Appliance design Flashcards
10 uses of casts
- Record treatment – mention outcome tx
- 3D representation of pt not there
- Design appliances
- Medical legal reasons
- Occlusions – assess for malocclusion
- get diagnosis
- treatment plan
- motivator – wax
- don’t want to good – want realistic expectations
- emphasise problems – more informed pt decision
- teaching
- forensics
- retrospective studies
aim of orthodontics
Functioning, aesthetics, stable occlusion
12 stainless steel properties
- malleable
- biocompatible
- doesn’t corrode
- non-toxic
- strong
- flexible
- resistant to abrasion
- high melting temperature
- elastomeric response – spring back into shape
- durable
- ductile
- cheap
5 components of stainless steel (and %)
72% Iron
18% Chromium
8% Nickel
- 7% Titanium
- 3% Carbon
URA
upper removable appliance
LRA
lower removable appliance
how do removable appliances working
move teeth
- tipping
- tilting
see saw effect
- around fulcrum – midpoint
move crown and root – not bending
advantages of removable appliances (9)
- tipping of teeth
- excellent anchorage
- generally cheaper than fixed – acrylic and SS – cheaper than fixed (bracket per tooth)
- LRA less tolerated – impinging on tongue space
- Shorter chairside time required
- Oral hygiene is easier to maintain – removable and clean them
- Non-destructive to tooth surface – no prep
- Composite bonds wire to teeth – need etch (destructive)
- Less specialised training needed to manage
- Can be easily adapted for overbite reduction
- How deep lowers coming up behind uppers
- Can be traumatic
- How deep lowers coming up behind uppers
- Can achieve block movements
disadvantages of removable appliances
- Less precise control of tooth movement
- only tipping/tilting, not lateral or intrusion/extrusion
- Can be easily removed by the pt
- Generally, only 1-2 teeth can be moved at a time (fixed can do multiple)
- Specialist technical staff required to construct the appliances
- check scope
- Rotations very difficult to correct – only small degree able to change
potential result due to crowding
common
- Rotated, overlapped, ectopic, PE anteriors due to lack of space
issues with overjet
horizontal
trauma, function, undesirable look, can get incompetent lips, lip trap (rest or infront of teeth)
how to create space in arch (2)
extract
widen arch - move teeth out
how to show extraction on design sheet
cross tooth out
common tooth to extract for ortho space creation
premolars
1st more – depends on angulation
- Cross out on design
what would the aim on URA design sheet be for
- anterior crowding + 6mm overjet
Aim - Please construct URA to retract 13 + 23
tell them what you want to achieve
retract
move distally
procline
push forward
retrocline
push back
notation used in appliance sheets
FDI in GDH
common to see palmer outwith
ARAB
- Active components
- Retentive
- Anchorage
- Baseplate
active component
- Part of moving teeth through application of force
active component for
- anterior crowding + 6mm overjet
13 and 23, palatal finger spread + guards, 0.5mm HSSW (hard, can get soft not in ortho)
why need to state gauge of wire on design sheet
- Direct relation to amount of force
- Thinner – lighter
- Thicker – greater
how to draw palatal finger spread (active component)
Round mesial aspect of tooth
Coil is where force exerted form
Retentive part
Guideplane
retentive
- Resistance to displacement forces
4 displacement forces URA subjected to everyday
- Tongue
- Mastication
- Speaking – vibrations in palate
- Gravity
- Active component – forces applied to teeth translate back onto the retentive component
posterior retentive element usually placed on
first permanent molars for posterior retnetion
common posterior retention design
16 + 26, Adam’s clasp, 0.7mm HSS
why thicker wire used for retentive component compared to active component?
Thicker as don’t want to be as flexible
(0.7mm HSSW compared to 0.5mm HSSW)
anterior retention example for
anterior crowding + 6mm overjet
11 + 21, Southend Clasp, 0.7mm HSSW
why should you always write and draw designs
to minimise the chance of errors
anchorage
- Resistance to unwanted tooth movement
anchorage based around what law
Newtons 3rd law – every action there’s equal opposite reaction
base plate
use Self-cure PMMA
where to mark distal of baseplate is 7s fully erupted
half way across them
3 functions of baseplate
- Unite all the components
- Retention – through adhesion, cohesion
- Anchorage
3 types of PMMA
- Heat
- Self
- Light
cure
what are the two optoins for URA PMMA
heat and self cure PMMA
not light
why choose self cure PMMA over heat cure PMMA for URA
Heat cure – 15 hours process – wax, lost wax
Self cure – less stages 15 mins -
easier and quicker -satisfactory for disposable
Heat cure Vs self cure
- Need heat
- Self – short working time
- Heat – significant working time till exposed to heat
- Heat cure stronger
- Heat cure – less monomers (monomer liquid, poly powder) – little residual monomer
- self cure more – allergic reactions and odour
- Heat cure shrinks less than self cure
Heat cure fundamentally better
But most URA in self-cure
aim for tooth movement per month in URA
1mm
what distances to measure pre treatment
space tooth being moved (e.g. premolar width that was extracted)
overjet
6mm gap distal to canine aim to be closed in
6 months
so 6mm gap mesial 3/distal 2
what happens is the canine/tooth to be moved is unable to move e.g. fixated to bone
Gap distal shorter
Whilst gap mesial increase
- Increased overjet -> 12mm
- Every action has equal and opposite reaction*
- Forward movement for distal canine
how does baseplate provide anchorage
covering entire palate so giving resistance to forward movement
what should you see on monthly measurements in ortho treatment of:
anterior crowding + 6mm overjet
distal (decrease) and mesial (increase)
overjet (remain)
balancing forces
only move 1-2 teeth at time
- Too many – balance wrong – anchorage goes wrong
- Snowball
