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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
Requirements of Clasp Assembly 6. Retention (1)
– Resists displacement of RPD away from supporting tissues – Area below survey line: ideally in gingival 1/3
26
retention • Clasp arm tip:
Terminal 1/3 below survey line
27
• Retention portion of tooth must be --- in relation to path of prosthesis insertion
undercut
28
Retention amount minimum necessary to
resist reasonable dislodging forces
29
Retention Factors (3)
• Angle of convergence of the undercut • Depth of undercut • Flexibility of the retentive clasp
30
• Depth of undercut (3)
– 0.010”, 0.020”, 0.030”
31
Retentive clasps should become active ONLY when
disclosing forces are applied to them.
32
Retentive Clasp Their ability to provide retention is based on the
resistance of the metal to deformation.
33
Retentive Clasp Flexibility Factors 1. Length (2)
– Flexibility = length^3 • Double length, 8x more flexible – Increase length, curve clasp
34
Retentive Clasp Flexibility Factors Diameter (1)
– Flexibility =1/diameter^3 • Double diameter, 8x less flexible
35
Retentive Clasp Flexibility Factors Taper (In 2 dimensions) (2)
– Clasp terminal ½ as thick as origin • 1mm to 0.5 mm – Clasp terminal ½ as wide as origin • ~2mm to 1mm
36
Retentive Clasp Flexibility Factors Cross-sectional form
– Round clasp more flexible than half- round • Round flexes in all spatial planes • Half-round flexes in one plane
37
Cross-sectional Shapes Half round: (2)
Almost always as in circumferential clasps ‣Flexes in only one direction
38
Cross-sectional Shapes Round: (3)
As in wrought wire clasps ‣Flexes omnidirectionally ‣Provides maximum flexibility
39
Retentive Clasp Flexibility Factors 5. Material (4)
– Cast chromium alloys less flexible than cast gold alloys – Wrought alloys more flexible than cast alloy – Cast Chromium
40
Material – With increasing clasp flexibility, must use deeper undercut to obtain equal retention • 0.010”: • 0.015”: • 0.020”:
Cast Chrome alloy Cast Gold alloy Wrought wire
41
Clasp Material ‣Alloy used in casting the framework: (2)
‣ Usually Ticonium (NiCr) or Vitallium (CoCr) ‣ Easy to fabricate
42
Clasp Material‣ Wrought wire (2)
‣ Produce by drawing metal through dies of smaller diameter ‣ Most flexible of all clasps
43
Clasp Material ‣ Other (2)
‣ Stainless steel, type IV gold
44
The design of a retentive clasp arm should incorporate
maximum clasp length for optimal flexibility.
45
Circumferential clasp (2)
– Approaches undercut from above the survey line – “Pulls” toward occlusal to resist displacement
46
Bar clasp (3)
– Approaches undercut from below survey line – “Pushes” toward occlusal to resist displacement – Easier to seat, more difficult to remove than circumferential clasp
47
Reciprocal Clasp • Must be --- • Shaped different than --- • Taper..
rigid flexible retentive clasp Not tapered
48
Reciprocation is the means by which
one part of the framework opposes the action of the retainer in function.
49
skipped Reciprocation may be achieved by: (5)
• Rigid plating (LINGUAL PLATE) • Minor connectors • Guide planes extended around the vertical line of abutments • Reciprocal clasp arms • Contact areas of proximal teeth
50
Most logical clasp for tooth-supported RPD (Class III)
Circumferential Clasps
51
Circumferential Clasps Advantages
– Excellent stabilization, support, bracing – Easiest to design & construct – Easier to repair
52
Circumferential Clasps • Disadvantages (3)
– 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
skipped Circumferential Clasp Configuration • Clasp kept as low on crown as survey line permits (4)
– 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
Circumferential Clasp Configuration • --- clasp
Retentive
55
Circumferential Clasp Configuration • Retentive clasp (4)
– Cast ½ Round – Proximal 2/3 – Terminal retentive 1/3 – Tapers from origin (2.0mm) to tip (1.0 mm)
56
Circumferential Clasp Configuration – Proximal 2/3 (2)
• In middle 1/3 of tooth • Above the survey line
57
Circumferential Clasp Configuration – Terminal retentive 1/3 (3)
• In gingival 1/3 • Below survey line • Tip curves to occlusal
58
Circumferential Clasp Configuration • Reciprocal clasp (4)
– Cast ½ round – Entire clasp in middle 1/3 – Above the survey line – No taper: Uniform width 1.5 –2.0 mm
59
Circumferential Clasp Configuration – Above the survey line (2)
• If survey line too high, must recontour • Prepare surface parallel to path of insertion
60
skipped Types of Circumferential Clasps (7)
1. Circlet 2. Embrasure clasp 3. Reverse Circlet (hairpin) clasp 4. Ring clasp 5. Reverse Circlet clasp 6. Combination Clasp 7. RPC clasp
61
Circumferential Clasps: Circlet (2)
• Circumferential clasp of choice Class III RPD • Engage undercut remote from edentulous area
62
Circumferential Clasps: Embrasure Clasp (3)
• 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
Circumferential Clasps: Embrasure Clasp • Used when retainer is necessary in a dentate area (3)
– Class III with no modification space – Class II with no modification space – Class IV
64
Circumferential Clasps: Embrasure Clasp • Requires heavy reduction of abutment teeth for adequate clasp bulk
– Inadequate preparation, clasp fracture common
65
Circumferential Clasps: Reverse Circlet (Hairpin Clasp) (5)
• 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
Circumferential Clasps: Reverse Circlet (Hairpin Clasp) • Indication: Mesially-tipped mandibular molar with mesiofacial undercut
– ½ T preferred for this situation, if no tissue undercut at approach arm
67
Circumferential Clasps: Ring Clasp (6)
• 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
Circumferential Clasps: Ring Clasp • Additional occlusal rest: – for
support, prevent further mesial movement
69
Circumferential Clasps: Reverse Circlet Clasp • Indication:
Retentive undercut adjacent to edentulous space
70
Circumferential Clasps: Reverse Circlet Clasp • Indication: Retentive undercut adjacent to edentulous space (3)
– 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
Circumferential Clasps: Reverse Circlet Clasp • Difficult to
obtain adequate occlusal clearance • Avoid, if possible
72
Circumferential Clasps: Combination Clasp (3)
• Wrought round wire retentive clasp • Cast ½ round reciprocal clasp Wrought wire soldered to framework
73
Circumferential Clasps: Combination Clasp • Indication:
Distal extension RPD (Class I & II)
74
Circumferential Clasps: Combination Clasp • Indication: Distal extension RPD (Class I & II) (2)
– Mesial rest not possible, distal rest must be used – Mesiofacial undercut
75
RPC Clasp (RPA)
• Rest (mesial), Proximal Plate, Circumferential (Akers) clasp
76
RPC Clasp (RPA) • Indication: (2)
– Class I, II RPDs – Mesiofacial retentive undercut
77
RPC Clasp (RPA) Circumferential retentive clasp (1)
– Cast ½ round (ALWAYS) except in periodontally compromised teeth, cast round.
78
RPC Clasp (RPA) • Reciprocation: (2)
– Distal proximal plate – ML minor connector

RPD (22 decks)

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