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BDS2 Prosthodontics (removable) > RPD system of design: support > Flashcards

RPD system of design: support Flashcards

1
Q

What are the features of design that we have to consider when thinking about RPDs?

A 
Saddles
Support
Retention
Bracing and reciprocation
Connector
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2
Q

What are the questions we have to ask ourselves when considering denture design

A

Will a prosthesis be made?
What type of prosthesis: fixed or removable?
What teeth will be replaced and why? (saddle)
How will occlusal loading be resisted by the denture? (support)
- tooth
- mucosa
- tooth and mucosa
How will the denture be retained? (retention)
How the denture will resist horizontal movement? (bracing and reciprocation)
How will the components be joined? (connector)

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3
Q

What is the kennedy classification

A

Kennedy classification is an anatomical classification that describes the number and distribution of saddle (edentulous) areas.

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4
Q

are 3rd molars included when considering kennedy classification

A

third molars are generally ignored unless they play a direct part in the denture design AND the most posterior saddle defines the classification

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5
Q

how many kennedy classifications are there

A

4

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6
Q

what is kenedy class 1

A

bilateral free end

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7
Q

what is kennedy class 2

A

unilateral free end

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8
Q

what is kennedy class 3

A

unilateral bounded

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9
Q

what is kennedy class 4

A

anterior bounded (crossing the midline)

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10
Q

How do you incorporate additional saddles to the one which determines the classification

A

Each additional saddle is referred to as a ‘modification’ e.g. if a case had two bounded saddles present it would be classified as a ‘kennedy class 3 modification 1

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11
Q

what kennedy classification cannot be modified and why

A 
class 4
because it's the most posterior saddle which takes the classification name and class 4 is anterior teeth that are missing
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12
Q

which saddle area determines the kennedy classification

A

posterior

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13
Q

what is meant by support

A

a term used to describe the resistance of a denture to occlusally directed load

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14
Q

what are the options for resisting movement towards the tissue?

A

utility of hard tissue - teeth

spread the load over large surface area - mucosa (but need a wide area)

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15
Q

why do you want to spread forces over a wide area

A

to minimise the direct load onto the bone

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16
Q

what is the craddock classification

A

craddock provides a simple classification based on support for a removable partial denture. It only gives the type of support and does not tell anything about the number or distribution of teeth

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17
Q

what is craddock classification 1

A

tooth support only

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18
Q

what is craddock classification 2

A

mucosa support only

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19
Q

what is craddock classification 3

A

tooth and mucosa support

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20
Q

why is it really good to use tooth support if you can

A
  • transmits load via the periodontal membrane
  • allows the supported denture base to feel like the natural dentition
  • is more comfortable for the patient
  • protects the soft tissue from trauma
  • is likely to stay in close contact with its supporting structures over a period of time
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21
Q

why must mucosal cover as large an area as possible?

A

for reduction of the occlusal table

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22
Q

why isn’t it good that the denture base is able to move slightly with mucosal support

A

could result in possible damage to adjacent gingival margins

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23
Q

how much load can a healthy tooth carry

A

a healthy tooth can potentially carry its own load plus one and a half similar teeth

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24
Q

how strong are each of the teeth in order

A

molars, canines, premolars, anteriors

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25
Q

Periodontal membrane for support is more than x times the mucosal coverage for a lost tooth

A

4

26
Q

what are rests

A

rests are the components which provide support for the denture from vertical opposing forces

27
Q

how are rests described

A

by the part of the tooth they contact e.g. cingulum, incisal, occlusal

28
Q

what material are rests made out of

A

cast or wrought metal

29
Q

what denture frame work are rests best used in

A

as part of a cast metal denture framework

30
Q

what movement do rests oppose

A

the movement of the base towards the tissues

31
Q

how common is it for wrought stainless steel to use used for rests on acrylic dentures

A

very rare

32
Q

how common is it for rests (whether cast or wrought metal) to be incorporated into acrylic bases

A

rare

33
Q

why is it a problem to incorporate rests into acrylic resin

A

gives low base strength

placing a metal component potentially weakens the acrylic surrounding it

34
Q

where are incisal rests usually used

A

lower arch (aesthetics)

35
Q

where are cingulum rests usually used

A

canines and upper centrals (not all teeth have significant cingulums)

36
Q

why are small occlusal rests not recommended

A

they apply large forces per unit area

37
Q

why are big occlusal rests recommended

A

this can direct force down the long axis (make as close to the midline as possible without adversely affecting occlusal relationship)

38
Q

where do incisal rests originate from

A

extended from the denture base framework

39
Q

problem with incisal rests?

