Common sense mechanics 4 /certified fixed orthodontic courses by Indian dental academy

Common Sense MechanicsCommon Sense Mechanics
part 4
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INDIAN DENTAL ACADEMY
Leader in continuing dental education

Expansion: -Expansion: -
If we have an individual tooth, such as a molar, in
crossbite— or an entire buccal segment— we know
beforehand that we would like to apply a force in the
necessary direction for correction on those teeth only.
But, most of us realize that there will be an equal and
opposite force applied elsewhere as well.
Common sense must enter the picture.

OverlaysOverlays
The term "overlay" as
used here will most often
refer to a heavy wire
overlaying the main
archwire.
 It can either be inserted
into the headgear tube or
be designed with terminal
hooks to engage the
archwire

An .045 headgear tube, prefer to use of an .036 overlay
for expansion.
It provides sufficient binding in the headgear tube when
activated, to provide the desired stability.
The force provided will be equal and opposite— not
unilateral in direction as might appear to be the case
when the overlay is inserted into one tube and observed

Case 1: -
A patient with a bilateral crossbite, but a lateral
mandibular shift which gives the clinical impression of a
unilateral crossbite.

Insertion of the .036 overlay, following activation by
expansion.
Also, remember that upon insertion into both molar
tubes, there exists a buccal force on both the left and
right sides. www.indiandentalacademy.com

The normal side will become "worse", while the opposite
side shows improvement.
 By the time overcorrection of the side in crossbite is
obtained, the "normal" side is in buccoversion

Relapse to normal followed by removal of overlay

Case following treatment and retention

Case 2: -Case 2: -
A unilateral Class II malocclusion and a unilateral tongue
thrust
Case was treated in the same manner

The Class II molar relationship on the right side was
corrected with cervical headgear and overlay treatment

After overtreatment and removal of the overlay, note that
the normal side has relapsed to its original position,
while the side in crossbite had its first opportunity for
some improvement in function.

The lateral opening was still present.
 The case was debanded and retained, since common
sense dictated there was insufficient lateral function to
expect the case to maintain itself.
No myofunctional therapy was ever instituted.

After the bite closed on the right side, retainers were
eliminated and, interestingly, the side which was in
crossbite now looks better than the normal side

Case 3: -Case 3: -
Late mixed dentition case where only a single tooth is in
crossbite.
The overbite is mild, as is the lower anterior crowding,
but this is pretty normal at this stage of development.

Use of an .036 overlay and two molar bands provides a
simple solution.
The overlay is referred to as "cosmetic" because it is
designed not to show when the patient smiles.

Crossbite correction will require an equal and opposite
force on the other molar, it can readily be assumed that
by the time the crossbite is corrected, the normal tooth
will have moved into buccoversion.
 But, the overali movement is very rapid— usually about
three to six weeks

The maxillary right first molar was overexpanded,
resulting in the normal molar moving into buccoversion.
Immediate relapse occurred with removal of the
expander and the corrected side was held with a
removable retainer while other teeth continued to erupt

Ultimately, the improved molar function, in itself,
stabilized the tooth and no further orthodontic treatment
was ever instituted.
 Additional improvement was noted after loss of the
second deciduous molars

Bodily movement: -Bodily movement: -
All of the movements thus far described have been
tipping movements only.
The force is heavy and applied at the crown level.
 If bodily movement is desired, a rectangular wire may
be placed to provide the necessary torque at the root
level.

Normally, when we attempt to "bodily expand", we find
that buccal root torque in the archwire causes the
crowns to initially move in the opposite direction we
intend— that is, they move lingually.

Reduction of posterior arch widthReduction of posterior arch width
Instead of the overlay being expanded, it is constricted.
All of these overlays are much easier to use in the
maxillary arch due to the tendency for occlusal
interference in the lower arch, as well as the fact that the
lower arch usually does not contain a headgear tube for
convenience.

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Common sense mechanics 4 /certified fixed orthodontic courses by Indian dental academy

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Common sense mechanics 4 /certified fixed orthodontic courses by Indian dental academy