Physiology of Tooth Movement

Question 1

What are the types of physiological tooth movement?

Answer 1

Tooth eruption
Mesial Drift

Question 2

What is orthodontic tooth movement?
What is bony remodelling mediated by?

Answer 2

If an external force is applied to a tooth, the tooth will move as the bone around it remodels
This bony remodelling is mediated by the PDL
If a tooth has no PDL or it is ankylosed it will not move
Cementum is much more resistant to resorption than bone, although some degree of root resorption after orthodontics should be expected

Question 3

What is the differential pressure theory?

Answer 3

In areas of compression bone is resorbed and in areas of tension bone is deposited
By osteoblasts and osteoclasts

Question 4

What is the Mechano-Chemical Theory?

Answer 4

Events at a cellular level (initially similar to the acute inflammatory response)
Cell shape changes occur within the PDL and adjacent alveolar bone
This initiates signalling interactions between cells (production & release of cytokines)
Cytokines are low molecular weight proteins that regulate the action of target cells

Question 5

What stimulates osteoclasts?

Answer 5

RANKL which stimulates the osteoclasts to become active and resorb the bone

Question 6

What do cytokines active osteoclasts to produce?

Answer 6

Prostaglandins (PGE-2) and leukotrienes

Question 7

What do the intracellular secondary messengers initiate?

Answer 7

The production of RANKL, CSF and interleukin-1

Question 8

What do osteoblasts and osteoclasts do in areas of compression?

Answer 8

Osteoblasts bunch up together and expose the osteoid layer giving osteoclasts access to resorb the bone
Osteoblasts send signals to osteoclasts (e.g. RANKL) to recruit and activate osteoclasts to resorb bone

Question 9

What do osteoblasts and osteoclasts do in areas of tension?

Answer 9

Osteoblasts are flattened covering the osteoid layer and preventing osteoclasts from gaining access to the bone
Osteoblasts secrete collagen and other proteins forming the organic matrix into which they then secrete hydroxyapatite crystals which forms new bone

Question 10

The balance between what regulates bone remodelling?

Answer 10

Between the around of RANKL produced and the amount of OPG production therefore regulates bone remodelling

Question 11

What does Osteoprotegrin (OPG) prevent?

Answer 11

Prevents osteoclastic differentiation and suppresses their activity

Question 12

What are the different types of tooth movement?

Answer 12

Tipping
Bodily Movement (crown and root move together)
Intrusion
Extrusion
Rotation
Torque (moves the root of the tooth)

Question 13

What is tipping movement done by?

Answer 13

Removable appliances

Question 14

What are the clinical effects of a twin block?

Answer 14

Causes lateral openbite

Question 15

What is the mode of action of functional appliances?

Answer 15

Skeletal change (30%)- growth of mandible, restraint of maxilla
Dentoalveolar change (70%), retroclination of upper teeth, proclination of lower teeth
Mesial migration of the lower teeth
Distal migration of the upper teeth

Question 16

What method has bodily movement?
What does this movement allow?

Answer 16

Fixed appliance
Allows tooth to retain normal PDL width and stability

Question 17

What is intrusion movement?

Answer 17

Pressure on the supporting structures is evenly distributed, and bone resorption is necessary, particularly at the apical area and at the alveolar crest

Question 18

Describe the histological changes during orthodontics when light forces are applied.

Answer 18

Hyperaemia within the PDL
Appearance of osteoclasts and osteoblasts
Resorption of lamina dura from pressure side (osteoclasts)
Apposition of osteoid (bone) on tension side (osteoblasts)
Remodelling of the socket- frontal resorption
Periodontal fibres reorganise
Gingival fibres appear not to become reorganised

Question 19

What does hyperaemia of the blood vessels allow in orthodontic movement?

Answer 19

Hyperaemia of the blood vessels allows the tooth to remain vital
Hyperaemia is the process by which the body adjusts blood flow to meet the metabolic needs

Question 20

Describe the histological changes during orthodontics when moderate forces are applied.

Answer 20

Occlusion of vessels of PDL on pressure side
Hyperaemia of vessels of PDL on tension side
Cell free areas on pressure side (hylinisation)
Period of stasis
–relative lack of change over a period of time
Increased endosteal vascularity- undermining resorption
Relatively rapid movement of tooth with bone deposition on the tension side- tooth may become slightly loose
Healing of the PDL-reorganisation & remodelling

Question 21

What are the consequences of excessive forces?

Answer 21

Unwanted side effects- Pain
Necrosis and undermining resorption takes place resulting in permanent changes
Root resorption- only significant if greater than 1/3 root length lost
Anchorage loss
Possible loss of vitality

Question 22

What are some factors affecting the response to force?

Answer 22

Magnitude
Duration
Age
Anatomy

Question 23

How does magnitude affect the response to force?

Answer 23

Light forces allow slow continuous tooth movement
Moderate/heavy forces- rapid movement initially then 10-14 days with little movement while undermining resorption occurs

Question 24

How does age affect the response to force?

Answer 24

Slower in older people, slower cell turnover

Question 25

How does anatomy affect the response to force?

Answer 25

Mid-palatal suture
-when closes, cannot move the maxilla bones
Teeth which have been root treated
No bone-wasting/cleft

Question 26

What are some deleterious effects of orthodontic force?

Answer 26

Pain and mobility
Pulpal changes
Root resorption
Loss of alveolar bone support
Relapse

Question 27

What is the ideal amount of tooth movement per month?

Answer 27

1mm per month is ideal