Removable appliances Flashcards
What are the reasons for decline in use of RAs? (3)
- poor rep as they were incorrectly used to treat malocclusion for which they were inadequate
- technical advances to fixed appliances have made treatment more efficient (used to take whole morning)
- cost reduced (used to be as $ as car)
What are the advantages of RAs? (6)
- removable for socially sensitive occasions
- short chairside time for adjustment
- moves blocks of teeth efficiently
- can remove occlusal interferes
- can provide good anchorage with use of palate
- cheap
What are the disadvantages of RAs? (6)
- heavily dependent on pt compliance (BIGGEST con)
- unable to perform complex tooth movements
- affects speech short term
- limited use in lower arch
- requires a lab to fabricate
- difficult to repair
What are the indications of RAs? (6)
- growth modification during mixed dentition stage (functional appliances)
- limited tooth movement (TIPPING ONLY)
- correction of individual tooth positions
- arch expansion
- differential eruption of teeth
- retention after comprehensive orthodontic treatment
Which malocclusions may RAs be indicated in?
increased overjet and overbite
posterior crossbite
How might RAs be used to fix overjet and overbite?
with differential eruption and retraction
deep bite: flat anterior bite planes can disengage the molars and cause over-eruption of molars, opening up the bite and cause some lower incisor intrusion
once, overbite is reduced, can grind away part of bite plane and use active component to retract anteriors to reduce overjet
When are RAs contraindicated for treating increased overjet and overbite
when you DONT want tipping movement
if retroclined in upper arch and proclined in lower arch (if uppers proclined then could be done)
What force may be put on the lower incisors when URAs are used to fix overbite and overjet?
intrusion force on lower incisors, it is away from the centre of resistance and thus creates a moment and small amount of rotation → can be helpful to tip lowers forward
What has happened in this case?
there was increased overjet but upper teeth already retroclined and lowers proclined → tx lead to opposite effect and bite was deepened
When might RAs be indicated in treating posterior crossbite?
- to move blocks of teeth (unilateral crossbite)
- single tooth crossbite
- cases which require tipping movements only e.g. upper teeth are not already proclined and lowers retroclined
What are the categories of components of URAs? (4) Give examples
ARAB
Active (springs, screws, bows)
Retentive (clasps, bows)
Anchorage (baseplate, headgear, elastics)
Baseplate (connects all components together)
What is the most common active component of URAs?
springs
What happens to the properties of a stainless steel as it is drawn out to make a wire? (3)
as metal passes through dies to become smaller wire it becomes work hardened
as it becomes work hardened it becomes more springy but more brittle
(the more springy the more prone to fracture)
What happens when wires are heated?
reduces work hardening
reduces brittleness but also springiness (more likely to bend and stay that way, not good for teeth)
What happens when wires are heated?
reduces work hardening
reduces brittleness but also springiness (more likely to bend and stay that way, not good for teeth)
What happens when a SS wire is bent to make springs?
outside of spring becomes more work hardened (more springy but brittle) and inside isnt stretched therefore not → advantageous to increase springyness
What shouldn’t you do when bending and working with wires and why?
excessive bending and heating
excessive bending will cause sufficient work hardening to fracture a wire
excessive heating can anneal the wire meaning it loses its spring properties
Name the 3 components of a spring in an URA.
Tag: embedded in baseplate
Coil: active part of spring, made so that it compresses when activated and tends to want to open
Arm: undergoes only slight bending and mainly a rigid lever (transfers force from coil to where you want it on a tooth)
Why is a coil spring more efficient when it is wound up than one which is activated in the opposite direction
when wound up: when arm moves up, coil compresses
when activated in opposite direction: when arm moves up, coil opens, less efficient as we dont use the work hardened property of spring
i.e. compressing spring and letting it open up is more efficient than opening spring and letting it contract
What is the path made by the spring known as? What does this depend on?
path of action
the longer the arm the greater the range of action
(short spring has short range of action as its tip forms the arc of a smaller circle)
When a force is applied by a spring touching a tooth, how does it work?
when a force is applied to tooth surface direction of movement is at right angles to the tangent at the point of contact (where the spring touches the tooth)
→ important to know for canines and premolars which have a large incline in the M and D, there will be some intrusion
What are some commonly used types of springs? (6)
simple cantilever
double cantilever (Z)
T-springs
buccal canine retractor
reverse loop canine retractor
coffin spring
When is a double cantilever (Z) spring used?
when space is tight (esp lateral incisors), uses 2 coils, similar mechanical principles to simple cantilever
When is T-spring used
good for buccal movement of canines and premolars, limited activation, difficult to adjust in the vertical plane therfore not recommended for incisors (may intrude)
When is a buccal canine retractor spring used?
