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Removable Partial Dentures > Direct Retainers Part 2 > Flashcards

Direct Retainers Part 2 Flashcards

1
Q

what is the clasp types for suprabuldge and where is it located

A
  • circumferential, akers, circlet ( synonyms)
  • retentive arm approaches undercut from above the survey line
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2
Q

what is the clasp type for infrabuldge and where is it located

A
  • retentive arm approaches undercut from below survey line
  • bar clasps
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3
Q

when are bar clasps indicate

A
  • distal extension RPD
  • tooth supported RPD, esthetics facor
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4
Q

what are the most common bar clasps

A
  • I bar clasp
  • 1/2 T bar clasp
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5
Q

what are the advantages and disadvantages to bar clasps

A
  • A: more esthetic, more flexible, less conducive to caries bc less tooth coverage, wider range of undercut adaptability (MF, mid -F : Ibar) (DF 1/2T bar)
  • D: less bracing, possible tissue impingement, food impaction, more difficult to repair or replace
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6
Q

what are the bar clasp rules of the approach arm

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
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7
Q

what falls under the category of tooth supported RPDs

A
  • class III RPD, short span class IV
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8
Q

what falls under the category of tooth tissue supported RPDs

A

-class I and II RPD, long span Class IV

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9
Q

what are the tooth supported RPD clasps in order of most favorable to least

A
  • circumferential
  • I bar
  • 1/2 T bar
  • reverse circlet (hairpin)
  • embrasure clasp
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10
Q

when is circumferential clasp used

A
  • most common
  • retentive undercut remote from edentulous area
  • used as reciprocal clasp
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11
Q

when is I bar used and what prevents use

A
  • Mesiofacial, midfacial undercut
  • used as reciprocal clasp
  • tissue undercut prevents use
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12
Q

when is 1/2 T bar used and what prevents its use

A
  • retentive undercut adjacent to edentulous area
  • distal facial undercut
  • reciprocal clasp
  • tissue undercut prevents use
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13
Q

when do you use reverse circlet (hairpin) and what is its disadvantage

A
  • retentive undercut adjacent to edentulous area
  • used when tissue undercut present and I/2 T bar or I bar cant be used
  • excess tooth coverage is disadvantage
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14
Q

when is embrasure clasp used-

A
  • when retainer is necessary in a dentate area
  • used in class IV and 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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15
Q

what is the fulcrum line

A

an imaginary line connecting occlusal rests around which a partial removable dental prosthesis tends to rotate under masticatory forces

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16
Q

what are the determinants for the fulcrum line

A

the cross arch occlusal rests located adjacent to the tissue borne components

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17
Q

describe what happens in rotation of the RPD toward the residual ridge around the horizontal fulcrum line

A
  • factor in class I and II RPDs
  • RPD functions as a lever
  • can result in detrimental clasp forces on the abutment teeth
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18
Q

why rotation of the RPD towards the residual ridge around the horizontal fulcrum line

A
  • difference in potential movement of abutment and mucoperiosteum over residual ridge
  • 0.25mm periodontal ligament, 2 mm mucoperiosteum
  • 0.25mm = 0.01’
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19
Q

where should distal abutment retentive clasp not be

A

anterior to terminal rest fulcrum line

20
Q

describe a distal rest/ distal guide plane-

A
  • class I lever
    -torquing force on abutment
21
Q

describe mesial rest/ distal guide plane

A
  • class II lever
  • retentive tip disengages abutment
  • stress release clasp design
22
Q

what does anterior placement of the rests help

A

direct the forces more verticaally onto the tissues of the residual ridge

23
Q

when are stress release clasps used

A

on class I and II RPDs distal abutmens

24
Q

what are the types of stress release clasps in order of most favorable to least

A
  • RPI clasp assembly
  • RPC class assembly
  • combination clasp
  • 1/2 T clasp
  • reverse circumferential clasp
25
Q

describe the RPI clasp assembly

A
  • Rest (mesial), Proximal plate (next to edentulous area, I bar (reciprocal clasp type)
  • mesiofacial or mid facial retentive undercut
  • reciprocation: ML minor connector, distal proximal plate
26
Q

