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Orthodontics > Tissue Reactions To Orthodontic Treatment > Flashcards

Tissue Reactions To Orthodontic Treatment Flashcards

1
Q

What is needed in the biological control of tooth movement?

A

Tooth
Healthy PDL
Bone
Applied force

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2
Q

What are the two theories of biological control of tooth movement?

A

Bioeletric theory via piezoelectricity and bioelectric potentials
Pressure-tension theory via cellular changes and chemical messengers

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3
Q

What is the bioelectric theory?

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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4
Q

What is piezoelectricity?

A

Piezoelectricity is a phenomenon observed in many crystal structures in which a deformation of crystal structure produces a flow of electric current, as electrons are displaced from one part of the crystal to another

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5
Q

What are bioelectric potentials?

A

Bioelectric potentials can be observed in bone that is not being stressed

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6
Q

What is the pressure-tension theory?

A

Relates tooth movement to changes in bone metabolism controlled by chemical rather than electric signals-alteration in blood flow associated with pressure within the PDL, formation and/or release of chemical messengers, activation of cells

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7
Q

What happens to the blood flow in tooth movement?

A

The vessels become compressed in the area of the PDL toward which the tooth is being moved. Alterations in blood flow quickly create changes in the chemical environment. These chemical changes, acting either directly or by stimulating the release of other biologically active agents, then stimulate cellular differentiation and activity

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8
Q

What changes occur in the PDL following orthodontic loading?

A

When a force is applied the PDL is compressed (compression side) and bone resorption occurs
On the opposite surface of the root (tension side) the movement of the tooth stretches the PDL and causes tension

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9
Q

What happens to the PDL on the compression side?

A

Compression of blood vessels
Attraction of osteoclasts
Resorption of bone (Howship’s lacunae)
Production of fibrous tissue in Howship’s lacunae

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10
Q

What happens to the PDL on the tension side?

A

Stretching of the periodontal ligament fibres
Stimulation of osteoblasts
Deposition of bone

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11
Q

What are osteoblasts?

A

Osteoblasts are derived form mesenchymal/stromal cells
There function is to construct the extracellular matrix of bone, demonstrate increased levels of the intracellular messenger cyclic adenosine monophosphate (cAMP) when stimulated and control osteoclast function

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12
Q

What are osteoclasts?

A

Large multinucleated cells, of the monocyte-macrophage lineage, they adhere to the bone surface and secrete acids/hydrolytic enzymes into it and they are found in well-defined pits known as ‘Howship’s lacunae’

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13
Q

How does bone remodelling take place?

A

Old bone is rapidly destroyed by large multinucleated osteoclasts with short lifespans (2 weeks)
The pits left by the osteoclast in bone resorption are invaded by long-lived osteoblasts (2 months) which gradually fill the pits
The ratio of osteoclast to osteoblast activity can result in a net loss or gain of bone

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14
Q

What controls bone remodelling?

A

Controlled by systemic hormones (e.g. parathyroid hormone) and by local factors (e.g. prostaglandins)

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15
Q

How do osteoblasts control osteoclasts?

A

By RANK ligand and OPG
Many factors (PTH, PGE) induce the expression of RANK ligand on osteoblasts
RANK ligand in combination with other factors induce the differentiation of osteoclasts from their precursors
Osteoblasts also secrete OPG which opposes the effects of RANK ligand
The RANK ligand binds to a receptor (RANK) on the osteoclast
OPG (osteoprotegerin) is secreted by osteoblasts and opposes RANK ligands actions

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16
Q

What happens during the typical tooth movement?

A

After the application of a moderate orthodontic loads (25-50g), tooth displacement is divided into 3 phases-
1- initial phase in the PDL and supporting bone
2- lag phase in which undermining resorption removes bone adjacent to crushed areas in the PDL
3- progressive tooth movement

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17
Q

What are types of resorption?

A

Frontal resorption

Undermining resorption

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18
Q

What is frontal resorption?

A

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

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19
Q

What is undermining resorption?

A

If the orthodontic force occludes the blood vessels the area becomes hyalinised. Resorption in this area will not take place until osteoclasts remove bone adjacent to the crushed areas in the PDL. When the osteoclasts reach the PDL the tooth will move.

20
Q

What happens after <1 second of light pressure is applied to a tooth?

