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BIOMECHANICS OF TOOTH MOVEMENT

Dr Karandish DDS, MS

Fellowship of Lasers in dentistryFellowship of Medical educationFellowship of researchFellowship of electronic learning

In the Name of Allah

The Compassionate

The Merciful

CONTENTS Introduction to

biomechanics Phases of tooth

movement Theories of tooth

movement Biologic control of tooth

movement Effects of force

magnitude

Effects of force distribution & types of tooth movement

Effects of force distribution & force decay

Anchorage control

References

Ch. 18 کتاب ملی

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Force

The force must have the right characteristics such as the magnitude and duration ---- it must meet certain threshold.

Force

contact noncontact

Force

point distributed

force

external internal

Force Types

Light, continuous forces Never declines to zero

Interrupted forces Declines to zero

Intermittent forces Declines to zero

Couple Force

Addition

Biomechanics of Tooth Movement

Center of Resistance --- A point on the tooth around which the tooth shall move. For most teeth, COR is ½ way between the apex and the crest of the alveolar bone.

Center of mass vs center of resistance

Center of Rotation --- The point around which rotation occurs when an object is being moved.

Force and Couple Force

Is applied by orthodontic appliances. Induces tipping, translation, intrusion, extrusion and/or

rotation. Couple

Two forces of opposite directions and with non-overlapping points of application.

Translation of teeth occurs in response to appropriate force couples.

Force Magnitude (Level)

In the range of 10 to 200 grams. Varies with the type of tooth movement. Light, continuous forces are currently considered to be

most effective in inducing tooth movement. Heavy forces cause damages and fail to move the teeth.

Force Duration

Threshold --- 6 hrs per day. No tooth movement if forces are applied less than 6 hrs/d. From 6 to 24 hrs/d, the longer the force is applied, the

more the teeth will move.

Eruption Active Passive

Lateral drifts Physiological Due to loss of adjacent teeth

Orthodontic tooth movement

Types of Tooth Movement

Types of Tooth Movement

Intrusion Extrusion Tipping Translation Rotation

Any questions???

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Now let’s trace and discuss biomechanics of different tooth movements

Anchorage

Newton’s law: for every action, there is reaction.

Defined as “resistance to unwanted tooth movement.”

The “anchorage value” of any tooth is roughly equivalent to its root surface area. Thus, molars and canines generally have higher anchorage values than incisors and bicuspids.

Anchorage types

Reciprocal anchorage Reinforced anchorage Stationary anchorage Cortical anchorage

Face bow

Both units move roughly equal distance.

Exemplified by closing a diastema between two central incisors.

Face Bow

Reinforced anchorage•Unit A has substantially more anchorage value than Unit

B. Thus, Unit A moves little but Unit B moves a lot.•Exemplified by retracting anterior teeth to close an

extraction space by using posterior teeth as a reinforced anchorage unit.

Unit BUnit A

Bone anchorage

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Thanks for Your Attention

Any Questions?