Intrusion mechanics /certified fixed orthodontic courses by Indian dental academy

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INTRODUCTION
The term intrusion refers to the apical movement of
the geometric center of the Root (centroid) in respect to the
occlusal plane or plane based on long axis of a tooth.
The intrusion mechanics is basically used in
orthodontics in one specific condition- DEEP BITE

GRABER defined deep bite as “ A condition of excessive over
bite, where the vertical measurements between the maxillary
and mandibular incisal margins is excessive when the mandible
is brought into habitual centric occlusion”.

Deep bite can be either skeletal or dentoalveolar
•Skeletal deep bite is due to
- upward rotation of mandible
- downward rotation of maxilla
- combination
•Dentoalveolar deep bite is due to
- overeruption of anteriors
- infra occlusion of the molars
- combination

Intrusion:
Absolute intrusion: where we intrude the incisors
keeping molars in place.
Relative intrusion: where we keep the incisors from
erupting further while growth provides vertical space into
which the posteriors are erupted.

In deep overbite cases correction of a bite occurs more
due to intrusion of lower anteriors rather than uppers. The reason
for this may be the size of the tooth. It has been proved that light
orthodontic forces, rather than causing any other type of tooth
movement, causes intrusion of teeth rapidly
When a tooth is intruded extremely light force of
optimum range of 25gms is what is required, as the force is
concentrated over a small area at the apex and produce
appropriate pressure within the periodontal ligament during the
process.

It is logical to intrude the maxillary incisors to a significant
degree for many advantages are immediately gained:
1.Bite opening is attained by moving the maxillary incisors into the
alveolus.
2. Potential for increasing a “gummy” smile is minimized.
3.The unfavorable tipping of the occlusal cant will not be as
common.
4. There will be a reduction in the total amount of class II elastics
that will be required

5. It will minimize the chances of moving the apices into juxta
position against the dense cortical bone.
6. The chances for root resorption are diminished
7. The need for lingualizing maxillary incisors will be lessened.
8.Torquing requirements will be reduced, and when needed will
be accomplished within a more adequate anatomical area, and
not restricted by the lingual cortical plate.
9. It will be easier to gain a class I relationship of the maxillary
cuspids.

Bite opening bends
Begg Technique is universally acknowledged for its efficient
bite opening mechanics, which is indeed one of the strength of
the technique.
this is the procedure where there is incorporation of
bends in the arch wire so that it helps in the intrusion of the
anterior teeth and extrusion of the molars. Many authors have
proposed different sites for the bite opening bends in the arch
wire.

Anchor bends
First in the conventional begg‟s , anchor bend is placed 3 mm
mesial to the molar tube in such a way that there is gingival
displacement of the anterior part of the arch wire therefore when
the arch wire is placed in the bracket, there is a intrusive force
acting on the anterior segment.

Gable bend
This is a modified bite opening bend given in the arch
wire distal to the canine. This tends to cause extrusion of
the canines and the intrusion of the central and laterals

Hocevar‟s modification
In a modification given by Hocevar, bite opening bends are placed
on either side of canine, which results in more intrusion of central
incisors and relative extrusion of lateral incisors and canine.

Mollenhauer‟s
In a modification given by Mollenhauer, where a bite
opening curve is given, it will result in extrusion of the canine
and intrusion of central and lateral incisors

Kameda‟s modification
In this modification both the anchor bends and gable
bends are given, there is extrusion of the canine and
intrusion of the incisors

Swain s modification
Swain advocates giving a mild gingival curve in the
anterior region which starts from mesial side of one canine
to the mesial side of the other canine for the better intrusion
of the anteriors.

Vertical step up bend
This intrusive action can be further augmented by
incorporating a vertical step up bend 3mm in height mesial to
the molar tube. After giving this bend, anchor bend of required
degree can be given in the upper end of the step up bend.

Even such a design may extrude the canine relative
to the lateral incisors. This is prevented by making the
cuspid circle in such a way that the posterior segment of
the arch wire is kept gingival and the anterior segment is
kept occlusal.

Class II Elastics
In the conventional beggs, the intrusive force from the
bite opening bends acts through the brackets which are placed in
the labial aspect of the incisor crown. This results in the labial
crown and the lingual root tipping. This displacement is
generally undesirable except in case of class II div II cases where
there is a lingually placed incisors.

