this part is made by den. Mussa majid its THE 2nd part of the seminar of orthodontic appliances show you the types and explain their uses and benefits enjoy it

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SCREWS
Screws are active components
that are used to provide
intermittent forces in removable
appliances. Screws can be used
to bring about various kinds of
tooth movement.
A screw consists of a rod with
left and right hand threads at both
ends and a nut in the center,
which is turned for activation.
The threads turn in metal blocks
that are embedded in the
baseplate, which is split at right
angles to the screw. The
appliance is retained with
Adams' clasps on posterior teeth.
When the screw is turned, the
two parts of the base plate
separate and put pressure on the
teeth. This causes the teeth to get
slightly displaced and over time
teeth move to 'new positions by
remodeling of the over- lying
bone. Therefore, a wide variety
of tooth movements are possible
based on the location of the
screw, number of screws and
location of the
e
split in the plate.
Advantage of Screw Over
Springs
1. Appliances with screws are
easier to manage than those with
springs. Therefore, they are
useful in the less skillful patient.
2. Screws are activated by the
patient at regular intervals using
a key, therefore, they are more
valuable in patients who cannot
visit the dentist frequently.
3. Appliance with a screw has
fewer tendencies to get dislodged
than those with springs.
Therefore, they offer more
stability for moving several
adjacent teeth in the same
direction.
4. Forces generated can be
controlled, based on the amount
of activation done. The patient
or parent using a key activates
the
screw. Activations may be done
either once or twice a week or
more frequently, depending on
the type and amount of tooth
movement required. Ideal tooth
movement is achieved by turning
the screw a quarter turn every 3-
7days. Most screws produce 0.2-
0.25mm movement per quarter
turn. The movement produced is
a direct function of the thread
height . More the thread height,
more the opening and higher the
forces generated. The amount of
force applied to each tooth by a
screw appliance also depends on
the number of teeth being moved,
each tooth receiving a part of the
total force. Screws should not
budge too much out of the acrylic

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Based on the location of the
screw and the acrylic split, three
types of tooth movements can be
brought about by screw
appliances:
center of the arch.
a.Arch expansion….screw
place in center of the arch
b. Labial/buccal movement of
one or a group of teeth
c. Mesial! distal movement of
one or more teeth
ELASTICS
Elastic bands have for many
years been used as a convenient
means for applying pressure in
orthodontic appliances. Elastics
are routinely used in conjunction
with fixed appliances but can
provide the force component in
removable appliances in suitable
circumstances. Elastics can be
used along with removable
appliances for retraction of
anterior teeth. For this purpose,
elastics are attached to hook
made in the labial bow distal to
the canine. Elastics are stretched
across the incisors, between the
canines. However, drawbacks of
such appliances are: 1. Flattening
of the arch form due to lack of
control 2. Gingival stripping due
to slippage of the elastics.
Advantage
Better esthetics, as they are less
visible.
The elastic should be change
every day.

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RETENTIVE COMPONENTS
(FIXATION)
These components help to retain
the appliance in place and resist
displacement due to active
components. The effectiveness of
the active components is
dependent on retention of the
appliance. Good fixation will
help patient compliance,
anchorage and tooth movement.
Retentive components are a very
important part of a removable
appliance. Retention in a
removable appliance is given for
the following reasons:
1.Active forces from bows,
springs, screws and elastics can
displace the appliance and make
it ill fitting.
2. A loose-fitting appliance is
uncomfortable and if it is
continually moving in the mouth,
it can lead to metal fatigue and
failure.
3. Because of the above reasons,
patient compliance will be poor
and necessary tooth movements
will not take place. Good
fixation is required to minimize
such problems. Adequate
retention in a removable
appliance is aided by wire
components, which are known as
clasps.
Ideal requirements of clasp
1. Easy to fabricate. 2. Provide
adequate retention. 3. No
interference with occlusion.
4.Should not apply active
force. 5. Able to use on both
fully and partially erupted
teeth. 6. No impingement on soft
tissues.
FULL_CLASP
C_CLASP
Adams' Clasp
Devised by Professor C Philip
Adams in 1948, the Adams' clasp
is one of the most effective
clasps. Tt makes use of the
mesial and distal proximal
undercuts of the first permanent
molars (Fig. 38.12F). It is also
known as modified arrowhead,
universal and Liverpool clasp. It
is made from 0.7 mm round
SSwire. This clasp offers
maximum retention as it engages
the undercuts on the mesial and
distal embrasures of first
permanent molars. The Adams'

