INTRUSION MECHANICS IN ORTHODONTICS..ppt

INTRUSION MECHANICS in orthodontucs

1. 1
INTRUSION MECHANICS

2. 2
1,Definition of intrusion
2,Basics of Intrusion mechanics
One couple system
Two couple system
3,Intrusion mechanics
a,PreadjustedEdgewiseTechnique
b,BeggTechnique
C,Differentialstraight arch technique
d,LingualTechnique
e,Implants
4,Root Resorption
5,Stability

3. 3
Mechanicsis an engineering science that describes the
effects of force on bodies.
Biomechanicsrefers to the science of mechanics in relation to
biologic systems.
Orthodontic mechanics are the key to understand
how orthodontic appliances work and are critical for designing
new appliances. Itis essential for executing efficient and
successful orthodontic treatment.

4. 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”.

5. 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

6. 6
INTRUSION
Definition:
True intrusion or absolute intrusionrefers to the apical
movement of the geometric center of the root (centroid) with
respect to the occlusal plane or a plane based on the long axis of the
tooth. It is an axial type of translation whose centre of rotation lies
at infinity.
Relative intrusionis the one which is achieved by preventing
eruption of the incisors, while growth provides vertical space into
which the posteriors erupt.
Pseudo-intrusion refers to the labial tipping of an incisor around
its centroid.

7. 7
Measurement of intrusion:
Incisal edges should not be used to evaluate intrusion, since
they are easily affected by tipping movements of the incisors. Ideally, a
point should be selected in the center of the root (centroid)& comparison
should be based upon the movement of this point.
Amount of intrusion:
orthodontically -as given in envelope of discrepancy
Maxillary Incisors 2mm Mandibular Incisors 4mm
Maxillary Posteriors 3mm Mandibular Posteriors 3mm
The intrusive tooth movement is used in the correction of overbite
malocclusion as anterior segment intrusion in deep bite cases
and posterior segment intrusion in openbite cases.

8. 8
Deepbitecorrection
Extrusion of posteriors
Combination
Intrusion of incisors may be particularly advantageous in
those with following clinical conditions
Vertical growth pattern
Extrusion of molars Increase facial convexity
Adults
Stability. . . . ? ? ? ?Extrusion of molars
Intrusionof incisors
Excessive maxillary incisor display
Short upper lip
Intrusion of mandibular incisors . . . ? ? ?
severity of curve of Spee & presence of palatal impingement.
Uprighting the posteriors
Flaring of incisors

9. 9
Force:
It is a load applied to an object that will tend to move it to a different
position in space. It is a vector having both magnitude and direction .It is
measured in units of grams or ounces.
Moment:
A moment is defined as the product of the force times the
perpendicular distance from the point of application to the CRes,& thus is
measured in units of gram-mm. If the line of action of an applied force does
not pass through the Cres, a moment is necessarily created .Not only the
force will tend to translate the object, moving it to a different position,it
also will tend to rotatethe object around the Cres –thus the tooth tipsas it
moves.
Cue Ball Concept
BASICSOFINTRUSIONMECHANICS

10. 10
Couple:
It is created by two forces equal in magnitude and opposite in
direction.The result of applying two forces in this way is a pure moment,
since the translatory effect of the forces cancels out. A couple will
produce pure rotation.
Irrespective of point of application of couple, a pure
moment is produced always.

11. 11
One Couple Appliances—Statically Determinate Systems
A 1-couple orthodontic appliance is inserted into a bracket or tube at 1 end
& is tied as a point contact at the other.
The end that is tied as a point contact only force
The end which is engaged in the bracket slot a force and a couple
The appliance is a 1-couple system because a couple is generated only at the
site of full engagement.
It is statically determinate because the magnitudes of the forces and
moments produced can be determined clinically after the appliance is inserted
into the bracket.

12. 12
Force and couple produced in the system:
When the activated wire is tied at the point contact, the arch wire engages
the bracket and two equal and opposite forces form the couple at the bracket. This
couple produces a Mc or tendency to rotate the tooth around its CRes.
The laws of equilibriumdictate that the sum of the moments exerted by
the wire be equal to zero. With a clockwise moment at the molar, there must be a
counter moment in the counter clockwise direction to maintain equilibrium. That
moment is produced by two equal and opposite forces exerted at the end of the
arch wire.
The magnitude of the forces and moments in a one-couple system
can be estimated clinically by measuring the force required to deform the wire
for the tie at the point contact using a gauge .

13. 13
Two Couple Appliances -Statically Indeterminate Systems:
When the free end of the arch wire in a one bracket system is
not used as a point contact, and instead is inserted into a second bracket, a
two-couple system is usually created. A couple, therefore, may be generated
by the wire at both attachment sites
In this case, inserting the wire into 1 attachment and using a
gauge to measure the force required to deflect the wire to the other
bracket will not give an accurate assessment of the force produced by the
appliance. Because of the inability to measure force systems produced by 2-
couple appliances clinically, they are referred to as being statically
indeterminate.
Force and couple produced in the system:
For purpose of establishing the direction of the associated
equilibrium forces, the two-bracket system can be considered as the sum of two
successive one-bracket systems.

14. 14
Thetotalsystemeffectonthetwoteethisacombinationofthe
separateeffectsofA&B.Theresultantistwoequal&opposite
coupleswitnonetassociatedequilibriumforces

15. 15
AsymmetricVbends.
Off center-the couple nearer the bend increases and the
couple further from the bend decreases. Forces result to maintain
appliance equilibrium
V bend is at 1/3 the distance -a couple is only present at the bracket
nearer the bend. No couple at the bracket further from the bend, and forces
result to maintain equilibrium.
V bend is very close to 1 bracket-couples in the same direction at
both brackets, with the larger couple at the bracket closer to the bend. Forces
increase as the bend is moved further off center.

16. 16
INTRUSION MECHANICS
PreadjustedEdgewiseTechnique
BeggTechnique
Differentialstraight arch technique
LingualTechnique
Implants

17. 17
PreadjustedEdgewiseTechnique

18. 18
Leveling the deep curve of Spee
Whenaroundarchwirewithanincorporatedreverse
curveofSpeeisplaced,theusualresponseisthatthebicuspidsare
extruded,themolarsuprighted(tippedback)andincisorstippedforward.
Tocounteracttheforwardmovementofthelowerarch,ClassIII
elasticsaresuperimposedtoholdthelowerincisorsbackasthelowerarchis
leveled.Hencetheuppermolars&lowerincisorsareundertheinfluenceof
eruptiveClassIIIelastics.Tocounteractthisresponse,eitherhi-pullheadgear
wasinitiatedorextractionswerenecessitatedtopreventtheunwantedside
effectsoftheroundarchleveling..
To avoid the forward movement of incisors, these arches are
either tied or cinched back.However, as the reverse curve of Spee in the
round arches expressed itself, the roots of the lower incisors are thrown
against the dense cortical bone of the lingual planum of the symphysis. This
acted as an anchor which resulted in the same forward movement of the
lower incisors & the lower molars.

