Week 6- Removable Appliances Flashcards
What are reasons for decline in use of removable appliances?
- Developed poor reputation
- Used inappropriately
- Technical advances to fixed appliances have made tx more efficient
- Relative costs of fixed appliances reduce
What are advantages of removable appliances?
- Removable for socially sensitive occasions
- Short chairside time for adjustment
- Move blocks of teeth efficiently
- Can remove occlusal interferences
- Can provide good anchorage with use of plate
- Cheap
What are disadvantages of removable appliances (6)?
- Heavily dependent upon patient compliance
- Unable to perform complex tooth movements
- Affect speech in short term
- Limited use in lower arch
- Require a laboratory to fabricate
- Difficult to repair
What are indications for removable appliances (9)?
- Growth modification during mixed dentition stage (functional appliances)
- Limited tooth movement (tipping)
- Correction of individual tooth positions
- Arch expansion
- Differential eruption of teeth
- Retention after comprehensive orthodontic treatment
- Crossbites
- Increase overjet and overbite
How can anterior bite planes treat deep bite?
Upper incisors contacting on bite plane, and molars are disengaged leading to over eruption of molars (and some lower incisor intrusion)
What are the components of a removable appliance?
- Active
- Retentive
- Anchorage
- Baseplate
How are stainless steel wires made
Made by drawing metal through series of dies
How does stainless steel wire become work hardened?
- As wire passes through die
- Bending loops in wire (outside of loop becomes work hardened)
What happens when stainless steel wire becomes work hardened?
Becomes more springy but also more brittle, making it more prone to fracture.
What happens when stainless steel wires becomes less work hard? How is this achieved?
Annealing (heating wire) reduced work hardening. This reduces brittleness but also springiness.
How does stainless steel wire become springy/brittle vs no spring/ductile?
Springy, brittle: Work hardening
No spring, ductile: Annealing
What are the components of a spring?
- Tag (embedded in baseplate)
- Coil (active part, compresses when activated, tends to open)
- Arm (undergoes slight bending, rigid lever)
How does the arm length on a spring impact?
Longer arm, greater range of action.
Since when has use of removable appliances been in decline?
1970’s
What are indications for anterior bite planes?
Increased overjet & overbite
What happens when there is intrusion force placed on lower incisors (e.g. anterior bite plane)
if intrusion force placed on lower incisors, it will create moment. Tip lower anteriors forward to help correct overjet.
What are contraindications for anterior bite plane?
If teeth are already quite retroclined in upper arch and proclined in lower arch
What has happened in this case?
There was increased overjet but upper teeth were already retroclined and lower teeth proclined. By retroclining the upper teeth further, it has lead to deepened bite as the result from the removable appliance was unstable. Teeth have relapsed into worse position.
What is the appliance used for in this case?
Posterior teeth moved buccally to correct unilateral cross bite
What can be used to correct single tooth crossbite?
Upper removable appliance (URA)
What are active components?
Springs
Screws
Bows
What are retentive components?
Clasps
Bows
What are anchorage components?
Baseplate
Headgear
Elastics
When a force is applied to tooth, where is the direction of movement?
Right angles to tangent at point of contact (where spring touches tooth).
Be careful with wire placed on canine/premolars as it has large incline on buccal and mesial surfaces- will get intrusive force.
How many points of contact on a tooth does a removable appliance have?
One point of contact. Therefore tipping movements only (no couples).
When can double cantilever (z) springs be used?
When spaces are tight
What are pros and cons of T springs?
- Good for buccal movement of canines and premolars
- Limited activation
- More difficult to adjust vertical plane so not recommended for incisors (may intrude)
What is a buccal canine retractor used for? Where should it be kept away from?
- When canine has to be moved palatally as well as distally.
- Large degree of activation
- Spring needs to be kept away from cheeks and muscle attachments within buccal sulcus.
When is a reverse loop canine retractor used?