A

poor aesthetic appearance, may interfere with incisal occlusion, not reccommended on wear facets

40
Q

where do cingulum rests originate from

A

extended from denture base framework

41
Q

how would you fit a cingulum rest if a prominent cingulum is not present

A

a preparation would be required to provide a vertical stop

42
Q

where are cingulum rests usually found

A

maxillary and mandibular canines

43
Q

which are more aesthetically pleasing, incisal or cingulum rests

A

cingulum

44
Q

where are cingulum rests usually found

A

maxillary and mandibular canines, maxillary incisors and laterals

45
Q

why are cingulum rests good

A

apply stress at lower level- less rotational forces

less likely to breakage, aesthetically good

46
Q

if possible how should you not place a cingulum rest

A

so that it protrudes from the tooth, should be in line with the rest of the natural tooth shape, because if not it provides an area for plaque build up and is normally not accepted by patient

47
Q

Features of a CoCr metal framework base

A
  • rigid and strong
  • all rests are integral to the base connected to the major connect directly or by minor connectors
  • the base is produced by casting using ‘lost wax technique’ - more extensive technique
48
Q

Features of a PMMA (acrylic resin) framework base

A
  • flexible and poor strength
  • rest are incorporated mechanically into (within) the base
  • any load resisted by rests through the denture base place an internal stress on the base material
  • rests for support within an acrylic base are the exception rather than the rule
  • although can be used when opposing forces are light e.g. complete denture
49
Q

Why have rests?

A
  1. prevent movement of an RPD towards the mucosa
  2. assist in distribution occlusal load
  3. direct retentive elements to work in a planned manner
  4. prevent over-eruption of unopposed teeth
  5. provide bracing on anterior teeth
  6. determine the axis of rotation for free-end saddle RPDs
  7. reciprocation and indirect retention
50
Q

how can you work out if it’s possible to go for a completely tooth borne rest

A

with a formula (to do with crown to root ratio)

51
Q

what is the purpose of a rest

A

to support the denture against vertical load-that is directed towards the tissue

52
Q

what surface are rests generally placed on and why

A

occlusal surface since this will direct occlusal forces down the long axis (root) of the abutment teeth

53
Q

what is the default rest position for a bounded saddle

A

immediately adjacent to the saddle on either side of the saddle (the default position may be changed depending on the opposing dentition)

54
Q

where are rests placed for free end saddles

A

NOT immediately adjacent to the saddle
- still abutment tooth but the mesial side to try and prevent torquing on the tooth

(caveat: occlusal relationship will need to be checked to ensure suitability for patient)

55
Q

where should the support be for tooth supported bases

A

on the tooth surface nearest to the base

56
Q

where should the support be for tooth and mucosa supported bases

A

on the tooth surface which is not next to the base

57
Q

where should rests not be placed on an occlusal surface

A

in an occlusal centric stop (denture will be unconfortable and the rest will interfere with the occlusion)

58
Q

what are possible consequneces for rest seats

A
  • loss of occlusal stop when denture is not worn
  • destruuction of tooth surface
  • exposure of dentine
59
Q

in mucosal support (craddock 2 and 3) where is the primary and secondary support on uppers and lowers

A

Uppers
primary: hard palate
secondary palatal side of alveolar ridge

Lowers

primary: buccal side of mucosa
secondary: lingual side of mucosa

60
Q

what is mucosal support dependent on

A

as large an area as possible of mucosa being covered

61
Q

because soft tissue is compressible where is it inadvisable to place the base

A

within 3mm of the gingival margins as this will place pressure at the gingival margin

62
Q

What is the Every partial denture design

A

a mucosa borne denture which restores the dental arch; with contact points between the denture and abutment teeth

to ensure the most distal tooth edoes not drift posteriorly a wire stop is incorporated

the gingival margins are not covered by this denture design

some designs such as these can produce narrow and therefore weak denture base areas

metal inserted into acrylic causes an inherent weakness in the denture base

BDS2 Prosthodontics (removable) (9 decks)

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