19. 19
Burstone Intrusion arch
The intrusion arch, as described by Burstone in 1977, is
significantly different in its force deliver because it is not engaged
in the incisor brackets. Properly designed and employed, an intrusion
arch will tip the molars back while simultaneously intruding the
incisors.
Theburstoneintrusionarchconsistsofthreeparts:
aposterioranchorageunit,
ananteriorsegment,
anintrusivearchspring.

20. 20
posterior anchorage unit
Early in treatment the posterior teeth are aligned and joined
together with a buccal stabilizing segment of 0.018 inch wire, square in
cross section for 0.022 inch slotted brackets.
Right and left posterior segments are joined together across the
arch by means of a transpalatal lingual archin the maxilla and a low
lingual arch in the mandible.
Whenever possible, at least the first molars and second premolars
should be used and the addition of other teeth would further enhance
the anchorage potential.

21. 21
Intrusive arch spring .
The intrusive arch consists of an 0.018 by 0.022inch or 0.018
by 0.025inch by edgewise wire with a 3 mm. helixwound 2½ times
placed mesial to the auxiliary tube.
Curvature is placed in the intrusive arch, so that the incisal
portion lies gingival to the central incisor. When the arch is tied to
the level of the incisors, an intrusive force is developed.
To avoid increase its length during the activation, a gentle
curvature should be placed with the amount of curvature increasing
as one approaches the helix. In this way the activated arch wire
will appear relatively straight, and as it works out during intrusion
arch length will decrease and no anterior flaring is produced

22. 22
Anterior segment
Six principlesmust be considered in incisor or canine intrusion:
(1) the use of optimal magnitudes of forceand the delivery of this
force constantlywith low-load-deflection springs
(2) the use of a single point contactin the anterior region
(3) the careful selection of the point of force applicationwith respect
to the center of resistance of the -teeth to be intruded
(4) selective intrusion based on anterior tooth geometry
(5) control over the reactive units by formation of a posterior
anchorage unit
(6) inhibition of eruption of the posterior teethand avoidance of
undesirable eruptive mechanics.
An anterior alignment arch or anterior segment is placed in the
central incisors or the four incisors and the intrusive arch is tied
either labially, incisally, or gingivally to that wire.

23. 23
Controlling the force magnitude and
constancy
The lowest magnitude of force is used to
intrude incisors.

24. 24
If the magnitudes of force are too great,
1, the rate of intrusion will not increase and the rate ofroot
resorption willincrease.
2,The posterior teeth will feel a vertical force which will tend to
extrude the buccal segments and a moment or torque which in
the upper arch will steepen the plane of occlusion and in the
lower arch flatten it .
If only a single tooth, as a first molar, is attached to
an intrusive spring, the undesirable side effect is seen primarily
as a tip-back action, with the crown moving distally and the root
mesially.
Loss of anchorage during intrusion is primarily produced
by the moment rather than by the force, since occlusal forces
tend to negate the eruptive tendency.
The moment is large because the distance from the
incisors to the posterior teeth

25. 25
Low load deflection mechanics
To intrude four incisors, 100 Gm. of force midline would be
required (25 Gm. per tooth).
Springs that deliver relatively constant force have low load-
deflection rates. An intrusive arch with a 30 mm. arm
(perpendicular distance from the incisor to the first molar) has
a load-deflection rate of 6 Gm. per millimeter.
 If this intrusive arch is activated 16.5 mm., 100 Gm. of force
is produced in the midline, 50 Gm per side.
As the incisors intrude 1 mm., there is a change of force
magnitude of only 6 Gm.; hence, the delivery of force is
relatively constant.

26. 26
Anterior single point contacts
The intrusive arch is placed as
single point contact.
The major reason who one avoids
bracket engagement of the intrusive
spring is that,
1 ) If, purposely or
inadvertently, labial root torque is placed
into the incisors, the intrusive forces are
increased on the anterior teeth & can
produce anchorage loss of the posterior
teeth.
On the other hand, if lingual root
torque is present, it will have the effect
of reducing the magnitude of intrusion on
the incisors.

27. 27
2 ) It allows the clinician to know more positively the force
system delivered. By having a single point of force application on
the incisors, one knows the full force system acting at both the
incisor point and the buccal tubes. A system of this type is
described as being statically determinant.
Placing the intrusive arch into the brackets produces a
statically indeterminant system which prevents from knowing
exactly what type of force it is delivering.

28. 28
Point of force application
In maxillary intrusion, the intrusive arch is placed slightly anterior
to the labial surface of the incisors as it is attached to the anterior segment.
This produces a moment which tends to flair the crown forward and move the
root distally .
In those patients who have markedly protruded incisors, an
intrusive force placed on the labial surface of an incisor will produce a moment
that is very large and produce lingual root movement of the incisor.
An anterior segment is made with a posterior extension . Right and
left sectional intrusive arches are constructed with a hook that catches on the
posterior extension so that the force can be directed through the center of
resistance of the incisors .

29. 29
Selective intrusion
In Class II, Division 2 maxillary arch the incisors are
Intruded to the level of the canines. A straight arch wire placed
through the brackets not only produces vertical forces but, also
moments which alter axial inclinations, and thus maxillary arch is
leveled by not producing any intrusion but by extrusion and
steepening of the maxillary plane of occlusion. The undesirable
moments will tend to converge the roots toward the midline.
The two central incisors should intruded to the level of
the lateral incisors before joining all four incisors together for
further intrusion. Many times canines that appear in infraocclusion
should not be extruded, but the four anterior teeth should be intruded
to their level bypassing the canines

30. 30
Control of the reactive units
The best control over the posterior teeth, the reactive
unit, is the minimization of force magnitude used for intrusion.
Two basic side effects could be anticipated from
intrusive mechanics.
1 ) Looking from the lateral view, a moment is
created which tends to alter the plane of occlusion of the
buccal segment;
To minimize these changes, the forces are kept as low
as possible.

