Role of the periodontal ligament in Orthodontic movement Flashcards
Why can we move teeth with orthodontic appliances?
Because the teeth are not bonded to bone but rather “held” in position by the periodontal ligament
What makes up the periodontal ligament?
- Mesenchymal cells
- Fibroblasts (main cell type)
- Osteoblasts
- Cementoblasts
- Blood vessels
- Nerve endings
What is the function of fibroblasts?
- Important role in response to mechanical loading due to occlusal forces
- The architect, builder and caretaker of the PDL
The PDL has a constant thickness at ________ mm
0.18 to 0.25
________ synthesis reported highest in PDL tissue than any other connective tissue in body
Collagen
What are the functions of the PDL?
- Supportive: Attach teeth to the alveolar bone with the principal fibers
- Shock absorber
- Remodeling
- Sensory
What are the features of the shock absorber function of PDL?
- Fluid displacement: light to moderate forces
- Principal fibers: heavier forces
What are the features of the remodeling function of PDL?
– 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
What are the features of the sensory function of PDL?
Nerve ending to provide
* Pain
* Pressure
* Spatial control of the lower dentition in relation to the upper (rest position)
* TMJ location
* Mastication
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
1
If a tooth is subjected to a large force for more than _____ seconds, there is compression of the PDL by the root against the alveolar bone and pain
3-5
The ______ is essential for tooth movement and adjustment to the occlusal changes
PDL
What is physiologic tooth movement?
Tooth migration or eruption
* Resorptive bone wall
* Depository bone wall
What causes tooth migration?
- Constant mesial shift caused by the wear of contact points (depends on the occlusion)
- Adjustment to occlusal wear (teeth stay in contact)
What are the features of the resorptive bone wall?
- Alveolar bone resorption on tooth-moving side
- Osteoclasts in scattered lacunae on the alveolar bone wall
On the resorptive bone wall, resorption stops when the tooth is in…
occlusal or neuro muscular balance
On the resorptive bone wall, _________ form new bone where new fibrils will attach
osteoblasts
On the resorptive bone wall, how is the PDL reconstructed?
- Fiber attachment is re-established
- Appears that same undifferentiated mesenchymal cells can become osteoclasts or osteoblasts
What are the features of the depository bone wall?
- 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
Goal is to use the physiologic capabilities of the PDL to achieve desirable ____________ movements
orthodontic
A force is placed on the tooth resulting in…
mechanical pressure or tension
The PDL will respond by bone resorption and remodeling of the ____________
periodontum
What is primary bone resorption?
- 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
What happens on the pressure side?
- 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