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clasp can be used on premolars,
permanent molars and even
deciduous molars in which case
0.6 mm diameter wire is used.
The Adams' clasp has a lot of
advantages over other clasps,
which are: 1. It is simple, strong
and easily constructed. 2. It
offers excellent retention. 3. It
can be used on any tooth be it
incisor, premolars
or molars. 4. It is neat and
unobtrusive and it makes an
appliance
easy to insert and remove using
the bridges of the
clasp. 5. Good patient
compliance as it is comfortable
to
wear and resistant to
breakage. 6. It can be used on
both deciduous and permanent
teeth. 7. A number of
modifications enable its use in a
wide variety of appliances.
Modifications of Adams'
Clasp
ADAMS CLASO WITH
SINGLE ARROWHEAD
ADAMS CLASP WITH
ADDITIONAL
ARROWHEAD
ADSMS CLASP WITH
DISTAL EXTENTION
J HOOK

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Southend Clasp
This clasp is used for retention in
the anterior region. This clasp
can be used when upper incisors
are not proclined and there is a
limited undercut.
FRAMEWORK/BASE PLATE
The material most often used for
base plate is cold cure or heat
cure acrylic. It forms a major part
of the removable appliance. Base
plate a support for pressure
sources and distributes the
reaction of these forces to the
anchorage areas.
USES OF BASE PLATE
1. It incorporates both the
retentive and active
components into a single
functional unit.
2. It helps in anchorage and
retention of the appliance in
the mouth.
3. It helps resist unwanted
drift during tooth
movement.
4. It distributes the forces
from the active components
over a large area.
5. It protects the palatal
springs against distortion in
the mouth (Fig. 38.3B).
6. Bitie planes can be
incorporated into the base
plate and used to treat
specific problems.
Modification of Base Plate
Anterior bite planes are required
for overbite reduction and are
made behind the incisors and
canines. The biteplane should be
flat and not inclined. This is to
avoid proclining forces on the
mandibular incisor teeth. The
thickness should be sufficient to
open the bi te in the premolar
region by 4- 5 mm. As the
overbite reduces, additional
acrylic can be added to raise the
platform and continue overbite
reduction. Grooves can be
provided in the anterior bite to
support the incisal tips of the
mandibular incisors. Also, the
maxillary incisors may be capped
to prevent their supra-eruption or
flaring . It also aids in retention
and increases the anchorage
potential of the appliance. An
inclined guide plane can also be
provided as a modification of the
anterior bite plane.This will
cause the patient to bite more
forward as compared to normal
and may cause the mandible to
grow forward. It can also
procline the mandibular incisors.
FLAT ANTERIOR BITE
PLANE

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FOR MANDIBULAR INCISOR
EDGE
FOR THE CAPPED
MAXILLARY INCISOR
Posterior bite planes are used
mainly when teeth have to be
pushed over the bite. The height
of the platform should be
sufficient enough to free the
teeth, that are to be moved, from
occlusal interference with the
opposing teeth. It is better to
adjust the posterior bite planes to
obliterate the freeway space to
aid compliance.
COMMON FAILURES FOR
NO TOOTH MOVEMENT
ANTEROPOSTERIOR
MOVEMENT
Reduction in Overjet
• Sometimes, upper incisors may
not be retracted as efficiently.
The reason may be that acrylic
has not been removed behind the
upper incisors.
• Another reason may be the
presence of an overbite, which
prevents incisor retraction.
Proclination of upper anteriors
Inadequate clearance of
occlusion prevents teeth from
moving anteriorly.
Vertical
The anterior /posterior bite
planes should be of such a height
that they do not obliterate the
freeway space. Thickness of the
bite plane can be increased once
neurophysiological adaptation
has taken place. If the bite plane
is too thick it will not be worn by
the patient. Insufficient height of
bite plane will not reduce the

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overbite or, in case of posterior
bite planes, will not eliminate
occlusal interference.
Transverse Movement
Failure to activate the screw will
lead to lack of expansion. Proper
instructions should be given to
the patient and/or parents. In
some cases, lower molars also
expand at the same rate as the
upper molars because of good
intercuspation between the two.
Clinically, no improvement of
the crossbite is seen; lower
intermolar distance should be
measured to identify this
problem.