31. 31
The second major side effect produced by an intrusive
arch can be seen from the frontal view . With an intrusive force on
the incisors, there is an equal and opposite extrusive force on the
molars. Since the extrusive force is operating buccally at a tube, it
can be seen that a moment is created that tends to tip the crowns
lingually and the roots buccally. The lingual arch is used to prevent
any undesirable change in axial inclination of the molars or change
in molar width.
An occipital headgear can be used in the upper arch,
designed so that its force is anterior to the center of resistance .
The headgear produces a moment opposite to the moment
produced by the intrusive arch and thus prevents the steepening
of the maxillary plane of occlusion.

32. 32
Avoiding extrusive mechanics
If the canine has a crown distal to the root &if the arch
wire is placed into the canine bracket, it will lie occlusal and hence
will produce eruption of the incisors. Incisors make very poor
anchorage for distal root movement of a canine, since eruption
occurs so much more easily than distal root movement. It is
preferable to bypass the canines during canine root movement, or in
certain situations canine root movement should be completed before
the incisors are joined to the rest of the arch.
The typical patient who requires intrusion also requires
minimization of extrusion of the posterior teeth. An exception is
found in some of the patients with flat mandibular planes who have
well-developed musculature.
Inhibition of the eruption of posterior teeth in the growing
patient can be accomplished using a number of procedures. Occipital
headgear can be worn to the upper arch, cervical headgear with high
outer bows to the lower arch. Chin caps can be useful in inhibiting
the eruption of posterior teeth.

33. 33
It is usually not possible to intrude all six
anterior teeth at one time without producing undesirable
axial inclination change in the posterior segment.
Using the suggested force values, typically 100
Gm. of force on a side is required to intrude the incisors
and the canines. shows moment of 3,000 Gm.mm, if the
perpendicular distance from the incisors to the center
of resistance of the posterior segment was 30 mm.
Since moments of this magnitude are
most effective, tipping of the posterior teeth will occur
more rapidly than the intrusion.
Canine intrusion

34. 34
In patients with deep overbite it is usually a
mistake to level and extrude infraerupted canines. Many of
these canines should be left in their original position and
the incisors should be intruded to their level.
A canine-intrusion spring which is activated to
produce 50 to 75 Gm. of force. It is fabricated from 0.018
by 0.025 inch wire inserted into the auxiliary tube of the
first molar and into the vertical tube of a canine bracket.
Since the intrusive force lies lateral to the center of
resistance of the canine, it is necessary to place a slight
constrictive force in the spring to keep the canine from
flaring labially.

35. 35
THREE PIECE INTRUSION ARCH
The application of an intrusive force at the bracket of flared
incisors tends to exacerbate the axial inclination. This is because for a given
amount of intrusive force, the perpendicular distance from the point of force
application to the center of resistance increases and the resulting
counterclockwise moment is considerably larger than normally inclined tooth.
Also uprighting of incisors often lengthens the crowns vertically and
increases the overbite.
So the selection of the point of application of the
intrusive force with respect to the center of resistance of the anterior
segment is important to precisely define the type of tooth movement that
will occur.
This is a segmented approach to simultaneously intrude and
retract the flared by using frictionless mechanics & was introduced by
Burstone.

36. 36
Appliancedesign:
Posterior segment:
After alignment of the premolars & molars, passive segmented
wires (0.017 * 0.025 stainless steel)are placed in the right and the left
posterior teeth for stabilization.
A precision stainless steel transpalatal arch(0.032 * 0.032) is
placed passively to control molar width & axial inclination in the frontal plane.
This consolidates the posterior unit now consisting of right and left posterior
teeth.
The intrusive force is applied with a 0.017 * 0.025 TMA tip-back
spring.
Toestablishthepointofforceapplicationduringintrusive
mechanics,lateralcephalometricfilmsareused.Thecenterofresistanceof
thefourincisorsisestimatedtobehalfwaybetweenthecrestofthe
alveolarbone&theapexofthelateralincisorrootinthesagittalplane.

37. 37
Anterior segment:
After aligning the anteriors, a heavy stainless steel segment
(0.018 * 0.025 or larger) with distal extensions below & 2 to 3 mm distal the
center of resistance of the anterior teeth is placed passively in the anterior
brackets.
A light, distal force delivered by a Class I elastic to the
anterior segment is used to get true intrusion of the incisors along their long
axes
Two other methods for redirecting the force:
1,The orientation of the tie is such that it is parallel to the
direction of force.
2,The posterior extension of the anterior segment is angled so
that the force is directed along the long axes of the teeth.

38. 38
Force system on anterior segment & direction of intrusive force:
An intrusive force perpendicular to the distal
extension of the anterior segment & passing through the center of
resistance of the anterior teeth will intrude the incisor segment. The
direction of this intrusive force can be changed by applying a small distal
force. The line of action of the resultant force will be lingual to the center of
resistance & a combination of intrusion and tip back of the anterior teeth will
occur.
The line of action of the resultant force can also be
made to pass through the center of resistance and parallel to the long axis of
the incisors by relocating the point of force application more anterior and as
close to the distal of the lateral incisor bracket as possible.

39. 39
Force system on posterior segment:
A tip back moment is created on the posterior segment
during intrusion of the anterior segment.If the force is redirected to be
parallel to the long axes of the incisors, the moment on the buccal segment of
teeth is reduced and hence the tendency for its natural plane of occlusion to
steepen is reduced.
Advantages:
1. The low load deflection rateof this appliance delivers a constant
intrusive force
2. It allows simultaneous control of tooth movement in the vertical and
anteroposterior planes.
3.The design of this appliance allows the clinician to deliver a well-
controlled, statically determinate force systemin which only minimal chairside
adjustments are required
4. Loss of anchorage is seldom observed because of the tipback
moment on the posterior teeth.

40. 40
UTILITY ARCH
The utility arch, as popularized by Ricketts, has been
recommended for the resolution of a variety of clinical
conditions. Perhaps the most frequent application has
been for leveling the Curve of Spee and reduction
of overbite (OB) through incisor intrusion.

41. 41
Appliance design:
The utility arch is usually fabricated from a continuous
rectangular stainless steel arch wireinserted into the edgewise
brackets on the incisors and the maxillary or mandibular molars .
For convenience and comfort it is stepped in a gingival direction
between the incisors and molars to bypass the buccal occlusion.
Avoiding engagement of the premolars and canines results in
improved load deflection properties because of the length of free
wire existing between the segments at each end of the appliance.
The utility arch is activated for incisor intrusion by placing tip-
back bendsmesial to the molar tubes.

