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RPD > retention > Flashcards

retention Flashcards

1
Q

what is retention

A

the resistance of RPD to dislodge

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2
Q

How can retention be achieved

A
  1. through mechanical means–> direct and indirect retainers
  2. through muscular control
  3. through physical forces
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3
Q

What are some examples of direct retainers

A
  1. clasp
  2. guide plane
  3. attachments
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4
Q

what is a direct retainer

A

a component of RPD that engages abutment teeth in a manner to resist displacement of prosthesis

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5
Q

what is an indirect retainer

A

it is a component that assist the direct retainers to prevent displacement of the distal extension of the denture base by functioning through lever action on the opposing side of the fulcrum line

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6
Q

What can act as an indirect retainer

A

rests

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7
Q

what are some muscular control that helps with retention

A

cheeks and tongue help to retain

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8
Q

what are some physical forces that help with retention

A
  1. surface force, associated with saliva to denture and mucosa
  2. fluid force, surface tension of saliva, cohesive forces within saliva film, viscosity of saliva
  3. atmospheric pressure, dependent on border seal
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9
Q

what are the functions of a proximal plate

A

provides path of insertion, stabilise against rotation, stabilise abutment tooth, provide frictional retention, eliminate negative strain on abutment teeth during insertion and removal of prosthesis

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10
Q

what are some examples of suprabulge clasp

A

circumferential clasp, embrasure clasp, ring clasp, hair pin clasp, half and half clasp

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11
Q

how much of the clasp should be in the undercut

A

terminal 1/3

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12
Q

What are the pros of suprabulge clasp

A

Provides support, retention and bracing.

does not impinge on gingival tissue

more rigid

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13
Q

What are the cons of suprabulge clasp

A

more tooth coverage than infrabulge clasp
poor aesthetics
adjustments difficult
may need to trim more of coronal structure if occlusion tight

For free end saddle case, C clasp will act as an extraction like forceps on abutment teeth

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14
Q

What are some examples of infrabulge clasp

A

I bar, roach clasp, C clasp

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15
Q

What are the advantages of infrabulge clasp

A

less tooth contact
more aesthetic
more hygienic
minimises harmful effect of torque on abutment tooth for free end saddle case
easier to adjust

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16
Q

What are the cons of infrabulge clasp

A

lack of rigidity, does not give support or bracing

Unaesthetic for people with high lip line

more bothersome to vestibular tissue

tendency to trap and collect food

17
Q

What are some contraindications for infrabulge clasp

A
  1. deep cervical tooth undercut
  2. very high survey line on abutment tooth
    3.excessive buccal lingual tilt of tooth
  3. severe soft tissue or bony undercut
  4. frenal attachment areas
  5. insufficient vestibular depth for approaching arm(need at least 4mm)
18
Q

What does a clasp need to take into account

A
  1. adequate retention
  2. flexible retentive clasp arm so clasp arm can pass over maximum bulbosity of tooth into undercut
  3. reciprocation
  4. encirclement( occlusally approaching clasp arm must involve more than half the circumference of the tooth to preclude movement of tooth out of confines of clasp arm)
  5. Support
  6. passivity( retentive clasp arm should not exert force against tooth under resting condition
19
Q

What are some factors affecting clasp retention

A
  1. depth of undercut engaged
  2. material of wire used for clasp
  3. length of clasp
  4. cross sectional of clasp arm
  5. shape of clasp arm
  6. taper of clasp arm
  7. number of retentive clasp arm
20
Q

why is indirect retainer used?

A

because free end saddle denture tend to rotate around fulcrum line when dislodging fro the saddle, movement should be resisted by the component placed on opposite side of fulcrum. A lack of indirect retainers is likely to move the distal extension base away from the basal tissue

21
Q

What type of kennedy class is an indirect retainer particularly important for

A

KC1, KC2, long span KC 3 and 4

22
Q

Where should indirect retainer be placed for best leverage

A

as far as possible from the distal extension base

23
Q

how does the fulcrum line look like for KC2

A

passes through the occlusal rest area of abutment on distal extension side and occlusal rest area of most distal abutment on other side

24
Q

How does fulcrum line look like for KC1

A

passes through the most posterior abutment on both side of the arch. Ususally canine or mesio-occlusal rest area of most distal abutment on other side

25
Q

How does the fulcrum line for KC4 look

A

passes through abutments adjacent to single edentulous space

RPD (10 decks)

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