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Prosthodontics > RPD DESIGN 2: Retention > Flashcards

RPD DESIGN 2: Retention Flashcards

1
Q

Colour code for saddles

A

Yellow

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2
Q

Colour code for support

A

Red

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3
Q

Colour code for retention

A

Green

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4
Q

Colour code for bracing + reciprocation

A

Blue

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5
Q

Colour code for connector

A

Black

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6
Q

Definition of retention

A

The dentures resistance to vertical dislodging forces away from the tissue

Stops denture falling out

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7
Q

What 3 things help achieve retention?

A
  1. Mechanical means
  2. Muscular means
  3. Physical forces
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8
Q

How can retention be achieved through

  1. Mechanical
  2. Muscular forces
  3. Physical forces
A
  1. Mechanical - clasps, guide planes
  2. Muscular forces - shape of the denture
  3. Physical forces - Coverage of the mucosa
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9
Q

Classification of DIRECT retention

A

Resistance to vertical displacement of denture

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10
Q

Classification of INDIRECT retention

A

Resistance to rotational displacement of denture

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11
Q

What is a form of direct retention that provides an extra form of retention?

A

Guide planes:
> Carve tooth to make it parallel with the fake teeth

> When a clasp tips is exhausted, the guide planes provide longer term retention

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12
Q

What is a clasp?

A

A metal arm that when in position contacts the tooth preventing removal of the denture base

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13
Q

On what part of the tooth is a clasp placed?

A

Below the bulbous part of the tooth (the undercut)

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14
Q

How are undercuts identified?

A

Surveying the casts

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15
Q

What material can clasps be made in?

A

Clasps can be made in wrought metal and incorporated into the denture base

Or be included as part of a cast denture base

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16
Q

Disadvantages of a gingival approaching clasp?

A

They cross the gingival margin (which may create a bridge for infection - food can accumulate which is a potential for breeding + infection)

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17
Q

What teeth use a gingival approach for the clasps?

A

Anteriors + canines as its the only way of guaranteeing you will achieve 50mm in length

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18
Q

What are the different types of clasp options? (2)

A

Clasps approach the undercut from either:

  1. Occlusally approaching
  2. Gingivally approaching
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19
Q

Define reciprocation

A

Each clasp unit will have an opposing element (reciprocal clasp arm) to the retentive clasp arm to prevent pressure from the clasp acting on the tooth

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20
Q

Function of survey lines (3)

A

Determine the position of:

  1. The clasps and the retentive areas
  2. The reciprocal arm
  3. The guide planes and proximal plates
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21
Q

What is the path of insertion?

What does it allow?

A
  • The direction in which a denture is placed or removed from the supporting tissues or abutment teeth
  • Path of I gives anterior retention without need of clasps
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22
Q

What is the path of displacement?

A

The direction in which the denture is dislodged from its position during function

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23
Q

Function of RPI

A

Used in free end saddle designs to prevent stress on the last abutment tooth

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24
Q

What are the components of an RPI? (3)

A

Mesial rest:

Proximal plate (adjacent to saddle):

  • Guide surface of 2-3mm
  • Undercut to permit movement

Gingival approaching I-bar clasp:

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25
Q

Name examples of indirect retainers (5)

A
  1. Major connectors
  2. Minor connectors
  3. Rest
  4. Saddle
  5. Denture base
26
Q

Name an example of direct retention

A

Clasps

27
Q

Factors affecting retention (2)

A

> Size of the angle of cervical convergence

> How far the clasp terminal is placed into the angle of the cervical convergence

28
Q

How is clasp flexibility achieved?

A
  • The longer the clasp arm the more flexible

- By increasing the length, horizontal stresses to the abutment are reduced

29
Q

Disadvantages of a clasp (2)

A
  1. Increases tooth coverage

2. Compromised aesthetics

30
Q

Advantages a rest (2)

A
  1. Maintains the position of the clasp in relation to the abutment
  2. Transmits forces along the long axis of the abutments
31
Q

What Kennedy classes require an I bar? (RPI)

A

1 + 2

32
Q

What Kennedy classes require an indirect retainer?

A

1, 2 + 4

33
Q

What is the desired pattern of retention shape?

A

Triangular to provide stability

34
Q

Abutment modifications

A
  1. Lower heights of contour (preparing guide planes = most effective way to do this)
  2. Create undercuts if necessary (raising heights of contour by adding composite)
35
Q

Describe how physical retention of a denture is achieved

A

Using forces of adhesion, cohesion and surface tension

36
Q

How do adhesion forces physically retain a denture?

A

Surface forces of saliva on denture and mucosa

37
Q

How do cohesion forces physically retain a denture?

A

Forces within saliva, viscosity

38
Q

Describe the position of direct retention

A

> Close to the base

> Adjacent to the abutment teeth

39
Q

Describe the position of guide planes

A

> Close to the base

> Parallel to the path of insertion

40
Q

Where is a clasp placed?

A

Below undercut

41
Q

When do clasps work most efficiently?

A

When used along with a rest (supporting component)

42
Q

Give the name for a gingivally approaching clasp

A

I bar clasp

43
Q

List the types of occlusally approaching clasps (3)

A
  1. Single arm clasp
  2. Circumferential clasp
  3. Ring clasp
44
Q

When can a single arm clasp be used?

A

Upper molar
> Distobuccal
> Distopalatal undercut

45
Q

What is a circumferential clasp?

A

Single arm with a reciprocal arm

46
Q

When can a ring clasp be used?

A

Lower molar
> Mesiobuccal
> Mesiolingual undercut

47
Q

What does clasp efficiency depend on? (3)

A
  1. Clasp material
  2. Cross-sectional thickness and shape
  3. Length of the clasp
48
Q

Give a non-metal material that can be used for clasps

A

Acetal resin

49
Q

Advantages of acetal resin as a clasp material (2)

A
  1. Appearance

2. Engages deep undercuts

50
Q

Disadvantages of acetal resin as a clasp material

A
  1. Bulkier
  2. Non-adjustable
  3. Cost
51
Q

Metal clasp length required toto engage a 0.25mm undercut?

A

15mm

52
Q

Exception for when an occlusally approaching clasp is used for a premolar?

A

When the tooth is larger than usual

53
Q

List the information required to position a clasp (4)

A
  1. The position of the survey line
  2. The type of abutment tooth
  3. Clasp length (15mm for cast Co-Cr)
  4. Type of material- cast or wrought
54
Q

How does reciprocation work to prevent the tooth moving? (2)

A
  1. The retentive element of the clasp flexes over the undercut
  2. The reciprocal element remains in contact preventing the tooth being moved horizontally by the clasp flexing.
55
Q

How can the efficiency of guide planes be maximised?

A

By making the guide planes as large as possible

56
Q

Benefits of an altered path of insertion (3)

A
  1. Avoids using anterior clasps
  2. Can provide frictional resistance retention
  3. Denture sitting over undercut is a food trap
57
Q

State the minimum number of clasps that should be used for a denture?

A

2 - one on each side

58
Q

List some factors that affects the placement of clasps

A
  1. Aesthetics

2. Saddle length

59
Q

How can retention be created if there are no undercuts?

A

TOOTH PREP

Addition of composite to create an undercut

60
Q

Is retention required on every adjacent tooth to the saddle?

A

No

61
Q

When is RPI mostly used?

A

Mostly in posterior mandibular cases, but can be present in maxillary arch too

Prosthodontics (4 decks)

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