Biology and histology of tooth movement

Question 1

List the ideal forces for orthodontic treatment

Answer 1

Light
Continuous
Prolonged

Question 2

Describe ‘light’ force in orthodontic tooth movement

Answer 2

Force must be sufficient enough to compress capillaries in PDL to reduce vascularity, but should not be excessive enough to occlude the vessels

Question 3

What is the ideal force in orthodontic tooth movement?

Answer 3

Slightly less than capillary blood pressure

25gm/cm2 of root surface area

Question 4

What does continuous force mean in orthodontic tooth movement

Answer 4

> 6 hours a day

Question 5

What does prolonged force mean in orthodontic tooth movement

Answer 5

Force should be applied for several months to bring out clinically useful movement

Question 6

How much movement occurs per month in ortho tooth movement? What is this called?

Answer 6

1mm per month

This means it is controlled movement

Question 7

What is the PDL?

Answer 7

Specialised connective tissue occupying the periodontal space between the root and the alveolus

Question 8

Describe the PDLs importance in ortho

Answer 8

Fundamental for tooth movement as it is responsible for bony remodelling

Question 9

What are the components of the PDL

Answer 9

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

Question 10

What is the main theory to explain orthodontic tooth movement?

Answer 10

Pressure-tension hypothesis

Question 11

What is the pressure tension hypothesis?

Answer 11

When forces are applied to the tooth, the tooth shifts in the PDL space causing tension and compression areas

Question 12

Describe the compression area in tooth movement

Answer 12

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

Question 13

Where does the compression side form in the tooth?

Answer 13

On the leading side (direction tooth is moving towards)

Question 14

Describe the tension area in tooth movement

Also describe the transition from early to mature bone here

Answer 14

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)

Question 15

Where is the tension side in tooth movement

Answer 15

The trailing side

Where the tooth is moving away from

Question 16

What is excessive force in tooth movement?

Answer 16

Any force exceeding capillary blood pressure

Question 17

What are the consequences of excessive ortho force?

Answer 17

• No tooth movement - Underming resorption and sterile necrosis
• Increased pain
• Increased risk of anchorage loss
• Increased risk of root resorption

Question 18

What is undermining resorption

Answer 18

Osteoclasts resorb the bone towards the PDL

Question 19

What is sterile necrosis

Answer 19

Loss of vascular flow causes necrosis of the vessels.

Question 20

What is sterile necrosis also called?

Answer 20

Hyalinisation

Question 21

List the types of tooth movement achieved in ortho

Answer 21

Tipping 
Bodily 
Torque 
Rotations 
Intrusion 
Extrusion

Question 22

Describe tipping movement

Answer 22

Crown movement > root movement

Question 23

Describe bodily movement

Answer 23

Crown movement = root movement

Root moves along the occlusal plane but remains in the same orientation

Question 24

Describe torque movement

Answer 24

Root > crown movement

Requires high forces

Question 25

Describe intrusions

Answer 25

Vertical movement apically into alveolar bone

Question 26

Describe extrusion movement

Answer 26

Vertical movement occlusally

Question 27

How long does remodelling of principal PDL fibres take

Answer 27

3-4 months

Question 28

How long does remodelling of collagenous fibres of the gingiva take

Answer 28

6 months

Question 29

How long does remodelling of elastic and supracrestal fibres of the gingiva take

Answer 29

1 year

Question 30

How long does remodelling of woven bone to lamellar bone take

Answer 30

1 year

Question 31

Describe rotation movement

Answer 31

Force applied mesially or distally to the labial aspect of a tooth