Orthodontic Tooth Movement

Tooth Movement

1. Biomechanics2. Mechanics

Biomechanics

1. Magnitude2. Type of Movement3. Duration

MagnitudeLIGHT FORCE HEAVY FORCE

<1s fluid stays in, bone bends, piezoelectric current

1-2s fluid expressed, tooth moves in socket

3-5s blood vessels distorted, no pain

blood vessels occluded, pain from crushing pressure

minutes blood flow and oxygen levels altered, ↑PGE, ↑RANKL

blood flow cut off

hours ↑cAMP, cell differentiation sterile necrosis, hyalinizedPDL (no cells)

2 days frontal resorption= osteoclasts and osteoblasts

3-5 days undermining resorption begins

7-14 days undermining resorption ends, tooth moves

Frontal vs. Undermining

Orthodontic Tooth Movement

Tooth Movement

1. Biomechanics2. Mechanics

Biomechanics

1. Magnitude2. Type of Movement3. Duration

Types of Movement

• P=F/A• How much force?• What area of the PDL is affected?

Uncontrolled Tipping

Controlled Tipping

Bodily Movement

Torque

Intrusion

“One Optimal Force”

Orthodontic Tooth Movement

Tooth Movement

1. Biomechanics2. Mechanics

Biomechanics

1. Magnitude2. Type of Movement3. Duration

Duration

Force Decay

Orthodontic Tooth Movement

Tooth Movement

1. Biomechanics2. Mechanics

Stress-Strain Curve

Performance of Material Depends On…

1. Material properties2. Geometric factors

Wire Materials

• NiTi > TMA > SS• Springy à Stiffer• NiTi is much more flexible, much less formable• SS is much less flexible, much more formable

Wire Geometry

• Round à sliding only, Rectangular à torque• 2x diameter– 8x strength, 16x stiffness, half range

• 2x length– half strength, 8x springier, 4x more range

• Supporting beam– Loose x2 to strength– Tightly fixed x4 to strength

Rubber Bands

• Great elastic range• Fatigues quickly• Interrupted rather than continuous