Periodontal Responses to Orthodontic Treatment 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.
Periodontal ligament
(6)
- Mesenchysmal cells
- Fibroblasts (main cell type)
- Osteoblasts
- Cementoblasts
- Blood vessels
- Nerve endings
Fibroblasts
(2)
- Important role in response to mechanical loading due to
occlusal forces - The architect, builder and caretaker of the PDL. (McCulloch
1966)
Periodontal ligament (PDL)
(3)
- 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
Periodontal ligament functions
(2)
- Supportive: Attach teeth to the alveolar bone with the
principal fibers - Shock absorber
- Shock absorber
(2)
– Fluid displacement: light to moderate forces
– Principal fibers: heavier forces
PDL function
3. Remodeling:
– Tissue formation:
– Tissue resorption:
– Compensate for
Mesenchysmal cells will differentiate into osteoblasts, cementoblasts, fibroblasts (signaling factors)
Same cells will transform into osteoclasts, cementoclasts
tooth wear and attrition
PDL function
4. Sensory:
– Nerve ending to provide
(5)
- Pain
- Pressure
- Spatial control of the lower dentition in relation to the upper (rest position)
- Tmj location
- Mastication
PDL Fluids
* Shock absorbing effect
(3)
- 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
The — is essential
for tooth movement
and adjustment to
the occlusal changes
PDL
Tooth migration or eruption
(2)
–Resorptive bone wall
–Depository bone wall
Tooth migration
1. Constant — shift caused by the wear of
contact points (depends on the occlusion)
2. Adjustment to — wear ( teeth stay in
contact)
mesial
occlusal
Resorptive Bone Wall
(2)
- Alveolar bone resorption on
tooth-moving side - Osteoclasts in scattered
lacunae on the alveolar bone
wall
Resorption stops when the tooth is
in
occlusal or neuro muscular
balance
Osteoblasts form new bone where new — will attach.
fibrils
Reconstruction of PDL
* — attachment is re-
established
*Appears that same
undifferentiated mesenchymal cells
can become osteoclasts or
osteoblasts
Fiber
Depository Bone Wall
* Mainly
* The PDL will maintain its normal
width of
*Thickness proportional to
apposition of bone and rearrangement of PDL fibers
0.25mm (key to bone remodeling.
cellular activity
ORTHODONTIC 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 by bone
resorption and remodeling of the
periodontium
Primary bone resorption
* Mimics the
* Resorption
* Bone formation
* — forces are needed to achieve this goal
physiologic bone remodeling process
of the alveolar bone wall on the pressure side
by the PDL on the tension side
Light
Pressure Side
*
*— resorption of alveolar bone wall by
osteoclasts coming form the PDL
* may begin
reduction of blood flow in the “pressure side”
direct
12 hours after force application, but usually at about 40 hours
Pressure Side
* in contrast to physiologic tooth
movement, there is
complete breakdown
of old fibers and fiber bundles with
formation of new fiber elements
Tension Side
(4)
- 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
The goal of the PDL response is to
maintain a constant width
(0.18-0.25mm)
- Response is related to the amount of — that is applied
on the alveolar wall. - As the — increases, there is a dramatic — in
blood flow in the PDL on the pressure side
pressure
pressure, reduction
“Excessive orthodontic force”
Instead of primary bone resorption,
hyalinization of the PDL occurs
The most frequent
“complication” in orthodontic
movement
Hyalinization
- Force dependent
- Forces of high magnitude press
the root against the alveolar
bone wall occluding the blood
vessels
Hyalinization
PDL responds with
local
degeneration and sterile necrosis
instead of the desired
proliferation and differentiation
of cells
Hyalinized Zone
* occurs in about
* bone resorption is
* tooth will not move until
1-2 days
indirect or undermining because there are no living cells in hyalinized area
hyalinized zone has been cleaned up and adjacent alveolar bone wall is resorbed
Repair
* Osteoclasts from
* Osteoclasts from
* Elimination of debris by
* Reorganization of the —
surrounding PDL
adjacent marrow spaces
scavenger cells and phagocytosis
PDL
Factors Influencing Orthodontic Tooth
Movement
(3)
- Character of bone (cancellous or cortical)
- Force application
- Applied force and time
Character of Bone
(3)
- 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.
Deleterious Effects of Orthodontic
Force
(2)
- Root resorption
- Long-term periodontal health
specially in adults
- — bone resorption is the method of choice for tooth
movement
Primary
- Impossible to achieve consistently with
fixed orthodontics
- Use the — force as possible
smallest
- Hyalinization may promote
root resorption (severity of the
cellular response?)
- Hyalinization may promote
root resorption (severity of the
cellular response?)
