6- Principles of Removable Appliances Flashcards
2 main types of appliances and when to use them
Another way of - Types of appliances
Removable appliances - Advantages + Distadvantages
Tooth movement with removable appliances- limitations
What movements are possible with removable appliances
Removable appliance design - 7 things a removable appliance should be:
4 components of removable appliances
- Active component
- Retention
- Anchorage
- Base plate
Active component - removable appliances
Definition
3 examples of active components:
Retention - removable appliances
Definition
Examples?
Adam’s clasp - main retention of posterior teeth
Southend clasp - retention for anterior teeth
Adam’s clasp
1 What is it + where is it used?
2 How is it constructed?
3 Explain 2 features
4 how can it be adjusted
5 Name 2 other teeth it can be used on for addition retention ?
1- major retention component
Adams clasp used on molars
2- Constructed in 0.7mm hard stainless steel wire
3 - Arrowheads engage in undercuts on mesiobuccal and distobuccal aspects of molar, but does not contact adjacent teeth
Clasp should fit model closely where embrasures are crossed to avoid damage by opposing teeth
4- using Adam’s pliers
5-
- premolars for addition retention
- deciduous molars
Southend clasp
1 Used for?
2 Construction / made of
1 - Anterior retention - MAIN anterior retention
used for additional retention anteriorly
2- Construction - 0.7mm wire
Placed around gingival margins of upper central incisors
Fitted labial row
1 What is it
2 Construction
3 When is it effective
1- used for additional anterior retention
(Used less commonly than Southend clasp)
2- construction - 0.7mm wire
3- only effective if incisors are proclined
Goes from 2-2
Planning retention
When are Adam’s clasps needed?
When are additional clasps needed?
Anchorage
1 What is it and what needs to be considered?
2 Resistance to tooth movement is related to?(3)
3 3 types of anchorage
1-
Site from which the forces are applied
Newtons 3rd law - for every action there’s an equal and opposite reaction
How we resist unwanted tooth movement
2-
- surface area of roots (MAIN factor)
- type of tooth movement, teeth can be tipped more readily than moved bodily
- Intercuspation of teeth may contribute
Eg tooth with large SA eg molars provide good anchorage whereas lower incisor with small root SA will provide little anchorage
- Simple anchorage - using a large tooth as anchorage to move a small tooth
- Compound anchorage - using a group of teeth as anchorage - (used in removable appliances -baseplate connects teeth together)
- Reciprocal anchorage
Fixed appliances may use any of the 3 anchorage
Removable appliances mostly always use compound anchorage except for in bilateral expansion where reciprocal anchorage is used
Reciprocal anchorage - eg if midline diastema (equal and opposite directions)
Baseplate
1 material
Purpose: (5)
What is the simplest active component?
Spring
Springs
1 Explain what springs used for?
2 Construction/ Made from:
3 Ideal requirements of a spring are: (3)
- Commonest force component
- Construction - hard stainless steel wire
3 - Ideal requirements of a spring are:
• Continuous force
• Correct magnitude
• Exerted over full range of tooth movement
Spring Design
How do we know what force to apply/ Formula for spring design:
2 features we want for springs:
What is wire width for buccal or palatal springs?
To keep force low - need long length and thin wire
Can increase length by having a coil
Radius of wire as thin as possible:
- Palatal springs wire width = 0.5mm
- Buccal springs wire width 0.7mm
Spring design
1 What force do we use for a single rooted tooth? Why this force?
2 Deflection of spring for buccal and palatal and why (how much is it bent)
3 What is the rate of tooth movement? How often do springs need to be adjusted?
1- For single rooted tooth = 25g → 50g
• Smaller forces → insufficient for adequate rate of tooth movement
• Larger forces → delay tooth movement and cause discomfort
2-
• palatal springs activate 3mms
• buccal springs activate 1mm
• if less → insufficient force
• if more → difficult to insert spring correctly
3- Rate of tooth movement = 1 to 2mms per month - need to adjust springs once a month
Types of springs (5)
Z spring and T springs are the main 2 used in removable
Palatal Finger Spring
1- Uses
2- Construction
3- Explain 2 design features
4- How do we activate it?
1- To move teeth in line of arch
2- Construction - 0·5mm wire
3- Design
- coil to increase wire length and positioned to unwind as tooth moves
- protect spring from damage by guard
4- Adjustment - activate 3mms at junction of coil and free arm
- check correct direction of movement
Tips tooth mesially or distally - if want tooth to move distal then place at mesial aspect of tooth and vice versa
Retracting canines
Is tipping (from removable appliance) or bodily tooth movement (from fixed) needed?
Bodily retraction by fixed appliances needed to prevent gross tilting
General rule -> if extracting to relieve crowding, a fixed appliance needed to bodily retract canines (or premolars)
Z spring
1 Uses
2 Construction
3 Position
1 - Proclination of incisors
2- Construction - 0·5mm wire
3 - Position - perpendicular to palatal surface of tooth
4- Adjustment - at each limb
(Does this mean limbs are bent?)
