W6 - Removable Appliances - Abdalla Flashcards
Reasons for declining use of removable appliances? (2)
Technical advances to fixed appliances
Cost of fixed appliances went down
Advantages of removable appliances (6)
- Removable for social circumstances
- Short chairside time for adjustment
- Move blocks of teeth efficiently
- Can remove occlusal interferences
- Can provide good anchorage with use of palate
- Cheap
Disadvantages of removable appliances (6)
- Dependent upon pt compliance
- Can’t perform complex tooth movements
- Affects speech
- Limited use in lower arch
- requires lab to make
- Difficult to repair
Indications for removable appliances
- Growth modification during mixed dentition (functional appliances)
- Limited tooth movement (tipping)
- Correction of individual tooth position
- Arch expansion
- Differential eruption of teeth
- Retention after ortho
Indication of removable appliances relating to overbite
Effective at treating deep bite
- Molars are diengaged and then overerupted
(Dahl effect)
How do removable appliances aid in reducing overjet?
listen to this section
tipping?
Contraindication of removable appliances
Increased overjet & overbite
- Ex. mx incisors already retroclined and md incisors proclined
How do removable appliances treat posterior crossbite
listen again
Palatal screw used to increase width of arch
Components of removable appliances (ARAB)
Active - springs, screws, bows
Retentive - clasps, bows
Anchorage - baseplate, headgear, elastics
Baseplate - connects all components
How does the production of wires change its properties
Wire passes thru die to become work hardened
→ makes the wire springy but brittle
→ the more springy, the more prone to fracture
What does it mean for a wire to be “work hardened”?
How to increase / decrease?
Any work done to the wire (bending, pulling, compressing) will cause “work hardening”
- increased spring
- increases brittleness
Annealing (heating wire) - reduces work hardening
- Reduce brittleness, but will also reduce spring
Bending/loops - increase work hardening
Which is a more efficient use of spring
A - spring is being further closed - more use of work hardened aspect (wound up is better)
B spring is being opened up - less “spring”
What is a spring’s “path of action”?
The path of movement made by the spring
- Longer the arm the greater its range if action
- Short spring has a short range of action as tis tip forms the arc of a smaller circle
Which is better?
B - coil is higher and closer to the tooth it needs to move
- Path of action of B spring is pushing in the correct vector compared to A
What kind of tooth movement do removable appliances produce?
Tipping only
What is this and where is it used?
Double cantilever (Z) spring
Tight spaces
Ex. lateral incisors
What are T-springs used for? Problem?
Used mostly for premolar buccal movement (though sometimes canines)
- Limited activation
- Difficult to adjust in the vertical plane (intrude) - don’t use for incisors
ID + when is it used + contraindication
Buccal Canine Retractor
- Used when canine has to be moved palatally AND distally
Contraindicated when sulcus is shallow
ID + indication + problem
Reverse loop canine retractor
- used when sulcus is shallow
- May have limited activation
- Has poor vertical stability
Indication for buccal canine retractor
When canine must be moved palatally as well as distally
ID + problem + alternative
Coffin Spring
- made from 1.25 mm wire (very strong)
- Used for arch expansion
- Difficult to make and adjust
- Alternative: screws
Biggest downside of screws
Relies on patient compliance
Needs to be activated more regularly than a spring
Force of the spring depends on _________ (3)
Amount of deflection
Cross sectional area of wire
Length of spring
What is the ideal amount of force to put on a tooth for ortho
40-50 g listen to lecture again (1:40)
What can overactivation of springs lead to?
May prevent the URA from seating correctly
What are labial bows used for?
Usually used for retention but can be made active
- Careful not to over active as they are 0.7 mm thick (lots of force)
- Can be used to retract upper incisors
What are Robert’s Retractors used for?
Type of labial bow
- Used to retract incisors
- 0.5 mm thick
Why are supported springs used?
support = sheath around spring
- Maintains strength without increasing force
- Spring stays active for longer
Main forms of retention for anterior teeth vs posterior teeth
Anterior teeth - labial bow
Posterior teeth - Adam’s clasp
What is an Adam’s Clasp? Features?
Mainly used for retention of posterior teeth
- Engages mesio and disto buccal undercuts of crowns
- 0.7mm wire
- May be prone to fracture at arrowheads
Features of ball ended clasps
- Uses undercut in embrasure
- Simple to construct
- Doesn’t allow for attachments of auxillary components
Features of southend clasps
- Passes around gingival margin of central incisors
- Simple to construct
- Well-tolerated (preferred anterior clasp)
What is meant by anchorage demand?
Amount of resistance / immovable support to “anchor” the dentition when moving other teeth
- low, medium and high - dependent on size of tooth that is being moved, number of teeth, etc.
How to increase anchorage when molar is not enough?
Employ anchorage from other arch
- Ex elastics, headgear
3 functions of the Baseplate
- Provides foundation for components (springs and clasps)
- Contributes to anchorage
- May be built up into bite planes to disengage occlusion (Dahl)
How should the baseplate fit? (3)
Cover most of hard palate
Finish just distal to first molars
Fits closesly around necks of teeth not being moved (prevent food packing, gingival hypoplasia)
Extended labial bow
Advantages of Adam’s clasps
- Bridge provides site for pt to apply pressure when inserting and removing
- Springs can be soldered onto bridge
- Hooks can be soldered on for elastics
- Tubes can be soldered on to attach facebow
Disadvantage of Adam’s clasps
Can become work hardened at arrowheads
- Increased risk of fracture
