Removable Appliances in Orthodontics Flashcards
What are the advanages of removable appliance?
It can be removed for brushing/aesthetics
Palatal coverage increases anchorage
Easy to adjust
Less risk of iatrogenic damage than with fixed
Acrylic can be thickened to form flat anterior bite-plane or buccal capping
Useful as passive retainer or space maintainer
Can be used to transmit forces to blocks of teeth
What are the disadvantages of removable appliance?
They can only tip teeth
Because removable, they wont be working when not in the mouth
Affects speech
Poorly tolerated in lower arch
Intermaxillary traction not possible (noramlly used to close spaces)
Inappropriate for multiple individual tooth movement
What is the risk with fixed that isn’t a problem for removable?
Demineralisation
Removable can be taken out, do OH isn’t a problem
Why is fixed better?
Have fully controlled movement - need attachement to the tooth to do this
Have full 3D control
What are the components to a removable appliance?
ARAB Active component - what moves the teeth Retention - stop it falling out Anchorage - stop the wrong teeth moving Baseplate and biteplanes
What are the different active components (what moves the teeth in the removable appliance)?
Springs - palatal or buccal springs
Screws
Elastics
- in decreasing order of preference
What does the force of the spring depend on?
Thickness of wire
Length of wire
Amount of deflection
What is the thickness of the wire used for spings, why?
0.5-0.6mm- exerting a light force on the teeth
Thicker wire = greater force
0.5mm wire can be coated in acrylic
When will a spring with a coil work more efficiently?
If it is activated in the direction that the wire has been wound, so that as the coil unwinds the tooth moves
The shorter the coil = the greater the force
What happens if the spring is overactivated?
This increases the force on the tooth. moves the centre of resistance more apically
What is a Z spring used for?
Anterior cross-bite - used on incisors
Used to procline the upper incisor
Loop to make the wire longer - exerting less force and gives space to expand
What are T springs used for?
Used for buccal movement of canines and premolars
What is a palatal finger sping and what is it used for?
0.5-0.6mm wire
Coil in acrylic and coil on side away from the direction of movement
it is used for mesio-distal tooth movement when teeth located correctly in bucco-lingual direction
What are screws used for?
More expensive than springs
Helpful when moving a number of teeth together e.g. if expanding the upper arch
if have a posterior cross-bite - dont put Z spings on each tooth
How does the most commonly used screw work?
Consists of 2 halves on a threaded cylinder turned by a means of a key which separates the 2 halves by a pre-determined distance - usually 0.2 for each 1/4 turn
What is activation of screw limited by?
The width of periodontal ligament
To exceed this would crush the ligament cells and cessation of tooth movement
If do 1 1/4 turn per week how much tooth movement will you get?
<1mm
If dor 2 1/4 turns per week of screw how much tooth movement will you get?
<2mm
Why are orthodontic elastics not used on removable applicances?
Poor control
What’s used for posterior retention?
Adams cribs
Where are Adam’s cribs placed?
On 1st molars and premolars
Engage the MB and DB undercuts of 1st molars
Only need undercut of 0.25mm
Why is anterior resistance needed?
If have an anterior cross-bite on UR1 need z-spring to procline it
Force is put on the UR1 labially to push it forwards
There will be a downwards vector of force too, procline and downwards forve displacing the appliance
What is done to resist the downwards force from the z-spring?
Z-spring on the upper right 1
and C-clasp on the upper left 2 to resist the downwards force from the z-spring
What else can be used for anterior rentention if doing something to posterior teeth?
Southend clasp
Utilised the undercut beneath the contact point between 2 incisors - fabricated in 0.7mm hard SS wire
