Extractions And Anchorage

Question 1

Why extract teeth?

Answer 1

To create space 
To relieve crowding 
Reduce an increased overjet 
Correct centrelines 
Open space for missing teeth 
Correct AOB

Question 2

What factors influence the extractions decision?

Answer 2

Amount and site of crowding 
Size of overjet 
Caries 
Centrelines 
Anchorage considerations

Question 3

What is anchorage?

Answer 3

Anchorage is the source of resistance to the reaction from the active components

Question 4

Why is anchorage important?

Answer 4

Gives something to pull or push against when moving teeth
Inadequate anchorage may prevent us achieving the desired treatment result leading to- residual crowding, residual overjet, residual centreline discrepancy

Question 5

What might anchorage loss result in?

Answer 5

Residual overjet
Residual crowding
Inadequate centreline correction

Question 6

How do we provide anchorage?

Answer 6

Other teeth- in the same arch, in the opposing arch
Baseplate on removable appliances
Orthodontic mini-implants
Extra-oral- conventional headgear, face mask/reverse pull headgear
Class 2 elastics

Question 7

What is the correlation in anchorage and root area?

Answer 7

The anchorage value of a tooth is closely related to the surface area of its root surface
The anchorage unit can be reinforced by incorporating more teeth to increase the total root surface area

Question 8

How can the demands on the anchorage be reduced?

Answer 8

Reducing the number of teeth being moved

Limiting the force from the active components to the optimum level for tooth movement (25-50g)

Question 9

When retracting canines, extracting which tooth improves the anchorage?

Answer 9

Extraction of the 1st rather than 2nd premolar improves the anchorage

Question 10

What are the most common upper arch extractions?

Answer 10

Upper 1st premolars

Sometimes upper 2nd premolars

Question 11

What does the extraction of upper 1st premolars provide space anteriorly for?

Answer 11

Overjet reduction
Crowded incisors and canines
Provides 7mm space per side
Most ideal for class II Div 1 cases

Question 12

Why are upper 2nd premolars sometimes extracted?

Answer 12

To relieve mild to moderate anterior crowding
When overjet reduction is not required
They provide about 3mm per side as some spaced is closed from behind (anchorage loss)

Question 13

What are the most common lower arch extractions?

Answer 13

Lower 2nd premolars

Sometimes lower 1st premolars

Question 14

Why are lower 2nd premolars extracted?

Answer 14

To relieve mild to moderate lower incisor crowding

Question 15

Why are lower 1st premolars sometimes extracted?

Answer 15

Severe lower incisor crowding
Class II malocclusions
Impacted lower 2nd premolars as an interceptive procedure
Poor prognosis

Question 16

Why are upper 2nd molars sometimes extracted?

Answer 16

To aid distalisation of 1st molars
For mild anterior crowding
When using an upper removable appliance and/or headgear

Question 17

Why are lower 2nd molars sometimes extracted?

Answer 17

To prevent impaction of 3rd molars

Question 18

Why do 1st molars sometimes have to extracted?

Answer 18

May be lost as a result of caries
But space difficult to use for treating anterior crowding and/or overjet
Spontaneous space closure good at age 8-9 years
Residual space if extracted later- upper 7s close better than lowers, lower 7s tend to tip mesially
Unopposed upper 6s may overerupt

Question 19

When are incisors extracted for orthodontic purposes?

Answer 19

Rarely extraction of choice
Upper laterals if other side absent or peg-shaped
Sometimes lower incisor extraction in adult patients with fixed appliances and lower incisor crowding

Question 20

When are canines extracted for orthodontic treatment?

Answer 20

Palatally ectopic upper canines (incidence of 2%)

Buccal lay crowded canines

Question 21

When are lower 3rd molars extracted?

Answer 21

Surgical removal of impacted 3rd molars should be limited to patients with evidence of pathology
Very weak association with lower incisor crowding
Late lower incisor crowding alone is not an indication for lower 3rd molar extraction

Question 22

What are common extraction patterns?

Answer 22

Extraction patterns are usually symmetrical 
But they are sometimes asymmetrical for:
-centreline correction 
-more space needed on one side 
-supernumeraries 
-caries/heavily restored tooth 
-more crowding in one quadrant 
-anchorage situation more challenging on one side

Question 23

What are some alternatives to extraction used to create space?

Answer 23

Arch expansion
Distalisation of teeth
Enamel reduction