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Biology of Orthodontic

Tooth Movement

Dr. Owais Khalid Durrani

Cellular Elements of PDL

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Osteoclatsts/Cementoclasts

Osteoclast

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Osteoblasts/Cementoblasts

Fibroblast

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Extra Cellular ElementsFibers

Vessels NervesFluid

Physiologic Response of a Tooth

to Force

Time< 1 sec

1-2 sec

3-5 sec

EventPDL fluid incompressible, alveolar bone bends, piezoelectric signal generated

PDL fluid expressed, tooth moves within the PDL space

PDL fluid Squeezed out, tissues compressed; immediate pain if pressure is heavy

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Theories of Orthodontic

Tooth Movement

Bioelectric / Piezoelectric theory

Pressure-Tension Theory

Piezoelectric Theory

Deformation of the crystal structure produces a flow of electric current as electrons are displaced from one part of the lattice to the other

These stress generated signals are important for maintenance of the skeleton by skeletal regeneration and repair

Atrophy of bone in astronauts

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Peizoelectric Effect

+ + + + + + + +

- - - - - - - - - - - - - - - - - - - - -

+ + + + + + +

Piezoelectric Effect

Charge

Seconds

Quick decay rate

Production of equivalent signal opposite in direction when the force is released

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Pressure-Tension Theory

Relies on chemical rather than electric signals

This theory explains the course of events reasonably well.

Divided into following stages1. Application of orthodontic force

2. Alterations in blood flow

3. Formation and release of chemical messengers

4. Activation of cells

5. Resorption/deposition of bone and cementum

6. Remodeling of PDL fibers

7. Movement of tooth

Light Continuous ForceBV

PGs/Cytokines

Osteoclast

Osteoblast

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Light Continuous Force

Heavy Continuous Force

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Drugs Effecting Orthodontic

Tooth Movement

Osteoporosis

Bisphosphonates

Estrogen

Prostaglandin E2 Corticosteroids

NSAIDs (Indomethacin)

Tissue

Phospholipids

Arachidonic Acid

Prostaglandin

X

X

Corticosteroids

NSAIDs

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Several other drugs can reduce the PG levels and can effect orthodontic tooth movement

Antidepressents (tricyclic)

Antiarrythmatic (procaine)

Antimalarial (chloro/quinine)

Anticonvulsants (phenytoin)

Antibiotics (tetracyclines)

!

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Deleterious Effects of

Orthodontic Force

Mobility & Pain

Effects on the Pulp

Effects on the Root Structure

Effects on Alveolar Bone

Mobility & Pain

Mobility is seen in every patient due to remodeling of fibers and alveolar bone.

Heavier the force, more the undermining resorption more the mobility.

Heavier forces cause immediate pain.

Normal forces produce pain on pressure after several hours and last for 2-4 days after activation

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Mobility & Pain

Pain is due to areas of ischemic hyalanization within the PDL

Control of pain

Light forces

Chewing gum

Allergic Reactions

Latex

Stainless steel

Nickel-Titanium

Effects on Pulp

Mild pulpitis might occur which may contribute to pain after activation, no long term effects

Heavy abrupt forces may cause severance of blood vessels as they enter the tooth

Inappropriate force direction can push the apex out of the alveolar bone

No Effects on Endo treated teeth, CaOH only required for traumatically intruded teeth

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Effects on Root Structure

Remodeling of cementum occurs with orthodontic forces, With restoration of root anatomy

Root loss occurs primarily at the apex, once a chunk of the cementum /dentin is removed completely that portion of the root will not heal.

Moderate generalized resorption is a norm, most root loss occurs in max incisors

Effects on Root Structure

Severe generalized resorption is rare

Cause unknown

High risk Patients;

History of resorption

Conical & Dilacerated roots

History of trauma are high risk factors

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Effects on Alveolar bone

0.5-1mm crestal bone height loss

Position of the teeth determines the position of the alveolar bone

Erupting teeth

Enucleation

Extrusion

Intrusion

Next Lecture

Basics of Biomechanics