This displacement is usually resisted by placing the
class II elastics thereby avoiding the labial tipping of the
anteriors.
KESLING analyzed this use of class II elastics and
found out that anchor bends produced around 45 grams of
force and the class II elastics produced around 30 grams of
force. Therefore the net resultant force was around 15 grams
on each side this 15 grams spread over three teeth amounting
about 5 grams on each tooth which was too little for active
intrusion

This problem gave rise to a modification of the force
delivery system where the proclination of the teeth is corrected
first, then latter intrusive force are applied.
So, initially the intrusive force through anchor bend should
be given around 45 grams and class II force should be 60 grams. In
this situation there is more of retractive force than the intrusive
force. Later the intrusive force is increased to 60 grams and the
class II decreased to 30 grams which will result in more intrusion.
The increase in the force of intrusion is obtained by the
increasing the degree of anchor bends gradually. Giving 30 degree
bend initially and increasing to 50 degrees. The decrease in class II
elastic force is done by placing the elastics for longer time i.e 3-5
days or by changing the elastics from yellow to road runner
elastics

Power arms
This method is given by Dr. JYOTHENDRA KUMAR
The power arms are made from .017 .025 or larger size wire.
The optimal length of the power arms is about 5 7mm and follows
the contour of the alveolus.
The power arms are soldered to the bands, just above the molar
tubes.

The power arm moves the point of force application close to
the center of resistance (CR).
This produces near pure translation, eliminating rotation
and the undesirable moments incident to force application further
away from the CR.
In the present technique elastics are placed from the molar
power arm posteriorly and on the intermaxillary circle anteriorly.
This not only helps to avoid labial tipping of the anteriors ,
but also bring about effective intrusion

Palatal elastics from TPA:
This modification given by Dr. JAYADE
TPA is fitted only after the molar relationship is corrected,
incisor proclination reduced and spacing closed.
The TPA carries a hook that is bent into the TPA itself or
soldered to it.the hook should lie in line with that of the lateral
incisors.

An additional oval shaped wire is soldered in the center, kept slightly
lower than the palate so that it rests on the dorsum of the tongue.
This helps to generate a constant intrusive force on the entire
assembly, which neutralizes the extrusive component of palatal
elastics on molars.
Four brackets are bonded onto the cingulum of incisors as gingivally
as possible with bracket slot facing incisally. A plain 0.016 sectional
wire, with ends bent is placed in palatal brackets.

High hat pins may be used in engaging elastics onto lateral
incisors. The force of palatal elastic not only neutralizes the
labially proclining component of archwire but also augments
the intrusive force on incisors. The resultant force passes close
to the center of resistance of the teeth and parallel to long axis
of the tooth.

Intrusion Utility Arch
This was devised by RICKETTS with the help of basic
biomechanical principles developed by BURSTONE. This
appliance consists of a continuous wire that extends across both
buccal segments but engages only the first permanent molars and
four incisors

Components
Molar section: This can have various bends for correction
of molar position.
Posterior vertical step: About 3 4mm in height and position
of vertical step varies depending on the type of utility arches
The buccal bridges: Which should be contoured to prevent
tissue irritation and sufficient expansion should be given in the wire
on both sides.
Anterior section which fits the bracket slot of incisors

Wire selection
Rectangular chrome cobalt alloy is much preferred as it can
be easily manipulated and loops can be formed with little
difficulty
For 0.018 slot – Mandible 0.016 X 0.022 or 0.016 X 0.016
Maxillary 0.016 X 0.022
For 0.022 slot - 0.019 X 0.019 for both the arches
Rectangular wire is preferred to the round wire to control
torque and to prevent the uncontrolled tipping

Fabrication
The intrusion arch is stepped gingivally at the molars, passes the
buccal vestibule and then it is stepped at the incisors to avoid
distortion from the occlusal forces. There should be 5 mm
distance between the anterior border of the auxiliary tube and
posterior vertical segment.
Activation
Activation are of 2 types :- Retraction
Intrusion

Retraction
Incisor retraction is achieved by bending down the end of
the molar segment gingivally. This helps in prevention of
protrusion of lower incisors during intrusion.

Intrusion
Intrusion is achieved by placing an occlusally directed
Gable bend in the posterior portion of the vestibular segment.
BENCH advocated giving a tip back bend in molar
segment which will cause the incisal segment to lie in the
vestibular sulcus. Intrusive force is created by placing the incisal
segment into incisal brackets. But the draw back is that it may
lead to the posterior tipping of the first molars.

Three piece intrusion arch
This appliance was introduced by BURSTONE, modified by
SHROFF, LINDHAUER
Along with the intrusion of the anterior teeth it also helps in the
retraction of the anteriors and thereby enhancing space closure

This consists of
A posterior anchorage unit, which is adapted into molars
and premolars
An anterior segment with posterior extension, which runs
through the four incisors and canine
Intrusion cantilever spring which is placed between the
anterior and posterior segment.
• After alignment of molars and premolars, the posterior
segment made up of 0.017 X 0.025 SS is placed in right and left
molars and premolars a TPA can also be given for more
consolidation of posterior teeth.

