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
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)
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
4
Q
what needs to be considered in relation to saddles
A
- what teeth will be replaced and why
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
6
Q
what needs to be considered in relation to retention
A
- how will denture be retained
7
Q
what needs to be considered in relation to bracing an reciprocation
A
- how will denture resits horizontal movement
8
Q
what needs to be considered in relation to the connector
A
- how will components be joined
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
10
Q
what classification is used for the saddles
A
Kennedy classification
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
12
Q
what is Kennedy classification 1
A
- bilateral free end saddle
13
Q
what is Kennedy classification 2
A
unilateral free end saddle
14
Q
what is Kennedy classification 3
A
unilateral bounded saddle
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
16
Q
what is support
A
- term used to describe the resistance of a denture to occlusally directed loads
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
18
Q
what is support used for
A
resistance to vertical masticatory forces
19
Q
what are the options for support
A
- teeth
- mucosa
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
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
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
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
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
25
what is Craddock classification 3
- tooth and mucosa borne
| - combination of hard tissue and large coverage when there are reduced number of teeth and large edentulous saddles
26
how does tooth support work
- 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
how does mucosal support work
- 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
what are the best teeth for providing support
those with the largest root area depending on the health of the periodontal attachment
29
what is the crown:ratio for different teeth
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
how much load can a healthy tooth take
- 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
how much more support can periodontal membrane take compared to mucosa coverage
periodontal membrane support is more than 4 times mucosa coverage for a lost tooth
32
what must you think about when deciding on tooth able for support
tooth:crown ratio
33
what is tooth support provided by
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
what should a rest do
transfer load through the long axis of the tooth
35
what are the denture components that provide support
- rests
36
what are rests
- 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
what are incisal rests
- placed on incisal edge of incisors
- will more likely be accepted on lower teeth rather than upper
- not aesthetically good
38
what are cingulum rests
- placed on the cingulum, of mainly canines
39
what are occlusal rests
- placed on occlusal surface of posterior teeth
40
what should all rests be in theoretically
- in a rest seat
| - doesn't happen often as people don't want to cut healthy tooth tissue
41
how are occlusal rests used
- 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
how are incisal rests used
- 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
haw are cingulum rests used
- 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
what occurs in metal framework base of cobalt chromium in relation to support
- 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
what occurs in PMMA (acrylic resin) in relation to support
- 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
what are the additional functions of rests
- 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
when do you need to use mucosal support
- 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
where are rests placed for a bounded saddle
- 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
where are rests placed for a free end saddle
- 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
where should the rest be positioned for tooth supported bases
support should be on tooth surface nearest to the base
51
where should the rest be positioned for tooth and mucosa supported bases
- support should be on tooth surface which is not next to the base
52
what should be the position/placement of an occlusal rest
- 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
what is the primary support for mucosal support
- hard palate (upper)
| - sulcus and pear-shaped pads (lower)
54
what is the secondary support for mucosal support
- rugae, incisive papilla, maxillary tuberosity (upper)
| - buccal shelf (lower)
55
what advantage does upper have for mucosal support
- hard palate
| - lower gives no support from lingual aspect as vertical contour would place too much force on floor of mouth
56
what is mucosal support dependant on
- 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
what is the mucosal support used in Craddock classification 2
- 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
what is the mucosal support used in Craddock classification 3
- 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
when are bounded saddle cases not just tooth borne
- if bounded saddle is more than 3 teeth missing then mucosal support also needed
60
why are mandibular supported dentures not recommended
there is insufficient are to provide support unless denture is being used as a training appliance in preparation for complete denture or overdenture
61
what is the 1st choice of support for RPD's
tooth support
| - depending on number and position