Preferred when sulcus is shallow
(has poor vertical stability and limited activation)
What is a coffin spring?
- Very strong spring made of 1.25mm wire
- Used for arch expansion
- Difficult to make and adjust
- Screws are preferred
- Remain active (pt needs to come back to prevent over expansion)
What is the disadvantage of screws?
- Relies more on pt compliance
- Needs to be activated more regularly than spring (2x per week)
What does force of spring depend on?
- Amount of deflections
- Cross sectional area of wire
- Length of spring
How does force compare between 0.7mm and 0.5mm diameter wire?
Force doubles
What mm and frequency of activation generally maintains adequate force on tooth?
3mm deflection (45g force) and monthly activation
What are characteristics of labial bows?
- Effective for retention
- Can be made active (retract upper incisors)
- Caution not to over activate as 0.7mm wire
What are advantages of supported springs?
Active 0.5mm wire supported with tube (gives properties of 0.7mm wire)
- Maintains strength without increasing force
- Spring remains active longer
What is the mainstay retention for anterior vs posterior teeth?
- Anterior: labial bow
- Posterior: adams clasps
What are adams clasps?
- Most common retention of posteriors
- Engages MB and DB undercuts of crowns
- Easy to make
- 0.7mm wire
What are advantages of adams clasps?
- Bridge provides a site where pt can dislodge appliance
- Can solder springs, hooks (for elastics) or tubes (for headgear) to clasp.
What are disadvantages of adams clasps?
Can become work hardened at arrowheads and can be prone to fracture
When are coiled springs most efficient?
When they’re wound up (compressing) rather than opened up
(a more efficient than b)
What is the force delivered by a spring made of 0.5mm wire?
15g per mm of deflection
What is the issue with overactivation of springs?
Can prevent the URA from seating correctly
What are the advantages of 0.7mm wire compared to 0.5mm
0.7mm: more resistant to bending or breaking as it’s thicker.
What is roberts retractor used for and its properties?
- Retracting upper anterior teeth
- Made out of 0.5mm wire
- Active component wire is placed in metal tube to give it properties of 0.7mm wire
Why aren’t adams clasps used for anterior teeth?
- Central incisors need to be relatively upright
- Clasp is prone to breaking
- Can be uncomfortable for patients if incisors are proclined due to undercut
What are ball ended clasps?
- Ball clasp uses undercut provided by embrasure
- Care must be taken they don’t open up spaces if overactivated
- Simple to construct but does not allow the attachments of auxiliary components
What are southend clasps?
- Passes around the gingival margin of central incisors
- Easy to construct and well tolerated
- Preferred anterior clasp (if don’t want to use labial bow)
What is anchorage?
Resistance to reactionary forces generated by the active components of an appliance.
Why is the following appliance low anchorage?
Small tooth with small root. When placing force on lat incisor to move palatally, reactionary force isn’t very large. Anchorage requirement low.
Why is this appliance medium anchorage demand?
When retracting canines, greater anchorage is required. Force of retracting canines palatally, will push whole appliance labially. Molars and premolars are resisting this appliance movement (anchorage)
How can anchorage be increased?
- Using more anchorage teeth
- Elastic band
- Headgear
What are 3 functions of baseplates?
- Supports other components
- Large anchorage contributor
- May be built up into bite planes to disengage occlusion to facilitate certain tooth movements
What are requirements of baseplates?
- Thick enough to carry active and retentive components
- Should cover most of hard palate & finish just distal to 1st molars
- Fit closely around necks of teeth not being moved (prevent food packing and gingival hypoplasia)
What is baseplate usually made from?
Cold cure acrylic
What are properties of cold cure acrylic?
- Cheaper
- Less time consuming
- Weaker than denture
How can you use a removable appliance to correct overjet and overbite?
Use anterior bite plane to correct overbite. Once overbite is reduced, you can grind away part of the bite plane and use labial bow to retract anterior teeth. Only favorable if you want tipping movement.
