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)
