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RPD > Direct Retainer part 2 > Flashcards

Direct Retainer part 2 Flashcards

1
Q

Where is the retentive arm on a suprabulge clasp?

A

Retentive arm approaches undercut from above the survey line

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2
Q

What are other names for the suprabulge clasp?

A

Circumferential, Akers, Circlet

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3
Q

Where is the retentive arm on a infrabulge clasp?

A

Retentive arm approaches undercut from below survey line

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4
Q

What is another name for an infrabulge clasp?

A

Bar clasps

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5
Q

When do you use bar clasps?

A

– Distal extension RPD
– Tooth-supported RPD, esthetics factor

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6
Q

What are the most common types of bar clasps?

A
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7
Q

What are the advantages of bar clasps?

A

– More esthetic
– More flexible
– Less conducive to caries (less tooth coverage)
– Wider range of undercut adaptability
* MF, Mid-F (I-bar)
* DF ( ½ T-bar)

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8
Q

What are the disadvantages of the bar clasps?

A

– Less bracing
– Possible tissue impingement
– Food impaction
– More difficult to repair or replace

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9
Q

What are the rules for the approach arm of the bar clasp?

A

– Must not impinge on soft tissue
– Tapered (Flexible minor connector: exception to rule)
– Cross gingival margin at 90 degrees
– Extend onto abutment tooth to the height of contour
– Not positioned over soft tissue undercut: food trap, tissue irritation (important)

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10
Q

What are the tooth-tissue supported RPDs?

A

– Class I & II RPD, long-span Class IV

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11
Q

What are tooth-supported RPDs?

A

– Class III RPD, short-span Class IV

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12
Q

What are the different tooth-supported RPD clasps?

A
  • Circumferential (Circlet)
  • I-bar
  • ½ T-bar
  • Reverse Circlet (Hairpin)
  • Embrasure clasp
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13
Q

What is the most common tooth-supported RPD clasp?

A

Circumferential (Circlet)

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14
Q

What are the features of a circumferential clasp?

A

– Most common
– Retentive undercut remote from edentulous area
– Reciprocal clasp

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15
Q

What are the features of an I-bar clasp?

A

– Mesiofacial, Midfacial undercut
– Reciprocal clasp
– Tissue undercut prevents use

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16
Q

What are the features of a 1/2 T-bar?

A

– Retentive undercut adjacent to edentulous area
–Distal facial undercut
– Reciprocal clasp
– Tissue undercut prevents use

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17
Q
A
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18
Q

What are the featurs of the reverese circlet (hairpin) clasp? (prolly not on test)

A

– Retentive undercut adjacent
to edentulous area
–Used when tissue undercut present
* ½ T or I-bar cannot be used
- Excess tooth coverage, disadvantage

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19
Q

What are the features of the embrasure clasp?

A

– Used when retainer is necessary in a dentate area
–Used in Class IV & Class III arch with no modification space
– Also used in Class II tooth-tissue supported RPD, when no modification space exists

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20
Q

When would you use an embrasure clasp?

A

– Used in Class IV & Class III arch with no modification space
– Also used in Class II tooth-tissue supported RPD, when no modification space exists

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21
Q

What is a fulcrum line?

A

an imaginary line, connecting occlusal rests, around which a partial removable dental prosthesis tends to rotate under masticatory forces. The determinants for the fulcrum line are usually the cross arch occlusal rests located adjacent to the tissue borne components

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22
Q

Is there a fulcrum line on a tooth supported partial?

A

NO

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23
Q

Rotation of the tooth-tissue supported RPD toward the residual ridge around the ___________ fulcrum line

A

horizontal

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24
Q

Rotation of the RPD toward the residual ridge around the horizontal fulcrum line factors in which class of RPD?

A

Class I and Class II

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25
Q

Rotation of the RPD toward the residual ridge around the horizontal fulcrum line can cause…

A

– RPD potentially functions as a lever
– Can result in detrimental clasp forces on the abutment teeth

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26
Q

Why rotation of the tooth-tissue supported RPD toward the residual ridge around the horizontal fulcrum line?

