lecture 7

Question 1

Why can we move teeth with
orthodontic appliances?

Answer 1

• Because the teeth are not bonded to bone but
  rather “held” in position by the periodontal
  ligament

Question 2

what bone is easier to move teeth in?

Answer 2

cancellous

Question 3

PDL components

Answer 3

• Mesenchysmal cells
• Fibroblasts (main cell type)
• Osteoblasts
• Cementoblasts
• Blood vessels
• Nerve endings

Question 4

mesenchymal cells

Answer 4

precursor cell to all PDL cell types

Question 5

nn endings at PDL role

Answer 5

used for proprioception and pain

Question 6

root resorb with ortho?

Answer 6

usually always occurs, amount is variable

Question 7

Fibroblasts

• Important role in?

Answer 7

Fibroblasts
* Important role in response to mechanical loading due to occlusal forces
* The architect, builder and caretaker of the PDL.

Question 8

Periodontal ligament (PDL)
* turnover of tissue?
*Collagen synthesis?
*Constant thickness at mm?

Answer 8

Periodontal ligament (PDL)
* High rate of turnover of tissue within the PDL
*Collagen synthesis reported highest in PDL tissue
than any other connective tissue in body
*Constant thickness at 0.18 to 0.25 mm

Question 9

Periodontal ligament functions
support and shock

Answer 9

1. Supportive: Attach teeth to the alveolar bone with the principal fibers
2. Shock absorber
   – Fluid displacement: light to moderate forces
   – Principal fibers: heavier forces

Question 10

how does PDL change with ortho

Answer 10

pressure placed on it will change widths and cause it to alter tooth posiiotn with bone apposition and resorb to resume width

Question 11

increased PDL size on PA with tx?

Answer 11

may app enlarged but actually just has osteoid in space yet to be mineralized

Question 12

PDL function: Remodeling:

Answer 12

3. Remodeling:
   – 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

Question 13

PDL function: Sensory

Answer 13

4. Sensory:
   – Nerve ending to provide
   * Pain
   * Pressure
   * Spatial control of the lower dentition in relation to the upper (rest position)
   * Tmj location
   * Mastication

Question 14

PDL Fluids

Answer 14

• Shock absorbing effect
• If a tooth is subjected to large force for <1 second, there is expression of fluid and the tooth moves within alveolus. The principal fibers take over
• If a tooth is subjected to a large force for more than 3-5 seconds, there is compression of the PDL by the root against the alveolar bone and pain
• Light and continuous forces will also express tissue fluids

Question 15

desired forces for ortho tx

Answer 15

light and continuous

Question 16

The PDL is essential
for tooth:

Answer 16

The PDL is essential
for tooth movement
and adjustment to
the occlusal changes

Question 17

Physiologic Tooth Movement

Answer 17

✓Tooth migration or eruption
–Resorptive bone wall
–Depository bone wall

Question 18

Tooth migration throughout life

Answer 18

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

Question 19

Resorptive Bone Wall

Answer 19

• Alveolar bone resorption on tooth-moving side
• Osteoclasts in scattered lacunae on the alveolar bone
  wall

Question 20

Resorptive Bone Wall
* Resorption stops when?
* Osteoblasts?

Answer 20

• Resorption stops when the tooth is in occlusal or neuro muscular balance
• Osteoblasts form new bone where new fibrils will attach.

Question 21

Reconstruction of PDL
*Fiber attachment is?
*Appears that same undifferentiated mesenchymal cells can become?

Answer 21

Reconstruction of PDL
*Fiber attachment is re-established
*Appears that same undifferentiated mesenchymal cells can become osteoclasts or osteoblasts

Question 22

Depository Bone Wall
*Mainly apposition of ? and rearrangement of ?
* The PDL will maintain its?
*Thickness proportional to?

Answer 22

*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

Question 23

goals of ortho tx

Answer 23

*Goal is to use the physiologic capabilities of the PDL to achieve desirable orthodontic movements.
*A force is placed on the tooth resulting in mechanical pressure or tension.
*The PDL will respond by bone resorption and remodeling of the periodontium

Question 24

Primary bone resorption
* Mimics?
* Resorption of the alveolar bone wall on the?
* Bone formation by the PDL on the?
* forces are needed to achieve this goal?

Answer 24

primary goal of ortho
* 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

Question 25

Pressure Side * blood flow? *direct resorption of alveolar bone wall by? * may begin ? hours after force application, but usually at about ? hours

Answer 25

*reduction of blood flow in the “pressure side” *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

Question 26

pain with ortho tx

Answer 26

usually due to excessive force bringing bone and root together which cuts off blood supply to PDL cauisng necrosis

Question 27

Pressure Side *in contrast to physiologic tooth movement?

Answer 27

*in contrast to physiologic tooth movement, there is complete breakdown of old fibers and fiber bundles with formation of new fiber elements

Question 28

Tension Side *cellular activity increases after ? hours of applying orthodontic force * new mineralized layer? * after some time what will cover this area? * mineralization of?

Answer 28

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

Question 29

* The goal of the PDL response is to:

Answer 29

* The goal of the PDL response is to maintain a constant width (0.18-0.25mm)

Question 30

Amount of pressure * Response is related to? * As the pressure increases?

Answer 30

* Response is related to the amount of pressure that is applied on the alveolar wall. * As the pressure increases, there is a dramatic reduction in blood flow in the PDL on the pressure side.

Question 31

“Excessive orthodontic force” what occurs

Answer 31

“Excessive orthodontic force” * Instead of primary bone resorption, hyalinization of the PDL occurs

Question 32

can we avoid hyalinization

Answer 32

Unavoidable in Clinical Orthodontics

Question 33

Hyalinization * The most frequent? * dependent on? * how does this occur?

Answer 33

* 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

Question 34

Hyalinization * PDL responds with?

Answer 34

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

Question 35

Hyalinized Zone *occurs in about what time period? * bone resorption is? * tooth movement?

Answer 35

*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

Question 36

repair with hyalinization * Osteoclasts from? * Osteoclasts from? * Elimination of debris by? * Reorganization of ?

Answer 36

* Osteoclasts from surrounding PDL * Osteoclasts from adjacent marrow spaces * Elimination of debris by scavenger cells and phagocytosis * Reorganization of the PDL

Question 37

Factors Influencing Orthodontic Tooth Movement

Answer 37

* Character of bone (cancellous or cortical) * Force application * Applied force and time

Question 38

Character of Bone

Answer 38

* 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.

Question 39

Deleterious Effects of Orthodontic Force

Answer 39

* Root resorption * Long-term periodontal health specially in adults

Question 40

Conclusions * Primary bone resorption? * Impossible to achieve? * Use the ? force as possible * Hyalinization may promote?

Answer 40

* Primary bone resorption is the method of choice for tooth movement * Impossible to achieve consistently with fixed orthodontics * Use the smallest force as possible * Hyalinization may promote root resorption (severity of the cellular response?)