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Orthodontics > removable appliances > Flashcards

removable appliances Flashcards

1
Q

How do RA work?

A

Tip teeth
Move blocks of teeth
influence eruption of opposing teeth

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2
Q

Why do RA only tip teeth?

A

Because they have only a single point of contact and applies a force which tilits a tooth about its fulcrum

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3
Q

Why can removable appliances move blocks of teeth?

A

because they are connected via a baseplate so more efficient than fixed appliances

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4
Q

How can RA affect the eruption of opposing teeth?

A

Flat anterior guide plane

Buccal capping

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5
Q

When is a flat anterior guide plane useful?

A

overbite reduction

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6
Q

When is buccal capping useful?

A

intruding posterior teeth

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7
Q

What are the problems arising from just tipping teeth?

A

aesthetics

occlusal fit

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8
Q

What are the advantages of removable appliances?

A 
removed for tooth brushing
palatal coverage increases area for anchorage
less risk of iatrogenic damage
used as a passive retainer
transmits forces to blocks ofteeth
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9
Q

What are the disadvantages of removable appliances?

A 
appliance can be left out
only tiliting movements possible
affects speech
intermaxiliiary traction not possible
lower appliances less tolerable
inefficient for mutliple tooth movements
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10
Q

Why are RA less succesful in the lower arch?

A

less tolerated as appliance encroaches on the tongue space
Less space
Less retention due to less undercut
Less sulcus depth for buccal springs

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11
Q

T/F RA can perform vertical movements?

A

F

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12
Q

T/F the movements of teeth in RA are less precise?

A

T

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13
Q

T/F RA cannot derotate a tooth?

A

T

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14
Q

When are RA most commonly used now?

A 
Space maintainence
retainer
tooth over the bite
bite opening
arch expansion
functional appliances
simple tooth movements
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15
Q

What are the advantages of an acrylic baseplate?

A

Can provide an anterior and posterior bite plane
accomadate a screw
gives anchorage from palatal vault

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16
Q

How can you be sure the patient is wearing the removable appliance?

A 
speech has improved
confident in removing and replacing
wear facets
has become loose/passive
gingivitis on palate
teeth have moved
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17
Q

What are the components of RA?

A

Active components
retentive components
base plate
anchorage

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18
Q

Which component should be designed first?

A

Active

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19
Q

When should extraction be done, before or after the RA is fitted? and why?

A

after (as a general rule)
because patient may decide once RA fitted that they do not want to continue with the treatment
AND
if there is a delay in time between extracting the tooth and fitting the RA the the space will close

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20
Q

What is the most commonly used active component?

A

spring

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21
Q

What is the relationship between F and othodontic springs?

A 
F proportional to dr^4/l^3
and elastic modulus 
d is deflection
r is radius
l is length
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22
Q

What are example of active components on removable appliances?

A

springs
bows
screws

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23
Q

WHat are the three types of springs used as buccally?

A

self supporting
sleeved
reversed loop

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24
Q

What is the type of spring used as a palatal springs?

A

palatal spring

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25
Q

What is the diameter of the wire used in the self supporting retractor and how mich do dou you activate it by?

A

0.7mm

activate 1mm

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26
Q

What are the advantages of the self supporting retractor?

A

still

good control of spring positions

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27
Q

What are the disadvantages of the self supporting retractor?

A

stiff so provides a high force

high in sulcus so damages mucosa

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28
Q

WHat are the advanatges of the sleeved buccal retractor?

A

flexible and good control

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29
Q

What are the disadvanatages of the sleeved buccal retractor?

A

high in sulcus so can traumatise mucosa

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30
Q

How thick is the sleved buccal retractor and by how much do you activate it?

A

0.5mm ss wire

2mm activation

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31
Q

What are the advanatges of the reverse loop buccal retractor?

A

it is short vertically so less traumatic

good lateral control of spring position

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32
Q

What are the disadvanatges of the reverse loop buccal retractor?

A

it is stiff

short range of action

33
Q

How thick is the wire in the reverse loop buccal retractor and how much do you activate it by?

A

0.7mm

activated by 1mm

34
Q

Which springs push teeth labially?

A

z springs

35
Q

Which springs push teeth buccally?

A

t springs

36
Q

How thick is the wire on the z springs?

A
  1. 5/0.6/0.7

0. 5mm used for single tooth

37
Q

How much do you activate z springs by?