A

– Difference in potential movement of abutment & mucoperiosteum over residual ridge
– 0.25mm periodontal ligament, 2mm mucoperiosteum
– 0.25mm = 0.01” (related to retentive clasp)

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27
Q

Distal abutment retentive clasp should or should not be anterior to terminal rest fulcrum line?

A

SHOULD NOT

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28
Q

The distal rest/distal guide plane causes what…

A
  • Class I lever
  • Torquing force on abutment
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29
Q

The mesial rest/mesial guide plane causes what?

A
  • Class II lever
  • Retentive tip disengages abutment
  • Stress-release clasp design
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30
Q

________ placement of the rest helps direct the forces more vertically onto the tissues of the residual ridge.

A

Anterior

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31
Q

On tooth-tissue supported RPD the clasp cannot be anterior to the…

A

rest

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32
Q

What class lever is this?

A

Class II

33
Q

What class lever is this?

A

Class I

34
Q

Stress-release clasps used on Class I & II RPDs distal abutments are…

A

– RPI clasp assembly
– RPC (A) clasp assembly
– Combination clasp
– ½ T clasp
– Reverse circumferential clasp

35
Q

What are the types of RPD clasps?

A
  • circlet
  • I-bar
  • 1/2 T clasp
  • reverse circlet (haripin)
  • embrasure
36
Q

What are the types of stress-release clasps?

A
  • RPI
  • RPC
  • combination clasp
  • modified 1/2 T clasp
  • reverse
37
Q

What is an RPI clasp assembly made of?

A
  • Rest (mesial), Proximal Plate, I-bar
38
Q

Where is the undercut on an RPI clasp assembly?

A

Mesiofacial or Mid-facial retentive undercut

39
Q

What is the reciprocation for an RPI clasp assembly?

A

– ML Minor connector
– Distal proximal plate

40
Q

What should the distal guiding plane be for an RPI clasp assembly?

A

Occlusal 1/3-1/2
* 2-3 mm
* Guide plate contacts 1-1.5mm of plane
* Undercut is necessary below the guide plane

41
Q

What should the mesiallingual minor connector guiding plane be for an RPI clasp assembly?

A

Occlusal 1/3
* 1-2 mm

42
Q

How far from the gingival margin is the approach arm for an RPI clasp assembly?

A

3 mm

43
Q

The approach arm for an RPI clasp assembly should cross the gingival margin at ____ degrees

A

90 degrees

44
Q

I-bar ___ mm contact at retentive undercut on an RPI clasp assembly

A

2 mm

45
Q

In an RPI clasp assembly where does the I-bar contact the retentive undercut?

A

2 mm

46
Q

In an RPI clasp assembly where does the approach arm sit?

A
  • 3mm from gingival margin
  • Crosses gingival margin 90°
47
Q

In an RPI clasp assembly where does the major connector sit?

A
  • 3mm from gingival margin: mandible
  • 6mm from gingival margin: maxilla
48
Q

In an RPI clasp assembly what is the width of the distal proximal plate?

A

Line angle to line angle

49
Q

What is the stress release system of the RPI clasp assembly?

A

– Rotation around mesial rest/fulcrum
– Distal guide plate & I-bar move mesiogingivally
* I-bar disengages from tooth (Stress release)
– ML minor connector rotates mesio-occlusally

50
Q

What needs to happen in order for the stress release design of the RPI clasp assembly?

A
  • Relief below distal plate, Undercut below guide plane (allows for proximal plate movement)
  • ML minor connector not contact adjacent tooth to allow rotation
51
Q

How much separation do you need between the vertical minor connectors on an RPI clasp assembly?

A

5 mm

  • if you don’t have 5 mm use a lingual plate
52
Q

When should you not use an RPI clasp assembly?

A

– Excess tissue undercut
– Shallow vestibule (Tissue impingement)
– Abutment excess facial inclination
* High survey line
* Retentive undercut too high (not in gingival 1/3)

53
Q

What are the main parts of an RPC clasp assembly (RPA)

A
  • Rest (mesial), Proximal Plate, Circumferential (Akers) clasp
54
Q

Where should the retentive undercut be for an RPC clasp assembly (RPA)?

