Introduction to Clinical Biomechanics 1

8/13/2019 Introduction to Clinical Biomechanics 1

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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.



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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.



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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

Documents

Introduction to Clinical Biomechanics 1