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Prosthodontics > RPD DESIGN 1: Saddles + Support > Flashcards

RPD DESIGN 1: Saddles + Support Flashcards

1
Q

List the main denture components (3)

A
  1. Saddle - an edentulous area
  2. Denture base - a connector (connects saddles)
  3. Flange - replacement tissue extending to the vestibular sulcus
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2
Q

What is the function of the Kennedy Classification?

A

Describes the number + distribution of saddle (edentulous) areas

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3
Q

Kennedy Class I

A

Bilateral free-end

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4
Q

Kennedy Class II

A

Unilateral free-end

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5
Q

Kennedy Class III

A

Unilateral bounded

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6
Q

Kennedy Class IV

A

Anterior bounded (crossing the midline)

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7
Q

What are options for resisting movements towards the tissue (2)

A
  1. Utility of hard tissue

2. Spread the load over large surface area

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8
Q

Function of

  1. Tooth support
  2. Mucosa support
A
  1. Tooth Support
    - Resists movement
    - Directs load through PDL of adjacent teeth
  2. Mucosa support
    - Needs large surface area = load distributed over a wide area
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9
Q

Craddock Class I

A

Tooth support

- Teeth provide a HARD tissue resistance to occlusal loading

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10
Q

Craddock Class II

A

Mucosa

- A LARGE coverage provides resistance to occlusal loading

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11
Q

Craddock Class III

A

Tooth + Mucosa

- A combination of HARD tissue and LARGE coverage when there are reduced numbers of teeth and large edentulous saddles

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12
Q

Tooth support/ tooth borne denture advantages (5)

A
  1. Transmits load via the PDL membrane
  2. Feels like the natural dentition
  3. Is more comfortable for the patient
  4. Protects the soft tissue from trauma
  5. Is likely to stay in close contact with its supporting structures over a period of time
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13
Q

Mucosal support disadvantage

A

Allows the denture base to move slightly

  • Possible damage to adjacent gingival margins
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14
Q

What teeth are the best for providing support?

A

MOLARS 2.7

- as they have the largest root area they can carry the greatest load

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15
Q

How much load can a healthy tooth carry?

A

A healthy tooth can carry its own load plus 1 and a half similar teeth

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16
Q

How is tooth support provided on the surface of adjacent abutment teeth?

A

Through metal alloy rests

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17
Q

Define rests

A

Provide support for the denture from vertical opposing forces

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18
Q

Why is incorporating rests into acrylic resin a problem?

A

Due to low base strength, placing a metal component potentially weakens the acrylic surrounding it

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19
Q

What are the 3 types of tooth rests?

A
  1. Occlusal
  2. Cingulum
  3. Incisal
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20
Q

Where are incisal rests most commonly used?

A

Lower anterior teeth due to aesthetic issues

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21
Q

Disadvantage of a small occlusal rest

A

If theres a small rest = small focus on load, which could have an adverse effect on tooth and tip it anteriorly

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22
Q

Advantage of a large occlusal rest

A

Recommended as this can direct the force down the long axis

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23
Q

Where are cingulum rests most commonly used?

A

Used mostly on maxillary and mandibular canines, but can be used on maxillary incisors

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24
Q

Advantages of cingulum rests (3)

A
  1. Aesthetically superior to incisal rests
  2. Apply stress at lower level - less rotation forces
  3. Less likely to break
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25
Q

What are the 2 possible materials for the denture

A
  1. Metal framework base (Co Cr)

2. PMMA

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26
Q

Advantage of Metal framework base

A

Rigid and strong

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27
Q

Properties of PMMA

A
  1. Flexible (not rigid) and poor strength

2. Can be used when opposing forces are light e.g. complete denture

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28
Q

State advantages of rests (3)

A
  1. Prevent movement of an RPD towards the mucosa
  2. Assist in distribution of occlusal load
  3. Prevent over-eruption of unopposed teeth
29
Q

What is the exception to the rest placement when it comes to a free-end saddle?

A

A rest is NOT placed immediately adjacent to the saddle

Placed either mesially or distally

30
Q

Rest placement for tooth supported bases?

A

The support should be on the tooth surface nearest to the base

31
Q

Rest placement for tooth and mucosa supported bases?

A

The support should be on the tooth surface which is NOT next to the base

32
Q

Why should occlusal rests NOT be placed in an occlusal centric stop?