what are the prepared guiding planes in RPI clasp assembly

A
  • distal guiding plane: occlusal 1/3-1/2
  • 2-3 mm reduction needed
  • guide plate contacts 1-1.5mm of plane
  • undercut is necessary below the guide plane
  • ML minor connector GP: occlusal 1/3
    -1-2mm reduction needed
27
Q

what are the structural details of the RPI clasp assembly

A
  • I bar 2mm contact at retentive undercut
  • approach arm: 3mm from gingival margin, crosses gingival margin at 90 degreees
  • distal proximal plate width: line angle to line angle
  • major connector: 3mm from gingival margin on mandible, 6mm from gingival margin on maxilla
28
Q

what is the stress release on RPI clasp assembly

A
  • rotation around mesial rest/ fulcrum
  • distal guide plate and I bar move mesiogingivally: I bar disengages from tooth
  • ML minor connector rotates mesio occlusally
29
Q

what is the stress relief design criteria for RPI clasp assembly

A
  • relief below distal plate, undercut below guide plane: allow proximal plate movement
  • ML minor connector not contact adjacent tooth to allow rotation
30
Q

what is the design criteria for RPI clasp assembly

A
  • need 5mm separation between vertical minor connector
  • if not 5mm then should use lingal plate
31
Q

when is RPI clasp assembly contraindicated

A

-excess tissue undercut
- shallow vestibule bc tissue impingement
- abutment excess facial inclination: high survey line, retentive undercut too high ( not in gingival 1/3)

32
Q

describe RPC clasp assembly

A

-Rest (mesial), proximal plate, circumferential clasp
- MF undercut
- circumferntial retentive clasp: cast round for Class I without modification and periodontally compromised teeth
- reciprocation: ML minor connector, distal proximal plate wraps to lingual

33
Q

describe the structural details of RPC clasp assembly

A
  • hybrid clasp: RPI and circumferential concepts
  • similar criteria to circumferential retentive class: proximal 2/3 (middle 1/3 of tooth on the survey line). terminal retentive 1/3 (gingival 1/3 below survey line
  • guide planes same as RPI
34
Q

describe the stress release on RPC clasp assembly

A
  • rotation around mesial rest/fulcrum
  • circumferential clasp and distal guide plate move mesiogingivally
  • clasp disengages from tooth
  • ML minor connector rotates mesio occlusally
35
Q

what is the stress release design criteria for RPC clasp assembly

A
  • relief below distal guide palte, 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
36
Q

what happens in failure to meet stress release design criteria in RPC clasp assembly

A

-fulcrum moves to proximal area of clasp
- class I lever with detrimental force

37
Q

describe the combination clasp

A
  • distal rest: wrought wire retentive clasp, cast reciprocal clasp
  • mesiofacial undercut
38
Q

when is combination clasp indicated

A

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

39
Q

what is the stress release for combination clasp

A
  • rotation occurs at distal rest minor connector
  • clasp moves occlusally
  • class I lever
  • distal torquing force occurs
  • flexibility of wrought wire limits torque
40
Q

describe the modified 1/2 T clasp

A
  • mesial rest, distal proximal plate, 1/2 T bar clasp
  • reciprocation: ML minor connector, distal plate
41
Q

when is modified 1/2 T clasp indicated

A

DF retentive undercut

42
Q

when is modified 1/2 T clasp contraindicated

A
  • tissue undercut
  • shallow vestibule
  • abutment excess facial inclination
  • high survey line
  • retentive undercut too high - not in gingival 1/3
43
Q

describe the reverse circumferential clasp

A
  • Mesial rest, distal guide plate, reverse cast circumferential retentive clasp
  • reciprocaton: ML minor connector, distal plate
44
Q

when is reverse circumferential clasp indicated

A

-DF retentive undercut
- 1/2 T clasp is contraindicated

45
Q

describe general tooth supported RPD clasp selection

A
  • rests adjacent to edentulous area
  • clasp by convenience: no fulcrum lines, no rotation, determine by site of retentive undercut, tissue undercut
  • reciprocation rules still apply
46
Q

describe general tooth tissue supported RPD clasp selection

A
  • mesial rests preferred
  • stress release clasps used to accomodate for rotation toward residual ridge around horizontal fulcrum
  • reciprocation still needed: often ML minor connector and distal plate rather than circumferential reciprocal clasp

Removable Partial Dentures (21 decks)

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