Removable appliances Flashcards
What type of movement is achieved by removable appliances?
Tipping movement only.
Single force applied to crown of tooth.
How much force is required for tipping?
30-60gm
How much force is required for bodily movement?
100-150gm
How much force is required for rotation?
50-75gm
How much force is required for extrusion?
50-75gm
How much force is required for intrusion?
15-25gm
Why are springs used?
Used to move teeth that are not being used for retention.
Spring needs to be correctly positioned on the tooth by the patient each time they insert the URA.
Why are bows used?
Usually used for retention but can be modified for movement of anterior teeth.
Describe the active labial bow.
Used to tip the teeth palatally to reduce an increased overjet, only if the labial segment is proclined and spaced.
Activated by bending the vertical arms of the bow towards the palate and trimming the acrylic behind the upper incisors to allow palatal movement.
What 3 springs are used in URAs?
Z-spring
T-spring
Palatal finger spring
Describe the Z-spring.
- 0.5mm stainless steel
- Used to move 1 or 2 teeth labially
- Activated by pulling the spring away from the baseplate at a 45 degree angle
- Activation will tend displace the appliance away from palate therefore good anterior retention is important
Describe the T-spring.
- 0.5mm stainless steel
- Used to move individual teeth labially or bucally
- Activation produced by pulling spring away from baseplate, retention must be good
Describe the palatal finger spring.
- 0.5mm stainless steel
- Moves teeth mesially or distaly along the dental arch
- Incorporated helix increases length of the wire and allows delivery of lighter forces
- Guard wire protects spring from distortion
- Helix is placed such that activation of the spring is achieved as it is tightened and it unwinds as tooth movment occurs
How many clasps are needed for an URA?
- Minimum: 2 posterior and 1 anterior clasp, prevents fulcrum developing
- 4 posterior clasps if pt worried about aesthetics
- Clasps can also serve as anchorage (resistance to forces generated in reaction to active components of the appliance)
What clasp types are used posteriorly?
- Adam’s clasp
- Plint clasp
Describe the Adam’s clasp.
- 0.7mm stainless steel molars
- 0.6mm stainless steel premolars
- Most commonly placed on 1st permanent molars
- Arrowheads engage undercuts at mesial and distal corners of tooth
- Easily adjusted chairside
Describe the Plint clasp.
- Useful when using a removable appliance in combination with a fixed appliance
- 0.7mm stainless steel, engaged undercuts on maxillary band
Describe the Southend clasp.
- 0.7mm stainless steel
-Activated by bending U-loop towards the baseplate, engages clasp into labial undercut of tooth
Describe the ball-ended clasp.
- Engages into interproximal undercuts between teeth
- Activated by bending the ball towards the contact point
Describe the FABP.
- Used to reduce an increased overbite in a growing pt
- Thick acrylic palatal to the upper incisors
- Lower incisors occlude on the FABP, overtime the posterior teeth erupt into occlusion (leveling the curve of spee)
- May also result in condylar growth
- All results in reduction of the overbite
How is an URA designed to correct a posterior crossbite?
- Acrylic covers occlusal surfacces of posterior teeth
- Adams clasps on molars and premolars (4 total)
- Midline expansion screw
- Props the incisors apart, allowing movement of incisors and facilitating correction of crossbite
What is this lab prescription for?
URA for reduction of overbite.
- No active component
- At least 3 clasps requied
- Describe acrylic colour, overjet and depth of FABP
What is this lab prescription for?
URA (posterior bite plane) for correction of anterior crossbite.
- Active component: spring or screw to procline the incisor in crossbite (this example shows a Z spring)
- At least 3 clasps or 4 posterior
- Acrylic colour, posterior capping (used to disclude incisor in crossbite which therefore faciliates its proclination)
