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Prosthetics > Direct Retention > Flashcards

Direct Retention Flashcards

1
Q

What is retention?

A

Resistance to displacement of the denture from the denture bearing tissues in a vertical direction

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2
Q

What is stability of a denture?

A

Ability of denture to resist functional displacement in any direction so the denture remains in steady constant position

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3
Q

Name 5 methods for direct retention

A
  1. Mechanical retention
  2. Guide planes
  3. Muscular control
  4. Physical forces of adhesion
  5. Precision attachments
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4
Q

Describe how indirect retention may be achieved

A

Change axis of rotational displacement to make clasps operate as intended

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5
Q

What is a clasp?

A

A resilient metal projection from the denture base which grips natural tooth and retains denture in its functional position

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6
Q

Where are clasps usually placed?

A

Teeth adjacent to saddles if they have suitable undercuts

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7
Q

Describe 5 general considerations when designing clasp retention

A
  1. Gingival health
  2. Presence and position of undercuts
  3. PoI and aesthetics
  4. Occlusion
  5. Do not complicate by using too many
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8
Q

Name 2 types of clasp design

A
  1. Occlusally approaching

2. Gingivally approaching

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9
Q

What is the difference between occlusally and gingivally approaching clasps?

A

Occlusally approaching clasps enter the undercut from the occlusal surface whereas gingivally approaching enter the undercut from gingival surface

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10
Q

Discuss occlusally approaching clasps

A
  • Consist of one or two arms which encircle tooth
  • Retentive arm approaches survey line form occlusal surface
  • Terminal 1/3 of the clasp is below survey line
  • One arm clasp referred to as circumferential if encircles tooth
  • Provide retention plus bracing and support
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11
Q

Discuss gingivally approaching clasps

A
  • Not in contact with the tooth surface along their whole length
  • Arm approaches survey line from gingival margin
  • Provide retention only (not bracing or support)
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12
Q

Name 3 types of GACs

A
  1. “I” bar
  2. “T” bar
  3. Reverse “L” bar
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13
Q

Name 4 considerations to take into account when designing clasps

A
  1. Flexibility of clasps
  2. Clasp materials
  3. Position of undercut
  4. Depth of undercut
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14
Q

What does the position of an undercut determine in terms of clasp design?

A

Effectiveness of clasp

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15
Q

What does the depth of an undercut determine in terms of clasp design?

A

Determines where the clasp tip is placed

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16
Q

Name 4 considerations with regards to the flexibility of clasp

A
  1. Material (MoE)
  2. Length of clasp
  3. Diameter
  4. Cross sectional form of clasp
17
Q

Name 5 common clasp materials

A
  1. Wrought gold
  2. Wrought stainless steel
  3. Wrought nickel-chrome
  4. Wrought nickel-titanium
  5. Cast cobalt-chrome
18
Q

Name a non-alloy which may be used as a clasp material

A

Nylon

19
Q

What is the depth a cast cobalt-chromium clasp is used at?

A

0.25mm

20
Q

Describe the differences between using cast CoCr and wrought stainless steel as clasp materials

A
  • CoCr has high MoE so must be longer, thinner and taper
  • CoCr must be at undercut 0.25mm and length 15mm
  • Stainless steel can be shorter and placed at 0.75mm
21
Q

Describe how uppercuts on upper and lowers differ and its effect on clasp placement

A
  • Lower molars have better undercut on lingual surface so circumferential OAC goes to mesiolingual U/C
  • Upper molars have better undercut on buccal surface so circumferential OAC goes to mesiobuccal U/C
22
Q

Explain when are GACs often employed

A

High survey line as not enough room above survey line for first 2/3 of clasp to be above survey line

23
Q

Name 4 ways to attach a clasp to a denture base

A
  1. Integral part of cast framework
  2. Embedded in acrylic resin
  3. Soldered to denture base
  4. Welded to denture base
24
Q

In terms of bracing, caries, gingival health, aesthetics and tolerance, describe where OACs or GACs are better

A 
Bracing - OACs
Caries - OACs
Gingival Health - OACs
Aesthetics - GACs
Tolerance - OACs
25
Q

Name 3 things which must be stated on a clasp prescription

A
  1. Select which tooth and undercut
  2. Decide if OAC or GAC
  3. Decide whether material is cast or wrought

Prosthetics (16 decks)

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