Ortho Lab
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What are the components of stainless steel and their percetnages
Iron - 72% Chromium -18% Nickel 8% Titanium 1.7% Carbon 0.3%
Name 4 advantages of removable orthodontics
Excellent anchorage Shorter Chairside time Oral hygiene is easier to maintain Non destructive to tooth surface Can be easily adapted for over bite reduction
What are 5 disadvantages of removable appliances
Less precise control of tooth movement ( tipping and tilting limited) Can be easily removed by the patient - non compliance Generally only 1-2 teeth can be removed at a time Specialist technical staff required to construct the appliances Rotations are very difficult to correct
What diameter is stainless steel in the claps used
0.7mm
What is the active component
Name of components that will be moving the teeth through force
What is retention
Resistance to displacement forces
What are the 5 forces which a removable appliance can be subjected to?
Gravity Mastication Speech = vibrations through the palate displace it Tongue Active components
What is anchorage
The resistance to unwanted tooth movement
Newtons 3rd law is related to anchorage and can make anchorage difficult. What is this law?
Every action as an equal and opposite reaction
What is the baseplate of a URAs function
To connect all the components Retention - adhesion/cohesion Resistance to unwanted movement - provides anchorage and assists with retention
What is the aim of the appliance design
Description of what the appliance is trying to achieve
What are the 4 advantages of heat cure over self cure PMMA
Heat cure has a better working time Heat cure is stronger Heat cure has less residual monomer - self cue has quite a bit Heat cure is more dimensionally stable. There is more shrinkage in self cure
There are many more advantages to heat cure over self cure PMMA , so why is self cure PMMA used and why is it adequate
Heat cure PMMA has to go though the lost wax technique and this an take up to 15 hours. Whereas self cure PMMA takes 15 mins. Self cure PMMA is adequate are these appliances are disposable and aren’t subjected to large forces the same way as dentures are.
How does the baseplate in a URA help with anchorage
Baseplate spreads the load over the other teeth so this helps with anchorage so the hinge movement doesn’t happen.
How many mm of tooth movement would we expect a month from URA
1mm
Why do we usually only move 1-2 teeth in a URA
This is because if we move too many teeth the anchorage would compromise and the teeth would push back
Why do we not take URAs back to the demarcation between the hard and soft palate
Younger patients tend to have a worse gag reflex - this will lead to non compliance
What is one reason that you may use heat cure PMMA over self cure
If a person has a monomer allergy
Do we use soft or hard stainless steel in ortho
Hard work
What combines with iron to forms steel
Carbon
What is the function of chromium in SS
It forms a passive oxide film over the surface of the metal that enables the stainless steel to be CORROSION RESISTANT
What is the function of the nickel in SS
Nickel and chromium both assist on achieving the austenitic structure at room temperate by lowering the critical temperature at which the austenitic structure breaks down on cooling Also aids in improving corrosion resistance
What is the purpose of ID tube sheathing
This gives strength and ridgity to the components on the bucco-labial surface and prevents distortion. This is not necessary on palatal components
What is the meausurement of ID tubing
0.5mm