Biology and histology of tooth movement Flashcards
List the ideal forces for orthodontic treatment
Light
Continuous
Prolonged
Describe ‘light’ force in orthodontic tooth movement
Force must be sufficient enough to compress capillaries in PDL to reduce vascularity, but should not be excessive enough to occlude the vessels
What is the ideal force in orthodontic tooth movement?
Slightly less than capillary blood pressure
25gm/cm2 of root surface area
What does continuous force mean in orthodontic tooth movement
> 6 hours a day
What does prolonged force mean in orthodontic tooth movement
Force should be applied for several months to bring out clinically useful movement
How much movement occurs per month in ortho tooth movement? What is this called?
1mm per month
This means it is controlled movement
What is the PDL?
Specialised connective tissue occupying the periodontal space between the root and the alveolus
Describe the PDLs importance in ortho
Fundamental for tooth movement as it is responsible for bony remodelling
What are the components of the PDL
Extracellular matrix - collagen fibres (type I and II) and ground substance (water and protein)
- Cells embedded in the ECM - osteoblasts, fibroblasts and cementoblasts
- Vessels and nerves
What is the main theory to explain orthodontic tooth movement?
Pressure-tension hypothesis
What is the pressure tension hypothesis?
When forces are applied to the tooth, the tooth shifts in the PDL space causing tension and compression areas
Describe the compression area in tooth movement
PDL is squashed to 1/3rd its width which incr vascularity and osteoclasts and fibroblasts are secreted, resorbing bone at the wall of the pocket
Where does the compression side form in the tooth?
On the leading side (direction tooth is moving towards)
Describe the tension area in tooth movement
Also describe the transition from early to mature bone here
PDL is stretched causing incr vascularity and osteoblast recruitment.
They lay down osteoids adjacent to lamina dura and it mineralises (to woven bone) then calcifies and matures (to lamellar)
Where is the tension side in tooth movement
The trailing side
Where the tooth is moving away from
What is excessive force in tooth movement?
Any force exceeding capillary blood pressure
What are the consequences of excessive ortho force?
- No tooth movement - Underming resorption and sterile necrosis
- Increased pain
- Increased risk of anchorage loss
- Increased risk of root resorption
What is undermining resorption
Osteoclasts resorb the bone towards the PDL
What is sterile necrosis
Loss of vascular flow causes necrosis of the vessels.
What is sterile necrosis also called?
Hyalinisation
List the types of tooth movement achieved in ortho
Tipping Bodily Torque Rotations Intrusion Extrusion
Describe tipping movement
Crown movement > root movement
Describe bodily movement
Crown movement = root movement
Root moves along the occlusal plane but remains in the same orientation
Describe torque movement
Root > crown movement
Requires high forces
Describe intrusions
Vertical movement apically into alveolar bone
Describe extrusion movement
Vertical movement occlusally
How long does remodelling of principal PDL fibres take
3-4 months
How long does remodelling of collagenous fibres of the gingiva take
6 months
How long does remodelling of elastic and supracrestal fibres of the gingiva take
1 year
How long does remodelling of woven bone to lamellar bone take
1 year
Describe rotation movement
Force applied mesially or distally to the labial aspect of a tooth