RPD DESIGN 1: Saddles + Support

Question 1

List the main denture components (3)

Answer 1

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

Question 2

What is the function of the Kennedy Classification?

Answer 2

Describes the number + distribution of saddle (edentulous) areas

Question 3

Kennedy Class I

Answer 3

Bilateral free-end

Question 4

Kennedy Class II

Answer 4

Unilateral free-end

Question 5

Kennedy Class III

Answer 5

Unilateral bounded

Question 6

Kennedy Class IV

Answer 6

Anterior bounded (crossing the midline)

Question 7

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

Answer 7

1. Utility of hard tissue

2. Spread the load over large surface area

Question 8

Function of

1. Tooth support
2. Mucosa support

Answer 8

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

Question 9

Craddock Class I

Answer 9

Tooth support

- Teeth provide a HARD tissue resistance to occlusal loading

Question 10

Craddock Class II

Answer 10

Mucosa

- A LARGE coverage provides resistance to occlusal loading

Question 11

Craddock Class III

Answer 11

Tooth + Mucosa

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

Question 12

Tooth support/ tooth borne denture advantages (5)

Answer 12

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

Question 13

Mucosal support disadvantage

Answer 13

Allows the denture base to move slightly

• Possible damage to adjacent gingival margins

Question 14

What teeth are the best for providing support?

Answer 14

MOLARS 2.7

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

Question 15

How much load can a healthy tooth carry?

Answer 15

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

Question 16

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

Answer 16

Through metal alloy rests

Question 17

Define rests

Answer 17

Provide support for the denture from vertical opposing forces

Question 18

Why is incorporating rests into acrylic resin a problem?

Answer 18

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

Question 19

What are the 3 types of tooth rests?

Answer 19

1. Occlusal
2. Cingulum
3. Incisal

Question 20

Where are incisal rests most commonly used?

Answer 20

Lower anterior teeth due to aesthetic issues

Question 21

Disadvantage of a small occlusal rest

Answer 21

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

Question 22

Advantage of a large occlusal rest

Answer 22

Recommended as this can direct the force down the long axis

Question 23

Where are cingulum rests most commonly used?

Answer 23

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

Question 24

Advantages of cingulum rests (3)

Answer 24

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

Question 25

What are the 2 possible materials for the denture

Answer 25

1. Metal framework base (Co Cr) | 2. PMMA

Question 26

Advantage of Metal framework base

Answer 26

Rigid and strong

Question 27

Properties of PMMA

Answer 27

1. Flexible (not rigid) and poor strength | 2. Can be used when opposing forces are light e.g. complete denture

Question 28

State advantages of rests (3)

Answer 28

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

Question 29

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

Answer 29

A rest is NOT placed immediately adjacent to the saddle | Placed either mesially or distally

Question 30

Rest placement for tooth supported bases?

Answer 30

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

Question 31

Rest placement for tooth and mucosa supported bases?

Answer 31

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

Question 32

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

Answer 32

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

Question 33

Disadvantages of rest seats (3)

Answer 33

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

Question 34

What is mucosal support dependent on?

Answer 34

As large an area possible of mucosa being covered

Question 35

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

Answer 35

As it will place pressure at the gingival margin

Question 36

Function of a wire stop?

Answer 36

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

Question 37

What is the less harmful denture design called?

Answer 37

'Every' denture design | Less harmful mucosa borne denture

Question 38

Why are mandibular mucosa supported dentures not recommended?

Answer 38

There is insufficient area to provide support

Question 39

How does a hard tissue provide denture support?

Answer 39

Resists movement

Question 40

How does large tissue coverage provide denture support?

Answer 40

Distributes load over a wide area

Question 41

What Craddock classification is used for a free end saddle?

Answer 41

Class III | Tooth + Mucosa borne

Question 42

What Craddock classification is generally used for bounded saddles?

Answer 42

Tooth borne

Question 43

When would a mucosa borne denture be used

Answer 43

Only if there are insufficient teeth for a tooth borne denture

Question 44

What Craddock classification is generally used for acrylic dentures?

Answer 44

Class II

Question 45

What is used to make a denture tooth borne?

Answer 45

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

Question 46

How does tooth support transmit load in a denture?

Answer 46

Periodontal membrane

Question 47

How does mucosa support transmit load in a denture?

Answer 47

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

Question 48

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

Answer 48

Possible damage to adjacent gingival margins

Question 49

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

Answer 49

Periodontal area lost in extraction: Left with mucous membrane which has 4x less coverage than the periodontal area NOT AS GOOD FOR SUPPORT

Question 50

What material is used for rests?

Answer 50

Metal

Question 51

What material is used for acrylic resin rests?

Answer 51

Wrought stainless steel

Question 52

When would a ledge usually be prepared for a rest?

Answer 52

In crown replacement

Question 53

When would a ring rest be recommended? (2)

Answer 53

- Single standing teeth | - If the occlusion prevents occlusal rest

Question 54

Why are ring rests usually avoided? (3)

Answer 54

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

Question 55

Where do incisal/ occlusal rests extended from?

Answer 55

Denture base framework

Question 56

Disadvantages of incisal rests (3)

Answer 56

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

Question 57

Disadvantages of a cingulum rest

Answer 57

If theres no prominent cingulum present tooth prep is required

Question 58

Advantages of a CoCr metal base framework (2)

Answer 58

1. Rigid and strong | 2. Single solid piece

Question 59

How is the metal framework base produced?

Answer 59

By casting via a 'lost wax technique'

Question 60

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

Answer 60

1. Flexible and poor strength | 2. Any load resisted by rests through the denture base place an internal stress on the base material

Question 61

When could PMMA denture bases be used?

Answer 61

When opposing forces are light e.g. complete denture

Question 62

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

Answer 62

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

Question 63

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

Answer 63

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

Question 64

Disadvantages of every partial design (2)

Answer 64

1. Can produce narrow and weak denture base areas | 2. Metal inserted into acrylic causes an inherent weakness in the denture base

Question 65

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

Answer 65

0.1mm

Question 66

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

Answer 66

2mm

Question 67

What is the problem with tooth and mucosa dentures?

Answer 67

Mucosa compresses more than the tooth within its periodontal attachment

Question 68

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

Answer 68

1. RPI | 2. Altered cast technique

Question 69

When would bounded saddles not be tooth supported?

Answer 69

If the saddles are longer than 3 teeth