors affecting intrusion
• Controlling force magnitude and constancy
• Anterior single point contacts
• Point of force application
• Selective intrusion
• Control of reactive units
• Avoid extrusive mechanics

Force magnitude and constancy
Lowest magnitude
of force
Force level
increased
Reciprocal effect on
posterior segment
No intrusion Root
resorption
Experience a
vertical force
Worsening of the
Class II Profile
TRUE
INTRUSIO
N

• Avoid cervical pull
headgear with outer
bows placed high
• Avoid use of class II or
class III elastics
• Avoid placement
of curve of Spee in
arch wire
Anterior single point
of contact
Possible to determine the
exact amount of force exerted
by the appliance system
No moment
introduced into the
wireTRUE INTRUSION

Point of application
Perpendicular to the distal
extension of the anterior
segment
Passing through center of
resistance
Intrusion of incisor segment
Apply a distal force –
changes the direction of the
resultant forcewww.indiandentalacademy.com

Point of Application
Point of application as close to the distal of the lateral
incisor bracket, anterior to the center of resistance
Force of application is redirected
with a distal force
Force of application is more
anterior
The force is passing through the
center of resistance and is parallel
to the long axis of the tooth
True intrusion and no retraction

Point of application
Force passing
through the
center of
resistance
Line of action is
lingual to center of
resistance and
parallel to the long
axis of the tooth
Combination of intrusion
and tipping of anteriors
Force of
application is
redirected with a
distal force

Control of the reactive unit
Minimize the
intrusive force
Minimize the
intrusive force
As many teeth as
possible joined to
form the posterior
segment
As many teeth as
possible joined to
form the posterior
segment
Transpalatal archTranspalatal arch
BEST CONTROL
OVER POSTERIOR
TEETH
Anchor loss
Moment arm is large
from the anterior to
posterior segment
Head gearHead gear www.indiandentalacademy.com

Histological aspect of intrusion
Pressure SideOn side towards
which force is applied
Resorption of the
cortical bone
DETACHMENT
Resorption of the
fibres embedded in
the alveolar bone

Histology of the tension side
Tension SideTension Side On side from which force
is applied
On side from which force
is applied
The fibre straightened as
the tooth moves away
from the alveolar bone
The fibre straightened as
the tooth moves away
from the alveolar bone
Bony wall not resorbed ~
fibres remain attached to
the cortical and the
cementum
Bony wall not resorbed ~
fibres remain attached to
the cortical and the
cementum
Lengthening of the
fibre in the
intermediate plexus
Lengthening of the
fibre in the
intermediate plexus
DETACHMENT

Lateral force importance in intrusion
• Depressing force
• Strongly resisted by the
oblique fibers of the
periodontal membrane
• Has to be pathological to
bring about tooth
movement
• Strongly resisted by the
oblique fibers of the
periodontal membrane
• Has to be pathological to
bring about tooth
movement
unaccompanied by lateral
force
• No complete detachment
of oblique fibres
• No intrusion possible
unaccompanied by lateral
force
• No complete detachment
of oblique fibres
• No intrusion possible
Graber and Aisenberg Stewart McDowell

IntrusionIntrusion
BEGGBEGG PAEPAE

Intrusion mechanics in Begg
Posterior
Distal tipping
Mesial in rotation
Extrusion
Anchor bend
Anterior
Class II elastics
Extrusion of anteriors
Retraction of the anteriors
Prevents the crown lingual –
root labial movement
Crown labial, root lingual
of the anteriors
Anterior
Posterior Extrusionwww.indiandentalacademy.com

Intrusion mechanics in Begg
• Consideration of the magnitude of the intrusive
force
– Optimal intrusive force value
– Role of class II elastics
• Consideration of the direction of the resultant
force
– Magnitude of the intrusive force
– Magnitude and direction of the elastic force
• Arch wire size for generating higher intrusive
force www.indiandentalacademy.com

