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
what does the B stand for in ARAB?
baseplate
where should the baseplate extend to?
half way across the 7’s
what is the baseplate made of?
self cure PMMA
What are the 3 main functions of a baseplate?
Connects all the components together
Helps with the anchorage
Provides a seal
why do we use self cure for the baseplate and not heat cure?
Although the properties of the heat cure are superior, the self cure is satisfactory and can be made quicker - more efficient.
what baseplate modification do we use to correct an overbite?
Flat anterior biteplane
what equation do we use to account for the FABP?
Overjet in mm + 3mm PMMA
describe how a FABP works. (4)
- Use the FABP to disengage the posteriors = posterior open bite
- Since the posterior teeth are not occluding the teeth will continue to erupt with bone remodelling around it to close the posterior open bite
- If the 3mm isn’t added the teeth would drift behind the FABP and retrocline the lower incisors
- Lower posterior teeth continue to erupt more as the uppers are restricted by the adams clasp
why is 3mm of acrylic PMMA added in a FABP?
If the 3mm isn’t added the teeth would drift behind the FABP and retrocline the lower incisors
what occurs once the FABP is removed?
Once the FABP is removed there will be a gap between the anterior teeth and the posterior teeth will be In occlusion.
why can a FABP not be used in adults?
The posterior teeth would over-erupt as opposed to the bone remodelling (which occurs in children/adolescents)
= leads to root exposure, sensitivity and a reduced life span of teeth
what type and thickness of wire is used in orthodontic stops?
0.7mm flattened HSSW
what are orthodontic stops used for?
used to stop canines moving back into their natural position during treatment
how do we incorporate retention if we are moving the anterior teeth and cannot place a southend clasp?
add additional Adams clasps 0.7mm
2 adams clasps on each side of the arch
when are posterior bite planes used? (2)
upper anterior crossbites
When an upper anterior tooth cannot move forward as the lower anterior teeth are preventing it from doing so.
or
in expanding the upper arch - disengage and prevent indirectly expanding the lower arch
describe how PBP’s work?
they disengage the upper and lower jaws using - must incorporate all of the posterior teeth - and create a temporary AOB
why must PBP’s incorporate all of the posterior teeth?
If the teeth are not incorporated in the PBP they would continue to over-erupt = undesirable in this instance.
what is the outcome when the PBP is removed?
This creates a temporary anterior open bite to allow the anterior teeth to move into the correct position
what prevents anterior teeth from moving back to their natural undesired position once the Posterior bite plane is removed?
the tooth will have natural retention from the lower incisors
why do the anterior teeth not overerupt in a PBP?
Unlike posterior teeth when anterior teeth reach their maximum eruption they just stop (only in humans)
what happens when both coils/sides of a Z spring are activated (active component)?
forward movement
what happens when one coils/side of a Z spring is activated (active component)?
rotation of the tooth to one side
when fitting a URA for the first time what checks do you do prior to fitting?
1) Make sure you have the correct appliance for the correct patient
2) Check that it matches the design
3) Run finger across it to ensure there are no sharp edges (safe for patient)
4) Make sure there are no signs of damage to the wirework (ensure integrity of the wirework)
when fitting a URA for the first time what checks do you do once its in the patients mouth? (6)
1) Ensure the fit doesn’t cause trauma – no blanching
2) Check the posterior retention – is it adequately going into the undercuts: check the flyover first and then the arrowhead in the undercut.
3) Check the anterior retention
4) Activate the appliance – they arrive to you passive and you have to activate this!! Activate a couple initially and active others later. Get the patient used to the appliance then come back and activate it later (not recommended as it prolongs the time) Want to achieve 1mm movement open month.
5) Show them the correct way to put in and take out the appliance and get them to demonstrate this back to you.
6) See patients every 4 to 6 weeks
what difficulties must you inform the patient of when getting a RA for the first time?
