Removable Appliances Flashcards
What are the three kinds of orthodontic appliances?
Removable appliances
Fixed appliances
Functional appliances
What action do removable appliances cause on teeth?
Simple tipping movements
Single force applied to crown
Fulcrum within root
What are some advantages of removable appliances?
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
What are some disadvantages of removable appliances?
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
What are the 3 components of removable appliances?
Active component
Retentive component
Baseplate
What are the active components?
Springs- 18:8 SS (18% Cr, 8% Ni -> corrosion resistance), usually 0.5 or 0.7mm thick
Screws
Labial bows
Elastics
What is the optimum force needed to be produced by springs to produce a tipping movement in a single rooted tooth?
25-60g
What are the principles of cantilever springs?
Force is proportionate to the thickness (to the power of 4) / length (to the power of 3)
What happens to the force if you change the thickness of the spring wire?
Increasing the wire thickness, increases the force
Decreasing the wire thickness, decreases the force
What happens to the force if you change the length of the spring wire?
Increasing the length will reduce the force
Decreasing the length will increase the force
What activation is usually needed in the spring to produce a force of 25-60g?
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
What is the purpose of the retentive components of a removable appliance?
To retain the appliance in the mouth
What methods of retention do removable appliances have?
Usually clasps 3 types- Adams clasps Southend & Half-Jackson clasps Ball ended clasps
What is the baseplate of a removable appliance?
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
What are anterior biteplanes used for?
To reduce deep overbites
What are posterior bite planes used for?
To temporality produce a vertical opening between the anterior teeth to allow proclination of lingually placed upper incisors
Anterior bite plane
Treatment of deep overbite
Crib 6’s
Posterior teeth separated by 2-3mm
Add acrylic as required
Midline expansion appliance (URA)
Correction of crossbite
Crib 6’s and 4’s
Midline screw adjusted by patient (1/4 turn) once or twice per week
Palatal finger spring retractor to proclined upper incisors
Crib 6’s and also 4’s
Activate by 2-3mm
Palatal finger spring retractor
Used to retract canines or premolars
Crib 6’s
0.5mm springs
Activate by 1/2 width of the canine or premolar
Robert’s retractor
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
Buccal canine retractor
Retracting canines (to relieve crowding or reduce overjet)
Crib 6’s
0.7mm springs
Activate by 1/3 width of the canine
When are adjustment visits carried out?
In 4-6 week intervals
What is also checked in adjustment visits?
Check for ulceration/discomfort
Assess progress- study models, measure overjet/overbite
Check retention
What are some signs that the patient is not wearing their appliance?
No tooth movement
Patient unable to speak with appliance in place
Springs still active
Patient has difficulty inserting and removing the appliance
What should you do if a patient isn’t wearing their appliance?
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
