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BDS2 - prosthetics > RPD design - support and saddles > Flashcards

RPD design - support and saddles Flashcards

1
Q

what are the components of a denture

A
  • saddle = edentulous area
  • denture base = connector
  • flange = replacement tissue extending from alveolar ridge to vestibular sulcus
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2
Q

what are the different components to the system of design

A
  • saddles (yellow)
  • support (red)
  • retention (green)
  • bracing and reciprocation (blue)
  • connector (black)
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3
Q

what needs to be considered before making a denture

A
  • will a prosthesis be made = is patient dentally fit

- what type of denture is required = fixed or removable

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4
Q

what needs to be considered in relation to saddles

A
  • what teeth will be replaced and why
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5
Q

what needs to be considered in relation to support

A
  • how will the occlusal loading be resisted by the denture

- tooth borne, mucosa borne or both

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6
Q

what needs to be considered in relation to retention

A
  • how will denture be retained
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7
Q

what needs to be considered in relation to bracing an reciprocation

A
  • how will denture resits horizontal movement
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8
Q

what needs to be considered in relation to the connector

A
  • how will components be joined
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9
Q

do you necessarily have the same amount of teeth on the denture as are missing in the mouth

A
  • no, as want to reduce occlusal load so only add the amount of teeth needed for occlusion
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10
Q

what classification is used for the saddles

A

Kennedy classification

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11
Q

what is the Kennedy classification

A
  • anatomical classification describing the number of edentulous areas (saddle) and distribution of them
  • 3rd molars are generally ignores unless they play a direct role in denture design (e.g. needed for occlusion)
  • most posterior saddle is used as classification and any other saddles are modifications (just add them)
  • there are 4 classifications
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12
Q

what is Kennedy classification 1

A
  • bilateral free end saddle
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13
Q

what is Kennedy classification 2

A

unilateral free end saddle

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14
Q

what is Kennedy classification 3

A

unilateral bounded saddle

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15
Q

what is Kennedy classification 4

A 
anterior bounded saddles crossing the midline 
- this can't have any modifications as if there were anymore saddles then these would be more posterior than class 4
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16
Q

what is support

A
  • term used to describe the resistance of a denture to occlusally directed loads
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17
Q

what are the options for resisting movement towards the tissue

A
  • using the hard tissue

- spreading the load over a large surface area

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18
Q

what is support used for

A

resistance to vertical masticatory forces

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19
Q

what are the options for support

A
  • teeth

- mucosa

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20
Q

how can teeth be used for support

A
  • prevents movement, directs load through the PDL of the adjacent tooth
  • forces goes through abutment tooth
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21
Q

how can mucosa be sued for support

A
  • needs large surface area = load distributor over a wide area
  • force goes over saddle areas or hold palate
  • wants to spread load as much as possible to not out too much pressure on the soft tissue
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22
Q

what is the Craddock classification

A

provides simple classification based on support for a removable partial denture
- only gives type of support and tells nothing about number and distribution fo teeth

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23
Q

what is Craddock classification 1

A
  • tooth borne
  • teeth provide hard tissue resistance to occlusal loading
  • goes from occlusal rests onto abutment teeth and through tooth to bone
  • root area provides wide distribution of load
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24
Q

what is Craddock classification 2

A
  • mucosa borne
  • a large coverage provides resistance to occlusal loading
  • through saddle areas and palate together to disperse load
  • not the best
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25
Q

what is Craddock classification 3

A
  • tooth and mucosa borne

- combination of hard tissue and large coverage when there are reduced number of teeth and large edentulous saddles

26
Q

how does tooth support work

A
  • transmits load via the periodontal membrane
  • natural dentition is used
  • allows supported denture base to feel like ‘natural’ dentition
  • more comfortable for patient
  • protects soft tissues from trauma as force goes through PDL
  • likely to stay with supporting structures over period of time
27
Q

how does mucosal support work

A
  • must cover as large an area as possible = may mean denture needs to be bigger
  • allows denture base to move slightly as tissue is compressive = possible damage to adjacent gingival margins
28
Q

what are the best teeth for providing support

A

those with the largest root area depending on the health of the periodontal attachment

29
Q

what is the crown:ratio for different teeth

A

UPPER

  • 1 = 1.3
  • 2 = 1.1
  • 3 = 1.7
  • 4 = 1.4
  • 5 = 1.4
  • 6 = 2.7
  • 7 = 2.7

LOWER

  • 1 = 1.0
  • 2 = 1.0
  • 3 = 1.7
  • 4 = 1.25
  • 5 = 1.25
  • 6 = 2.7
  • 7 = 2.7
30
Q

how much load can a healthy tooth take

A
  • healthy tooth can potentially carry its own load plus some and a half similar teeth
  • molars can carry their own weight and that of a premolar
  • load ability will depend on bone quality
31
Q

how much more support can periodontal membrane take compared to mucosa coverage

A

periodontal membrane support is more than 4 times mucosa coverage for a lost tooth

32
Q

what must you think about when deciding on tooth able for support

A

tooth:crown ratio

33
Q

what is tooth support provided by

A

provided by metal alloys rests on surface of adjacent abutment teeth - metal allow not common in acrylic however (problem due to low base strength, metal could weaken acrylic around it)