A

The denture will be uncomfortable and the rest will interfere with the occlusion

33
Q

Disadvantages of rest seats (3)

A
  1. Loss of occlusal stop when denture is not worn
  2. Destruction of tooth surface
  3. Exposure of dentine
34
Q

What is mucosal support dependent on?

A

As large an area possible of mucosa being covered

35
Q

Why should the base not be placed within 3mm of the gingival margins?

A

As it will place pressure at the gingival margin

36
Q

Function of a wire stop?

A

To ensure the most distal tooth in an every design does not drift posteriorly

37
Q

What is the less harmful denture design called?

A

‘Every’ denture design

Less harmful mucosa borne denture

38
Q

Why are mandibular mucosa supported dentures not recommended?

A

There is insufficient area to provide support

39
Q

How does a hard tissue provide denture support?

A

Resists movement

40
Q

How does large tissue coverage provide denture support?

A

Distributes load over a wide area

41
Q

What Craddock classification is used for a free end saddle?

A

Class III

Tooth + Mucosa borne

42
Q

What Craddock classification is generally used for bounded saddles?

A

Tooth borne

43
Q

When would a mucosa borne denture be used

A

Only if there are insufficient teeth for a tooth borne denture

44
Q

What Craddock classification is generally used for acrylic dentures?

A

Class II

45
Q

What is used to make a denture tooth borne?

A

OCCLUSAL RESTS
So there isn’t loading onto the bone below
Root area provides wide distribution of load

46
Q

How does tooth support transmit load in a denture?

A

Periodontal membrane

47
Q

How does mucosa support transmit load in a denture?

A

Has to cover as large an area as possible- reduction of the occlusal table

48
Q

Why should slight movement of the denture base in mucosa borne dentures be avoided?

A

Possible damage to adjacent gingival margins

49
Q

Give the problem with tooth extraction with reference to tooth support?

A

Periodontal area lost in extraction:

Left with mucous membrane which has 4x less coverage than the periodontal area
NOT AS GOOD FOR SUPPORT

50
Q

What material is used for rests?

A

Metal

51
Q

What material is used for acrylic resin rests?

A

Wrought stainless steel

52
Q

When would a ledge usually be prepared for a rest?

A

In crown replacement

53
Q

When would a ring rest be recommended? (2)

A
  • Single standing teeth

- If the occlusion prevents occlusal rest

54
Q

Why are ring rests usually avoided? (3)

A
  1. The ring is above the survey line but below the occlusal surface
  2. Could impact on occlusal surface
  3. Unaesthetic
55
Q

Where do incisal/ occlusal rests extended from?

A

Denture base framework

56
Q

Disadvantages of incisal rests (3)

A
  1. Poor aesthetics
  2. May interfere with incisal occlusion
  3. Not recommended on wear facets
57
Q

Disadvantages of a cingulum rest

A

If theres no prominent cingulum present tooth prep is required

58
Q

Advantages of a CoCr metal base framework (2)

A
  1. Rigid and strong

2. Single solid piece

59
Q

How is the metal framework base produced?

A

By casting via a ‘lost wax technique’

60
Q

Disadvantages of a PMMA (acrylic resin) denture base? (2)

A
  1. Flexible and poor strength

2. Any load resisted by rests through the denture base place an internal stress on the base material

61
Q

When could PMMA denture bases be used?

A

When opposing forces are light e.g. complete denture

62
Q

Why are rests often placed on the occlusal surface of a tooth?

A

To direct occlusal forces along the long axis of the abutment teeth

63
Q

How is the problem of compressibility of soft tissue with mucosa borne dentures overcome?

A

Base placed within 3mm of the gingival margins as this will place pressure at the tooth and tissue gingival attachment

64
Q

Disadvantages of every partial design (2)

A
  1. Can produce narrow and weak denture base areas

2. Metal inserted into acrylic causes an inherent weakness in the denture base

65
Q

Give the vertical displacement of tooth attachment within its socket (periodontium).

A

0.1mm

66
Q

Give the compression of mucosal covering over alveolar bone (mucoperiosteum).

A

2mm

67
Q

What is the problem with tooth and mucosa dentures?

A

Mucosa compresses more than the tooth within its periodontal attachment

68
Q

How is the load on teeth involved in tooth and mucosa support reduced?

A
  1. RPI

2. Altered cast technique

69
Q

When would bounded saddles not be tooth supported?

A

If the saddles are longer than 3 teeth

Prosthodontics (4 decks)

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