Retention of a removable appliance

Question 1

What are the retentive components of a removable appliance?

Answer 1

• Adams clasp - 0.7ss wire (Post)
– may be made of 0.6 on premolars
• Southend Clasp - 0.7ss wire (Ant, very effective)
• Labial Bow (Reversed loop)-0.8mm (Ant, not as effective)

Question 2

What are the components of an Adams clasp?

Answer 2

1. A bridge
2. Two arrowheads (gain retention by engaging undercut)
3. Two flyovers
4. Two tags

Question 3

What are the four functions of the labial bow?

Answer 3

– Retention, holding the appliance up
anteriorly
– Guidance of canines during retraction
– Active, retracting the incisors
– Retention, holding the corrected teeth in
their new positions
(note the two meanings of the word “retention”)

Question 4

What are the four elements of a removable appliance?

Answer 4

• Active components (springs, bows, screws) should always be constructed first
• Retentive components
• Baseplate
• Anchorage

Question 5

How is tooth movement achieved?

Answer 5

1. Teeth move at right angles to point
of contact of the spring
2. Where the line of force does not
pass through the centre of
resistance the tooth will rotate

Question 6

What thickness of wire should be used for a labial bow?

Answer 6

• For retention we need:
– Stiff (thick)wire
• For guiding a canine we need:
– Stiff (thick) wire
• For retracting incisors we need:
– Flexible wire (splitting the bow makes it much more flexible and can be made stiffer again by soldering the ends together)
• For retaining tooth positions we need:
– Thick (stiff) wire

Question 7

What does a removable appliance do?

Answer 7

Tips teeth (only fixed appliances can bodily move teeth)

Question 8

What are the problems with removable appliances in the lower arch?

Answer 8

Less undercut for retention
 Less buccal sulcus for springs
 Tongue severely limits lingual space
for springs

Question 9

What are removable appliances currently used for?

Answer 9

 Space maintenance
 Retainers
 Tooth over the bite
 Bite opening
 Expansion
 Other simple tooth movements
 (Functional appliances)

Question 10

What can retainers be?

Answer 10

Either removable appliances or fixed to the teeth

Question 11

What are the pros of removable retainers?

Answer 11

 ALL the teeth can be retained
 Partial withdrawal possible
 Less dental health hazard
 Oral hygiene
 Responsibility of the patient

Question 12

What are the cons of removable retainers?

Answer 12

 Rotations
 Anterior diastemas
 Vertical tooth position
 Need to be worn
 Tipping
 Lower arch
 Inter-arch elastics
 Precision
 Multiple tooth movements

Question 13

What are the advantages of the acrylic baseplate?

Answer 13

 Can provide anterior and posterior
biteplanes
 Can accommodate a screw
 Give some anchorage from the palate

Question 14

What are the screws used for?

Answer 14

 Unilateral or bilateral distal
movement
 Arch expansion
Anterior crossbite correction

Question 15

How to tell if they’re wearing the appliance?

Answer 15

 Good speech
 Palatal gingivitis
 Wear facets on acrylic
 Springs passive
 Teeth have moved
 Confident removal and insertion