Refined Begg
• Mollenhauer - 018 premium plus wire for
intrusion - 75 grams of force and 50 degree
anchor bend
• To prevent the distal tipping of molars
– Distal vertical elastics
– Molar tubes on both first and second molars
– Bite opening curve instead of bite opening bend

Factors affecting intrusive force
• Intrusive force varies with
– Different root sizes and tooth inclination
– Different arch sizes which affect the length of the
wire span and stretch of the elastics
– Change in the dental arch sizes during treatment
– Individual biomechanical response
– Changing elastic force during rest and functionwww.indiandentalacademy.com

Refined Begg
• To keep the intrusive forces within limits
and still give a gradually increasing vertical
orientation of the resultant
– Class II elastic of lesser magnitude
– Upper class I restraining force may be used
after the inclination of the tooth has improved
– Resultant force can be made more vertical by
applying the elastic from a higher attachment as
from a TPA
– High pull head gear force directly upon the
incisor www.indiandentalacademy.com

Continuous and segmental arch
Deep bite correction
Extrusion of molars
Flaring of the incisors
Genuine intrusion with
minimal extrusive
movement in the molar
area
Source:evaluation of continuous arch and segmented arch leveling
technique in adult patients 1996 AJO

Burstone intrusion arch

Reverse curve of spee

Bioprogressive therapy
Source : Bioprogressive therapy part 7, JCO, 1978www.indiandentalacademy.com

Up righting of the lower molar
• Up righting effect of (a) simple tip back on lower
first molars shows center of resistance (b) at the
gingival base of mesial root. This allows a forward
movement of the mesial root (c) and trades space
in the alveolar trough for arch length (d).www.indiandentalacademy.com

Expansion of 2mm in utility arch
• Liberal expansion (2mm)
of the lower utility arch
allows a center of
resistance (a) high enough
to minimize lingual crown
movement. A utility arch
without expansion (b)
results in a lower center of
resistance and more lingual
crown movement than
buccal root movement.

Arc of intrusion
• The arc of intrusion from
the lower molar (A) that is
parallel to the long axis of
the tooth (B) results in a
more effective intrusion
(typical of brachyfacial
types). The same arc (C)
applied to a labially
inclined tooth (D) results in
a further labial flaring and
less intrusion.

Labial root torque of lower incisor
The utility arch works as an arc (A) off of the lower
molar and no torque (B) in the lower incisor region
progressively becomes labial crown torque (C) as the
incisors intrude. Mild labial root torque counteracts
this mechanical response and allows the incisors to
avoid the lingual planum of bone.www.indiandentalacademy.com

Effects on the lower molar
The uprighting action and distal tipping of the lower
molar is affected in the reciprocal action of the utility
arch allowing for the maintenance of the E space
Distolingual rotation of lower first molar positions it
to properly receive well rotated upper molar
The buccal torquing of the lower molar roots under the
cortical bone of the oblique ridge is a basic movement in
the mandibular anchorage
Buccal expansion resulting in slight buccal movement
of the lower molar root helps to keep the arch from
crowding inward anterior to the second molarwww.indiandentalacademy.com

Utility arches
Source : utility arches McNamara, 1986, JCO

Three piece base arch wire
Source : segmented approach to simultaneous intrusion and
space closure,1995, AJOwww.indiandentalacademy.com

Three piece base arch wire

Advantages
• Simultaneous control of tooth movement in the vertical
and anteroposterior planes
• True intrusion achieved
• Axial inclination of the incisor controlled
• Low load deflection rate allows delivery of constant
intrusive force
• Low magnitude of force applied on the reactive or
anchorage unit
• Spring design allows low friction sliding to occur
• Well controlled statically determinate system
• Minimal chair side timewww.indiandentalacademy.com

K sir arch

Before and after
activation
K sir arch

– Simplicity of the design with minimal amount of wire in the loop
configuration
– Easy to fabricate, comfortable to the patient and less likely to
cause tissue impingement
– .019" X.025" TMA provides sufficient strength to resist
distortion, as well as enough stiffness to generate the required
moments. The design of the archwire and the properties of TMA
combine to produce relatively low forces, a low load-deflection
rate, and a range of activation that allows the appliance to continue
closing space over an eight-week period.
– The presence of the off center V bend acts as a anchor bend and
produces excellent molar control
– No head gear, minimal patient cooperation
– Intrusion and retraction of 6 anterior teeth simultaneously, thus
shortens the treatment time
– Avoid the unsightly space between the lateral and canine generally
seen in the conventional mechanics
Advantages

