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Ortho 1 Lecture > Role of the periodontal ligament in Orthodontic movement > Flashcards

Role of the periodontal ligament in Orthodontic movement 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 periodontal ligament

no PDL = no movement of teeth

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2
Q

What is the 1st cell that form PDL? And what do they differentiate into?

A
  • Mesenchymal cells

Which differentiate into:
* Fibroblasts (main cell type)
* Osteoblasts
* Cementoblasts
* Blood vessels
* Nerve endings

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3
Q

What is the function of fibroblasts?

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

The PDL has a constant thickness at ________ mm

A

0.18 to 0.25

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5
Q

________ synthesis reported highest in PDL tissue than any other connective tissue in body

A

Collagen

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6
Q

What are the functions of the PDL?

A
  • Supportive: Attach teeth to the alveolar bone with the principal fibers
  • Shock absorber
  • Remodeling
  • Sensory
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7
Q

What are the features of the shock absorber function of PDL?

A
  • fluid displacement: light to moderate forces (Depends on the amount of forces exerted on the PDL)
  • principal fibers: heavier forces
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8
Q

What are the features of the remodeling the alveolar bone function of PDL?

A

– Tissue formation: Mesenchysmal cells will differentiate into osteoblasts, cementoblasts, fibroblasts (signaling factors)
– Tissue resorption: Same cells will transform into osteoclasts, cementoclasts
– Compensate for tooth wear and attrition

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9
Q

What are the features of the sensory function of PDL?

A

Nerve ending to provide
* Pain
* Pressure on tooth
* Spatial control of the lower dentition in relation to the upper (rest position) - proprioception
* TMJ location (occlusion guides this)
* Mastication (shock absorber during this)

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10
Q

If a tooth is subjected to large force for >___ second, there is expression of fluid and the tooth moves within alveolus. The principal fibers take over

A

1

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11
Q

If a tooth is subjected to a large force for more than _____ seconds, there is ____________________________________________________________

A

3-5; compression of the PDL by the root against the alveolar bone and pain

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12
Q

The ______ is essential for tooth movement and adjustment to the occlusal changes or forces

A

PDL

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13
Q

What does tooth migration of eruption cause?

A

Resorptive bone wall and Depository bone wall

  • When you move a tooth you have resorption on one side and apposition on the other

Bucket full of water, hand inside bucket, and you move the bucket with your hand inside it, water is displaced on one side and filled on the other side

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14
Q

What causes tooth migration?

A
  1. Constant mesial shift caused by the wear of contact points (depends on the occlusion)
  2. Adjustment to occlusal wear (teeth stay in contact)
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15
Q

What are the features of the resorptive bone wall?

A
  • Alveolar bone resorption on tooth-moving side (when moving a tooth, on the pressure side we have bone resorption - alveolar bone is resorbing on the moving side too)
  • Osteoclasts in scattered lacunae on the alveolar bone wall
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16
Q

On the resorptive bone wall, resorption stops when the tooth is in…

A

occlusal or neuro muscular balance

  • On one side, osteoclast activity removing bone on the cortical plate and the stretching of the PDL fibers creating new bone
    Hand in bucket moving - resorbing the bone (water), and on the tension side creating new bone where the hand is covered all the time with water
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17
Q

On the tension side, _________ form new bone where new fibrils will attach

A

osteoblasts

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18
Q

During primary bone resorption, how is the PDL reconstructed?

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

What are the features of the depository bone wall?

A
  • Mainly apposition of bone and rearrangement of PDL fibers - as tooth moves from left to right, bone is resorbed on the right and new bone is getting formed on the left
  • The PDL will maintain its normal width of 0.25mm (maintaining 0.25mm is the key to bone remodeling)
  • Thickness proportional to cellular activity
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20
Q

Goal in ortho tooth movement is to use the physiologic capabilities of the PDL to achieve desirable ____________ movements

A

orthodontic

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21
Q

A force is placed on the tooth resulting in…

A

mechanical pressure or tension

  • force from left to right = pressure on right = tension on left
22
Q

The PDL will respond by bone resorption and remodeling of the ____________

A

periodontum

  • Force from left to right = bone resorption/remodeling of periodontum on right
23
Q

What is 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
  • Exerting pressure, compressind PDL, light and continuous force = primary resorption
24
Q

What happens on the pressure side?