42. 42
Physiological Vs. Mechanical Responses

43. 43
30°to 45°Tip-back Applied to the Lower Molars:
Tip-back applied singularly to the lower molars will upright these
teeth bringing their roots mesially and the crown distally. Since the
lower molar is supported on the buccal by a heavy cortical plate and at
the distal by the lower second molars, the most usual movement of this
tooth with a straight uprighting force is a distal rotation.
In extraction cases, where there is both a mesial component of
force (the retraction section) and an uprighting component of force, a
definite distal rotation must be placed to avoid a mesial rotation of the
lower molars.

44. 44
when a 45°buccal root torque is placed on the distal legs of
the utility arch, the amount of movement of the root to the buccal is
proportionate to the amount of movement of the crown to the lingual.
The only way that buccal root torque can be expressed by
buccal movement of the root and stabilization of the crown is by expansion
of the arch.
It is important that the distal legs of the utility arch be
generously expanded prior to placement in the mouth.
30°to 45°Buccal Root Torque Applied to the Lower Molar.

45. 45
.
The mandibular utility arch is fabricated from .016 ´.016 Blue
Elgiloy wire in order to create a lever system that will deliver a continuous
force to the lower incisors in the range of 50 to 75 grams.
The design of the mandibular utility arch is dictated by the
requirement that this light force be delivered in a continuous manner of a
long lever arm from the molar to the incisors.
The arch is stepped down at the molar, lies in the buccal vestibule,
and is stepped back up at the incisors to avoid interference from the
forces of occlusion that would distort it. This buccal bridge section is
flared slightly buccally to prevent tissue irritation opposite the vertical
steps as the arch approaches the tissue and the incisor teeth are
intruded.
75 Grams of Intrusive Force Applied to the Lower Incisors

46. 46
.
When a long lever arm works off of the lower molars, the effect at
the lower incisors is a change in torque which bring the lower incisor root
back into the lingual planum alveolare, and minimize or prevent its further
intrusion. This will often result in a labial flaring or tipping of the lower
incisors.
In those cases where the lower incisor is proclined more labially
,straight downward pressures to intrude the lower incisors will quite often
end up tipping these teeth even further labially.
In such cases, a slight labial root torque (5°to 10°) will free the
apex of the lower incisor teeth from the lingual planum and allow its
intrusion without labial flaring.
Long Lever Arms Applied to the Lower Incisors

47. 47
Cuspid Intrusion
In approximately 50 percent of the deep bite cases,
the lower canines must also be intruded slightly to bring them to the
level of the functioning buccal occlusion.
This is normally accomplished by lightly tying these
teeth to the stabilizing utility arch with an elastic thread .
To keep the elastic thread from sliding along the utility arch,
a small vertical loop is pinched into the wire.This elastic thread is
brought around the vertical loop and tied prior to encircling the
cuspid bracket.
The elastic thread should completely encircle the cuspid
bracket and a knot tied behind the base of the bracket so that it
does not irritate the buccal mucosa. Normal intrusion time for the
lower cuspids should be no more than one month.

48. 48
K-SIR APPLIANCE
The K-SIR (Kalra Simultaneous Intrusion and Retraction) archwire is a
modification of the segmented loop mechanics of Burstone and Nanda.
Appliance Design:
It is a continuous .019” ´.025” TMA archwire with closed 7mm ´
2mm Uloops at the extraction sites .
To obtain bodily movement and prevent tipping of the teeth into the
extraction spaces, a 90°V-bend is placed in the archwire at the level of
each U-loop . This V-bend, when centered between the first molar & canine
during space closure, creates two equal & opposite moments to counter the
moments caused by the activation forces of the closing loops.

49. 49
A 60°V-bend located posterior to the center of the interbracket
distance produces an increased clockwise moment on the first molar, which
augments molar anchorage as well as the intrusion of the anterior teeth .
To prevent the buccal segments from rolling mesiolingually due to the force
produced by the loop activation, a 20°antirotation bend is placed in the
archwire just distal to each U-loop .

50. 50
Activation
After the trial activation (releases the stress built up from bending
the wire and thus reduces the severity of the V-bends), the neutral position of
the each loop is determined with the legs extended horizontally . In neutral
position, the U-loop will be about 3.5mm wide. The archwire is inserted into the
auxiliary tubes of the first molars and engaged in the six anterior brackets . It
is activated about 3mm, so that the mesial and distal legs of the loops are
barely apart .

51. 51
The second premolars are bypassed to increase the interbracket
distance between the two ends of attachment. This allows the clinician to
utilize the mechanics of the off-center V-bend.
When the loops are first activated, the tipping moments generated by
the retraction force will be greater than the opposing moments produced by
the V-bends in the archwire. This will initially cause controlled tipping of the
teeth into the extraction sites.
As the loops deactivate and the force decreases, the moment-to-
force ratio will increase to cause first bodily and then root movement of the
teeth. The archwire should therefore not be reactivated at short intervals,
but only every six to eight weeks until all space has been closed.
The archwire is typically in place for four to five months.

52. 52
Control of Reactive Forces:
The K-SIR archwire exerts about 125g of intrusive force on the anterior
segment and a similar amount of extrusive force distributed between the two
buccal segments—generally the first permanent molars and the second
premolars, connected by segments of TMA wire .
If even more anchorage is needed to resist both anterior movement
and the extrusive force on the buccal segments, a high-pull headgear can
be added to the molars.
Including the second molar will, reduce the effects of the reactive
force also increase anchorage in the anteroposterior direction.
The force of 125g is effective for intrusion of the anterior teeth, while
the reactive extrusive force on the buccal segments is countered by the
forces of occlusion and mastication.

53. 53
Advantages
It is particularly advantageous in the retraction of anterior teeth in a
first-premolar extraction patient who has a deep overbite and excessive
overjet, and who requires both intrusion of the anterior teeth and maximum
molar anchorage.
Due to the frictionless mechanics used for space closure in this system
and the presence of the off-center V-bend, which acts like an anchor bend,
molar anchorage control is excellent, even without headgear. The clinician is
thus less dependent on patient cooperation.
Because the intrusion of the six anterior teeth occurs at the same time as
their retraction, & the canines and incisors are retracted as a unit, it
shortens treatment time.
The en masse retraction of the six anterior teeth prevents the
appearance of an unsightly space distal to the incisors, which occurs if the
canines are retracted separately.

