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Orthodontics > Periodontal Response to Ortho Tx > Flashcards

Periodontal Response to Ortho Tx Flashcards

1
Q

why can we move teeth with orthodontic appliances

A

because the teeth are not bonded to bone but rather held in position by the PDL

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2
Q

what forms the PDL

A
  • mesenchymal cells
  • fibrobasts
  • osteoblasts
  • cementoblasts
  • blood vessels
  • nerve endings
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3
Q

what do fibroblasts do

A
  • important role in response to mechanical loading due to occlusal forces
  • the architect, builder ,and caretaker of the PDL
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4
Q

describe the PDL

A
  • high rate of turnover of tissue within the PDL
  • collagen synthesis reported highest in PDL tissue than any other CT in the body
  • constant thickness at 0.18 to 0.25mm
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5
Q

what are the PDL functions

A
  • supportive: attach teeth to the alveolar bone with the prinicipal fibers
  • shock absorber: fluid displacement: light to moderate forces. principle fibers: heavier forces
  • remodeling: tissue formation, tissue resorption, compensate for tooth wear and attrition
  • sensory
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6
Q

what does tissue formation in the PDL

A

mesenchymal cells will differentiate into osteblasts, cementoblasts, and fibroblasts

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7
Q

what does tissue resorption in the PDL

A

same cells will transform into osteoclasts and cementoclasts

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8
Q

the nerve endings in the PDL provide:

A
  • pain
  • pressure
  • spatial control of the lower dentition in relation to the upper - rest position
  • TMJ location
  • mastication
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9
Q

what do perioodntal ligament fluids do

A

shock absorbing effecti

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10
Q

if a tooth is subjected to large force for more than 1 second:

A

there is expression of fluid and the tooth moves within the alveolus
- the principal fibers take over

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11
Q

if a tooth is subjected to a large force for more than 3-5 seconds:

A

there is compression of the PDL by the root against the alveolar bone and pain

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12
Q

what other forces will also express tissue fluids

A

light and continuous

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13
Q

the PDL is essential for:

A

tooth movement and adjustment to the occlusal changes

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14
Q

in tooth migration or eruption there is a:

A
  • resorptive bone wall
  • depository bone wall
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15
Q

what happens in tooth migration

A
  • constant mesial shift caused by the wear of contact points
  • adjustment to occlusal wear
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16
Q

describe the resorptive bone wall

A
  • alveolar bone resorption on tooth moving side
  • osteoclasts in scattered lacunae on the alveolar bone wall
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17
Q

describe the resorptive bone wall

A
  • resorption stops when the tooth is in occlusal or neuro muscular balance
  • osteoblasts form new bone where new fibrils will attach
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18
Q

what happens in the reconstruction of the PDLq

A
  • fiber attachment is re-established
  • appears that same undifferentiated mesenchymal cells can become osteoblasts or osteoclasts
19
Q

what happens in the depository bone wall

A
  • mainly apposition of bone and rearrangement of PDL fibers
  • the PDL will maintain its normal width of 0.25mm- key to bone remodeling
  • thickness proportional to cellular activity
20
Q

what is the goal of orthodontic tooth movement

A
  • goal is to use the physiologic capabilities of the PDL to achieve desirable orthodontic movements
21
Q

a force is placed on the tooth resulting in:

A

mechanical pressure or tension

22
Q

the PDL will respond to force by:

A

bone resorption and remodeling of the periodontium

23
Q

what happens in primary bone resorption

A
  • mimics the physiologic bone remodeling process
  • resorption of the alveolar bone wall on the pressure side
  • bone formation by the PDL on the tension side
  • light forces are needed to achieve this goal
24
Q

what is happening on the pressure side

A
  • reduction of blood flow in the pressure side
  • direct resorption of alveolar bone wall by osteoclasts coming from the PDL
  • may begin 12 hours after force application but usually at about 40 hours
25
Q

on the pressure side- in contrast to physiologic tooth movement:

A

there is complete breakdown of old fibers and fiber bundles with formation of new fiber elements

26
Q

what is happening on the tension side

A
  • cellular activity increases after 30-40 hours of applying orthodontic force
  • new mineralized layer close to alveolar bone walll
  • after some time, osteoid produced by osteoblasts will cover this area
  • mineralization of osteoid
27
Q

what is the goal of the PDL response

A

to maintain a constant width of 0.18- 0.25mm

28
Q

response is related to:

A

the amount of pressure that is applied on the alveolar wall

29
Q

as the pressure increases:

A

there is a dramatic reduction in blood flow in the PDL on the pressure side

30
Q

instead of primary bone resorption in excessive orthodontic force what occurs

A

hyalinization of the PDL

31
Q

what is hyalinization

A
  • the most frequent complication in orthodontic movement
  • force dependent
  • forces of high magnitude press the root against the alveolar bone wall occluding the blood vessels
32
Q

how does the PDL respond in hyalinization

A

with local degeneration and sterile necrosis instead of the desired proliferation and differentiation of cells

33
Q

how long does the hyalinized zone take to form

A

1-2 days

34
Q

bone resorption in the hyalinized zone is:

A

indirect or undermining because there are no living cells in hyalinized area

35
Q

tooth will not move until hyalinized zone has been:

A

cleaned up and adjacent alveolar bone wall is resorbed

36
Q

describe what happens in repair

A
  • osteoclasts from surrounding PDL
  • osteoclasts from adjacent marrow spaces
  • elimination of debris by scavenger cells and phagocytosis
  • reorganization of the PDL
37
Q

what are the factors influencing orthodontic tooth movement

A
  • bone characteristics (cancellous or cortical)
  • force application
  • applied force and time
38
Q

what are the bone characteristics

A
  • spongy, cancellous bone has the best characteristics for tooth movement
  • old bone is more difficult to resorb than young bone
  • dense cortical bone is much harder to resorb
39
Q

what are the deleterious effects of orthodontic force

A
  • root resorption
  • long term periodontal health specially in adults
40
Q

what type of resorption is the method of choice for tooth movement

A

primary bone resorption

41
Q

primary bone resorption is:

A

impossible to achieve constitently with fixed orthodontics

42
Q

in primary bone resorption use the ___ force as possible

A

smallest

43
Q

_____ may promote root resorption

A

hyalinization

44
Q
A

Orthodontics (9 decks)

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