A
  • Reduction of blood flow in the “pressure side” - ischemia of PDL
  • Direct resorption of alveolar bone wall by osteoclasts coming form the PDL
  • May begin 12 hours after force application, but usually at about 40 hours
25
On the pressure side, in contrast to physiologic tooth movement, there is...
complete breakdown of old fibers and fiber bundles with formation of new fiber elements
26
What happens on the tension side?
* cellular activity increases after 30-40 hours of applying orthodontic force * new mineralized layer close to alveolar bone wall - as PDL gets stretched they bring new bone * after some time, osteoid produced by osteoblasts will cover this area * mineralization of osteoid tissue
27
The goal of the PDL response is to maintain a constant width of ______mm
0.18-0.25
28
Response is related to the amount of _________ that is applied on the alveolar wall
pressure
29
As the pressure increases, there is a dramatic reduction in ____________ in the PDL on the pressure side
blood flow pressure = how much force is getting put on the tooth to move it
30
In excessive orthodontic force, instead of primary bone resorption, ___________ of the PDL occurs
hyalinization
31
What is the most frequent complication in orthodontic movement?
hyalinization
32
What is hyalinization?
* Forces of high magnitude press the root against the alveolar bone wall occluding the blood vessels * PDL responds with local degeneration and sterile necrosis instead of the desired proliferation and differentiation of cells - Cell free area on the PDL, some people call sterile necrosis, its unavoidable. Always will be some degree of this bc of the amount of force we exert
33
What are the features of the hyalinized zone?
* occurs in about 1-2 days * bone resorption is indirect or undermining because there are no living cells in hyalinized area * tooth will not move until hyalinized zone has been cleaned up and adjacent alveolar bone wall is resorbed
34
How is hyalinization repaired?
* Osteoclasts from surrounding PDL * Osteoclasts from adjacent marrow spaces * Elimination of debris by scavenger cells and phagocytosis * Reorganization of the PDL
35
What are the factors that influence orthodontic tooth movement?
* Bone characteristics (cancellous or cortical) * Force application - If you exert 100g of force, there is going to be tipping, you have 50g of force on the apex and 50g of force close to the crown so the PDL will have A LOT of compression If you exert 100g of force, and distribute that force along the root, those 100g are going to be distributed over a wider surface area - like walking on the snow with regular shoes vs snow shoes - difference is that it has same amount of pressure just over wider area so the PDL responds much better than exerting all the pressure on a single point * Applied force and time
36
What type of bone is best for orthodontic movement?
Spongy, cancellous bone has the best characteristics for tooth movement - cortical is difficult to move
37
# True/false “Old” bone is more difficult to resorb than “young” bone
True - bc blood supply decreases as we age
38
# True/false Dense cortical bone is much harder to resorb than cancellous
True - not saying you CANT resorb, just takes a LONGER period of time
39
What are the deleterious effects of orthodontic force?
* Root resorption - Lets say we put a lot of force and want to move tooth to the right side, sometimes the mesenchymal cells DO NOT differentiate between the root of the tooth and the alveolar bone, so if they cant differentiate then you can get root resorption * Long-term periodontal health especially in adults - for adults need to get sent for perio consult to make sure no active perio disease
40
__________ bone resorption is the method of choice for tooth movement
Primary
41
# True/false Primary bone resorption is possible with fixed orthodontics
False - its impossibe to achieve bc theres always SOME degree of hyalinization | Impossible to achieve consistently with fixed orthodontics
42
_____________ MAY promote root resorption
Hyalinization "may" is important - all depends on how long we are exerting that pressure and the severity of the response | (severity of the cellular response?)
43
In ortho you should use the _______ force possible
lightest
44
What within the PDL is responsible for shock absorbing effect?
Fluid within PDL
45
more cellular activity = __________ PDL less cellular activity = __________ PDL
thicker; thinner
46
Is there a difference in blood supply between adult pt and child?
Yes - younger the pt, the MORE blood supply the PDL has (big difference in response on tooth movement between adolescent and adult) Easier to have direct resorption on young pt than adult due to blood supply
47
The heavier the force, the ______ blood supply
LESS - bc we are putting pressure, and also big difference between the resposnes of the PDL when the force is heavier vs light
48
What is the most frequent "complication" in ortho movement?
Hyalinization
49
Hyalinization is _______ dependent
Force
50
How does hyalinization. work?
Forces of high magnitude press the root against the alveolar bone wall occluding the blood vessels
51
What happens to the mesenchymal if the blood vessels are compressed and occluded?
the mesenchymal cells WONT get the signaling for differentiation If the mesenchymal cells on the PDL DONT get the signal for differentiation = teeth are moved in hyalinized tissue instead of coming from PDL of alveolar bone comes from alveolar bone to the PDL
52
What kind of forces do we prefer in ortho?
Light and continuous forces

Ortho 1 Lecture (13 decks)

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