Orthodontic Appliance Design Flashcards
what are the advantages of orthodontic study models?
Automatically goes into centric occlusion without having to mount the models
Can balance the model on the table whilst moving it 360 degrees to see all views
what are the uses of study models?
Show the patient what you are planning to do - used for consent
Can be used for medicolegal - record of whats been done (12 years kept)
Assess quality of treatment - take casts before add after
Diagnosis and Treatment planning without the patient
Appliance design - you don’t make them on models as these are patient records cannot be damaged
Used for motivational purposes to aid compliance (take one at start, middle, end)
Teaching
Retrospective studies i.e. comparing studies
Diagnosis
Forensic
what are the properties of stainless steel? (6)
Biocompatible Cheap Malleable Corrosion reistant Strong Spring like
what are the limitations of study models in terms of orthodontics?
Don’t show roots - these will be moving too
why does orthodontics a lengthy process?
Bone remodelling takes a long time
Apply too much force at one time = can rupture the PDL ligament, cut off blood supply to the tooth and cause pain.
what instruments are used in constructing an URA?
No.64 universal plyers/Adam’s
No.65 universal coil formers
Wire cutters - do not point the wire at your face
What process gives the hard stainless steel its spring like properties?
work hardening
define the Bauschinger effect.
when the coil is activated in the same direction as it had been previously its elastic recovery is greaten than if it was bent/activated in another direction
what causes fractures in stainless steel? (4)
overworking - bending and straightening at the same point
mechanical abrasion - crushed or marked
fatigue - repeated straining action
weld decay - overheating the alloy
what stainless steel is used in orthodontics?
18/8 austenitic stainless steel alloys
list the percentages of metals within the stainless steel alloy.
72% iron 18% chromium 8% nickel 1.7% titanium 0.3% carbon
what are the advantages of upper removable appliances?
Tip teeth/tilt teeth
Excellent anchorage - from the baseplate
Cheaper
Less chair time
OH easier to maintain - can be removed
No destruction to teeth surfaces (etch teeth for fixed appliance)
Less specialised training required to manage (GDPs can work)
Can be easily adapted for reduce an overbite
Can achieve block movement - move a few teeth at once
what are the disadvantages of URA’s?
Less precise control of tooth movement - only tipping and tilting cannot maintain the angulation or intrusion/extrusion.
Easily removed and forgotten to put back in/don’t want to put back in
1-2 teeth are able to be moved at one time : if you move more It compromise anchorage
Specialist staff needed to make these
Rotations are difficult to correct
what mnemonic is used in appliance design?
ARAB
What does the A stand for in ARAB? - define
Active component:
The component that is moving the teeth with the application of force
List the names of palatally placed active components.
- Finger springs and guards
- Z- spring – push tooth forward
- Flapper spring – push tooth forward
- T spring
what type and thickness of wire is used in palatally placed active components?
0.5mm HSSW
List the names of buccally placed active components.
- Roberts retractor
* Buccal canine retractor
what type and thickness of wire is used in buccally placed active components?
0.5mm HSSW with 0.5mm ID (internal diameter) tubing
how do we note the active component on the design sheet?
What teeth you want to move
What you’re using to move them
The type and thickness of the wire used (the thicker the wire the greater the force)
e.g. “13+23 palatal finger springs & guards with 0.5mm H.S.S.W
on a palatal finger spring, where does the active arm come off?
distal aspect of the coil
What does the R stand for in ARAB?
retention:
Resistance to displacement forces
what displacement forces are present within the mouth?
Tongue
Gravity
Mastication - patients should eat with the appliances in
Talking - creates vibrations through the palate
Active component - difficult to control
how do we note the retentive component on the design sheet?
Where you want to place the retention
What component you are using
The type and thickness of the wire
List the names of retentive components.
- Adams – can be used in a mixed dentition/newly erupted teeth using 0.6mm wire instead
- Southend
- Labial bow
what type and thickness of wire is used in retentive components?
0.7mm HSSW
where in the mouth are Adams clasps used for retention?
posterior teeth
where in the mouth are southend clasps used for retention?
anterior teeth
What does the second A stand for in ARAB?
Anchorage:
The resistance to unwanted tooth movement (ensure that only the teeth you want to move moves)
how many teeth should we move at a time?
1-2 teeth
what intra-oral measurements are taken during treatment with URA?
Measure the space distal to the tooth that you are trying to move (on both the left and the right)
Measure the space mesial to the tooth being moved
Measure the overjet
what is the principle of anchorage?
Works on the basis of Newtons 3rd law: For every action there is an equal and opposite reaction.
how much tooth movement do we ideally want per month?
1mm movement per month
A patient with an overjet has a premolar removed which leaves 6mm of space distal to the canine, we now want to move the canine back. Describe the intra-oral measurements after 6 months of canine movement? (3)
Initially, there is a 6mm gap created from the removal of a tooth
After 1 month = there has been 1mm of movement so the gap now measures 5mm / 5mm of space distal to the tooth being moved
Since the gap now measures 5mm there should be 1mm of space anterior to the canine
Therefore;
After 6 months;
The overjet should still be the same (no change!)
The space distal to the canine goes from 6mm to 0 (space closes)
The space mesial to canine goes from 0 to 6mm
why do we only move 1-2 teeth at a time?
to prevent compromising anchorage and ensuring that we resist unwanted tooth movement