Connecticut intrusion arch

Mechanism of action
• Basic mechanism for the
force delivery is the V
bend calibrated to deliver
40-60 grams of force,the
bend lies just mesial to
the molar
• On activation there is a
vertical force in the
anterior region and
moment on the posterior
segment

Connecticut intrusion arch
• Advantages
– The intrusion arch will tip the molars back and
simultaneously bring about intrusion
– Single design can correct multiple problems
with no wire changes
– Minimal chair side time
– Niti wire delivers light continuous forces under
large activation
– These alloys have high memory and low load
deflection rate producing small increments of
deactivation over time and thus reducing the
number of reactivation

J hook head gear

Molar intrusion
• Norton and Lopes suggested that intrusion of an
over erupted tooth was problematic and proposed
grinding the crown before full-coverage
reconstruction.
• Mostafa and colleagues recommended that a
subapical osteotomy should be performed to avoid
unwanted side effects of intrusive mechanics.
• Miller and Jacobs showed that molar intrusion
with intra maxillary mechanics, using the forces of
occlusion and a third molar as anchorage

Extra oral forces in intrusion
• High pull head gear

High pull head gear
SHORT OUTER BOW
Angulated high to create
head gear force line of
action anterior to the
center of resistance
Intrusive component
Distal component
Large moment that
Tends to flatten the
Occlusal plane
Anticlockwise
Momentwww.indiandentalacademy.com

High pull head gear
OUTER BOW
Angulated such that head
gear force line of action
passes through the center
of resistance
Intrusive component
Distal component
No moment that
Tends to alter the
Occlusal plane
Equal to the inner bow

High pull head gear
LONG OUTER BOW
Angulated to create head
gear force line of action
posterior to the center of
résistance
Intrusive component
Distal component
Large moment that
Tends to steepen the
Occlusal plane
Clockwise
Momentwww.indiandentalacademy.com

Vertical pull head gear
The main purpose of this
headgear is to produce an
intrusive direction of force to
maxillary teeth with
posteriorly directed forces

Maxillary intrusion splint
• Full coverage heat cured palatal plate and
both anterior and posterior capping carried
into the labial surface of the teeth
• Kloehn bow at 600
to the occlusal plane and
high pull head gear
• Force of about 600 grams
• 14 hours wear per day
• Reduces incisor proclination and overjet
together with the distal movement of the
first molar and intrusion of the molar

Molar intrusion
• Desired force system..
Universal T-loop delivers
apical and mesial force. .
Full-coverage splint
combined with labiolingual
appliance for molar intrusion
and mesial movement. .
Uprighting appliance, with
cantilever from splint
delivering intrusive force
distal to center of resistance
Source: upper molar intrusion, Brite Melsen,
1996, JCO

Apical root resorption and
intrusive movements
• Dermout and DeMunck during intrusion
resorption of upper incisors was observed
with a mean resorption of 18%
• Linge and Linge intrusion seemed to cause
more resorption than overall orthodontic
treatment
• Costopoulous and Nanda showed that over
a period of four months of intrusion, root
resorption was 0.6mm versus 0.2mm for
controls

Intrusion of incisors aggravate the
periodontal problems in the presence of
plaque and inflammation
Shift of the supra gingival plaque to
subgingival position
Infra bony pockets

Skeletal
anchorage system

Conclusion
• Though this tooth movement has been the topic of
discussion regarding the possibility, a thorough
study of the clinical situation, diagnosis and
treatment planning can definitely help in achieving
intrusion of the anterior or posterior segment.
Nevertheless it is important to understand the
biomechanical and histological basis of the tooth
movement.

Thank you

intrusion

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