A

single tooth: 1-2mm

double tooth: 3-4mm

38
Q

WHat are the disadvanatges to Z springs?

A

displaces the appliance so need good retention

39
Q

WHat are the advanatges of z springs?

A

easy to adjust

vary degree of activation depending upon the amount of teeth needing to move

40
Q

How do you activate z springs?

A

activate by turning 45 degrees in direction of movement

41
Q

When are T srprings needed?

A

buccal segment teth

42
Q

What are the advanatges of T springs?

A

easy to adjust

43
Q

What are the disadvanatges of T springs?

A

displaces the appliance so need good retention

Limited range of action

44
Q

What is so special about screws?

A

only means in a RA that can the tooth being retained can also be moved

45
Q

WHen are screws used?

A

mesio-distal movement
expansion
correcting x bite

46
Q

How do you activate T springs?

A

by pulling away from he acylic

47
Q

How do you activate a screw?

A

turn 0.25mm/week

48
Q

Why can you only activate a screw by 0.25mm?

A

this is dependant upon the space of the pdl

if you were to exceeed this, you would crush the pdl and this would cause cessation of movement

49
Q

What feature is designed after active components?

A

retention

50
Q

WHat is retention?

A

the resistance to movement away from tissues

51
Q

How do we retain on posterior teeth?

A

adams clasp

52
Q

How do we retain on anterior teeth?

A

Southend clasp (BEST RETENTION)
Labial bow
Adams clasp

53
Q

WHat is the size of the wire used on adams clasps?

A
  1. 7mm ss wire

0. 6mm ss wrire can be used on premolars too

54
Q

What is the size of wire used on southend clasp?

A

0.7mm ss wire

55
Q

What is the size of wire used on a labial bow?

A

0.8mm ss wire

56
Q

What are the components of an adams clasp?

A

a bridge
two arrowheads
two flyovers
two tags

57
Q

How do adams clasps gain retention?

A

by engaging into the undercut beneath the maximum bulbosity of the tooth

58
Q

What are the advantages of using adams cribs?

A

E/O traction tubes can be soldered onto them

Double cribs can be used to straddle two teeth

59
Q

WHat is the purpose of a labial bow?

A

retention
guidance (canines during retraction)
Active (retract incisors)
retention

60
Q

where should the labial bow be placed on the crown?

A

near the gingival sulcus to engage in some undercut

61
Q

How can labial bows be used for incisor retraction?

A

split the labial bow

and then re solder once teeth moved

62
Q

By which direction do teeth move relative to point of contact of spring?

A

90 degrees to point of contact

63
Q

Where must the line of force pass through to avoid rotation of the tooth?

A

must pass through the centre of resistance

64
Q

When using labial bows as active components, do we need a thin or thick wire?

A

thin

so it is more flexible

65
Q

When is buccal capping used in remoable appliances?

A

occlusal interferences need to be removed to allow tooth movement and where a reduction in the overbite is undesirable

66
Q

WHat is the name of the appliance used in conjusvtion with head gear?

A

Nudger appliance

67
Q

When would you use a nudger appliance?

A

when you want distal movement of posteror teeth and then move on to fixed appliances

68
Q

What are the ideal requirements of a spring?

A 
apply the correct force over a good range
move the tooth in the right direction
difficult to position incorrectly
recistant to accidental damage
atraumatic
hygeinic
69
Q

what is the stress of wire?

A

F/unit area

70
Q

What is the strain of the wire?

A

deflection/unit length

71
Q

What is the modulus?

A

stress/strain

72
Q

if you double the length of the wire what happens to the stiffness?

A

it decreases by a factor of 8

73
Q

What happens if you double the radius of the wire?

A

the stiffness increases by a factor of 16

74
Q

What happens to the force upon activation of the wire?

A

double the activation doubles the force

75
Q

What is the size wire used for the palatal retractor?

A

0.5mm

ss

76
Q

How much force is created with a 3mm activation on the palatal spring?

A

20-40g

77
Q

what happens if you activate the palatal spring more then 3mm what happes?

A

it may self insert on the wrong side

applies too much force

78
Q

When can you use palatal springs?

A

for mesiodstal movement of canines premolars and moalrs

79
Q

What are the forces used to tip teeth?

A

25-50gms

Orthodontics (28 decks)

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