The appliance will feel big and bulk – don’t worry you will get used to it
You will encounter mild discomfort and pressure on the teeth – that indicated that this is working correctly (don’t use sore and pain)
Practice reading aloud to let your tongue adapt to the appliance (patient will have a lisp)
Initially you will produce lots of saliva – will disappear over 24 hours
what patient instructions should you give with a removable appliance? (6)
1) Wear the appliance 24/7 including eating and sleeping
2) Take it out and clean it with a soft brush and soap under the luke warm tap after every meal
3) Remove and put it in a protective container when carrying out contact (rugby) /active (sharp intake of breath) sports
4) Avoid hard and sticky food and exercise caution with hot food/drinks – heat is insulated as it acts as palatal coverage
5) Emphasise that non-compliance prolongs treatment
6) Provide emergency contact details – use if you have problems with the appliance
how do springs become activated?
uncoil them
why are finger springs used instead of buccal canine retractors where possible?
less likely to become distorted
less likely to irritate the soft tissues
when would finger springs be used instead of buccal canine retractors?
when the canine you want to move is in the line of arch
why do we move canines back into the correct position before correcting the overjet?
If we moved all of these teeth at once it would cause a failure of anchorage and the posterior teeth would move forward as opposed to the anterior tooth moving back.
List the components of an adam’s claps and what their function is?
Bridge – allows patient to take appliance in and out and keeps the cheek away from the component.
Arrowhead: engages the undercut
Flyover – should go as neat as possible between the tooth and the adjacent tooth
Leg – the extended part of the clasp that goes into the palate has to lie 1mm from the palate to allow room for the baseplate
tag – Provides mechanical retention when its embedded into the acrylic
why do adam’s clasps need to be adjusted?
The clasp can become distorted and high
what are the problems with a distorted/high flyover on an Adam’s clasp?
Interferes with the occlusion
Biting on the wire = metal fatigue and will fracture
Continuously biting on a high flyover with the arrowhead is in the undercut = gum stripping
List the components of an finger spring and what their function is?
Tag- mechanical retention to hold the component in the acrylic
Coil – where the force is exerted
Guard wire
Active arm – engages the tooth, must closely adapt to the buccal aspect of the tooth
why do we have to ensure the finger spring is closely adapted to the tooth at each appointment?
To prevent losing control of the tooth and to prevent the tooth rotating and moving out of the arch.
how does a finger spring become loose?
As the coil uncoils to become active and move the tooth, the wire gets longer and becomes less adapted.
As the tooth moves into the arch from its original position the distance from the coil to the arm around the tooth shortens and the wire becomes longer and less adapted.
how do we reduce an overjet?
Roberts retractor 0. 5mm HSSW and 0.5mm ID tubing
what type and thickness of wire is used in orthodontic stops (passive)?
0.7mm flattened HSSW
when reducing an overjet, what component can also act as retention?
the roberts retractor
comment on the anchorage when reducing an overjet?
not ideal since we’re moving more than 1-2 teeth
however can be achieved since the centrals and laterals have the shortest roots.
Explain what the problem is when using a FABP to reduce the overbite and using a roberts retractor to reduce the overjet? (1)
When trying to reduce the overjet the FABP prevents this – so the FABP must be gradually altered by removing sections of it following the angulation of the tooth, on a monthly base.
at the same time the posterior teeth are disengaging and over erupting into occlusion.
why must we maintain the use of a FABP when reducing the overjet? (3)
prevent intrusion of the molars and allow the bone to form and harden around the teeth.
As you reduce the overjet the angulation will be inhibited by the lower teeth so you must maintain the FABP.
The overbite increases as we reduce the overjet – why we must maintain the FABP.
why would we want to expand the upper arch? (2)
create more space
correct crossbites
what is the active component when expanding the upper arch?
Midline palatal screw
what retention do we have when expanding the upper arch?
cant use anterior as it would inhibit expansion;
additional Adam’s clasps 0.7mm HSSW
2 on each side of the arch
comment on the anchorage when expanding the arch.
X - reciprocal anchorage
once the appliance for expansion is constructed what must they do?
cut the appliance in half so that its only connected via the screw
in a URA used for expansion how many times is the midline palatal screw turned?
1/2x per week
in a URA used for expansion how much movement is there per month?
1mm
0.25mm per week
what problems can occur when expanding the upper arch?
if the upper and lower jaws are occluding the lower cusps can inhibit the expansion movement and then eventually we can indirectly expand the lower arch
how can we prevent indirectly expanding the lower arch when expanding the upper arch? how is this achieved?
take the teeth out of occlusion using a PBP
how do we expand only one side of the maxilla?
Alter how you cut the appliance so that its only 1/4 of the appliance that’s moving.
Greater coverage of the baseplate (over the anteriors, and the right posteriors) balances the force – only slight movement on the opposite side.
how do we expand only the posterior aspect of the maxilla?
Finish the appliance short of the anteriors
appliance only covers the posteriors