What is a contraindication?
when canine has to be moved palatally as well as distally
has large range of activation
but spring needs to be kept away from cheeks and muscle attachments within buccal sulcus (contraindicated in patients with shallow bulcus sulcus)
When is a reverse loop canine retractor used?
patients with shallow buclus sulcus
but it has poor vertical stability and limited activation
When is a coffin spring used?
arch expansion
very strong wire, difficult to make and adjust, screws are usually preferred as they are more controlled
very active, keeps expanding if u dont see pt
What is the biggest disadvantage with screws?
relies on patient compliance, needs to be activated more regularly than a spring
What is the biggest disadvantage with screws?
relies on patient compliance, needs to be activated more regularly than a spring
What does the force of the spring depend on? (3)
amount of deflection
cross sectional area of wire (biggest influence - 0.7 vs 0.5mm diameter doubles force)
length of the spring
What does the force of the spring depend on? (3)
amount of deflection
cross sectional area of wire (biggest influence - 0.7 vs 0.5mm diameter doubles force)
length of the spring
T/F Force delivered by 0.7mm wire is 0.15g per mm
F
force delivered by spring made of 0.5mm wire is 15g per mm of deflection
What are some components used for retention of URAs?
labial bows - anteriors
Adam’s clasps - posteriors
ball ended clasps
Southend clasps
Are labial bows always purely retentive?
no can be both retentive and active (careful not to overactivate as 0.7mm will cause alot of force)
*image - if you squeeze loops it will move palatal
What is a roberts retractor?
type of labial bow designed to retract upper incisors, made from 0.5mm wire
uses supported springs (placing 0.5mm wire into tubing gives it properties of a stronger wire which resists bending but still get 0.5mm action on active side)
What are the advantages of supported springs? (2)
- maintains strength without increasing force
- spring remains active for longer
What is another way to counteract 0.7mm wire putting too much force on a tooth (other than supported springs)?
extended labial bow
What are Adam’s clasps used for in URAs?
retention of posterior teeth
engages mesio and disto-buccal undercuts of crowns
0.7mm wire
prone to fracture at arrowheads
What are the advantages and disadvantages of Adam’s clasps?
advantages:
bridge provides site to which patient can apply pressure with fingertips during insertion and removal
auxillary springs, hooks (for elastics) and tubes (for headgear) can be soldered
disadvantages: arrowheads can become work hardened and prone to fracture
Why are Adam’s Clasps not favourable for anterior teeth?
central incisors need to be relatively upright
clasp is prone to breaking
can be uncomfortable for patient if incisors are proclined due to undercu
How are ball ended clasps used in URAs? Name 2 cons?
engages undercut
cons: if overactivated they can open up spaces
+
doesnt allow attachments of auxillary components
What are Southend clasps?
sits around gingival margin of central incisors
well tolerated, good passive option instead of labial bow
Label the appliance
labial bow
2 adams clasps
What is anchorage about?
any force producing tooth movement leads to a reactive force on other teeth usually in opposite direction
→ anchorage control is about maxisming the wanted tooth movement and minimsing unwanted tooth movements
Does this scenario have low, medium or high anchorage demands?
low (small tooth/root, reactionary force is not much therefore anchorage needs to resist less)
Does this scenario have low, medium or high anchorage demands?
moderate
(canines larger teeth, more anchorage needed as reactionary force pushes whole appliance forward, there is premolars and molars which can probably provide enough anchorage)
Does this scenario have low, medium or high anchorage demands?
high
retracting both canines and pms, alot of reactionary force, probably will have froward movement of appliance and molars
How has anchorage been used in this scenario?
canine being retracted, in order to keep pm and molar in correct position, elastic attached to increase anchorage from just those 2 teeth to all the lowers aswell
What are the 3 main functions of the baseplate? (3)*
- foundation to hold other components together
- anchorage by being in contact with palatal vault and teeth arent being moved
- may be built up to bite planes to disengage occlusion to faciliate certain tooth movements
What properties should a baseplate have? (4)*
- thick enough to carry active and retentive components
- but as thin as possible as thick appliances difficult to tolerate
- should cover most of hard palate just distal to 1st molars
- needs to fit closely around necks of teeth not being moved so that food packing and gingival hyperplasia dont occur
How can an anterior and posterior bite plane be used to correct malocclusion?
anterior - for molar extrusion and overbite correction
posterior - eliminates occlusal interferences for posterior and anterior crossbite correction
What are the 2 types of retainers?
Hawleys
Vacuum formed
