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Orthodontics > Tissue Reactions to Orthodontics > Flashcards

Tissue Reactions to Orthodontics Flashcards

1
Q

What is the primary principle on which orthodontic treatment is based?

A

If prolonged pressure is applied to a tooth, tooth movement will occur as the bone around the tooth remodels

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2
Q

Describe the important tooth anatomy to orthodontics

A
  • Each tooth is attached to and separated from alveolar bone by PDL
  • PDL is heavy collagenous supporting structure
  • PDL fibres resist displacement of tooth during normal function
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3
Q

Describe 2 theories of biological control of tooth movement

A
  1. Bioelectric (piezoelectricity and bioelectric potentials)

2. Pressure tension theory (cellular changed and chemical messengers)

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4
Q

What is the bioelectric theory of tooth movement?

A

Relates tooth movement to changes in bone metabolism controlled by the electric signals that are produced when alveolar bone and collagen flex and bend

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5
Q

What is piezoelectricity?

A

A phenomenon observed in crystal structures in which deformation produces flow of current as electrons are displaced (bone mineral is crystal structure)

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6
Q

What are bioelectric potentials?

A

Observed in bone which is not being stressed

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7
Q

What is the pressure tension theory of tooth movement?

A

Relates tooth movement to changes in bone metabolism controlled by chemical rather than electric signals

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8
Q

Describe 3 ways the pressure tension theory is said to work

A
  1. Alteration in blood flow associated with pressure within PDL
  2. Formation and/or release of chemical messengers
  3. Activation of cells
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9
Q

Name 2 sites of remodelling following orthodontic loading

A
  1. Compression (force going towards)

2. Tension (force going away from)

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10
Q

Describe 4 changes on the compression side during orthodontic loading

A
  1. Compression of blood vessels
  2. Attraction of osteoclasts
  3. Resorption of bone
  4. Production of fibrous tissue in Howship’s lacunae
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11
Q

Describe 3 changes on the tension side during orthodontic loading

A
  1. Stretching of PDL fibres
  2. Stimulation of osteoblasts
  3. Deposition of bone
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12
Q

Name 2 major cells in the bone responsible for remodelling its structure

A
  1. Osteoblasts

2. Osteoclasts

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13
Q

Describe osteoblasts and their function

A
  • Derived from mesenchymal cells
  • Function to construct ECM of bone
  • Control osteoclast function
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14
Q

Describe osteoclasts and their function

A
  • Large multinucleated cells of the monocyte lineage
  • Adhere to bone surface and secrete hydrolytic enzymes
  • Found in Howship’s Lacunae
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15
Q

Describe how bone remodelling occurs

A
  • Old bone is rapidly destroyed by short lived osteoclasts
  • Pit left by resorption are filled by long lived osteoblasts which fill pits with new bone
  • Ratio of osteoclast to osteoblast activity can result in net loss or gain of bone
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16
Q

Name 2 ways bone remodelling is controlled

A
  1. Systemic hormone

2. Local factors

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17
Q

Give an example of a hormone which systemically affects bone remodelling

A
  1. Parathyroid hormone
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18
Q

Name a local factor which influences bone remodelling

A

Prostaglandins

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19
Q

Describe how osteoblasts control osteoclasts

A
  • Many factors e.g PTH, PGE2 influence the expression of RANK ligand expression on osteoblasts
  • RANK ligand in combination with other factors e.g VEGF, induce the differentiation of osteoclasts from their precursors
  • Osteoblasts secrete OPG to oppose RANK ligand effects
20
Q

Describe the typical tooth movement response after application of moderate orthodontic load

A

Split into 3 phases

 1. Initial phase in PDL and support bone
 2. Lag phase bone adjacent to crushed areas in PDL is removed
 3. Progressive tooth movement
21
Q

Name 2 types of bone resorption

A
  1. Frontal resorption

2. Undermining resorption

22
Q

What is frontal resorption?

A

If orthodontic force does not occlude blood vessels in PDL steady remodelling of the tooth socket will result in smooth continuous tooth movement

23
Q

What is undermining resorption?

