Ortho - Physiology of tooth movement

Question 1

What is tooth movement regulated by?

Answer 1

Periodontium

Question 2

What are the 6 different types of movement?

Answer 2

Tipping 
Bodily movements 
Intrusion 
extrusion 
Rotation 
Torque

Question 3

How do functional appliances (twin blocks work)

Answer 3

Can be useful for class ll div l. The Patient must wear it all the time.
The mandible is protruded away from its normal position. Edge to edge contact of the teeth is then established over time. When removed a lateral open bite is visible. This is easily fixed in growing patients as the molars just erupt into the free space.

Question 4

What are functional appliances used for?

Answer 4

Underdeveloped mandible - to move it forward

Widen the upper or lower jaw.

Question 5

For the 6 types of movement how much force is exerted for each?

Answer 5

Tipping - 35-60g
Bodily movements -150-220g 
Intrusion - 10-20g
extrusion 35-60g
Rotation - 35-60g
Torque - 50-100g

Question 6

What is bodily movement?

Answer 6

This is when the tooth isn’t moved by tipping or tilting. Instead, the tooth remains upright and translates through bone.

Question 7

What is the most common source of relapse in orthodontics?

Answer 7

Spacing and rotation

Question 8

What is torque?

Answer 8

50-100g of force
The crown and root and forced in opposite directions and this causes changes in the inclination or rotation of the crown.

Question 9

What are the two sides of the tooth called in orthodontic movement?

Answer 9

Pressure side - Side the tooth is moving

Tension side - side that tooth is moving away from

Question 10

Explain the steps involved in the light orthodontic movement?

Answer 10

Hyperaemia within PDL on the tension side.
The appearance of osteoclasts on the pressure side, which slowly resorb bone away to make space for the tooth to move into.
Appearance of osteoblasts on the tension side, which as the tooth moves away lays down new bone.
This is called remodelling by frontal resorption
The PDL fibres rearrange, but the supracrestal gingival fibres do not, which can lead to relapse. BODILY movement

Question 11

Which fibres in slow movement are not rearranged which can lead to relapse?

Answer 11

The supracrestal gingival fibres.

Question 12

What is hyalinisation? and where does it occur

Answer 12

Is when there is an area of no cells that looks like hyaline cartilage (under a microscope), due to the lack of BF. This occurs on the pressure side.

Question 13

What is undermining resorption?

Answer 13

This is when there is increased vascularity on the underside of bone, supporting the tooth and an increased number of osteoclasts. Leading to the tooth being undermined.
This causes sudden larger movements.

Question 14

Explain how moderate tooth forces cause tooth movement?

Answer 14

hyperaemia on the tension side.
Hyalinisation on the pressure side (areas of no cells due to lack of BF).
The tooth doesn’t move.
Undermining resorption takes place where the osteoclasts are found under the tooth and allow for larger sudden tooth movement.
Healing of the PDL fibres occurs and then the process repeats.

Question 15

Explain histology of Heavy forces of tooth movement?

Answer 15

Blood vessels are occluded which leads to necrotic PDL tissue formation.
Undermining resorption
Resorption of tooth surfaces (of adjacent teeth)
Pain due to the release of inflammatory mediators
Permanent change

Question 16

4 factors affecting the response to orthodontic force?

Answer 16

The magnitude of the force
Duration
Age
Anatomy

Question 17

Possible deleterious effects of orthodontic force?

Answer 17

Pain and mobility 
pulpal involvement (pulpitis)
root resorption 
Loss of alveolar support 
Relapse ( main source rotational and mediated by transeptal fibres)

Question 18

What is the desired amount of tooth movement a month?

Answer 18

1mm