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RPD > Direct Retainers > Flashcards

Direct Retainers Flashcards

1
Q

What is primary retention?

A

Mechanical from retaining elements on abutment teeth

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2
Q

What is secondary retention?

A

– Intimate contact of minor connector with guide planes
– Intimate contact of denture base & maxillary major connector with underlying tissues

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3
Q

What is a direct retainer?

A

RPD component used to retain and prevent dislodgement

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4
Q

What are the two clasp types?

A
  • suprabulge
  • infrabulge
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5
Q

What is a suprabulge clasp?

A

Retentive arm approaches undercut from above the survey line

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6
Q

What is the infrabulge clasp?

A

Retentive arm approaches undercut from below survey line

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7
Q

What are synonyms for suprabulge clasps?

A

Circumferential, Akers, Circlet

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8
Q

What is another name for an infrabulge clasp?

A

bar clasps

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9
Q

A properly constructed suprabulge or infrabulge clasp assembly must incorporate the following components:

A
  • a rest
  • a retentive clasp
  • a reciprocal element
  • one or more minor connectors
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10
Q
A
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11
Q
A
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12
Q

What is the rest component of the clasp?

A

lies on occlusal, lingual, incisal surface

– Prevent tissueward movement of clasp

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13
Q

What is the reciprocal component of the clasp?

A

– Rigid component
– Above height of contour

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14
Q

What are the different parts of the reciprocal component?

A

Reciprocal clasp, Lingual plate, Proximal plate, Guide plate

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15
Q

On what part of the tooth is the retentive clasp arm?

A

proximal 2/3
- rigid part, above the height of contour

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16
Q

On what part of the tooth is the retentive terminal?

A

distal 1/3
- flexible, below the height of contour

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17
Q

What provides direct retention: the retentive clasp arm or the retentive terminal?

A

retentive terminal

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18
Q

What is the minor connector?

A
  • Joins body of clasp to framework
  • Rigid
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19
Q

What is the approach arm?

A
  • Component of bar clasp
  • Connects clasp to framework
  • Flexible minor connector
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20
Q

Minor connectors are usually rigid. What part of the clasp is an exeption to this rule?

A

approach arm
- is flexible rather than rigid

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21
Q

What are the requirements of clasp assembly?

A
  • support
  • stability
  • encirclement of more than 180 degrees
  • reciprocation
  • passivity
  • retention
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22
Q

Why does the clasp need to encircle more than 180 degrees?

A

Prevents tooth from moving away from the clasp

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23
Q

How many points do you need for a clasp asembly?

A

minimum of 3

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24
Q

Does the clasp encirclement of 180 degrees need to be continous?

A

– May be continuous or broken

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25
Q

What allows for the clasp to have stability?

A

– Areas above the survey line

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26
Q

What is reciprocation of the clasp?

A

– Resist retentive tip lateral forces
– Requires parallel surface to path of insertion

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27
Q

___________ component contact tooth at same time or sooner than retentive clasp

A

Reciprocal

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28
Q

What is passivity of the clasp?

A

– Components of direct retainer exert no force when fully seated

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29
Q

Where on the tooth does the clasp allow for retention?

A

Area below survey line: ideally in gingival 1/3

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30
Q

Retention portion of tooth must be ___________ in relation to path of prosthesis insertion

A

undercut

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31
Q

What determines the amoutn of retention?

A
  • Angle of convergence of the undercut
  • Depth of undercut
  • Flexibility of the retentive clasp
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32
Q

Retentive clasps should become active ONLY when…

A

disclosing forces are applied to them

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33
Q

The ability of the retentive clasp to provide retention is based on…

A

the resistance of the metal to deformation

34
Q

What are the flexibility factors for the retentive clasp?

A
  • length
  • diameter
  • taper
  • cross-sectional form
  • material
35
Q

How is flexibility related to length of the retentive clasp?

A

Flexibility = length^3

  • Double length, 8x more flexible
36
Q

How is diameter related to flexibility of the retentive clasp?

A

Flexibility = 1/diameter^3

  • Double diameter, 8x LESS flexible
37
Q

The clasp terminal needs to taper in how many dimensions?

A

2
– Clasp terminal ½ as thick as origin
* 1mm to 0.5 mm
– Clasp terminal ½ as wide as origin
* ~2mm to 1mm

38
Q

How thick and how wide shoudl the clasp terminal be compared to the origin?

A

– Clasp terminal ½ as thick as origin
* 1mm to 0.5 mm
– Clasp terminal ½ as wide as origin
* ~2mm to 1mm

39
Q

Round clasp _______ flexible than half-round

A

more

40
Q

Round clasp flexes in _____ planes
Half-round flexes in ____ planes

A
  • Round flexes in all spatial planes
  • Half-round flexes in one plane
41
Q

Half-round clasps are almost always…

A

circumferential clasps

42
Q

Half-round clasps flexes in how many directions?

A

1

43
Q

Round clasps are usually…

A

wrought wire clasps

44
Q

Round clasps flex in how many directions?

A

omnidirectionally
‣ Provides maximum flexibility

45
Q

Cast chromium alloys are ______ flexible than cast gold alloys

A

less

46
Q

Wrought alloys ______ flexible than cast alloy

A

more

47
Q

With increasing clasp flexibility, must use _______ undercut to obtain equal retention

A

deeper

48
Q

What are the undercuts for the differently alloys?