• The anterior segment is bent gingivally distal to the laterals
and then bent horizontally creating a step approximately 3mm.
The distal part extends posteriorly to the distal end of canine
bracket where it forms a hook.
•Now the intrusion springs are fabricated. First the wire is bend
gingivally, mesial to the molar tube helix is formed. On the mesial
end of the spring, a hook is made through which it is attached to
the anterior segment

• Now the spring is activated by making a bend mesial to
helix and then sinched back and attached to the anterior
segment. This will cause anterior intrusion and molar extrusion.

•Along with this an elastic chain can be attached from the hook of
the anterior segment to the molar tube to facilitate intrusion
along with retraction.

Headgears
High pull headgears:
The effect on the dentition results on the location of center of
resistance relative to the line of action of force.
•a) When the direction of pull is placed behind the center of
resistance of the maxilla and maxillary dentition a clockwise rotation
of maxilla and dentition is observed. Molars will show intrusion and
incisors will extrude. Net effect is clockwise rotation of Occlusal
plane.
•b) When pull in front of center of resistance of both maxilla and
the maxillary dentition, an anti clockwise rotation is observed.
Molars tend to extrude and incisors intrude. Occlusal plane also
rotates anti clockwise. Therefore bite opening is facilitated.www.indiandentalacademy.com

Cervical pull headgears:
Here when the inner and outer bows are in same plane there
is clockwise rotation of both maxilla and maxillary dentition. The
incisors will move inferiorly to a greater extent than molar region.
The Occlusal plane will also rotate in clockwise direction and bite
will deepen up. But if the outer bow is bent upwards so that direction
of traction is between the maxilla and maxillary dentition, maxilla
will rotate clockwise and dentition in anticlockwise direction. Hence
incisors will experience upward influence and molars a downward
influence and bite will be opened up.

Combination headgears:
In these cases also the resultant force vector which moves
through the center of resistance brings about a more of distal
movement of molars and a minimal amount of intrusion of the
molars.
The outer bow is angulated about 15o
Headgears can be used in combination with other appliances
or by itself to bring about active or absolute intrusion of the teeth.

The K. Sir (Kalra simultaneous Intrusion and
Retraction Springs)
This appliance was introduced by Dr Varun Kalra in the year
1998.
This is a continuous 0.019 0.025” TMA archwire with
closed 7mm 2mm U loops at the extraction sites.

To obtain bodily movement and preventing tipping of teeth into
extraction space a 90o V bend is placed at the level of each „U‟ loop,
this „V‟ bend when placed between first molar & canine during
space closure, creates two equal and opposite moments to counter
the moments caused by the activation forces of closing loops.

A 60o V bend is located posterior to the center of inter bracket
distance produces an increased clockwise moment in the first
molar, which augments molar anchorage as well as intrusion of
anterior teeth.

Then a 20o anti rotation bend is placed in the arch wire just distal
to the „U‟ loop. This prevents the buccal segments from rolling
mesio-lingually due to the fore produced by loop activation.

Activation
Before the arch wire is used in the mouth, a trial activation
should be done out side the mouth this is done to reduce the
stress build up from bending the wire and thus reduce the
severity of the „V‟ bends.

After the TRIAL ACTIVATION, the neutral position of the loop
is determined by extending the mesial and distal edges of the „U‟
loop. The neutral position is established when the „U‟ loop is 3.5
mm wide.

Now the arch wire is inserted into the auxiliary tubes of
the molars and engaged into the 6 anterior teeth.
Then it is activated by 3 mm so that the mesial and distal
ends of the loop is barely apart

When the loop is first activated, tipping movement generated
by the retraction force will be greater than opposing movements
produced by the V bends, which will lead to controlled tipping
movements of the teeth into extraction sites.
When the loop deactivates there will be more bodily
movement and root movement of the teeth.
Therefore the loop should be activated only after 6-8 weeks.
It is usually placed for 4-5 months.

Reverse Curve Nitinol Wire
When a reverse curve NiTi wire is in the molar tubes of the
lower arch, the anterior segment curves gingivally. So when the
anterior segment is forced occlusally into the bracket slot, it will
result in the intrusive force on the incisors and extrusive force on the
molars, therefore opening the bite
DRAWBACKS:
•Anterior flaring of the incisors
•Anterior proclination cant be corrected
•Space closure cannot be initiated

Removable appliances for Intrusion
Though these appliances do not fall under the exact classification of
Intrusive appliances. Many of the removable appliances we use in
our day-to-day practice can be modified to bring about the intrusion
of teeth to correct the vertical discrepancies.

