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BDS2: Prosthodontics > RPD Design > Flashcards

RPD Design Flashcards

0
Q

How is retention achieved in mucosa borne dentures?

A

Frictional
Musculature
Sometimes Adam’s clasps e.g. Every design

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1
Q

How is retention achieved in removable partial dentures?

A

Mechanical - clasps, guide planes, precision attachments
Muscular forces - shape of the denture, oral musculature
Physical forces - coverage of the mucosa, adhesion, cohesion, atmospheric pressure, closeness of adaptation

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2
Q

What is direct retention?

A

Resistance to vertical displacement

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3
Q

What is indirect retention?

A

Resistance to rotational displacement of the denture

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4
Q

What factors does the efficiency of a clasp depend on?

A

Clasp material
Cross-sectional thickness and shape
Length of the clasp

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5
Q

What are some materials commonly used for clasps?

A 
Cast CoCr
Cast gold alloy
Wrought stainless steel
Cast titanium
Acetyl resin (blends with tooth colour)
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6
Q

What are the two most important properties of materials used for clasps?

A

Modulus of elasticity (rigidity)

Proportional limit

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7
Q

What length must a denture clasp be?

A

Minimum length for a metal clasp is 15mm to engage in a 0.25mm undercut. This is the approximate length of a molar clasp arm.
*The length, thickness and cross-sectional shape of a clasp provide its flexibility.

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8
Q

What is the purpose of reciprocation?

A

To prevent pressure from the clasp acting on the tooth.

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9
Q

Name the two types of clasps.

A

Gingivally approaching

Occlusally approaching

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10
Q

What are the different Craddock’s classifications?

A 
I - tooth borne
II - mucosa borne
III - tooth and mucosa borne
IV - implant
V - implant and mucosa
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11
Q

What are the different Kennedy Classifications?

A

Class I - bilateral free end saddle
Class II - unilateral free end saddle
Class III - bounded saddle
Class IV - anterior bounded saddle crossing the midline

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12
Q

What is the common path of displacement?

A

90 degrees

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13
Q

What can be used as indirect retainers?

A 
Major connectors
Minor connectors
Rest
Saddle
Denture base
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14
Q

What is the stress relieving clasp system (RPI) used for?

A

Mainly mandibular free-end saddles but can be used in the maxillary arch also.

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15
Q

What is support?

A

Resistance of a denture to occlusally directed loads

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16
Q

What two principles should be employed for support?

A

A hard surface - prevents/resists movement

A large surface area - distributes load over wide area

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17
Q

What is a flange?

A

Replacement tissue extending into the vestibular sulcus

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18
Q

What are the benefits of a tooth supported denture?

A

Transmits load via the PD membrane
Allows the supported denture base to feel like the natural dentition
Comfort
Protects the soft tissue from trauma

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19
Q

What is the function of rests?

A

Oppose movement of the base towards the tissue
Direct occlusal load down the long axis of the tooth
Direct retentive elements to work in a planned manner
Prevent overeruption of unopposed teeth
Provide bracing on anterior teeth
Determine the axis of rotation for free-end saddle RPDs
Indirect retention
Reciprocation

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20
Q

What are the different types of rests?

A 
Occlusal
Cingulum
Incisal
Onlay
Overlay
Ledge
Ring
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21
Q

What is the compressibility of

a) tooth
b) mucosa

A

a) 0.1mm

b) 2.0mm

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22
Q

What are the possible consequences of preparing rest seats?

A

Loss of occlusal stop when denture is not worn
Destruction of tooth surface
Exposure of dentine

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23
Q

What is blocking out?

A

The preparation of undercut areas on the master cast to provide the common path of insertion for the partial denture. The areas to be blocked out are all those areas the denture will contact - where there are possible recesses or undercuts in hard or soft tissue.