A

PDL fluid incompressible, alveolar bone bends

21
Q

What happens 1-2 seconds after light pressure is applied to a tooth?

A

PDL fluid expressed, tooth moves within PDL space

22
Q

What happens 3-5 seconds after light pressure is applied to a tooth?

A

Blood vessels within PDL partially compressed on pressure side, dilated on tension side, PDL fibres and cells are mechanically distorted

23
Q

What happens minutes after light pressure is applied to a tooth?

A

Blood flow altered, oxygen tension begins to change, prostaglandins and cytokines released

24
Q

What happens hours after light pressure is applied to a tooth?

A

Metabolic changes occurring, chemical messengers affect cellular activity, enzyme levels change

25
Q

What happens around 4 hours after light pressure is applied to a tooth?

A

Increased cAMP levels detectable, cellular differentiation begins within PDL

26
Q

What happens around 2 days after light pressure is applied to a tooth?

A

Tooth movement beginning as osteoclasts/osteoblasts remodel bony socket

27
Q

What happens 3.5 seconds after heavy pressure is applied to a tooth?

A

Blood vessels within PDL occluded on pressure side

28
Q

What happens minutes after heavy pressure is applied to a tooth?

A

Blood flow cut off to compressed PDL area

29
Q

What happens hours after heavy pressure is applied to a tooth?

A

Cell death in compressed area

30
Q

What happens 3-5 days after heavy pressure is applied to a tooth?

A

Cell differentiation in adjacent marrow spaces, undermining resorption begins

31
Q

What happens 7-14 days after heavy pressure is applied to a tooth?

A

Undermining resorption removes lamina dura adjacent to compressed PDL, tooth movement occurs

32
Q

What biochemical and cellular responses occur when sustained pressure is applied to a tooth?

A

Within a couple of hours of the onset of pressure and tension in the PDL, molecules such as prostaglandin and interleukin 1 beta levels will increase within the PDL
Osteoclasts arrive and attack the adjacent lamina dura, removing bone in the process and tooth movement begins soon thereafter
Osteoblasts are recruited locally from progenitor cells in the PDL. They form bone on the tension side and begin remodelling activity on the compression side

33
Q

What is the rate limiting factor in tooth movement?

A

Efficiency of bone resorption

34
Q

What is the relationship between force and tooth movement?

A

Level of force- the force should be just high enough to stimulate cellular activity without completely occluding the blood vessels in the PDL
Duration of force- clinical experience suggest there is a threshold for force duration in humans of approximately 6 hours and that increasingly effective tooth movement is produced if force is maintained for a longer duration
Minimum threshold of 6 hours in any 24 hours

35
Q

What is the optimum force for tooth movement?

A

Approximately 20-25g/cm2 of root surface area

36
Q

What are the different duration of forces?

A

Continuous
Interrupted
Intermittent

37
Q

What is continuous force?

A

Force maintained at some appreciable fraction of the original from one patient visit to the next
This is achievable with fixed appliances

38
Q

What is interrupted force?

A

Force levels decline to zero between activations

This results in undermining resorption which repairs between visits

39
Q

What is intermittent force?

A

Force evens decline abruptly to zero intermittently when the orthodontic appliance is taken out or when a fixed appliance is temporarily deactivated
Intermittent forces can also become interrupted between adjustments of the appliance
Appliances must be worn for a minimum of 6 hours

40
Q

What is the most efficient force of tooth movement?

A

Light continuous force- this allows a smooth transition through bone because there is a balance between osteoclastic activity on one side of the tooth and osteoblastic activity on the other side

41
Q

What is the least efficient force of tooth movement?

A

Heavy continuous forces- these cause an excessive inflammatory response

42
Q

What helps to reduce the risk of permanent root damage?

A

A rest and repair period

2 weeks movement + 2 weeks rest + 2 weeks repair before next activation of orthodontic appliance

43
Q

What are the adverse effects of orthodontic appliances?

A 
Crestal bone loss 
Root resorption 
Pulpal damage 
Periodontal ligament damage 
Decalcification
44
Q

In what teeth does root resorption tend to be common?

A

Upper incisors and first permanent molars

45
Q

What teeth are most commonly affected by pulpal necrosis after orthodontic treatment?

A

Upper incisors due to their susceptibility to trauma

Orthodontics (11 decks)

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