introduction to clinical biomechanics 1
TRANSCRIPT
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Introduction to fixed
orthodontics
Dr Jean Marc Retrouvey
McGill University
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Case selection and planning
1. Concept of minor, limited and
comprehensive Orthodontics
2. Patients treated at the McGill Dentalclinic
3. Importance of screenings
4. Fixed does not equal magic
5. Limitations of therapy provided
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Case study
a. Complete Orthodontic records
b. Precise diagnosis
c. Treatment objectives
d. Skeletal corrections
e. Space requirements
f. Treatment in the three dimensions of spaceg. Management of the vertical dimension
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Mechanotherapy
a. Molar relationship
b. Space management
c. Type of movements (biomechanics)
d. Advantages over a removable
approach
e. Duration of treatment
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Molar relationship
In our clinic, the molars should be in Cl I
before bracketing is started
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Crowding management
Overjet
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Cl II molar and management of
crowding
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Space management
You must create the space before
alignment is attempted. If the space is present, it must be used
judiciously
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ACCO
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Space creation
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Vertical dimension
The bite must be opened before
retraction of the incisors is attempted.
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Tooth movement
a. Tipping
b. Rotation
c. Translation
d. Root movement (torque)
e. Intrusionf. Extrusion
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The crown moves in
the direction of the
force The apex moves in
the opposite
direction
Tipping
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Tipping
Sometimes desirable if the crown of the
tooth has been pushed labially by a finger
habit.
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Tipping
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Tipping from occlusal view
The force being away from the
center of resistance will create a
moment. This moment will tend to rotate the
tooth in the direction of the force.
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Intrusion
Slow movement
Used to level the
incisal edges or themarginal ridges
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Intrusion
Usually achieved by positioning brackets
strategically on the crown of a tooth
You can also place bends (step ups) instainless steel wires.
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Intrusion
Extrusion of the adjacent teeth
Newtons principle of action-reaction.
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Extrusion
Fixed orthodontics isneeded to achieve
this movement
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Extrusion
Superelastic wires of small diameter
must be used (light forces must be
applied) Bracket placement will dictate the
amount of extrusion
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Extrusion
Purpose of extrusion?
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1. Position incisal edges or
marginal ridges
Position all the teeth at their proper levelon the occlusal plane
Bracketing position will dictate the
amount of extrusion Combination of extrusion-intrusion
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2. Extrude a tooth to be restored
Needed to restore a tooth with
Sub gingival fracture
Deep decay
Inadequate crown length
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2. Extrusion of a tooth to be restored
Biological width
Extrusion vs CCL or in combination
Supracrestal fiberotomy should be
performed to enhance the root extrusion and
minimize bone deposition at the crestal
margin
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Limited orthodontics
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Rotation
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Rotation
Easy procedure with fixed orthodontics
Very difficult with removable appliances
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Rotation
Rotation (pure)
(http://en.wikipedia.org/wiki/Rotation)
When a body rotates about the center ofresistance (ie when the center of rotation
is at the center of resistance.
From K.Kousaie: Physics in Orthodontics
http://en.wikipedia.org/wiki/Rotationhttp://en.wikipedia.org/wiki/Rotation -
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Root movement
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Root movement
Large moment to
move the apex in
the desired direction The crown must be
held stationary (High
anchorage
requirements)
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Root Movement
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Wires (Nickel titanium) may be used
Stainless steel wires with special bends are
also an option
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Root movement
The center of rotation is at or near the
incisal edge, and the rotation occurs about
this point. The crown therefore moves asmaller distance than the root. These
movements take time because of the large
amount of bone resorbtion required for themovement.
From K.Kousaie: Physics in Orthodontics
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Translation
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Translation
All points on the body move in the same
direction and with the same magnitude.
The center of rotation is effectively at aninfinite distance away from the tooth
because there is no rotation.
From K.Kousaie: Physics in Orthodontics
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Translation
Combination of a moment and a single
force to move the tooth bodily(equivalent force system as we cannot
apply directly a simple force on the
center of resistance)
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End of sept 2007 lecture
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Translation: View from the
occlusal plane
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Clinical applications of
biomechanical concepts
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Tipping
Simple force:
Hawley with a finger spring to push a tooth
labiallyAdjust the spring with a bird beak
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Activation of the spring will result in a simple
force applied to the lingual of the tooth: labial
tipping will occur
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Tipping with round wire
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Intrusion
Depends on the amount and the desired
movement of the adjacent teeth
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Intrusion appliances
Removable Essix type (Invisalign)
Fixed orthodontics (2x4; full arch with
bends)
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Intrusion arch
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Brackets, wires and auxiliaries
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Height gage
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Height gage
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Direct bracketing
Clean teeth
Etch for 30 seconds
Resin cure 5 seconds
Place bracket as close as possible, press
Remove excess of composite
Reposition
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Cure for 20 seconds mesial then distal
Wait 10 minutes
Select wire (usually Niti for alignment)
Insert wire
Lightly engage the wire in the brackets
Instructions to the patient
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End oct 2007