Removable Appliance

Question 1

What is the two most important factors to consider in designing a removable appliacne?

Answer 1

Whether the apex is in the right position: if not then tipping tooth will result in unstable position

When tipping tooth it’s occlusion will be modified–>will usually end up in supraocclusion unless some sort of intrusive force is applied

Question 2

T/F removable appliances are good at retruding teeth

Answer 2

F

Question 3

What are some types of removable appliaces? What are examples?

Answer 3

Passive: Maintain teeth in place (space maintainers, orthodontic retainers)

Active: appliances that use springs, expansion screws

Functional: Attempt to alter masticatory function by modifying growth to patient’s best interest (e.g. attempting to promote growth of mandible for class II case)

Question 4

What can happen if an appliance is too complex?

Answer 4

• Poorer OH
• More difficult management
• Less patient compliance
• More frequent complications such as breakages
• Undesirable result
• Loss of anchorage

Question 5

What are the 3 main rules in designing an appliance?

Answer 5

Retention, Accuracy of fit (comfort), Activation (don’t overactivate–>greater dislodging, discomfort, poor tooth movemetn due to necrosis caused by blockage of blood supply, pain, loss of anchorage)

Question 6

How much force is required to move a tooth?

Answer 6

25grams (roughly the force of capillary blood flow)

Question 7

What are the components of a removable appliance?

Answer 7

Retentive (Adam’s Crib)

Active component: apply appropriate force at appropriate spot in appropriate direction

Connectors: parts that join the active and retentive components together (can be wire or acrylic base)

Passive remind components: (some incorporte extra bits of wire ridges to remind patient not to suck thumb or stick tongue up, keeping soft tissues retracted so they don’t inteferfere with occlusion)

Passive bite planes (free the occlusion for things like allowing teeth to move out of cross bite or to allow teeth to erupt)–>note that if using for the latter reason (e.g. anterior bite block to allow posteriors to erupt)–> will leave a space in anterior region and deep bite may come back–>need fixed appliances or to trim appliance

Passive gaurd: protects spring

Question 8

What are the uses of thick wires and thin wires?

Answer 8

• Thin: moving teeth (less than 0.5mm diameter)

- Thick: holding teeth (apply too much pressure to move)

Question 9

What types of springs are tehre?

Answer 9

• Finger springs: move teeth in an arc (single loop spring/basic spring you were taught originally)
• Apron springs: tip incisors backwards or forwards (imagine a u-shape paper clip pushing on incisors)–>not often used as not the best way
• Coffin spring (u shaped): =tip molars bucally
• Quadhelix (full coil)=tip molars bucally, but wire is thick (0.9mm) so risk of applying excessive force
• Double helical spring: procline teeth (s shape pushes on them),
• T spring: moves a tooth in a specific direction
• Robert Retractor: retracts anterior teeth

Question 10

What effect does increasing the length of a wire have?

Answer 10

Increased flexibility, easier insertion

Question 11

What are the two most important aspects for the acrylic base?

Answer 11

• Smooth

- Well fitting

Question 12

What extra role does the acrylic base play in addition to retention?

Answer 12

-Reciprocating the retentive component (hence requires butt joint with tooth as apposed to feather edge)

Question 13

T/F ortho appliances need a palatal seal?

Answer 13

F

Question 14

T/F ortho appliances extend to soft palate?

Answer 14

F: stay away from there because kids don’t like

Question 15

What are the components of an adam’s crib?

Answer 15

• Arrow head (Retentive component)
• Bridge (Matches length of tooth and makes arrow head engage appropriate areas)–>position of arrow head
• Tag: Run across embrasure to lock into acrylic base and determine arrowhead angulation

Question 16

What angle should the bridge have relative to the tooth?

Answer 16

-Parallel to occlusal and buccal

Question 17

What angle should the arrowhead have vs long axis of tooth?

Answer 17

45 degrees

Question 18

What rule governs tag position other than runnign across the embrasures?

Answer 18

-Should not touch palate or soft tissues

Question 19

How thick should an adam’s crib be?

Answer 19

0. 7mm for posterior

0. 6mm for anterior

Question 20

What can you do to create undercuts?

Answer 20

• Burs on deciduous teeth

- Acid etch and build composite to provide point of engagement

Question 21

What are the key points on the stress strain curve?

Answer 21

Proprtional limit: Point at which wire deforms permanently

Yield point: Point after proportional limit where wire bends permanently

Range: How far a tooth can be moved (is the x-value for the proportional limit)–>makes sense as the maximum strain you can put on the wire before it deforms is equal to the strain it will put on the tooth, and if you go past the proportional limit the wire will deform permanantly rather than trying to revert to its original shape thus no longer putting force on tooth

Fracture point: point at which wire breaks

Area beneath the graph up to the proportional limit: defines the resiliency of the wire (ability to store energy)

Question 22

What is the formula governing the deflection of the wire?

Answer 22

D directly proportional ((L^3)F)/(E(d)^4)

Where D = defelction of wire
L= length of wire
F=force needed for deflection
E= Young's modulus
d= wire diameter

Question 23

What can happen if you try to move more than 1-2 teeth at at ime with a removable appliance?

Answer 23

• Loss of anchorage
• Unfavorable movement
• Decreased pt compliance
• Increased breakage + cost

Question 24

Does putting more coils lighten or increase the force?

Answer 24

Lighten–>as length of wire increased

Question 25

T/F finger springs used in retraction face the opposite way to normal? Why?

Answer 25

• True

- Avoid impinging on gingiva

Question 26

What is the issue with using rubber bands to retract teeth?

Answer 26

• Apply significant amount of force + can’t be controlled

- Too much force may been anterior teeth don’t retract and retainer comes forward instead