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Orthodontics > Biomechanics and tooth movement > Flashcards

Biomechanics and tooth movement Flashcards

1
Q

What are the 3 types of tooth movement?

A

Pre-eruptive
Eruptive
Post-eruptive

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2
Q

What are pre-eruptive movements

A

Always erupt lingually

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3
Q

What are eruptive movements?

A

Occurs at 1mm per month - cant speed up

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4
Q

What are post-eruptive movements?

A

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

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5
Q

What is meant by a tooth being infraoccluded?

A

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

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6
Q

What stops orthodontic tooth movement

A

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

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7
Q

What are the resting forces on teeth?

A

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

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8
Q

What are the cells of the PDL?

A 
Osteoblasts 
Osteoclasts
Fibroclasts 
Epithelial cell rests of malassez 
Macrophages 
Undifferentiated mesenchymal cells
Cementoblasts
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9
Q

What are the different ligament fibres?

A

Collagen fibres

Oxytalan fibres

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10
Q

What is in the extracellular component of the PDL?

A 
Fibres - collagen type I, These cause relapse - midline diastema
Ground substance:
Glycosaminoglycans 
Glycoproteins
Glycolipids
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11
Q

What can be done to fibres to remodel quicker?

A

Fibrectomy - cut fibres

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12
Q

What are the resting forces?

A

Stable position between lips and cheeks and outside of the tongue

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13
Q

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

A

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

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14
Q

While teeth moving why do you get pressure and tension?

A

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

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15
Q

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

A

Where the tooth is pushed against the PDL

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16
Q

Where do you get tension?

A

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

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17
Q

What 2 things are happening when tooth movement is happening?

A

Differentiation of osteoclasts

Collagen fibre remodelling

18
Q

What are the 3 phases of tooth movement?

A
  1. initial phase
  2. Delay phase - 2-14 days
  3. Tooth movement
19
Q

What happens at the initial compression stage?

A

Tooth moves through PDL and then stops when gets to bone

20
Q

What happens at the delay stage?

A

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

21
Q

What happens at the tooth movement stage?

A

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

22
Q

What is the result of mechanical stress?

A

Intracellular response - processes to recruit osteoblasts

23
Q

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

A

Too small to measure

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

24
Q

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

A

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

25
Q

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

A

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

26
Q

What happens when the optimum force is applied for minutes?

A

Blood flow altered, oxygen tension changes, chemicals released

27
Q

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

A

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

28
Q

How is it different if excessive force is applied?

A

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

29
Q

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

A

From outside of the PDL- this delays the process

Osteoblasts recruited from endosteal surface of bone

30
Q

What is the problem with excessive force?

A 
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
31
Q

What does the optimum force depend on?

A

Size of root

Type of movement

32
Q

What is the pressure applied to moving tooth?

A

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

33
Q

What is orthodontic anchorage?

A

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

34
Q

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

A

The root SA

35
Q

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

A

Loss of anchorage - the tooth will move

so need a low level of force on that tooth

36
Q

What are the different types of tooth movement?

A 
Tipping
Bodily movement - springs to close space, rectangular arch wire 
Rotation - arch wire 
Torque - use springs when retroclined
Vertical movement
37
Q

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

A

35-60g

38
Q

What is the optimum force for bodily movement?

A

70-120g

39
Q

Optimum force for intrusion?

A

10-20g

40
Q

Whch movements can be done with a removable appliance?

A

tipping

41
Q

Wich movements can be dont with fixed appliance?

A

Bodily movement
Rotation
Excursion
Intrusion

Orthodontics (16 decks)

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