54. 54
The Connecticut Intrusion Arch
The wire materials used for intrusion are diverse, but all recognize the
need for a light, continuous force. Nickel titanium alloys are currently the
materials of choice having high memory & low load-deflection rates, producing
small increments of deactivation over time and thus reducing the number of
reactivation appointments.
The CIA is fabricated from a nickel titanium alloy & used for
absolute intrusion of anterior teeth.

55. 55
Appliance Design:
It incorporates the characteristics of the utility arch as well as those of
the conventional intrusion arch. The CIA is preformed with the appropriate
bends necessary for easy insertion and use.
Two wire sizes are available: .016” * .022” and .017” * .025”. The maxillary
and mandibular versions have anterior dimensions of 34mm & 28mm,
respectively.
The bypass, located distal to the lateral incisors, is available in two
different lengths to accommodate for extraction, nonextraction, and mixed
dentition cases.
It requires triple tubes on the maxillary molars and double tubes on the
mandibular molars. An .018” * .025” auxiliary tube allows the CTA to be used in
conjunction with other wires.
Piggyback wires and posterior segments may be used where necessary.
Transpalatal bars may be added to maintain buccal width or for anchorage
purposes.

56. 56
Mechanics:
The CIA’s basic mechanism for force delivery is a V-bend
calibrated to deliver approximately 40-60g of force. Upon
insertion, the 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.
A slight difference in placement may alter the force
system during activation. The moment created at the molar will also
vary. These minor changes can be measured with a spring gauge
when the arch is inserted, and the necessary adjustments can be
made to ensure proper force delivery.

57. 57
About 1mm of intrusion can be expected every six weeks. If
needed, use of headgear to counteract these effects and correct
molar root positions is advocated.
During intrusion of flared incisors, the CIA’s point of force
application is anterior to the center of resistance, which will flare
the incisors unless the length of wire between them and the molars is
fixed.
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.

58. 58
Modification of Lingual Arch For Deep bite
This appliance was developed by Winston Senior.
Many mechanical systems have been described for intrusion of the lower
incisors-reverse curve of Spee, and sectional arch inserted in double buccal
molar tubes.Both systems apply pressure to the labial surfaces of the lower
incisors, creating a downward force vector that passes anterior to the
incisors’ center of resistance.
This causes the crowns of the lower incisors to procline labially and the
roots to impinge on the planum alveolare—the cortical bone on the posterior
aspect of the symphysis. An illusion is created that the incisal edges are
intruding when, in fact, they are merely tipping labially.
To counteract this tendency, intrusive force is applied lingually in this
appliance.

59. 59
An .036” lower lingual arch is soldered to first molar bands.
Distal extensions form occlusal rests on the second molars to prevent
distal tipping of the first molars as the incisors are intruded.
Four elastic chains are attached to the anterior bridge of the lingual arch
with a mosquito forceps
Appliance Design:

60. 60
If intrusion is the primary goal and the teeth are already fairly
upright, the elastic chains should come off the lingual arch on the labial
side.
If the priority is to retrocline the lower incisors, the elastics should
come off on the lingual side. This will reduce the risk of the root apices
impinging on the planum alveolare.
After cementation of the arch, the elastics are stretched to four lingual
buttons on the lower incisors

61. 61
 AlQabandi et al AJO 1999 compared the effects of rectangularand
round continuous archwires with a mild reverse curve of Speeon the axial
inclination of lower incisors during the initial stage of treatment. The intention
of rectangular arch wires is to counteract the labial crown moment usually
produced during leveling the curve of Spee with full arch mechanics.
 Group 1 (N = 12) received round arch wires throughout the leveling
stage. Group 2 (N = 16) started with flat 0.016 ´0.022 nickel titanium arch
wires progressing to 0.016 ´0.022 stainless steel.
 In group 1, the lower incisor proclined a mean of 6.75°±4.85°( P< .01)
and in group 2 it proclined a mean of 6.10°±3.95°( P< .01). However, no
significant difference in proclination was detected between the 2 groups.
 Statistically significant,In both groups, the lower incisors proclined
with uncontrolled tipping that can probably be attributed to the intrusive
force introduced by the arch wire being labial to the center of resistance of
the lower incisors.
 The ability of the rectangular arch wires to control labial proclination
following leveling of the curve of Spee, as used in this study, was not
supported.

62. 62
DakeandSinclairAJO1989compared30deep-bitelow-angle
nonextractioncasestreatedbyRicketts,toasimilargrouptreatedby
SchudyinwhichClassIIIelasticswereaddedtocontinuousarchwires
whilelevelingthecurveofSpeeinthetraditionalway.
TheRickettsgroupshowedmoreproclinationofthelowerincisors
thantheSchudygroup(>5°ofproclinationin64%oftheRickettscases
comparedwith40%ofShudycases).
TheRickettsgroupalsodemonstratedanaverageof1.2mmofactual
intrusionofthelowerincisorsinadditiontoholdingagainstgrowth,
whichwasrelativelystableanaverageof4yearsposttreatment.
Bothgroupsproducedsimilaramountsofdistaltippingofthe
mandibularmolarsaswellasextrusion/eruption,thelatterbeing
relativelystableposttreatment.
TheRickettsgroupalsodemonstratedmoreposttreatment
uprightingandoverbiterelapse(notethattheoverbitewasintentionally
overcorrectedintheRickettsgroup).

63. 63
BeggTechnique

64. 64
OneofthemaingoalsofstageoneofBeggtreatmentiscorrection
ofdeepbite.Thisisachievedbytheapplicationoflightcontinuousforce
throughhightensileroundstainlesssteelwire.
Appliance design for correction of deepbite:
In the use of standard or pure Begg technique deepbite is reduced by
the combined effects of the anchor bends and the vertical components of force
of the class II intermaxillary elastics.
The degree or the angle of the anchor bend is influenced by the stage
of the treatment depth of overbite, rate of progress of the case , inclination of
the anchor molars at commencement of treatment, second and third stage
treatment mechanics. A Class II elastic force of 2.5oz is generally
recommended.

