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RPD > Direct Retainers Part 1 > Flashcards

Direct Retainers Part 1 Flashcards

1
Q

RPD Retention
• Resist

A

dislodging forces

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2
Q

Primary Retention

A

– Mechanical from retaining elements on abutment
teeth

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3
Q

Secondary Retention
(2)

A

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

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4
Q

Direct Retainer

A

• RPD component used to retain and prevent
dislodgement

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5
Q

Types of Direct Retainers (2)

A

Intracoronal
Extracoronal

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6
Q

Intracoronal
(2)

A

– Internal precision attachment: key/keyway
– Most esthetic

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7
Q

Intracoronal
Disadvantages: (3)

A

require crown,
complex fabrication, & high maintenance

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8
Q

Extracoronal
(2)

A

– Clasp assembly
– More commonly used

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9
Q

Clasp Types (2)

A

Suprabulge
Infrabulge

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10
Q

Suprabulge
(2)

A

– Retentive arm approaches undercut from above the
survey line
– Circumferential, Akers, Circlet
• Synonyms

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11
Q

Infrabulge
(2)

A

– Retentive arm approaches undercut from below survey
line
– Bar clasps

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12
Q

A properly constructed suprabulge or infrabulge clasp assembly must incorporate the following
components:
(4)

A

a rest (A),
a retentive clasp (B),
a reciprocal element (C),
and one or more minor connectors (D).

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13
Q

skipped
Specific design features of the various components include (4)

A

vertical and horizontal approach arms, clasp
termini, clasp bodies, and clasp shoulders.

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14
Q

Rest: lies on (3)
– Prevent

A

occlusal, lingual, incisal surface

tissueward movement of clasp

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15
Q

Reciprocal components
(3)

A

– Rigid component
– Above height of contour
– Reciprocal clasp,
Lingual plate,
Proximal plate, Guide plate (minor
connectors)

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16
Q

Retentive clasp arm
(2)

A

• Proximal 2/3
• Rigid portion, above height of contour

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17
Q

Retentive terminal
(4)

A

• Distal 1/3
• Flexible
• Below height of contour
• Provides direct retention

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18
Q

Minor Connector
(2)

A

• Joins body of clasp to framework
• Rigid

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19
Q

Approach arm
(3)

A

• Component of bar clasp
• Connects clasp to framework
• Flexible minor connector (Exception to rule)

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20
Q

Requirements of Clasp Assembly
1. Support

A

– Resist vertical movement toward tissue
– Rests

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21
Q

Requirements of Clasp Assembly
2. Stability
(3)

A

– Resist horizontal displacement
– Areas above the survey line
– All rigid components of direct retainer

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22
Q

Requirements of Clasp Assembly
3. Encirclement of more than 180 degrees
(3)

A

– May be continuous or broken
– Minimum of 3 points used
– Prevents tooth from moving away from the
clasp

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23
Q

Requirements of Clasp Assembly
4. Reciprocation
(4)

A

– Reciprocal component contact tooth at same
time or sooner than retentive clasp
– Remain in contact while
retentive tip passes over
height of contour
– Resist retentive tip
lateral forces
– Requires parallel surface
to path of insertion

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24
Q

Requirements of Clasp Assembly
5. Passivity
(1)

A

– Components of direct retainer exert no force
when fully seated

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25
Q

Requirements of Clasp Assembly
6. Retention
(1)

A

– Resists displacement of RPD away from
supporting tissues
– Area below survey line: ideally in gingival 1/3

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26
Q

retention
• Clasp arm tip:

A

Terminal 1/3 below survey line

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27
Q

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

A

undercut

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28
Q

Retention amount minimum necessary to

A

resist
reasonable dislodging forces

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29
Q

Retention Factors
(3)

A

• Angle of convergence of the undercut
• Depth of undercut
• Flexibility of the retentive clasp

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30
Q

• Depth of undercut
(3)

A

– 0.010”, 0.020”, 0.030”

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31
Q

Retentive clasps should become active ONLY
when

A

disclosing forces are applied to them.

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32
Q

Retentive Clasp
Their ability to provide retention is based on
the

A

resistance of the metal to deformation.

33
Q

Retentive Clasp
Flexibility Factors
1. Length
(2)

A

– Flexibility = length^3
• Double length, 8x more flexible
– Increase length, curve clasp

34
Q

Retentive Clasp
Flexibility Factors
Diameter
(1)

A

– Flexibility =1/diameter^3
• Double diameter,
8x less flexible

35
Q

Retentive Clasp
Flexibility Factors
Taper (In 2 dimensions)
(2)

A

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

36
Q

Retentive Clasp
Flexibility Factors
Cross-sectional form

A

– Round clasp more flexible than half-
round
• Round flexes in all spatial planes
• Half-round flexes in one plane

37
Q

Cross-sectional Shapes
Half round: (2)

A

Almost always as in
circumferential clasps
‣Flexes in only one direction

38
Q

Cross-sectional Shapes
Round: (3)

A

As in wrought wire clasps
‣Flexes omnidirectionally
‣Provides maximum flexibility

39
Q

Retentive Clasp
Flexibility Factors
5. Material
(4)

A

– Cast chromium alloys less flexible than cast gold
alloys
– Wrought alloys more flexible than cast alloy
– Cast Chromium

40
Q

Material
– With increasing clasp flexibility, must use deeper
undercut to obtain equal retention
• 0.010”:
• 0.015”:
• 0.020”:

A

Cast Chrome alloy
Cast Gold alloy
Wrought wire

41
Q

Clasp Material
‣Alloy used in casting the
framework:
(2)

A

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

42
Q

Clasp Material‣ Wrought wire
(2)

A

‣ Produce by drawing metal through dies of smaller diameter
‣ Most flexible of all clasps

43
Q

Clasp Material
‣ Other
(2)

A

‣ Stainless steel, type IV gold

44
Q

The design of a retentive clasp arm should incorporate

A

maximum clasp length for optimal flexibility.