A

Mesiofacial retentive undercut

55
Q

What is the reciprocation for the RPC clasp assembly (RPA)?

A

– ML minor connector
– Distal proximal plate (wrap to lingual)

56
Q

If the patient has a shallow vestible what kind of clasp would you use?

A

circumfrential

  • not an infrabulge clasp
57
Q

What type of clasp is used on a RPC clasp assembly (RPA)?

A

Circumferential retentive clasp
– Cast round for Kennedy I w/o modification and periodontally compromised teeth

58
Q

What type of clasp is used on a RPI clasp assembly?

A

I-bar

59
Q

What is a RPC (RPA) clasp a hybrid of?

A

RPI and circumferential concepts

60
Q

What are the criteria for the retentive clasp on the RPC (RPA) clasp assembly?

A
  • Proximal 2/3
    – Middle 1/3 of tooth
    – On the survey line
  • Terminal retentive 1/3
    – Gingival 1/3, Below survey line
61
Q

What is the stress release system for the RPC (RPA) clasp assembly?

A

– Rotation around mesial rest/fulcrum
– Circumferential clasp & distal guide plate move mesiogingivally
* Clasp disengages from tooth
* ML minor connector rotates mesio-occlusally

62
Q

What is the design criteria for the stress release of the RPC (RPA) clasp assembly?

A

– Relief below distal guide plate, undercut below plane
– Proximal 2/3 of retentive clasp exactly on survey line
* Relief is provided below proximal 2/3
* Allow clasp to disengage during rotation

63
Q

What can happen if you do not follow the stress release design criteria for the RPC (RPA) clasp assembly?

A
  • Fulcrum moves to proximal area of clasp
  • Class I lever with detrimental force
64
Q

What are the parts of the combination clasp concept?

A

Distal rest, Wrought wire retentive clasp, Cast reciprocal clasp

65
Q

What type of undercut do you use for a combination clasp concept?

A

Mesiofacial undercut

66
Q

When would you use a combination clasp concept?

A

– Mesial-inclination of abutment distal surface
* No undercut below guide plane
* RPC, RPI no stress release
– Mesial rest cannot be used

67
Q

What is the stress release concept for the combination clasp?

A

– Rotation occurs at distal rest minor connector
– Clasp moves occlusally
* Class I lever occurs
* Distal torquing force occurs
* Flexibility of wrought wire limits torque

68
Q

What does wrought wire do to the flexibility and torque?

A

decreases flexibility and torque

69
Q

What are the parts of the modified (1/2) T clasp concept?

A

Mesial rest, Distal Proximal plate, ½ T-bar clasp

70
Q

When do you use a modified (1/2) T clasp concept (what kind of undercut)?

A

– Distofacial retentive undercut

71
Q

What reciprocation do you use with a modified (1/2) T clasp concept?

A
  • ML minor connector
  • Distal plate
72
Q

When do you not use a modified (1/2) T clasp concept?

A

– Tissue undercut
– Shallow vestibule
– Abutment excess facial inclination
* High survey line
* Retentive undercut too high (not in gingival 1/3)

73
Q

What are the parts of the reverse circumferential clasp?

A
  • Mesial rest
  • Distal guide plate
  • Reverse cast circumferential retentive clasp
74
Q

When should you use the rever circumferential clasp?

A

– Distofacial retentive undercut
– ½ T clasp contraindicated

75
Q

What on the reverse circumferential clasp allows for reciprocation?

A

ML minor connector
Distal plate

76
Q

On tooth-tissue supported RPDs the rests are adjacent to what areas?

A

edentulous areas

77
Q

On tooth-tissue supported (distal extenstion) RPDs ______ rests are preferred?

A

mesial

78
Q

On tooth-tissue supported (distal extenstion) RPDs the stress-release clasps are used to…

A

Accommodate for rotation toward residual ridge around horizontal fulcrum

RPD (13 decks)

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