65. 65
Anchor bends:
The incorporation of anchor bends causes the upper and lower arch
wires to lie well into the mucobuccal fold anteriorly so that once pinned into
the bracket slots of the incisors, intrusive forces are created.
The intrusive force of the lower arch wire, when it is
applied to the lower incisors which are usually labially inclined causes an
accompanying increase in the long axis angle of these teeth relative to the
mandibular plane due to the lingual movement of the root apices with little
associated labial movement of the incisal edges.
Biomechanics:

66. 66
In the case of a narrow cross section of bone , labial tilt may be
controlled resulting in the continuous pressure of the roots on the cortical
plates .This is a situation productive of bone and root resorption.
The pivotal point for this movement is near the necks of these incisors, a
fulcrum being provided by the presence of the labial cortical plate. There is
lingual movement of the root until slowed by the contact of the lingual plate.
In cases of wider alveolar process opposite to point B, lingual
displacement of the apices will be greater Mechanical control may be
needed to prevent excessive tilt and to keep the intrusion forces more in
line with the long axis of the teeth.

67. 67
The force exerted by the anchor bends in the lower arch
wire is not great enough to tip the lower anchor molars distally, but
to give the lower molars the power to resist the forward pull of
class2 intermaxilarry elastics giving sufficient “ toe hold” .
If the excessive force is exerted through anchorage bends
in heavy arch wires the deepbite will be opened , chiefly by elevating
the mesial marginal ridges of the anchor molars in their sockets and
only to a small extent by the depression of the six anterior teeth.
These elevated mesial marginal ridges off the anchor molars
would sink back to the general plane of occlusion after active
treatment and the original deep overbite of the upper and lower
anterior teeth would recur to a large extent .

68. 68
Class II intermaxillary elastics:
These elastics by the force of their pull tip the crown of
the six anterior teeth back and, at the same time correct the
anteroposterior occlusal relations of the buccal teeth.
The intermaxxilary elastics, through their vertical component
of force , produce not only elevation of the lower molars posteriorly, but
also have a similar effect on the anterior of the upper arch wire. The
latter fact is not conducive to the upper incisor intrusion, in that it
cancels, or partially cancels the intrusive force of the arch wire in that
region.

69. 69
Long axis control of lower incisors during
intrusion:
In order to minimize the root resorption, prevent premature
angling of the lower incisors across the alveolar section with the
threat of penetration of the lingual plate by the root apices, coupled
with the possibility of labial movement of the Incisal edges, it may be
desirable to apply a modest amount of labial root torque during the
action of incisor intrusion.
The application of labial root torque will have the effect of
uprighting the lower incisors over the basal bone, which ensures that
the direction of intrusive forces more in line with their long axis.

70. 70
In severe deepbite, the resistance to intrusion of the incisors can
build up quickly against the force supplied through the anchor bends. If the
anchor bends remain active but meet resistance from the anterior teeth,
their continued activity can produce distal crown tipping with elevation of
the mesial marginal ridge
The lower anchor bend will gradually become closer to the
buccal cusps of upper teeth and will be more exposed to the subsequent
damage from the occlusal forces.
This effect can be controlled by banding the second molars
and extending the main arch wire to attachments on these teeth to support
against the possible tilt to the first.
As an alternative posterior vertical elasticscan be used to
support the distal of the first molars against depression.
Supplementing the vertical anchorage:

71. 71
Differential straight arch technique

72. 72
The Tip-Edge concept is to provide an edgewise type bracket that can be
used to treat malocclusions through differential tooth movement , this can
be accomplished by diagonally opposed corners of the bracket slot.
Goals of stage one:
1,Vertical correction of deep or anterior open bite.
2,Horizontal correction of anterior over or under jet.
3,Align anterior teeth to eliminate anterior crowding or spacing.
Tip-Edge arch wire slots with their one point contact with arch wire
permit the roots to intrude in an unhindered fashion, without the need for
extra oral forces.

73. 73
Appliance design:
The arch wires are formed from 0.016-inch high tensile stainless steel
wires with a tip back bendsfor bite opening and cuspid circlesto engage class
II elastics for over jet reduction.
The bite opening bends are placed 2mm mesial
to the molar tubes which induce intrusion of upper
and lower labial segments as well as mesial root
movement of the molars, thereby preventing the
loss of anchorage.
Placing the anchor bends 2mm mesial to the
molar tube allows for distal sliding of the arch
wires as retraction of the anterior teeth occurs. If
these bends are positioned any further forward
the anterior intrusive forces delivered by the arch
wires could be reduced.
 The premolars are not engaged at the start
of treatment , because this dissipates the intrusive
forces produced by the bite opening bends and
instead turns them into molar tip back bends.

74. 74
Force vectors of intrusion and
retraction mechanics:
A –The gingivally directed force is
created by bite opening bends mesial to
the anchor molars and delivered to the
anterior teeth by the arch wire
B-The incisally directed vertical
component of class 2 intermaxillary
elastics
C-The net gingivally directed force on
the anterior teeth
D-Horizontal component of class2
elastics
E -The resultant of the force vector in
the horizontal and vertical direction
Biomechanics:
The length of the force vector is
proportional to the force magnitude

75. 75
The type of tooth movement is determined by the direction of the
resultant force vector.
If the force vector passes through Cres the result is translation,
(no labio lingual rotation). (A)
When the force vector passes below the Cres but within the root
area, the tooth intrudes while rotating to a more upright position. (B)
If the force vector passes through the root area above the Cres
the tooth rotates tending to flare labially as it intrudes.

76. 76
Magnitude of forces:
The amount of force applied to the anterior teeth is
directly related to the distance between the bite opening bend and the
anterior bracket slots.
A 25mm displacement results in approximately 1.5 oz
(42gms) of depressive force on the six anterior teeth when the wire is
engaged in the brackets.
Two class II elastics (2oz each)pull the maxillary arch wire
half way toward the anterior brackets. The 12 to 13mm of travel
remaining to the bracket slots generates approximately 1 oz (28gms) of
depression.

77. 77
Use of stronger intermaxillary elastics and/or
softer arch wires could also result in negative or
undesired imbalance between arch wire and elastic
forces.
The key to the desired opening lies in the continual
use of light (2oz) elastics and the highest tensile, 0.016”
archwires with proper bite opening bends or curves.

78. 78
LINGUALTECHNIQUE

79. 79
One of the distinct situations where the lingual appliance
may be more efficient than the labial appliance because of the
unique mechanical characteristics is intrusion of the anterior
teeth.
Lingual bracket position which is dictated by the
morphology of the lingual surface of the tooth places the
bracket close to the CRes of the tooth than is found with the
labial bracket placement.
An important clinical implication of this unique bracket
position and design is that the intrusive force vector is
directed through the CRes of the tooth.

80. 80
Anterior horizontal plane of the
maxillary anterior brackets:
According to Gorman as the
mandibular anterior dentition occludes with
the anterior horizontal plane of the maxillary
anterior brackets, a bite plane effect results.
The net effect of this appears to be a light
continuous intrusive force. In addition a
passive extrusion of the posterior segment
occurs.
Two common bite opening mechanisms used with lingual brackets are
those of Gorman et al and Fujita.