45
Q

Circumferential clasp
(2)

A

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

46
Q

Bar clasp
(3)

A

– Approaches undercut from below survey line
– “Pushes” toward occlusal to resist displacement
– Easier to seat, more difficult to remove than
circumferential clasp

47
Q

Reciprocal Clasp
• Must be —
• Shaped different than —
• Taper..

A

rigid
flexible retentive clasp
Not tapered

48
Q

Reciprocation is the means by which

A

one part of the
framework opposes the action of the retainer in
function.

49
Q

skipped
Reciprocation may be achieved by:
(5)

A

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

50
Q

Most logical clasp for tooth-supported RPD
(Class III)

A

Circumferential Clasps

51
Q

Circumferential Clasps
Advantages

A

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

52
Q

Circumferential Clasps
• Disadvantages
(3)

A

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

53
Q

skipped
Circumferential Clasp Configuration
• Clasp kept as low on crown as survey line permits
(4)

A

– Less torquing action on tooth
– Less interference with occlusion
– If survey line is too high, enamel surface must be
recontoured to lower the survey line
– Survey line too low, Surveyed crown required

54
Q

Circumferential Clasp Configuration
• — clasp

A

Retentive

55
Q

Circumferential Clasp Configuration
• Retentive clasp (4)

A

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

56
Q

Circumferential Clasp Configuration
– Proximal 2/3
(2)

A

• In middle 1/3 of tooth
• Above the survey line

57
Q

Circumferential Clasp Configuration
– Terminal retentive 1/3
(3)

A

• In gingival 1/3
• Below survey line
• Tip curves to occlusal

58
Q

Circumferential Clasp Configuration
• Reciprocal clasp
(4)

A

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

59
Q

Circumferential Clasp Configuration
– Above the survey line
(2)

A

• If survey line too high, must recontour
• Prepare surface parallel to path of insertion

60
Q

skipped
Types of Circumferential Clasps
(7)

A
  1. Circlet
  2. Embrasure clasp
  3. Reverse Circlet (hairpin) clasp
  4. Ring clasp
  5. Reverse Circlet clasp
  6. Combination Clasp
  7. RPC clasp
61
Q

Circumferential Clasps:
Circlet
(2)

A

• Circumferential clasp of choice Class III RPD
• Engage undercut remote from edentulous
area

62
Q

Circumferential Clasps:
Embrasure Clasp
(3)

A

• 2 circlet clasps joined at body
• Used when retainer is necessary in a dentate area
• Requires heavy reduction of abutment teeth for
adequate clasp bulk

63
Q

Circumferential Clasps:
Embrasure Clasp
• Used when retainer is necessary in a dentate area
(3)

A

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

64
Q

Circumferential Clasps:
Embrasure Clasp
• Requires heavy reduction of abutment teeth for
adequate clasp bulk

A

– Inadequate preparation, clasp fracture common

65
Q

Circumferential Clasps:
Reverse Circlet (Hairpin Clasp)
(5)

A

• Engage undercut adjacent to edentulous area Class
III RPD
• Covers extensive tooth surface, increased caries risk
• Difficult to fabricate
• Indication: Mesially-tipped mandibular molar with
mesiofacial undercut
• “Last choice” for mesially-tipped molars

66
Q

Circumferential Clasps:
Reverse Circlet (Hairpin Clasp)
• Indication: Mesially-tipped mandibular molar with
mesiofacial undercut

A

– ½ T preferred for this situation, if no tissue undercut at
approach arm

67
Q

Circumferential Clasps:
Ring Clasp
(6)

A

• Indication: Mesiolingually-tipped mandibular
molars Class III RPD
• Engage mesiolingual undercut
• Auxillary bracing arm for reciprocity
• Additional occlusal rest:
• Avoid if possible
• Incorrect Ring clasp: No reciprocation, No support

68
Q

Circumferential Clasps:
Ring Clasp
• Additional occlusal rest:
– for

A

support, prevent further mesial movement

69
Q

Circumferential Clasps:
Reverse Circlet Clasp
• Indication:

A

Retentive undercut adjacent to
edentulous space

70
Q

Circumferential Clasps:
Reverse Circlet Clasp
• Indication: Retentive undercut adjacent to
edentulous space
(3)

A

– 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

71
Q

Circumferential Clasps:
Reverse Circlet Clasp
• Difficult to

A

obtain adequate occlusal clearance
• Avoid, if possible

72
Q

Circumferential Clasps:
Combination Clasp
(3)

A

• Wrought round wire retentive clasp
• Cast ½ round reciprocal clasp
Wrought wire soldered to framework

73
Q

Circumferential Clasps:
Combination Clasp
• Indication:

A

Distal extension RPD (Class I & II)

74
Q

Circumferential Clasps:
Combination Clasp
• Indication: Distal extension RPD (Class I & II)
(2)

A

– Mesial rest not possible, distal rest must be used
– Mesiofacial undercut

75
Q

RPC Clasp (RPA)

A

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

76
Q

RPC Clasp (RPA)
• Indication:
(2)

A

– Class I, II RPDs
– Mesiofacial retentive undercut

77
Q

RPC Clasp (RPA)
Circumferential retentive clasp
(1)

A

– Cast ½ round (ALWAYS) except in periodontally
compromised teeth, cast round.

78
Q

RPC Clasp (RPA)
• Reciprocation:
(2)

A

– Distal proximal plate
– ML minor connector

RPD (22 decks)

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