Removable Appliances Flashcards
What are advantages of removable appliances?
Easy cleaning Allow for good anchorage- resist unwanted tooth movement Can move blocks of teeth Cheap Less chair side time Easy to adjust
What are the disadvantages of removable appliances?
Dependant of patient cooperation Allow for tipping movements only Speech may be affected Retention can be hard to achieve Lower RA can be harder for patient to tolerate
What tooth movement can be achieved from RAs
Tipping Space maintenance Bite opening Bite opening Correction of cross bite Single tooth movements
What are the main components of RA
Base plate- made of acrylic
Activation
Retention
Anchorage
What materials are there within removable appliances?
Stainless steel 18:8 chromium:nickel
Acrylic- polymerising polymethyle methacrylate
Elgiloy- heat treated to increase strength to equivelant of stainless steel
What stages are there to to construction of RAs
Clinical examination Radiographic examination Imps and wax bite Design Decon- lab
What is the function of the base plate?
Hold components together
Provides anchorage
Bite planes can be added
Bulk should be minimised re. Comfort
What is the purpose of anterior bite planes?
Reduction of overbite
What is the purpose of posterior bite planes?
Eliminates cross bite
What components make up activation?
Springs, screws, bows
What is force of the springs dependant on?
Length of wire
Radius/ diameter of wire
Elastic modulus- stiffness of wire
What is the equation related to force?
F= E. d. r4/l3
E= stiffness of wire d = deflection of wire r= radius of wire l= length of spring
What effect to force does increasing the length of the wire?
Lighter forces are exerted
How can length of wire be increased while being allowed to be accommodated by the size of mouth?
Coils can be added
What effect to force does doubling the diameter or wire have? X16
Increase in force
What effect to force does doubling the length of wire? X8
Reduction in force
How does tooth move in relation to point of contact with the tooth?
Tooth moves perpendicular to point of contact
How much activation does a 0.5 mm wire spring need?
3mm
How much activation does a 0.7mm wire need?
1mm
What movements do palatal springs allow for?
Mesio distal and buccal movements
What is the guard wires function?
Prevent palatal springs coming too far away from base plate
Describe buccal canine retractors?
Can move bucally placed canines palatal lay as well as distally
Activated by winding coil or adjusting anterior arm
Describe z springs and their function
0.5mm stainless steel
Spring perpendicular to palatal surface
Activated- spring pulled 1-2 mm away from base plate
45 degrees in direction of desired movement
Describe T springs and their function
0.5mm stainless steel
Used to move teeth buccally
Often used for canines and premolars
Activation- pull spring away from base plate at 45 degrees
Describe bows and their function
Can be active or passive
Active- facilitates retraction of proclined incisors( Roberts retractor)
Describe screws and their function
Move teeth labio- lingually
Transmit force via acrylic contacting teeth
Transverse expansion
Turn 1-2x weekly
Describe means of retention
Minimum of 3 components
Adams clasp and cribs- engage undercuts at Mesial and distal
Southend clasps- engage undercuts interproximally
Labial bows- anterior retention
What is anchorage and how is it provided?
Resistance to unwanted tooth movements
Force created as reaction to active component
Provided by other teeth
Provided by base plate
How can anchorage be increased?
Clasping more teeth
Using lighter forces
Moving only one or two teeth at a time
What equipment is required for fitting RA
Adams pliers 64s Spring forming pliers 65s Marker Ruler Acrylic trimmer
What problems are there with removable appliances?
Breakages Patient compliance Can become loose fitting Palatal inflammation re. Poor oh due to stagnation areas created Fungal infections of the palate
How are forces applied via removable appliances?
Springs
Screws
Bows