81. 81
Inthemesiofacialanddolichofacialtypes,wherebiteopening
maynotbedesirable,thehigh-pullheadgearisusedtomaintain
posteriorcontrol.
Ifadecisionismadetotreatahighanglecase,itmaybe
desirabletoplaceaconventionalfixedapplianceonthelower
archandlimitthelingualappliancetothemaxillaryincisorsand
bicuspids.
Byutilizingahigh-pullfacebowandClassIIIelastics,the
lowerarchcanbealignedandleveledwithoutposterior
extrusion.
Extrusionofthemaxillarymolarscanthenbelimitedwith
thecombineduseofhigh-pullmechanicsandamolar-to-molar
transpalatalarch.

82. 82
Reverse curve mushroom arch:
Fujita recommended a bite opening mechanism that intrudes lower
incisors until space is available for placement of upper anterior lingual
brackets without interference.
The reverse curve mushroom arch is placed in the occlusal slot of the
Fujita lingual bracket from lower right first molar to lower left first
molar.
The undesirable reaction forces generated during intrusion seem to be
neutralized by the 0.016-inch * 0.022-inch stainless steel buccal stabilizing
segment of the lower first and second molars.

83. 83
Appliance design:
Fujita lingual anterior and premolar
brackets have three slots:occlusal(0.019”),lingual(0.018”), and
vertical(0.016”.).The molar brackets have 5 slots: one occlusal,
two lingual, two vertical. Each of these three types of slots
provides different capabilities for tooth movement.
Modified intrusive mechanics of Burstone’s segmented arch technique:
( JCO 2005)

84. 84
In the lower arch bilateral 0.017*0.025 TMA springs (IS) are engaged in
the inner lingual slots of first molar bracket for intrusion & hooked to
anterior segment between lateral incisor & canine.
0.018” * 0.018” stainless steel segment (SEG) is placed in the occlusal
slots of the anterior & posterior segments.
0.016” * 0.022”stainless steel segments are added on the first and
second molars to stabilize the posterior segments on the buccal aspect.
The multiple slots of Fujita lingual bracket thus allowed to apply intrusive
mechanics of Burrstone’s segmented –arch technique to lingual orthodontic
treatment.

85. 85
About 80 gm of force per side is generally recommended to
intrude the lower incisors and canines.
In Burstone’s original technique, with a perpendicular distance
of 30mm from the incisors to center of resistance of the posterior
teeth, 80gm of force would produce a moment of 2400gm-mm on
posterior segment. Thus in labial treatment, it is virtually impossible
to intrude all 6 anterior teeth without posterior tipping.
However in this technique, an intrusive force of 70gm from
lingual springs hooked to the anterior segment between lateral
incisors and canines produced simultaneous intrusion of lower
anterior without any undesirable side effects on posterior teeth .
This is probably because the lingual intrusive force passes
close to the centre of resistance of the anterior teeth.

86. 86
Implants

87. 87
Creekmore in AJO 1983reported a case of class II division 2
malocclusion with severe deepbite treated with implant for incisors
intrusion.
A surgical vitallium bone screwwas inserted just below anterior
nasal spine. Ten days after the screw was placed, a light elastic thread was
tied from the head of the screw to the archwire
The elastic threadwas renewed throughout treatment, so that a
continuous force was maintained 24 hours a day until the screw was removed
.
During this time, the maxillary central incisors were elevated
approximately 6mm and torqued lingually about 25 degrees The bone screw
did not move during treatment and was not mobile at the time it was
removed
Anchorage control is a major concern in the design of all orthodontic
appliances. Recently,implants started replacing the exra oral anchorage
devices to reinforce anchorage.
Maxillary anteriors Intrusion

88. 88
Takada et al in AO 2005used an orthodonticmini-implantas
anchorage for the intrusion of the upper incisor segment, followed by
alignment of the upper and lower dental arches with an edgewise appliance
without tooth extraction..
The mini-implant was implanted in the alveolar bone between the root
apices of the maxillary central incisors under local anesthesia
The orthodontic appliances were placed on the maxillary teeth for
leveling. After a healing period of six months, the second operation for the
implantation procedure was performed and an abutment was placed and fixed.
Two months after the second operation, an orthodontic ligature wire
was tied from the head of the abutment to the upper arch wire. A light force
(20 g) was maintained The maxillary central incisors were elevated
approximately four mm and given a 5°lingual root torque.
The overbite was corrected from +7.2 mm to +1.7 mm by upper incisor
intrusion, and the gummy smile was improved

89. 89
MIKAKO UMEMORl et al., 1999 has described about the skeletal
anchorage system for open-bite correction by intrusion of molars. It consists
of titanium miniplate that is temporally implanted in the maxilla (or) in the
Mandible as an immobile anchorage.
The titanium L-shapedminiplateswere fixed by bone screws
(length, 5 mm or 7 mm) at the buccal part of the bone around the apical
region of 1st and 2nd molars, on both right and left sides.
Elastic threadsare used as a source of intrusive orthodontic
force.
Maxillary Posteriors Intrusion

90. 90
KurodaetalAO2004usedtitaniumscrewstocorrect
severeopenbite.Titaniumscrews(2.3-mmdiameter,14-mmlength)
areinsertedbilaterallyinthezygomaticprocessofthemaxillaand
thebuccalalveolarboneofthemandiblethroughthebuccal
mucosa.
Atranspalatalarchapplianceandalowerlingualarch
appliancewereplacedbetweenthefirstmolarstocompensatefor
thecrownbuccaltorquethatwouldbecausedbytheintrusion
force.
Threemonthsaftertheimplantationofthetitaniumscrews,
loadingoftheintrusionforcewasstartedwithelasticchains
Asaresultofintrusionoftheupperandlowermolars,the
mandiblerotatedcounterclockwise,andthesevereanterioropen
bitecanbeimproved.

91. Headgears
Highpullheadgears:
Theeffectonthedentitionresultsonthelocationofcenterofresistance
relativetothelineofactionofforce.
•a) Whenthedirectionofpullisplacedbehindthecenterofresistanceofthe
maxillaandmaxillarydentitionaclockwiserotationofmaxillaanddentitionis
observed.Molarswillshowintrusionandincisorswillextrude.Neteffectis
clockwiserotationofOcclusalplane.
•b) Whenpullinfrontofcenterofresistanceofbothmaxillaandthemaxillary
dentition,ananticlockwiserotationisobserved.Molarstendtoextrudeandincisors
intrude.Occlusalplanealsorotatesanticlockwise.Thereforebiteopeningis
facilitated.