34
Q

what should a rest do

A

transfer load through the long axis of the tooth

35
Q

what are the denture components that provide support

A
  • rests
36
Q

what are rests

A
  • components which provide support for the denture from vertical opposing forces
  • they are described by the part of the tooth they contact
  • made out of cast or wrought iron metal
  • best used as part of a cast metal denture framework
  • they oppose movement of the base towards the tissues
37
Q

what are incisal rests

A
  • placed on incisal edge of incisors
  • will more likely be accepted on lower teeth rather than upper
  • not aesthetically good
38
Q

what are cingulum rests

A
  • placed on the cingulum, of mainly canines
39
Q

what are occlusal rests

A
  • placed on occlusal surface of posterior teeth
40
Q

what should all rests be in theoretically

A
  • in a rest seat

- doesn’t happen often as people don’t want to cut healthy tooth tissue

41
Q

how are occlusal rests used

A
  • small rests are not recommended as they apply large forces per unit area = would tip tooth if only on the side
  • want a large rest as this will direct eh force down the long axis of the tooth = want to come as close to the midline as possible
42
Q

how are incisal rests used

A
  • extended from the denture base framework
  • used mostly on lower anterior teeth
  • poor aesthetics
  • may interfere with incisal occlusion
  • not recommended on wear facets
43
Q

haw are cingulum rests used

A
  • extend from the denture base framework
  • unless prominent cingulum available, a preparation is required to provide a vertical stop = not as self cleaning without rest seat, food gets stuck
  • used mainly on canines, but can be used on incisors and laterals
  • aesthetically superior to incisal rests
  • applies stress at a low level = less rotational force, less likely to break
44
Q

what occurs in metal framework base of cobalt chromium in relation to support

A
  • rigid and strong
  • all rests are integral to the base connected to the major connector directly or by minor connectors
  • base produced by casting using a ‘lost wax technique’
45
Q

what occurs in PMMA (acrylic resin) in relation to support

A
  • flexible and poor strength
  • rests incorporated mechanically into the base
  • any load resisted by rests through the denture base place an interstitial stress on base material
  • rests for support within an acrylic base are the exception rather than the rule = can be used when opposing forces are light (complete denture)
46
Q

what are the additional functions of rests

A
  • prevent movement of RPD to mucosa
  • assist in distribution of occlusal load
  • have direct retentive elements to work in a planned manner
  • prevent over-eruption of unopposed teeth
  • provide bracing on anterior teeth
  • determine axis of rotation for free-end saddle
  • indirect retention
47
Q

when do you need to use mucosal support

A
  • if crown to root ratio is higher for missing teeth and available teeth for only rests to be used, then need to use mucosa support along with both
48
Q

where are rests placed for a bounded saddle

A
  • rest placed immediately adjacent to the saddle
  • on mesial side of saddle, rest will be on distal of abutment tooth, on distal side of saddle rest will be on mesial of abutment tooth
  • could sometimes get away with rest on only one side of saddle though
  • default position may have to be changed depending on opposing dentition = other types of posterior rests used
49
Q

where are rests placed for a free end saddle

A
  • rest is NOT placed immediately adjacent to saddle
  • instead on other side of abutment tooth as saddle to prevent torque from load
  • if don’t have space, need to create space
  • could maybe do it on upper next to saddle but not on lower
50
Q

where should the rest be positioned for tooth supported bases

A

support should be on tooth surface nearest to the base

51
Q

where should the rest be positioned for tooth and mucosa supported bases

A
  • support should be on tooth surface which is not next to the base
52
Q

what should be the position/placement of an occlusal rest

A
  • avoid placing rest in an occlusal centric stop = denture will be uncomfortable and affect occlusion
  • rest seats can be prepared but consequences are = loss of occlusal stop when denture not worn, destruction of tooth surface, exposure of dentine
53
Q

what is the primary support for mucosal support

A
  • hard palate (upper)

- sulcus and pear-shaped pads (lower)

54
Q

what is the secondary support for mucosal support

A
  • rugae, incisive papilla, maxillary tuberosity (upper)

- buccal shelf (lower)

55
Q

what advantage does upper have for mucosal support

A
  • hard palate

- lower gives no support from lingual aspect as vertical contour would place too much force on floor of mouth

56
Q

what is mucosal support dependant on

A
  • as large an area as possible being covered
  • risk of causing bone resorption if focused in one area
  • however since soft tissue is compressible it Is advisable to place the base within 3mm of the gingival margins as this will place pressure at gingival margin
57
Q

what is the mucosal support used in Craddock classification 2

A
  • the ‘every’ partial denture design us a mucosa brown denture which restores the dental arch - with contact points between the denture and abutment teeth
  • wire at posterior end prevents distal tooth drifting as this would affect natural dentition
  • gingival margins are to covered by this denture design
  • some design like this can produce narrow and weak denture base areas
  • metal inserted into acrylic causes an inherent weakness in the denture base
58
Q

what is the mucosal support used in Craddock classification 3

A
  • there is a difference in compressibility between preiodontium and mucoperiosteum
  • uniform foundation spreads the load evenly and rest or sink depending on compressibility
  • denture will rock if the surfaces are of unequal compressibility
59
Q

when are bounded saddle cases not just tooth borne

A
  • if bounded saddle is more than 3 teeth missing then mucosal support also needed
60
Q

why are mandibular supported dentures not recommended

A

there is insufficient are to provide support unless denture is being used as a training appliance in preparation for complete denture or overdenture

61
Q

what is the 1st choice of support for RPD’s

A

tooth support

- depending on number and position

BDS2 - prosthetics (10 decks)

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