It is in Z shape
To activate need to open each coil - moves tooth by tilting or tipping action
Explain what you can see
Top left - Anterior cross bite. Upper incisor biting inside lower incisor
Want to correct in early mixed dentition
Solution = as not many dentition, good to use removable appliance
Z springs on upper incisors - can see in top right image these have been activated- will procline incisors forward
Need good rentetion - so Adam’s clasps on 6s and Ds or if 4 was present
Prop open bite with postierior capping so have clearance to push incisor over the bite
2 common uses of Z spring
- Correcting Anterior cross bite - can procline the upper incisors - central or laterals
- Can be used for in standing upper canine / upper central or lateral incisors
Explain what you can see
Instanding upper canine
Z springs
Adam’s clasps on 6,4,4,6
Posterior capping to prop open the occlusion - otherwise occlusal interference
T spring
1- Uses
2- Construction
3- Adjustment
4- Disadvantages
1- move premolars buccally
(correcting an instanding premolar - with premolar cant fit Z spring )
2- 0·5mm wire
3- pull spring away from baseplate
4- vertical displacing effect therefore need good retention
(Ideally Adam’s clasps on 6s or 4s or Southend clasp - need 2 lots of retention)
(Normally would also use posterior capping)
Coffin spring
1- Uses
2- Construction
3- Adjustment
4- Advantages
Rarely used
1- transverse upper arch expansion
2- heavy wire 1.25mm
3- pull laterally
4- differential expansion
Buccal canine retractor
1- Uses
2- Construction
3- Adjustement
4- Disadvantages
Rarely used
1- Retraction of buccally placed canine by tilting/tipping (but usually need bodily retraction using fixed appliance)
2- 0·7mm wire
3- Activate 1mm
4-
• may be uncomfortable
• difficult to adjust
• less flexible than finger spring
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Bows
1- Bows can either be:
2- What are flexible or less flexible bows used for?
3- Name 2 types of bows we use:
1- Bows are either:
1. Passive - used on retainers
2. Active - used to retract incisors
2-
Flexible bows = used to reduce moderate overjet
Less flexible bows = used to reduce a small overjet or irregularities
3-
1. Robert’s retractor
2. Labial bow (with U loops)
Retracting incisors / Trying to reduce an overjet
Which of below would you use tipping and which bodily movement ?
Need to consider if possible using tipping movement with removable appliance OR bodily tooth movement needed with fixed appliance- decide by:
- inclination of incisors
- size of overjet
How proclined are incisors
If incisors are fairly proclined and overjet is relatively modest may be able to tip teeth back BUT if incisors are only slightly proclined and large overjet then would end with very retroclined incisors so not suitable
TOP- very proclined incisors and moderate overjet so may be able to use tipping to reduce overjet
BOTTOM - very large overjet and incisors not very proclined - if we tipped these incisors back to reduce overjet they would be pointing backwards so need fixed appliance - bodily movement
Can you reduce this overjet using a removable appliance:
Yes
Modest overjet
Very proclined and spaced incisors - only need to tilt teeth back and gather up space to reduce the overjet
Overall very few cases where we can reduce overjet using removable appliances
Robert’s retractor
1 what is it?
2 Construction
3 Adjustment
1- Flexible bow
2- 0·5mm wire with buccal arms sheathed in tubing to provide strength
3-
- 3mms activation
- the bow should lie half way up the incisor crowns
- base plate is cut away palatally in advance of tooth movement
Robert’s retractor
Advantages (4)
Disadvantages (2)typ
Type of bow we would use to reduce an overjet
Labial bow (with U loops)
1- what is it
2- construction
3- adjustment
1- less flexible bow
2- 0.7mm wire
3- 1mm activation by closing U loops
Labial bow (with U loops)
Advantages - 2
Disadvantages - 2
Hawley retainer - has Adam’s clasps on 6s in 0.7mm wire, and labial bow with u loops from 3-3
Most common use - passively in hawley retainer
Screw type appliance design
1 Uses
2 Force - provided by?
3 adjustment
4 disadvantages - 3
1 for movement of individual or groups of teeth
2 - Active force is provided by screw
• Large intermittent force (not continuous)
• but activation only small (0.2mm)
3 - 1 to 2 turns per week gives rate of tooth movement 1 to 2 mm per month
4-
• expensive, bulky, need patient co- operation
(LARGE FORCE UNLIKE springs and bows)
Screw type appliance design - Clinical indications
What is Midline screw plate used for?
- expansion of upper buccal segments - (where narrow upper arch, will expand)
Screw type appliance design - Clinical indications
What is sectional screw plate used for?
Eg want to expand one side only out eg unilateral cross bite
Screw type appliance design - Clinical indications
When is screw placed in mesial distal direction?
If we want to move a molar tooth distally - place screw in mesial distal direction
Screw type appliance design - Clinical indications
Can it fix anterior crossbite
If we want to move all four incisors forward eg to correct anterior cross bite
Screw type appliance design - Clinical indications
- expansion of upper buccal segments
- buccal movement of individual segment
- buccal movement of individual tooth
- Distal movement of molar tooth
- labial movement of upper incisors (if wanted to move all 4)
How often are patients expected to wear removable appliances ?
Warn patients of
1-
- All the time
- Should taken out for cleaning - morning and night and after each meal , and contact sports
- Can keep in whilst eating
2- saliva pooling because something new in mouth - willl stop soon
Upper appliance may affect speech - will resume normal speech after
If problems occurs should return
Contraindications of removable appliances
- epilepsy
- recurrent fits
As both can obstruct airway
Would opt for fixed appliances
Removable appliances
Only able to
Should be limited to
Most commonly used for
Also common,y used for
