Biology of Tooth Movement Flashcards
What is the width of the PDL?
0.5mm
What is the job of osteocytes?
Most abundant cells in bone – Involved in cell signalling/responses to mechanical forces
What is the relation between the PDL and tooth movement?
The PDL has an intrinsic force which needs to be overcome before teeth move
Loss of PDL support – loss of force required – uncontrolled movement
What % of cancellous bone is calcified?
15-25% calcified with the remainder being bone marrow, CT and blood vessels
In terms of ortho teeth define centre of resistance
Point on the tooth when a single force is passed through it, it will bring about its translation along the line of action of the force
On average how much root can be resorbed during ortho tx?
1-2mm
What is the job of osteoclasts?
Responsible for bone resorption
What type of roots have an increased risk of resorption?
Blunt, short, pipette roots
What can be found in the cellular component of bone?
Osteoclasts
Osteoblasts
Osteocytes
What is an extra-oral anchorage device that is commonly used? What are its components?
HEADGEAR
* Uses Kloehn bow which attaches to headgear tubes on upper 6 bands to prevent mesial molar movement & loss of anchorage
* Can also be used to distalise molars by increasing forces needed to create space
What type of tooth movement is this?
How much force is required?
Bodily movement
100-150g
What factors of ortho tx can increase the risk of root resorption?
Long treatment time
Use of class II elastics
Pushing roots into cortical plate
Tartrate resistant acid phophatase (TRAP) is secrected by osteoclasts. What is its role?
Important for differentiation, activation and proliferation of osteoclasts
What are the two components of bone?
Matrix (organic and mineral)
Cellular
What does the anchorage value of a tooth mean? What increases this value?
Anchorage value of a tooth is proportional to the surface area of the root
The tooth with larger root surface area requires greater force to move (higher anchor value)
In regards to tooth movement why do we recall ortho pts every 4-6 weeks?
A 4 week period is required to allow for removal of hyalinized bone and PDL to recover, hence why every 4-6weeks to allow for the desired tooth movement to occur in the appropriate time required for bone and PDL turnover.
What type of tooth movement is this?
How much force is required?
Tipping
30-60g
2 areas of compression here
What is an ideal amount of froce required for orthodontic tooth movement?
Just greater than capillary pressure
↓Risk of tissue & cell necrosis – hyalinisation
↓Pulpal damage
↓Patient discomfort
What can be found in the matrix component of bone?
35% Organic phase
Collagen type 1 (90%)
Osteonectin
Osteocalcin
Proteoglycans
65% Mineral phase
Hydroxyapatite
Calcium
Phosphate
What is the role of calcitonin receptors in osteoclasts?
Reduces osteoclast activity
What are the biological changes that occur to the PDL and bone when light force is applied to a tooth?
1-2 secs = PDL fluid expressed
5 secs = PDL fibres & cells compressed
Minutes = Altered blood flow leads to PGs & Cytokines release
Hours = Metabolic changes (OB & OC cell activity)
2-3 days = Frontal resorption & slight OTM
5-14 days = Lamina dura resorption (no OTM until this is removed)
14-30 days = OTM occurs again (resorption & deposition)
OTM = Orthodontic teeth movement
What medications can affect ortho tooth movement and how?
NSAIDS & Tricyclic Anti-depressants
Inhibit COX pathway which reduces osteoclast signalling
What type of tooth movement is this?
How much force is required?
Intrusion
15-25g
Force over a small area so much lighter forces
What are the two components of basic bone strcuture?
Cortical bone
Cancellous bone
What factors affect centre of resistance in ortho teeth?
1) Number of Roots/Root Surface Area
2) Degree of Alveolar Bone Loss
3) Degree of Root resorption
What is the mechanism of bone resorption?
- External stimulus recruits Osteoclasts to site
- Osteoclasts attach to bone matrix at “clear zone” to form seal under cell
- Secretion of H+ ions from osteoclast ruffled border leads to the demineralisation of bone
- Organic matrix is removed by lysosomal enzymes (MMPs) released by Osteoblasts
- Osteoclasts resorb pits of bone called “lacunae”
What are the biological changes that occur to the PDL and bone when heavy force is applied to a tooth?
1-5 secs = PDL completely compressed
Minutes = Blood flow completely ceases
Hours = Tissue ischaemia leads to Necrosis/Hyalinisation
2-3 days = OB & OCs recruited – Undermining resorption begins
14 days = Hyalinised zone removed
15-30 days = Lamina dura must be removed first, then OTM occurs
What type of tooth movement is this?
How much force is required?
Tipping
30-60g
2 areas of compression here
How can oestrogen levels affect ortho tooth movement?
Reduced oestrogen levels can inhibit OTM
What are the different types/degrees of root resorption?
Slight blunting
Moderate resorption (upto 1/4)
Severe resorption (more than 1/4)
What is the job of osteoblasts?
Responsible for bone production & coordination of bone deposition & resorption
(main cells involved in ortho tooth movement)
What is the role of response to calcitropic hormones in osteoclasts?
Important for bone growth and remodelling
What do osteoblasts synthesise?
- Type 1 collagen
- Bone matrix proteins (osteocalcin, osteopontin & bone sialoprotein)
- Alkaline phosphatase (indicator of bone metabolism)
What type of bone is found in the socket of alveolar bone?
What can be found in this bone?
Bone lining the socket is bundle bone
Embedded in bundle bone are the Sharpey’s fibres of the PDL
Comment on bone turnover in alveolar bone?
There is continuous bone turnover in alveolar bone
What % of cortical bone is calcified?
80-90%
How do osteocytes communicate with eachother?
Communicate with each other (network of long-lasting cells) via canaliculi
Define anchorage in relation of orthodontic tooth movement
Resistance to unwanted tooth movement