Anterior bite plane is the most commonly used removable
appliance for treatment of deep bite. It is a modified hawley‟s
appliance with a ledge of acrylic behind the upper incisors. The
presence of acrylic will result in disoccluding the posterior teeth
and thereby free to erupt. As the posterior teeth erupt the height of
the bite plate is gradually increased.
Bite Planes

Functional Appliance
Activator: Selective trimming is done for the extrusion of molars
and intrusion of incisors.
Extrusion of the molars is achieved by loading acrylic in the lingual
surface above the area of maximum convexity of the maxillary
molars and below the area of maximum convexity of mandibular
molars
Intrusion of the incisors is done by
loading of the acrylic in the incisal
edge of the anterior teeth

Magnetic Appliance
The Active vertical Corrector:
This was introduced by DELLINGER in 1986. This
consisted of upper and lower bite blocks with samarium cobalt
magnets in stainless steel cases embedded in them. These helped in
the intrusion of anteriors.

Seated Active Vertical Corrector (AVC).

Magnetic Activator Device (MAD II)
This was developed in 1993 by DARENDILIER. These are
used for correction of open bite and deep bite cases.
They bring about intrusion by placing repelling magnets,
which are placed opposing each other. In cases of class II mal
occlusion with open bite, the posterior repelling magnets on
maxillary plate, bring about expansion of maxillary arches and also
the intrusion of molars.

This appliance by Kalra, Burstone, and Nanda increases the
interocclusal space and allows upward and forward autorotation of
the mandible, thereby decreasing lower facial height and facial
convexity. This appliance resulted in intrusion of posterior teeth and
an upward and forward autorotation of the mandible.

The Magnetic Twin Block Appliance:
The functions of twin block were made more accurate by
incorporation of magnets by clerk. He used samarium cobalt and
neodymium Iron Boron in his well-accepted twin block. These
magnets were embedded in the inclined surfaces of the twin block
in repulsive mode. This reduced the need for any reactivation.

Tip Back Springs: (Intrusion springs):
This was proposed by Burstone. These are made of 0.017 0.025”
TMA wire. Prior to this the U/L arches have to be leveled and
aligned and preferably a rigid 0.017 0.025” S.S. wire should be
engaged in the bracket. These are indicated in patients requiring
true intrusion of the incisors and can be used in the following
conditions.
Growing patients with forward growth rotations.
For every deep curve of spee in lower arch.
Cases of deep overbite due to extrusion of incisors.
For steepened natural plane of occlusion.

This is defined as a pre calibrated spring to
produce the desired retraction, uprighting and
intrusion of the incisors. The segmentation
requires formation of the active unit
anterior segment consisting of the four
incisors whereas the two posterior segments
include the buccal teeth of each side.
Investigations have shown that center of resistance measures to be
about 7mm distal and 9 to 10mm gingival to the center of lateral
incisor bracket for the anterior unit. The posterior segments are
connected by a TPA to form one rigid multirooted entity of the
reactive unit.
PG Retraction Spring (Poul Gjessing)

The point of force application is located at the first molar
tube in a suggested horizontal distance of 10mm posterior to the
center of resistance of the posterior segment. This can result in a
moment of the extrusional force of 10 20gm/mm=200gm/mm.
The direction of this moment is opposite to moment of
couple. The segmented arch offers freedom in selection of the
points of force application relative to the center of resistance of
anteriors and the posterior units or the retraction spring can be
monitored to improve the desired movement of the active unit and
reduce unwanted side effects in the reactive unit.

The wire has been made of 0.016 0.022”S.S wire so as to make it
more rigid and to secure undisturbed structure of the activated spring,
stability in placement of the spring in the mucobuccal fold and
resistance against masticatory functions.

The advantages of P.G. springs are
• The PG retraction spring can be used as a module for controlled
retraction of both canines and incisors.
• The initial horizontal force of 100gm suggested for incisor
retraction can be identified by the shape of the activated spring.
• The incisor segments intrusion is induced with a magnitude of 10 to
25gm on each side.
• Reduced moment to force ratio as a result of larger inter bracket
distance.
• Unwanted side effects on buccal segments are low.
• Reactivation is done every 4 6 weeks. The treatment time is about
5 6 months. www.indiandentalacademy.com

It was believed that actual intrusion of incisors or molars are not
exactly possible and one that occurred for the correction of some cases
was relative intrusion.
But over the years advancements in orthodontic technique and
appliances have proved that diagnosis, treatment planning and
application of precise appliance system can bring about the true
intrusion of anteriors and to some extend posterior units with an
application of optimum force.
The final result with the use of an intrusive appliance lies in the
hands of the orthodontist.
Conclusion

Thank you
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Intrusion mechanics /certified fixed orthodontic courses by Indian dental academy

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