Week 5- Biomechanics of tooth movement

Question 1

What are the 3 phases of physiological tooth movement?

Answer 1

• Pre-eruptive tooth movement
• Eruptive tooth movement
• Post-eruptive tooth movement

Question 2

What tooth movement does orthodontic tooth movement manipulate?

Answer 2

Post-eruptive tooth movement

Question 3

Describe tooth movement in terms of force and velocity

Answer 3

1. Rate of tooth movement increases quickly in relation to small amount of force
2. Plateaus
3. As you continue to apply force, rate of tooth movement goes down.

Question 4

How much occlusal force can be applied to teeth?

Answer 4

50kg

Question 5

Describe the timeline of light force applied to tooth

Answer 5

• Secs: blood vessels distorted
• Minutes: blood flow altered, osteoclast signalling.
• Hours: cell differentiation
• 2 days: frontal resorption
• 3-5 days: Tooth moves as bone is resorbed.

Question 6

What tooth movement has greatest force?

Answer 6

Bodily movement

Question 7

Why does tooth movement force differ?

Answer 7

Reason the forces are different is because the area is different between different tooth movement.

Question 8

What is centre of resistance?

Answer 8

Fixed point that a force must pass through to move an object in a linear manner.

Question 9

What is centre of rotation?

Answer 9

Unfixed point around which an object rotates

Question 10

What is a “moment”?

Answer 10

Tendency for a body to rotate around a specific point as a response to a force delivered away from the centre of resistance. (same force, lesser distance from centre of resistance=lesser moment)

Question 11

Why can’t we move tooth at centre of resistance?

Answer 11

Centre of resistance is halfway between crestal bone of PDL space and apex. Can’t place bracket there.

In ortho, there is always tendency for moment and rotation as it’s away from centre of resistance.

Question 12

What is “couple”?

Answer 12

Pair of equal and opposite non collinear forces, creating pure rotation.

Question 13

Describe PDL fluid during short vs sustained light force

Answer 13

1. Fluid in pdl ligament can’t compress when pressing on tooth for <1sec which stops tooth displacing.
2. If you continue to place force, the fluid starts expelling from PDL space, putting tension on PDL.
3. This can then lead to altered blood flow in PDL which leads to osteoclasts and osteoblasts collecting in PDL space.

Question 14

Where are osteoclasts vs osteoblasts recruited in PDL space?

Answer 14

Osteoclasts: PDL compression/resorption side (side tooth moving)

Osteoblasts: PDL tension/deposition side (side tooth moving away from)

Question 15

Describe timeline of heavy force applied to tooth?

Answer 15

Secs: Blood vessels occluded

Minutes: blood flow obstructed completely.

Hours: no blood supply to PDL

3-5 days: undermining resorption (osteoclasts recruited from alveolar bone- resorb alveolar bone from outside in towards PDL space)

7-14 days: Tooth movement.

Question 16

Why is frontal resorption better than undermining resorption?

Answer 16

• Lighter force
• Teeth move quicker
• Kinder to PDL
• Less likely to get root resorption

Question 17

Which tooth movement has the least force?

Answer 17

Intrusion (easy to overload PDL)

Question 18

How can couple work in orthodontics?

Answer 18

Wire placed on angle between brackets, placing force upwards and downwards.

Question 19

How can teeth translate forwards?

Answer 19

If you push tooth with wire going through bracket forwards, there will always be tipping. As it rotates, the bracket engages the wire at both points, resisting rotation and creating rotational force in opposite direction. 2 tipping forces cancel eachother out (force applied to tooth and uprighting force from wire), creating translation.