Tooth Movement

Question 1

What problems are there when excessive force is placed on a tooth?

Answer 1

• delays tooth movement (10-14 days)
• increases change of anchorage loss
• more patient discomfort
• increased tooth mobility
• increased risk of root resorption

Question 2

What do osteoclasts do?

Answer 2

Resorb bone

Question 3

What do osteoblasts do?

Answer 3

Produce new bone

Question 4

What do fibroblasts do?

Answer 4

Produce and destroy collagen fibres

Question 5

What do cementoblasts do?

Answer 5

Form new cementum

Question 6

What do cementoclasts do?

Answer 6

Removes cementum

Question 7

What are the 3 types of forces?

Answer 7

• continuous force - force is maintained between activities
• intermittent - force drops to zero
• interrupted - force declines to zero

Question 8

What are the effects of excessive force?

Answer 8

• delays movement of teeth
• increase chance of anchorage loss
• more patient discomfort
• increased tooth mobility
• increased risk of root resorption
• hyalinisation of the area
• undermining resorption

Question 9

What is the ideal force for tipping movements?

Answer 9

Tipping - 35-60g

Question 9

What is the ideal force for bodily movements?

Answer 9

Bodily movement - 70-120g

Question 10

What is the ideal force for extrusion?

Answer 10

Extrusion - 35-60g

Question 11

What is the ideal force for intrusion?

Answer 11

Intrusion - 10-20g

Question 12

What is the ideal force for torque?

Answer 12

Torque - 50-100g

Question 13

What is the ideal force for rotational movements?

Answer 13

Rotation - 35-60g

Question 14

What happens on the pressure side when optimum force is applied to the tooth?

Answer 14

• PDL is compressed
• within seconds alveolar bone bends and blood supply is altered
• when pressure is continued over a period of hours there is a chemical reaction within the blood cells
• cytokines and prostaglandins are released which signals the need for osteoclasts to the area
• within two days osteoclasts migrate to the area and begin bone resorption = tooth can move

Question 15

What happens on the tension side when optimum force is applied to the tooth?

Answer 15

• PDL is stretched
• blood supply alters and chemical reaction within blood cells
• signals are sent for the need of osteoblasts and fibroblasts to migrate to the area and lay down osteoid bone and new PDL fibres

Question 16

How long does it take for osteoid to calcify?

Answer 16

6 weeks

Question 17

What happens what excessive force is placed in the pressure side?

Answer 17

• force is above capillary pressure
• osteoclasts are not able to reach pressure area to resorb bone
• area becomes hyalinised and appears like ground glass as there are no cells
• once pressure is relieved osteoclasts can reach the area
• undermining resorption occurs, bone is resorped from back to front
• creates a lag time for movement of 10-14 days

Question 18

What happens on the tension side when high force is applied to a tooth?

Answer 18

Blood vessels rupture

Question 19

What factors can increase root resorption?

Answer 19

• torque on teeth
• excessive force
• nail biting
• previous orthodontic treatment
• previous trauma
• distance to move teeth
• root shape - blunt roots, pipette shape
• type of movement

Question 20

How much root resorption occurs during orthodontic treatment?

Answer 20

1-2mm

Question 21

What are the time frames with regards to tooth movement on the pressure side?

Answer 21

1-5 seconds - PDL compressed and change in cell shape

Minutes - O2 levels change, chemicals released

4 hours - osteoclasts differentiate

1-2 days - bone remodels

Question 22

What are time frames with regards to tooth movement on the tension side?

Answer 22

1-5 seconds - PDL stretches, change in cell shape

Minutes - O2 levels change, chemicals released

4 hours - osteoblasts differentiate

1-2 days - bone remodels

Question 23

The centre of rotation on a single rooted tooth is?

Answer 23

Approximately one third down the root from the apex

Question 24

What is compression in regards to tooth movement?

Answer 24

The direction the tooth is moved into

Question 25

What is tension in regards to tooth movement?

Answer 25

The areas behind which the tooth has been moved from

Question 26

What is undermining resorption?

Answer 26

• osteoclasts need to remove dead bond before new bone is placed
• resorption occurs back to front
• lag phase of 10-14 days

Question 27

What is tip?

Answer 27

The mesio disto angulation of a tooth

Question 28

What is torque?

Answer 28

The labio palatal angulation of the tooth

Question 29

What is the ideal force that should be used to move a tooth?

Answer 29

20-25g/cm2

Question 30

How can root resorption be minimised?

Answer 30

• take careful history and examination
• take pre treatment X-rays
• light forces and mechanics
• minimise treatment length
• monitor susceptible patients

Question 31

What can make a patient more prone to root resorption?

Answer 31

• root form - blunt, pipette roots are more susceptible
• ectopic canines
• trauma
• treatment mechanics - fixed appliance, class II elastics, torque, intrusion
• age
• gender
• length of treatment
• individual variety
• systemic problems

Question 32

What effect does excessive force have on teeth?

Answer 32

Delayed movement
Anchorage loss risks
More discomfort 
Tooth mobility 
Root resorption risk

Question 33

What is friction influenced by?

Answer 33

Arch wire factors
Bracket factors
Ligation factors

Question 34

What is friction?

Answer 34

The force resisting the relative motion of surfaces sliding against each other