92. Cervicalpullheadgears:
Herewhentheinnerandouterbowsareinsameplanethereisclockwise
rotationofbothmaxillaandmaxillarydentition.Theincisorswillmoveinferiorlytoa
greaterextentthanmolarregion.TheOcclusalplanewillalsorotateinclockwise
directionandbitewilldeepenup.Butiftheouterbowisbentupwardssothat
directionoftractionisbetweenthemaxillaandmaxillarydentition,maxillawill
rotateclockwiseanddentitioninanticlockwisedirection.Henceincisorswill
experienceupwardinfluenceandmolarsadownwardinfluenceandbitewillbe
openedup.

93. Combinationheadgears:
Inthesecasesalsotheresultantforcevectorwhichmovesthroughthe
centerofresistancebringsaboutamoreofdistalmovementofmolarsanda
minimalamountofintrusionofthemolars.
Theouterbowisangulatedabout15
o
Headgearscanbeusedincombinationwithotherappliancesorbyitself
tobringaboutactiveorabsoluteintrusionoftheteeth.

94. Removable appliances for
Intrusion
ThoughtheseappliancesdonotfallundertheexactclassificationofIntrusive
appliances.Manyoftheremovableappliancesweuseinourday-to-daypractice
canbemodifiedtobringabouttheintrusionofteethtocorrectthevertical
discrepancies.

95. Anteriorbiteplaneisthemostcommonlyusedremovableappliancefortreatment
ofdeepbite.Itisamodifiedhawley’sappliancewithaledgeofacrylicbehindthe
upperincisors.Thepresenceofacrylicwillresultindisoccludingtheposterior
teethandtherebyfreetoerupt.Astheposteriorteetherupttheheightofthebite
plateisgraduallyincreased.
Bite
Planes

96. Functional
Appliance
Activator:Selectivetrimmingisdonefortheextrusionofmolarsandintrusionof
incisors.
Extrusionofthemolarsisachievedbyloadingacrylicinthelingualsurfaceabove
theareaofmaximumconvexityofthemaxillarymolarsandbelowtheareaof
maximumconvexityofmandibularmolars
Intrusionoftheincisorsisdonebyloadingof
theacrylicintheincisaledgeoftheanterior
teeth

97. Magnetic
Appliance
TheActiveverticalCorrector:
ThiswasintroducedbyDELLINGERin1986.Thisconsistedofupperand
lowerbiteblockswithsamariumcobaltmagnetsinstainlesssteel
casesembeddedinthem.Thesehelpedintheintrusionofanteriors.

98. Seated Active Vertical Corrector (AVC).

99. MagneticActivatorDevice(MADII)
Thiswasdevelopedin1993byDARENDILIER.Theseareusedfor
correctionofopenbiteanddeepbitecases.
Theybringaboutintrusionbyplacingrepellingmagnets,whichareplaced
opposingeachother.IncasesofclassIImalocclusionwithopenbite,theposterior
repellingmagnetsonmaxillaryplate,bringaboutexpansionofmaxillaryarchesand
alsotheintrusionofmolars.

100. ThisappliancebyKalra,Burstone,andNandaincreasestheinterocclusalspace
andallowsupwardandforwardautorotationofthemandible,therebydecreasing
lowerfacialheightandfacialconvexity.Thisapplianceresultedinintrusionof
posteriorteethandanupwardandforwardautorotationofthemandible.

101. TheMagneticTwinBlockAppliance:
Thefunctionsoftwinblockweremademoreaccuratebyincorporation
ofmagnetsbyclerk.HeusedsamariumcobaltandneodymiumIronBoronin
hiswell-acceptedtwinblock.Thesemagnetswereembeddedintheinclined
surfacesofthetwinblockinrepulsivemode.Thisreducedtheneedforany
reactivation.

102. 102
Apical Root Resorption &
Intrusive Tooth Movements

103. 103
Costopoulos and Nanda (AJO 1996) studied the effect of intrusion on
root resorption.
The experimental group consisted of 17 patients with excessive
overbite who were treated with a Burstone-type intrusion arch, which
delivered a low level of force (about 15 gm per tooth).
After a period of 4 months, the intrusion group had only slightly
more root resorption than the controls, 0.6 mm versus 0.2 mm
(statistically significant difference).
Intrusion measured at the center of resistance of the central incisor
averaged 1.9 mm.
The amount of resorption was not correlated with the amount of
intrusion.
Results of this study seem to indicate that intrusion with low forces
can be effective in reducing overbite while causing only a negligible amount
of apical root resorption.

104. 104
Dermaut and De Munckused a modified Burstone intrusionarch
with Begg brackets in 20 patients for an average of 6-7 months.
The initial intrusion force on the maxillary incisors was 100 g. They
showed an average intrusion of 3.6 mm with a mean apical
resorption of 18% of root length.
Faber,in a recent clinical study using a Connecticut intrusion arch
with an average force of 38 gm found negligible amount of root
resorption of incisors. This confirms that lower force values
provide a healthy biologic responses.

105. 105
Stability

106. 106
Burzin and Nandastudied the stability of incisor intrusion in 26
patients 2.32 years post-treatment. The incisors were intruded an
average of 2.30 mm and relapse was only 0.15 mm. The study concluded
that the overbite correction by intrusion is a stable procedure.
Sadowsky et al in AJO 2005studied the effectiveness & stability of
over bite correction with incisor intrusion.
The treated group consists of 25 subjects who were treated using
lever intrusive mechanics and cervical head gear .
The results showed that the mechanics used were efficient. The
overbite increased by 0.7mm(from 3.3mmto 2.6mm ).
Although this is statistically significant, it is considered clinically
insignificant.

107. 107
Judicious prescription of medication requires an understanding of the
mechanism of action of therapeutic agents in order to obtain the desired
clinical results. Orthodontist depends on a similar application of mechanical
force system for treatment success. An appreciation of the forces being applied
irrespective of the mechanotherapy chosen is essential for minimizing
anchorage loss, root resorption, and other adverse sequellae.
The challenge for the modern orthodontist is to institute
mechanotherapy that would give the best opportunity for a successful
treatment outcome while remaining mindful of the biologic mechanisms and
the unpredictability of individual patient response.
CONCLUSION: