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BDS3 - Orthodontics > Physiology of tooth movement and appliances > Flashcards

Physiology of tooth movement and appliances Flashcards

1
Q

What are the two types of tooth movement?

A

Physiological and orthodontic.

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2
Q

What tooth do you need to be weary of when completing orthodontic treatment as mucosal penetration is very fast?

A

2nd permanent molar.

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3
Q

What are the different stages of tooth development you can see on an OPT?

A

Post occlusal
Mucosal (1-2mm a month through mucosa, open bite will get worse if we dont watch this. PDL will become established when it hits something hard- post eruption is very slow again)
Pre-eruptive
Intra-osseous (1mm every 3 months).

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4
Q

What should you do first when receiving an OPT for a patient?

A

Check OPT is the right way around, check it is for the right patient, check it is up to date and always count the teeth from the back first.

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5
Q

What are some tooth eruption theories?

A 
Pulpal pressure
Pulpal growth
Fibroblast traction
Vascular pressure
Blood vessel thrust
Root elongation
Alveolar bone remodel
PDL formation.
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6
Q

Name two examples of when orthodontics can be used to utilise tooth eruption to minimise the impact of a developing malocclusion.

A
  • Ectopic upper permanent canines can be treated by interceptive extraction of the deciduous canine (ages 10-13)
  • Permanent teeth can be encouraged to erupt if the deciduous tooth is extracted at the correct stage (one half to two-thirds root development).
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7
Q

At what age of the child should you be palpating for ectopic upper permanent canines?

A

From age 9-10 years.

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8
Q

What can happen due to the early loss of LRe?

A

Mesial drift of LR6.

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9
Q

What is the physiological basis of orthodontics?

A

IF AN EXTERNAL FORCE IS APPLIED TO A TOOTH, THE TOOTH WILL NOT MOVE AS THE BONE AROUND IT REMODELS
THIS BONY REMODELLING IS MEDIATED BY THE PERIODONTAL LIGAMENT
IF A TOOTH HAS NO PDL OR IS IS ANKYLOSED IT WILL NOT MOVE
CEMENTUM IS MUCH MORE RESISTANT TO RESORPTION THAN BONE, ALTHOUGH SOME DEGREE OF ROOT RESORPTION AFTER ORTHODONTICS SHOULD BE EXPECTED.

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10
Q

Histologically- what happens in response to orthodontic forces?

A

Osteoclasts and osteoblasts appear.

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11
Q

What are the three different theories for orthodontic tooth movement?

A

Differential pressure theory
Piezo-electric theory
Mechano-chemical theory.

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12
Q

What is the differential pressure theory?

A

Tension bony reposition, compression bone resorption.

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13
Q

What is the Piezoelectric theory?

A

Piezoelectric currents are generated when crystalline structures, such as bone, are deformed
These currents have been suggested as the prime mechanism by which tooth movement is modulated (compression side becomes more positive).

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14
Q

What is the mechano-chemical pressure theory?

A

Mechanical stress=
Release of neuropeptides from nerve endings=
Stimulates fibroblasts, endothelial cells and alveolar bone=
Fibroblasts also communicate with osteoblasts and osteoclasts=
Alveolar bone and periodontal ligament remodelling=
TOOTH MOVEMENT.

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15
Q

What are the types of orthodontic appliances?

A

Removables (URA)
Functionals
Fixed.

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16
Q

What occlusion is the twin block appliance the best for?

A

Good for class 2 division 1.

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17
Q

What are the different types of tooth movement?

A 
Tipping
Bodily movement
Intrusion
Extrusion
Rotation
Torque.
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18
Q

What is torque?

A

A tipping movement that moves the root rather than the crown.

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19
Q

How many grams of pressure does a tipping movement possess?

A

35-60g.

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20
Q

How do functional appliances work?

A

The mandible is postured away from its normal rest position
The facial musculature is stretched which generates forces transmitted to the teeth and alveolus
There may be an effect on facial growth eg. class 3 cases (restrict maxillary growth, promote mandibular growth and remodel the glenoid fossa).

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21
Q

How does the twin block appliance work?

A

The Twin Block is designed so that each time you bite, swallow or talk, the appliance is activated. These actions exert gentle pressure on the teeth and dental arches while still giving stability to the jaw joints. With time, the lower jaw is permanently positioned forward and the bite is corrected

Wearing twin block- top teeth tip back, maxillary restriction and growth, lower teeth tip forward and might get some forward growth
-got to watch you don’t make lower teeth tipped too forward.

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22
Q

What is the mode of action of functional appliances?

A

Skeletal change (30%), growth of mandible and restraint of the maxilla
Dentoalveolar change (70%) retroclination of upper teeth, proclination of lower teeth
Mesial migration of lower teeth
Distal migration of the upper teeth
Combination of the above achieves class 1.

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23
Q

How many grams of pressure does bodily movement apply to a tooth?

A

150-200 grams.

24
Q

How many grams of pressure does intrusion movement apply to a tooth?

A

10-20 grams.

25
Q

How many grams of pressure does extrusion movement apply to a tooth?

A

35-60 grams.

26
Q

How many grams of pressure does rotational movement apply to a tooth?

A

35-60 grams.

27
Q

How many grams of pressure does apical root torque movement apply to a tooth?

A

50-100 grams.

28
Q

How many grams of pressure does bodily movement apply to a tooth?

A

150-200 grams.

29
Q

How many grams of pressure does intrusion movement apply to a tooth?

A

10-20 grams.

30
Q

How many grams of pressure does extrusion movement apply to a tooth?

A

35-60 grams.

31
Q

How many grams of pressure does rotational movement apply to a tooth?

A

35-60 grams.

32
Q

How many grams of pressure does apical root torque movement apply to a tooth?

A

50-100 grams.

33
Q

What happens to the periodontal ligament when light force is applied?

A

Hyperaemia within the PDL
Appearance of osteoclasts and osteoblasts
Resorption of lamina dura from pressure side
Apposition of osteoid on tension side
Remodelling of socket “frontal resorption”
Periodontal fibres reorganise
Gingival fibres appear not to become reorganised but remain distorted.

34
Q

What happens to the PDL when moderate forces are applied?

A

Occlusion of vessels of PDL on pressure side
Hyperaemia of vessels PDL on tension side
Cell free areas on pressure side (hylinisation)
Period of stasis
Increased endosteal vascularity (undermining resorption)
Relatively rapid movement of tooth with bone deposition on the tension side (tooth may become slightly loose)
Healing of PDL- reorganisation and remodelling.

35
Q

What happens to the mouth when excessive force is applied?

A 
Necrosis
Undermining resorption
Resorption of root surfaces
Pain
Remanent change.
36
Q

What is the histological effects of excessive force?

A

Extensive lateral root resorption (RR) and undermining resorption.

37
Q

What factors affect the response to orthodontic force?

A

Magnitude
Duration
Age
Anatomy.

38
Q

What is alveolar necking?

A

Cortical bone left = harder = more difficult to close the space.

39
Q

What are anatomical features that effect the response to force?

A

Anterior open bite
Alveolar necking
RCT teeth.

40
Q

What are some deleterious effects of orthodontic force?

A 
Pain and mobility
Pulpal changes
Root resorption
Loss of alveolar bone support
Relapse.
41
Q

What is the ideal time for tooth movement?

A

1mm of tooth movement per month is thought to be ideal- treatment time 24 months for fixed appliances.

42
Q

What histological feature is thought to play the biggest role in tooth eruption?

A

Dental follicle.

43
Q

In order to promote eruption of an upper second premolar we are considering extracting the deciduous second molar. What would be the ideal stage of root development of the unerupted second premolar to produce an optimal result?

A

One half to two thirds root formed.

44
Q

Which of the following force ranges would be the most appropriate to apply when trying to intrude teeth with a fixed appliance?

A

10-20g.

45
Q

With regards to the mechanism by which bodily orthodontic tooth movement takes place during fixed appliance treatment- explain this?

A

Bone is laid down in response to tension of the PDL on the opposite side of the tooth to the direction of intended tooth movement.

46
Q

Characteristics of the ideal pt to lose the 1st permanent molar?

A

Age 8 1/2 - 10yrs old
Class I
Mild incisor crowding
All permanent teeth present.

47
Q

Implications of loss of the 1st permanent molars?

A

Disturbs occlusion - especially in lower arch extraction
Ortho treatment prolonged e.g if pt has high caries rate and doubtful cooperation
Treatment may be more difficult e.g. if carious/restored = remove 6s
Pts unsuitable.

48
Q

When extracting 6s, what factors influence success?

A

Degree of crowding - avoid if no crowding
Upper or lower (upper 6s rarely a problem)
Timing of extraction - immediate XLA (unrestorable) or retain it and have ortho later
Balancing or compensating extractions.

49
Q

Why are lower 6s a problem?

A

As the lower 7 after 6 is extracted:
Tilts mesially
Rotates mesio-lingually = occlusal problems
Leans lingually
Over eruption of upper 6 = stops any mesial movement of lower 7.

50
Q

What occurs when the 6 is extracted too late or too early?

A

Too late = Minimal spontaneous space closure

Too early = 5 moves distally or can become ectopic.

51
Q

When is the ideal time to extract lower 6s to achieve spontaneous space closure?

A 
When bifurcation of lower 7 visible
Other favourable factors:
- Lower 5 engaged in bifurfaction of E
- Lower 7 mesially angulated
- Lower 8 present.
52
Q

What to consider when thinking about extracting the lower 6s?

A

Will the pt need ortho treatment:
- Yes = refer
Will the affected tooth require a crown or RCT in future?
- Yes = consider extraction or extraction of the other 1st molars.

53
Q

What is an advantage of XLA of 6s?

A

Less likely to get impacted lower 8s.

54
Q

How to extract 6s with class II pts?

A 
Extract 1st molars early
Correct class II with functional appliance OR maintain and incorporate into ortho Rx.
55
Q

XLA of 6s in class III pts?

A

Delay ortho treatment to assess mandibular growth

Timing of extraction can alter if orthognathic surgery is planned.

BDS3 - Orthodontics (14 decks)

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