A
  • 0.010”: Cast Chrome alloy
  • 0.015”: Cast Gold alloy
  • 0.020”: Wrought wire
49
Q

What alloy is used in casting the framework?

A

‣ Usually Ticonium (NiCr) or Vitallium (CoCr)
‣ Easy to fabricate

50
Q

How do you produce a wrought wire clasp?

A

Produce by drawing metal through dies of smaller diameter

51
Q

What is the most flexible of all clasps?

A

wrought wire

52
Q

What are the different options for clasp material?

A

wrought wire
- also stainless steel and type IV gold

53
Q

The design of a retentive clasp arm should incorporate maximum clasp length for…

A

optimal flexibility

54
Q

What is a circumferential clasp?

A

– Approaches undercut from above the survey line
– “Pulls” toward occlusal to resist displacement

55
Q

What is the bar clasp?

A

– Approaches undercut from below survey line
– “Pushes” toward occlusal to resist displacement

56
Q

Which clasp is easier to seat but more difficult to remove?

A

bar clasp

57
Q

Should the reciprocal clasp be rigid or flexible?

A

rigid
- not tapered

58
Q

What is the definition of reciprocation?

A

the means by which one part of the framework opposes the action of the retainer in function

59
Q

Reciprocation may be achieved by…

A
  • Rigid plating (LINGUAL PLATE)
  • Minor connectors
  • Guide planes extended around the vertical line of abutments
  • Reciprocal clasp arms
  • Contact areas of proximal teeth
60
Q

What is the most logical clasp for tooth-supported RPD (kennedy class III)?

A

Circumferential Clasps

61
Q

What are the advantages of the circumferential clasps?

A

– Excellent stabilization, support, bracing
– Easiest to design & construct
– Easier to repair

62
Q

What are the disadvantages of the circumferential clasps?

A

– Covers more tooth surface: more conducive to caries by more plaque retention
– Increases tooth circumference/greater occlusal force exerted on tooth
– More difficult to adjust

63
Q

What is the ideal configuration of the circumferential clasp?

A
  • Clasp kept as low on crown as survey line permits
  • Retentive clasp
  • Reciprocal clasp
64
Q

Why should a circumferentail clasp be kept as low as the survey line permits?

A

– Less torquing action on tooth
– Less interference with occlusion

65
Q

If survey line is too high for a circumferential clasp…

A

enamel surface must be recontoured to lower the survey line

66
Q

If survey line is too low for a circumferential clasp…

A

surveyed crown required

67
Q

What is the ideal configuration of the retentive clasp for the circumferential clasp?

A

– Cast ½ Round
– Proximal 2/3 (above survey line)
– Terminal retentive 1/3 (below survey line)
– Tapers from origin (2.0mm)
to tip (1.0 mm)

68
Q

What is the ideal configuration of the reciprocal clasp for the circumferential clasp?

A

– Cast ½ round
– Entire clasp in middle 1/3
– Above the survey line
– No taper: Uniform width 1.5 – 2.0 mm

69
Q

What are the different types of circumferential clasps?

A
  1. Circlet
  2. Embrasure clasp
  3. Ring clasp
  4. Combination Clasp
70
Q

What is the best type of circumferential clasp for class III RPD?

A

circlet

71
Q

What is an embrasure clasp?

A

2 circlet clasps joined at body

72
Q

When do you use an embrasure type circumferential clasp?

A
  • Used when retainer is necessary in a dentate area

– Class III with no modification space
– Class II with no modification space
– Class IV

73
Q
A
74
Q

When should you use a ring type circumferential clasp?

A

Mesiolingually-tipped mandibular
molars Class III RPD

75
Q

What does a ring type circumferential clasp need?

A

Additional occlusal rest: support, prevent further mesial movement
* Incorrect Ring clasp: No reciprocation, No support

76
Q

When should you use a reverse circlet type circumferential clasp?

A

Retentive undercut adjacent to edentulous space
– Class III RPD
– Tooth-tissue supported RPD (Class I or II distal extension)
– ½ T bar clasp preferred, if no tissue undercut at approach arm

77
Q

What two types of circumferential clasps should you avoid if possible?

A
  • ring clasp
  • reverse circlet clasp
78
Q

What is a combination type circumferential clasp?

A
  • Wrought round wire retentive clasp
  • Cast ½ round reciprocal clasp
79
Q

When should you use a combination type circumferential clasp?

A

Distal extension RPD (Class I & II)
– Mesial rest not possible, distal rest must be used
– Mesiofacial undercut

80
Q

What is the RPC class assembly (RPA)?

A

Rest (mesial), Proximal Plate, Circumferential (Akers) clasp

81
Q

When should you use the RPC class assembly (RPA)?

A

– Class I, II RPDs
– Mesiofacial retentive undercut

82
Q

The circumferential retentive clasp in the RPC class assembly (RPA) should be…

A

– Cast ½ round (ALWAYS)
– except in periodontally compromised teeth and Kennedy I w/o modification (use cast round for these)

RPD (13 decks)

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