Removable Appliances

Question 1

What are the three kinds of orthodontic appliances?

Answer 1

Removable appliances
Fixed appliances
Functional appliances

Question 2

What action do removable appliances cause on teeth?

Answer 2

Simple tipping movements
Single force applied to crown
Fulcrum within root

Question 3

What are some advantages of removable appliances?

Answer 3

Simple to use
Require less chair side time than fixed appliances
Less demanding on oral hygiene than fixed appliances
Reduced risk of decalcification
Relatively simple to add pontic teeth
Well accepted by patients

Question 4

What are some disadvantages of removable appliances?

Answer 4

Limited range of tooth movements- usually only 1 or 2 teeth at a time, tipping only, only suitable for a limited range of malocclusions
Require more laboratory time than fixed appliances, therefore expensive
Lower removable appliances are uncomfortable and have limited use
They’re removable so patients may take them out

Question 5

What are the 3 components of removable appliances?

Answer 5

Active component
Retentive component
Baseplate

Question 6

What are the active components?

Answer 6

Springs- 18:8 SS (18% Cr, 8% Ni -> corrosion resistance), usually 0.5 or 0.7mm thick
Screws
Labial bows
Elastics

Question 7

What is the optimum force needed to be produced by springs to produce a tipping movement in a single rooted tooth?

Answer 7

25-60g

Question 8

What are the principles of cantilever springs?

Answer 8

Force is proportionate to the thickness (to the power of 4) / length (to the power of 3)

Question 9

What happens to the force if you change the thickness of the spring wire?

Answer 9

Increasing the wire thickness, increases the force

Decreasing the wire thickness, decreases the force

Question 10

What happens to the force if you change the length of the spring wire?

Answer 10

Increasing the length will reduce the force

Decreasing the length will increase the force

Question 11

What activation is usually needed in the spring to produce a force of 25-60g?

Answer 11

0.7mm wire requires less activation than 0.5mm
Usually aim to have 2-4mm activation
Too small, <1mm, rapid force decay as the tooth moves
Too large, >4mm, difficult to insert appliance
The direction of the force applied is perpendicular to the tangent at the point of contact

Question 12

What is the purpose of the retentive components of a removable appliance?

Answer 12

To retain the appliance in the mouth

Question 13

What methods of retention do removable appliances have?

Answer 13

Usually clasps 
3 types-
Adams clasps 
Southend & Half-Jackson clasps 
Ball ended clasps

Question 14

What is the baseplate of a removable appliance?

Answer 14

Cold cured acrylic resin
Added to the model after the wire components have been fabricated
Holds the various components together
Can be built up to form biteplanes

Question 15

What are anterior biteplanes used for?

Answer 15

To reduce deep overbites

Question 16

What are posterior bite planes used for?

Answer 16

To temporality produce a vertical opening between the anterior teeth to allow proclination of lingually placed upper incisors

Question 17

Anterior bite plane

Answer 17

Treatment of deep overbite
Crib 6’s
Posterior teeth separated by 2-3mm
Add acrylic as required

Question 18

Midline expansion appliance (URA)

Answer 18

Correction of crossbite
Crib 6’s and 4’s
Midline screw adjusted by patient (1/4 turn) once or twice per week

Question 19

Palatal finger spring retractor to proclined upper incisors

Answer 19

Crib 6’s and also 4’s

Activate by 2-3mm

Question 20

Palatal finger spring retractor

Answer 20

Used to retract canines or premolars
Crib 6’s
0.5mm springs
Activate by 1/2 width of the canine or premolar

Question 21

Robert’s retractor

Answer 21

Retracting incisors (Class II Div 1)
Crib 6’s
0.5mm labial bow supported by SS tube
Should lie just behind incisal edges when passive

Question 22

Buccal canine retractor

Answer 22

Retracting canines (to relieve crowding or reduce overjet)
Crib 6’s
0.7mm springs
Activate by 1/3 width of the canine

Question 23

When are adjustment visits carried out?

Answer 23

In 4-6 week intervals

Question 24

What is also checked in adjustment visits?

Answer 24

Check for ulceration/discomfort
Assess progress- study models, measure overjet/overbite
Check retention

Question 25

What are some signs that the patient is not wearing their appliance?

Answer 25

No tooth movement
Patient unable to speak with appliance in place
Springs still active
Patient has difficulty inserting and removing the appliance

Question 26

What should you do if a patient isn’t wearing their appliance?

Answer 26

Reinforce instructions to patient and parent
Adjust if necessary
Don’t carry out extractions until patient is wearing the appliance full time
Reconsider whether or not the patient is suitable for treatment