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24
What are the consequences of not 'blocking out'?
The denture will not fit without chairside adjustment - time consuming and difficult to get right. Most likely will result in an ill-fitting denture.
25
What materials can be used for blocking out?
Plaster (heat cure PMMA) Wax (auto-polymerising PMMA) *Either this cast is used to make the denture or a duplicate is made which will recreate the blocked out cast in dental stone
26
Why do you tripod a cast when surveying?
Enables the cast to be set up in future in the correct path of insertion.
27
What are the two different methods of blocking out?
The duplicate cast method | Preparing with the master cast
28
Where should the food dam (a.k.a. pin dam) sit?
At least 3mm from the gingival margin
29
What is the post dam?
A groove cut into the surface of the cast. Where the maxillary denture ends on the soft palate. Only used for maxillary dentures, where few teeth are present, to provide retention.
30
What is the function of the post dam?
Provides a seal at the periphery of the palatal extension of the denture, enabling intimate contact with the compressible tissue surface that will prevent air from breaking the denture seal. Enables the denture to have a precise finished edge. Enables the denture to be thinned at the edge to blend with the tissues due to the rounded beading. Prevents the ingress of food beneath the denture base.
31
What is beading?
A shallow groove is cut in the surface of the cast at the periphery of the baseplate to provide an intimate contact between the denture and the palate. The beading should stop 3mm from the gingival margins and be 0.5mm deep and 1mm wide.
32
What are the problems caused by excess blocking out?
Spaces created which are subject to food impaction. | Tissue proliferation.
33
What materials can be used for duplicating the blocked out master cast?
``` Reversible hydrocolloid (agar gel) Condensation cured silicone ```
34
What are the benefits of a closed denture design? (covers gingival margins)
More contact Greater retention Guide planes
35
What are the disadvantages of a closed denture design?
Possible increase irritation to gingival tissues | Patient must have good periodontal health
36
What are the benefits of an open denture design? (no gingival coverage)
Greater clearance Possible reduced irritation to gingival tissue e.g. Every design
37
What are the disadvantages of an open denture design?
If there are many rests then there will be many windows that could cause food impaction. The patient may also be more aware of the denture in their mouth due to the large number of edges.
38
When would you need a metal backing for the artificial teeth in an RPD?
Where the occlusion is limited or a deep overlap is encountered.
39
What should the distance be between the gingival margins and an upper major connector?
Ideally 5mm
40
What should the angle of the major connector to the tooth be?
90 degrees
41
In the mandibular arch what is the ideal space between the major connector and the gingival margin?
3mm as there is less space in the mandible compared to the maxilla
42
What should the thickness of rests be?
0.5mm minimum | 1mm at junction with minor connector
43
What are the dimensions of the lingual bar connector?
``` Height 4mm Thickness 2mm Oval or half pear shaped Should sit 1mm above the functioning sulcus Therefore depth of 8mm is required ```
44
What are the dimensions of a sublingual bar?
Thickness 4mm Kidney shaped Thickest cross sectional area sits horizontally
45
What are the dimensions of the pin dam?
0.5mm deep to 1mm wide
46
What is the general dimensions of bar connectors? (Maxilla)
Width 6mm | Thickness 1.5mm
47
What are the general dimensions of plate/strap connectors?
Thickness 0.4mm minimum
48
What are the dimensions of clasps?
Length 15mm to engage in 0.25mm undercut
49
What functions do connectors provide?
Stability Indirect Retention Bracing
50
What properties do you look for in a maxillary connector?
``` Function - connection, support, retention, indirect retention Anatomical restraints Hygiene - open gingival margins Rigidity Patient tolerance ```
51
What are the pros & cons of a palatal plate connector?
Well tolerated by patients - few edges Open at gingival margins Good rigidity Offers good support as it covers a large surface Heavy - can lead to easy displacement Once made, position of post dam cannot be altered Covers the palate
52
What are the pros and cons of a maxillary ring connector?
Used for multiple widely distributed saddles. Covers little of the palate so patient still gets normal sensation. Useful if patient has a large palatal torus. Doesn't provide support, so tooth support must be utilised. Anterior bar can interfere with speech & swallowing. Lots of edges can mean low patient tolerance.
53
What properties do you look for in mandibular connectors?
``` Connection Bracing Indirect retention Rigidity Hygiene Tolerance ```
54
What are the pros and cons of a lingual bar connector?
Default connector Good patient tolerance Good hygiene - doesn't cover gingival margins Doesn't provide bracing or indirect retention Anatomical restraints - lingual frenum, mandibular torus 8mm sulcus depth required
55
What are the pros and cons of a sub lingual bar connector?
Good rigidity Good hygiene - doesn't cover gingival margins Good patient tolerance Smaller lingual sulcus height required Doesn't provide bracing or indirect retention Very technique sensitive - specialised impressions required
56
What are the pros and cons of a lingual plate connector?
Provides bracing and indirect retention Good rigidity Good patient tolerance Poor hygiene - AVOID unless patient has perfect oral hygiene
57
What are the pros and cons of a dental bar connector?
Provides bracing and indirect retention Good hygiene - doesn't cover gingival margins Clinical crowns must be long enough Low patient tolerance ? Rigidity AVOID if patient has anterior spacing as the metal will show through
58
What are the pros and cons of a labial bar connector?
Good hygiene Used when anterior teeth are lingually inclined preventing any lingual connectors. ? Rigidity ? Tolerance Doesn't provide bracing or indirect retention
59
What are the pros and cons of a lingual bar w/ dental bar connector?
Good rigidity Very complex to create ? tolerance AVOID if there are simpler alternatives
60
What are the key stages in denture design?
``` Saddles Support Retention Indirect retention Bracing and reciprocation Connector ```
61
What is adhesion?
Retentive factor in RPD design. | Adhesion is the bonding of one material to another, usually a substrate to an adhesive.
62
What is an embrasure rest?
Rest that sits over two teeth (distal surface of one tooth and mesial surface of other tooth)
63
What are the components of an RPI?
Rest - Mesial Proximal plate - for reciprocation I Bar Clasp - mesial?

BDS2: Prosthodontics (3 decks)

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