W5 - Biomechanics of Ortho Tooth Mvmt - Abdalla Flashcards
Three phases of tooth movement
Pre-eruptive mvmt
Eruptive mvmt
Post eruptive mvmt → orthodontic tooth movement
Orthodontics manipulates what phase of tooth movement
Post eruptive tooth movement
How can the dentition withstand repeated heavy forces and remain stable?
Is it related to time → can withstand for short durations
- Teeth do not contact for long durations during mastication
Physiological response to heavy pressure against tooth (related to time)
Describe how the teeth move in response to ortho force
Orthodontic force is sustained
→ Follows the light pressure response
Describe the difference in response to light force vs heavy force
Light forces - PDL fibers get squashed, blood vessels remain intact and thus PDL still alive
- Frontal resorption begins
- Tooth moves as bone is resorbed
Heavy forces - blood vessels get completely occluded/obstructed → necrosis of PDL (hyalinised PDL)
- Tooth movement via undermining resorption
What is undermining resorption? Why is it slower than frontal resorption?
- Osteoclasts must arrive (due to force) but they cannot get access thru usual route (PDL)
- Must be recruited from alveolar bone of socket
- OC will start resorbing from the alveolar bone towards the PDL space, thus “undermining resorption”
Takes longer for tooth movement (7-14 days)
Frontal resorption is exclusively from osteoclasts within the PDL space (no need for migration = quicker)
Frontal vs undermining resorption
Frontal is better bc its lighter force
- Teeth move quicker
- Less harm to PDL
- Undermining resorption elicits larger biological response by recruiting more OC → more likely to cause root resorption
Why do different tooth movements require different amounts of force?
Amount of force is proportional to the area that the PDL is strained
Ex. Tipping requires less area of force than translation
What is the centre of resistance? (physics)
- Fixed point that a force must pass through to move an object in a linear manner (translation)
- Consistent with the centre of mass
What is the centre of rotation? (physics)
- Unfixed point around which an object rotates
- Determined from the original and final position
What is a moment? (physics)
- Tendency for a body to rotate around a specific point as a response to a force delivered away from the centre of resistance
Moment = Force x Distance
*moving the arrow up or down to increase the distance will increase the amount of rotation
Why is there always a tendency for moments in orthodontic force? (2:41)
Because youre never applying the pressure on the centre of resistance (because its in the root)
- Brackets can only go on the crown
What is a couple? (physics)
Pair of equal and opposite noncollinear forces
Force couple creates pure rotation (no translation)
Requires 2 points of contact
Describe the physiological response to sustained pressure against a tooth (light pressure)
