Biomechanics and tooth movement

Question 1

What are the 3 types of tooth movement?

Answer 1

Pre-eruptive
Eruptive
Post-eruptive

Question 2

What are pre-eruptive movements

Answer 2

Always erupt lingually

Question 3

What are eruptive movements?

Answer 3

Occurs at 1mm per month - cant speed up

Question 4

What are post-eruptive movements?

Answer 4

Accommodate growing jaws
Compensate for occlusal wear
Compensate for interproximal wear
Lower jaw grows anteriorly - Teeth move to adapt
Occlusal wear - increased cementum on the root - increased vertical face height
Increased mesial drift - associated with 8’s growing

Question 5

What is meant by a tooth being infraoccluded?

Answer 5

A condition where teeth are found with their occlusal surface below the adjacent teeth after they should have reached occlusion

Question 6

What stops orthodontic tooth movement

Answer 6

Some situations when cant move teeth
Periodontal ligament needs to be vital
If have ankylosis - when bone replaces PDL - cant move it. Happens in traumatised adult teeth and atrophic canines

Question 7

What are the resting forces on teeth?

Answer 7

Tongue to lower incisors = 10g, to upper = <5g
Lips = 5g
PDL metabolic activity = 5-10g

Question 8

What are the cells of the PDL?

Answer 8

Osteoblasts 
Osteoclasts
Fibroclasts 
Epithelial cell rests of malassez 
Macrophages 
Undifferentiated mesenchymal cells
Cementoblasts

Question 9

What are the different ligament fibres?

Answer 9

Collagen fibres

Oxytalan fibres

Question 10

What is in the extracellular component of the PDL?

Answer 10

Fibres - collagen type I, These cause relapse - midline diastema
Ground substance:
Glycosaminoglycans 
Glycoproteins
Glycolipids

Question 11

What can be done to fibres to remodel quicker?

Answer 11

Fibrectomy - cut fibres

Question 12

What are the resting forces?

Answer 12

Stable position between lips and cheeks and outside of the tongue

Question 13

What are some different ways of putting force on a tooth?

Answer 13

Flexible wire to bring tooth into place
Spring to close space
Elastic between top and bottom to bring teeth into occlusion

Question 14

While teeth moving why do you get pressure and tension?

Answer 14

Pressure - tip the crown back, get pressure in the middle 1/3 of the root
The apex is below the point of rotation - so get both

Question 15

When have a moving tooth, where do you get pressure?

Answer 15

Where the tooth is pushed against the PDL

Question 16

Where do you get tension?

Answer 16

The opposite side to pressure - where the PDL is beinc stretched

Question 17

What 2 things are happening when tooth movement is happening?

Answer 17

Differentiation of osteoclasts

Collagen fibre remodelling

Question 18

What are the 3 phases of tooth movement?

Answer 18

1. initial phase
2. Delay phase - 2-14 days
3. Tooth movement

Question 19

What happens at the initial compression stage?

Answer 19

Tooth moves through PDL and then stops when gets to bone

Question 20

What happens at the delay stage?

Answer 20

Have a loss of cells from the area - so no movement
New cells move into the area: osteoclasts and fibroblasts
Get bone resorption

Question 21

What happens at the tooth movement stage?

Answer 21

Periodontal ligament populated by new cells - get osteoclasts from the vascular system
Bone resorption
Collagen fibre remodelling

Question 22

What is the result of mechanical stress?

Answer 22

Intracellular response - processes to recruit osteoblasts

Question 23

What is the minimum amount of force required to move tooth?

Answer 23

Too small to measure

Know force has to be applied 6/24 hours - the more they wear the appliance the better

Question 24

What is a good guide for knowing how much force is needed?

Answer 24

By compressing the blood vessels - want enough force to get biochemical reactions allows osteoblasts to get in - get tooth movement - tooth starts moving

Question 25

What happens when the optimum force is applied for 3-5 secs?

Answer 25

blood vessels compressed on pressure side, dilated on tension side, PDL fibres and cells distorted

Question 26

What happens when the optimum force is applied for minutes?

Answer 26

Blood flow altered, oxygen tension changes, chemicals released

Question 27

What happens when the optimum force is applied for 2 days?

Answer 27

Tooth movement begins as osteoclasts/blasts within the PDL remodel bony socket

Question 28

How is it different if excessive force is applied?

Answer 28

3-5 secs - blood vessels with PDL occluded on the pressure side minutes - blood flow cut off hours - cell death in PDL compressed area 3-5 days - Cell differentiation in adjacent narrow spaces, undermining resorption begins 7-14 days - Undermining resorption removes lamina dura adjacent to compressed PDL - tooth movement occurs

Question 29

Where are the osteoclasts recruited form if excessive force is applies to tooth?

Answer 29

From outside of the PDL- this delays the process | Osteoblasts recruited from endosteal surface of bone

Question 30

What is the problem with excessive force?

Answer 30

``` Delay in tooth movement Pain Loss of vitality Mobility - want to minimise this Root resorption - lose 1mm of their rooth - short roots get more resorption Loss of anchorage ```

Question 31

What does the optimum force depend on?

Answer 31

Size of root | Type of movement

Question 32

What is the pressure applied to moving tooth?

Answer 32

Pressure = Force per unit root area 20-25g/cm2

Question 33

What is orthodontic anchorage?

Answer 33

The control of unwanted movement 3rd law of motion - for every motion there is an equal and opposite reaction Teeth respond to pressure

Question 34

What do you need to know to have the ideal force?

Answer 34

The root SA

Question 35

What can happen to the anchor tooth if have a heavy force?

Answer 35

Loss of anchorage - the tooth will move | so need a low level of force on that tooth

Question 36

What are the different types of tooth movement?

Answer 36

``` Tipping Bodily movement - springs to close space, rectangular arch wire Rotation - arch wire Torque - use springs when retroclined Vertical movement ```

Question 37

What is the optimum force for tipping, rotation, extrusion?

Answer 37

35-60g

Question 38

What is the optimum force for bodily movement?

Answer 38

70-120g

Question 39

Optimum force for intrusion?

Answer 39

10-20g

Question 40

Whch movements can be done with a removable appliance?

Answer 40

tipping

Question 41

Wich movements can be dont with fixed appliance?

Answer 41

Bodily movement Rotation Excursion Intrusion