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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
Periodontal membrane for support is more than x times the mucosal coverage for a lost tooth
4
26
what are rests
rests are the components which provide support for the denture from vertical opposing forces
27
how are rests described
by the part of the tooth they contact e.g. cingulum, incisal, occlusal
28
what material are rests made out of
cast or wrought metal
29
what denture frame work are rests best used in
as part of a cast metal denture framework
30
what movement do rests oppose
the movement of the base towards the tissues
31
how common is it for wrought stainless steel to use used for rests on acrylic dentures
very rare
32
how common is it for rests (whether cast or wrought metal) to be incorporated into acrylic bases
rare
33
why is it a problem to incorporate rests into acrylic resin
gives low base strength | placing a metal component potentially weakens the acrylic surrounding it
34
where are incisal rests usually used
lower arch (aesthetics)
35
where are cingulum rests usually used
canines and upper centrals (not all teeth have significant cingulums)
36
why are small occlusal rests not recommended
they apply large forces per unit area
37
why are big occlusal rests recommended
this can direct force down the long axis (make as close to the midline as possible without adversely affecting occlusal relationship)
38
where do incisal rests originate from
extended from the denture base framework
39
problem with incisal rests?
poor aesthetic appearance, may interfere with incisal occlusion, not reccommended on wear facets
40
where do cingulum rests originate from
extended from denture base framework
41
how would you fit a cingulum rest if a prominent cingulum is not present
a preparation would be required to provide a vertical stop
42
where are cingulum rests usually found
maxillary and mandibular canines
43
which are more aesthetically pleasing, incisal or cingulum rests
cingulum
44
where are cingulum rests usually found
maxillary and mandibular canines, maxillary incisors and laterals
45
why are cingulum rests good
apply stress at lower level- less rotational forces | less likely to breakage, aesthetically good
46
if possible how should you not place a cingulum rest
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
Features of a CoCr metal framework base
- 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
Features of a PMMA (acrylic resin) framework base
- 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
Why have rests?
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
how can you work out if it's possible to go for a completely tooth borne rest
with a formula (to do with crown to root ratio)
51
what is the purpose of a rest
to support the denture against vertical load-that is directed towards the tissue
52
what surface are rests generally placed on and why
occlusal surface since this will direct occlusal forces down the long axis (root) of the abutment teeth
53
what is the default rest position for a bounded saddle
immediately adjacent to the saddle on either side of the saddle (the default position may be changed depending on the opposing dentition)
54
where are rests placed for free end saddles
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
where should the support be for tooth supported bases
on the tooth surface nearest to the base
56
where should the support be for tooth and mucosa supported bases
on the tooth surface which is not next to the base
57
where should rests not be placed on an occlusal surface
in an occlusal centric stop (denture will be unconfortable and the rest will interfere with the occlusion)
58
what are possible consequneces for rest seats
- loss of occlusal stop when denture is not worn - destruuction of tooth surface - exposure of dentine
59
in mucosal support (craddock 2 and 3) where is the primary and secondary support on uppers and lowers
Uppers primary: hard palate secondary palatal side of alveolar ridge Lowers primary: buccal side of mucosa secondary: lingual side of mucosa
60
what is mucosal support dependent on
as large an area as possible of mucosa being covered
61
because soft tissue is compressible where is it inadvisable to place the base
within 3mm of the gingival margins as this will place pressure at the gingival margin
62
What is the Every partial denture design
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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