Periodontal Response to Ortho Tx Flashcards
why can we move teeth with orthodontic appliances
because the teeth are not bonded to bone but rather held in position by the PDL
what forms the PDL
- mesenchymal cells
- fibrobasts
- osteoblasts
- cementoblasts
- blood vessels
- nerve endings
what do fibroblasts do
- important role in response to mechanical loading due to occlusal forces
- the architect, builder ,and caretaker of the PDL
describe the PDL
- 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
what are the PDL functions
- 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
what does tissue formation in the PDL
mesenchymal cells will differentiate into osteblasts, cementoblasts, and fibroblasts
what does tissue resorption in the PDL
same cells will transform into osteoclasts and cementoclasts
the nerve endings in the PDL provide:
- pain
- pressure
- spatial control of the lower dentition in relation to the upper - rest position
- TMJ location
- mastication
what do perioodntal ligament fluids do
shock absorbing effecti
if a tooth is subjected to large force for more than 1 second:
there is expression of fluid and the tooth moves within the 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
what other forces will also express tissue fluids
light and continuous
the PDL is essential for:
tooth movement and adjustment to the occlusal changes
in tooth migration or eruption there is a:
- resorptive bone wall
- depository bone wall
what happens in tooth migration
- constant mesial shift caused by the wear of contact points
- adjustment to occlusal wear
describe the resorptive bone wall
- alveolar bone resorption on tooth moving side
- osteoclasts in scattered lacunae on the alveolar bone wall
describe the resorptive bone wall
- resorption stops when the tooth is in occlusal or neuro muscular balance
- osteoblasts form new bone where new fibrils will attach
what happens in the reconstruction of the PDLq
- fiber attachment is re-established
- appears that same undifferentiated mesenchymal cells can become osteoblasts or osteoclasts
what happens in 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
what is the goal of orthodontic tooth movement
- 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 to force by:
bone resorption and remodeling of the periodontium
what happens in 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 is happening on the pressure side
- 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
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
what is happening on the tension side
- 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
what is the goal of the PDL response
to maintain a constant width of 0.18- 0.25mm
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
instead of primary bone resorption in excessive orthodontic force what occurs
hyalinization of the PDL
what is hyalinization
- 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
how does the PDL respond in hyalinization
with local degeneration and sterile necrosis instead of the desired proliferation and differentiation of cells
how long does the hyalinized zone take to form
1-2 days
bone resorption in the hyalinized zone 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
describe what happens in repair
- osteoclasts from surrounding PDL
- osteoclasts from adjacent marrow spaces
- elimination of debris by scavenger cells and phagocytosis
- reorganization of the PDL
what are the factors influencing orthodontic tooth movement
- bone characteristics (cancellous or cortical)
- force application
- applied force and time
what are the bone characteristics
- 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
what are the deleterious effects of orthodontic force
- root resorption
- long term periodontal health specially in adults
what type of resorption is the method of choice for tooth movement
primary bone resorption
primary bone resorption is:
impossible to achieve constitently with fixed orthodontics
in primary bone resorption use the ___ force as possible
smallest
_____ may promote root resorption
hyalinization
