biomechanics of tooth movement Flashcards
What is physiological tooth movement?
Multifactorial process
1. Pre eruptive
2. Eruptive
3. Post eruptive
Why?
Root growth/change in PDL, alv bone growth/hydrostatic forces/follicular theory
What is the pre eruptive phase?
Starts when root develops
Overlying bone resorbs (no predecessor)
Primary tooth resorbs (successor)

Dental lamina moves underneath primary tooth bud (if too long/short- tooth can develop in malposition)
What is the eruption phass?
When root formation is 2/3 to 3/4 complete
Around 0.3-1mm movement a month
1. Pressure from developing root membrane (neuro ectoderm)- creates force behind eruption
2. Adaptation of perio membrane (formation/reorganisation)
3. Breakdown of overlying tissue (upper crown follicle)
What is the post eruptive phase?
Accommodates continued growth of jaws
Juvenile occlusal equilibrium
- erupts at slower rate to keep pace a vertical skeletal growth
Adult occlusal equilibrium
- teeth continue to erupt through life
- compensates for occlusal/interproximal wear and small increments of vertical growth
How do teeth move orthodontically at a cellular level?
Due to PDL which consists of cells, fibres (collagen bundles, oxytalan) and ground substance (glycosaminoglycans, glycoproteins/lipids)
What cells are in the PDL?
Osteoblasts- bone production, coordinate bone deposition and resorption
Osteoclasts- bone resorption
Fibroblasts- produce and degrade fibres
Cementoblasts- produce cementum
Macrophage
Undifferentiated mesenchymal cells
HIGH CELL TURNOVER- so good blood supply from superior and inferior alveolar arteries
What do the cells do in bone homeostasis?
OSTEOBLAST (Builds bone)- lives 3 months, appear on alveolar bone at tension areas, recruited from osteogenic cell (stem cell), appears 2 days after ortho force, contain growth factors, role in regulation
When osteoblast has laid down matrix and is trapped- becomes OSTEOCYTE- main mechanoreceptors detecting loading, maintain calcium and phosphate levels
OSTEOCLAST (Clears bone)- appear on alv bone surface at compression areas in 2 days, lives 12.5 days
What do osteoblasts and osteoclasts look histologically?
Osteoclast- ruffled border to increase SA, multinucleated giant cells
Osteoblasts- on outer border, single nucleated cell
What is the process of bone homeostasis?
1. Compression of the PDL results in the disturbance of blood flow stimulating undifferentiated mesenchyme cells and osteoclastic transformation occurs, secreting acid and enzymes to breakdown matrix
2. Tension of PDL results in increased blood flow stimulating undifferentiated mesenchyme and activates osteoblasts and fibroblasts, deposits bone matrix and secretes alkaline phosphatase
What is frontal resorption?
When the ortho force doesn’t exceed the capillary pressure
Term for resorption at compression side
What is the timeline of ortho tooth movement?
1. Initial compression (1-3 days)- rapid pseudo movement- cellular recruitment
2. Delay/lag phase (2-20 days)- NO active movement- cellular recruitment/bone resorption
3. Tooth movement (20+ days)- ACTUAL- frontal resorption/collagen fibre remodelling
WHICH IS WHY 6 WEEKS BETWEEN APPTS (allows time for actual movement)
What are ortho movements?
Tipping
Torquing
Bodily (translation)
Extrusion
Intrusion
What is the centre of resistance?
For single rooted- middle of root
For multi rooted- at furcation
If you apply force to this area, the whole tooth will move in that direction (bodily)- can achieve w fixed
If you apply force to the crown, it will result in tipping
What is extrusion?
Pulls teeth into oral cavity
Via fixed and headgear
Elastics (eg. boxed)
Active- mechanics (eg. wire bends)
Passive- removable w bite plane
What is intrusion?
TRUE (v difficult)- mini screws
Relative- head gear, auxiliary arches
High risk of root resorption