A
  • When orthodontic forces occlude blood vessels and the area is hyalinised
  • Resorption in this area will not take place until osteoclasts removed bone adjacent to hyalinised areas of PDL
  • When osteoclasts reach PDL the tooth will move
24
Q

Associate frontal and undermining resorption with the phases of tooth movement

A
  • Undermining resorption occurs in the lag phase until osteoclasts reach PDL
  • Frontal resorption occurs in progressive tooth movement stage which occurs once osteoclasts have reached PDL
25
Q

Describe the changes which occur in 1-2 seconds on light or heavy sustained pressure against a tooth

A
  • PDL fluid incompressible and alveolar bone bends

- Tooth moves within PDL space

26
Q

Describe how tooth movement occurs with regards to time if light pressure is applied

A

3.5 secs - Blood vessels in PDL partially compressed on one side and dilated on other, cells and fibres are distorted
Minutes - Blood flow altered and prostaglandins and cytokines released
Hours - Metabolic changes occur and affect cellular activity
Days - Tooth movement begins as osteoclasts and blasts remodel socket

27
Q

Describe how tooth movement occurs with regards to time if heavy pressure is applied

A

3.5 secs - Blood vessels within PDL completely occluded on one side
Minutes - Blood flow cut off to compressed PDL area
Hours - Cell death in area
Days - Cell differentiation in adjacent marrow spaces and resorption begins

28
Q

What is the rate limiting factor in tooth movement?

A

Efficiency of bone resorption

29
Q

Describe 4 cellular reactions in pressure areas when optimal orthodontic forces are applied

A
  1. Cellular proliferation
  2. Osteoclasts migrate to PDL
  3. Resorption of bone
  4. Tooth movement occurs
30
Q

Describe 5 cellular reactions in tension areas when optimal or excessive orthodontic forces are applied

A
  1. Stretching of PDL fibres
  2. Cellular proliferation of fibro and osteoblasts
  3. Increase length of PDL fibres
  4. Deposition of osteoid
  5. Remodelling and reattachment of PDL fibres
31
Q

Describe 4 cellular reactions in pressure areas when excessive orthodontic forces are applied

A
  1. Capillary blood vessels are occluded resulting in death of PDL cells
  2. Cellular proliferation occurs adjacent to hyalinised sections of PDL
  3. Resorption occurs in hyalinised area from cancellous bone towards lamina dura
  4. Tooth movement occurs
32
Q

Describe the ideal relationship between the level of force and tooth movement

A

The force should be just high enough to stimulate cellular activity without completely occluding blood vessels in PDL

33
Q

Describe the ideal relationship between the duration of force and tooth movement

A

Clinical experience suggests threshold for force duration for approx. 6 hours that increasingly effective tooth movement is produced if force is maintained longer than this duration (6 hours in any 24 hours)

34
Q

What is the optimum orthodontic force for tooth movement?

A

20-25 g/cm2 of the root surface

35
Q

Describe 3 types of durations of forces

A

Continuous - Force maintained at some fraction of the original from one visit to the next
Interrupted - Force levels decline to 0 between activations
Intermittent - Force levels decline abruptly to 0 intermittently when orthodontic appliance is taken out or fixed appliance is deactivated

36
Q

How is light continuous force achieved?

A

Fixed appliances

37
Q

Describe how interrupted force is achieved

A

Removable appliance springs

38
Q

Describe how intermittent forces are achieved

A
  • Removable appliances or headgear being worn

- Must be worn for minimum 6 hours a day due to threshold for force duration

39
Q

Describe 3 factors which affect pain during orthodontic treatment

A

Attitude - Attitude and discomfort have correlation on compliance
Age - Adult subjects tend to perceive more pain than younger patients
Appliance type - Fixed appliances have higher values for pain

40
Q

Name 5 adverse effects of orthodontics

A
  1. Crestal bone loss
  2. Root resorption
  3. Pulpal damage
  4. PDL damage
  5. Decalcification
41
Q

Describe the loss of crestal bone during orthodontics

A
  • Slight reduction can occur but is usually of little clinical relevance
  • In active periodontitis crestal bone should not be put at risk as bone resorption is already occuring
  • Orthodontic tooth movement avoided in this case
42
Q

What are the most common teeth for root resorption to occur during orthodontic treatment?

A

Upper incisors or first permanent molars

43
Q

Describe how pulpal damage can occur during orthodontics

A

If a pulp is fibrotic with poor blood supply, orthodontic movement can strangulate vessels resulting in necrosis

44
Q

Name 2 occasions when damage to the PDL by orthodontic forces is not minimal and transient

A
  1. Excessive force used

2. Pre-existing periodontal disease

45
Q

Describe decalcification as an adverse effect of orthodontics

A
  • Fixed appliances predispose to plaque accumulation as tooth cleaning is difficult
  • Lesions can regress following removal of appliance but some patients may be left with enamel scarring

Orthodontics (11 decks)

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