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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
Q

What are the consequences of not ‘blocking out’?

A

The denture will not fit without chairside adjustment - time consuming and difficult to get right.
Most likely will result in an ill-fitting denture.

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25
Q

What materials can be used for blocking out?

A

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
Q

Why do you tripod a cast when surveying?

A

Enables the cast to be set up in future in the correct path of insertion.

27
Q

What are the two different methods of blocking out?

A

The duplicate cast method

Preparing with the master cast

28
Q

Where should the food dam (a.k.a. pin dam) sit?

A

At least 3mm from the gingival margin

29
Q

What is the post dam?

A

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
Q

What is the function of the post dam?

A

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
Q

What is beading?

A

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
Q

What are the problems caused by excess blocking out?

A

Spaces created which are subject to food impaction.

Tissue proliferation.

33
Q

What materials can be used for duplicating the blocked out master cast?

A 
Reversible hydrocolloid (agar gel)
Condensation cured silicone
34
Q

What are the benefits of a closed denture design? (covers gingival margins)

A

More contact
Greater retention
Guide planes

35
Q

What are the disadvantages of a closed denture design?

A

Possible increase irritation to gingival tissues

Patient must have good periodontal health

36
Q

What are the benefits of an open denture design? (no gingival coverage)

A

Greater clearance
Possible reduced irritation to gingival tissue
e.g. Every design

37
Q

What are the disadvantages of an open denture design?

A

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
Q

When would you need a metal backing for the artificial teeth in an RPD?

A

Where the occlusion is limited or a deep overlap is encountered.

39
Q

What should the distance be between the gingival margins and an upper major connector?

A

Ideally 5mm

40
Q

What should the angle of the major connector to the tooth be?

A

90 degrees

41
Q

In the mandibular arch what is the ideal space between the major connector and the gingival margin?

A

3mm as there is less space in the mandible compared to the maxilla

42
Q

What should the thickness of rests be?

A

0.5mm minimum

1mm at junction with minor connector

43
Q

What are the dimensions of the lingual bar connector?

A 
Height 4mm
Thickness 2mm
Oval or half pear shaped
Should sit 1mm above the functioning sulcus
Therefore depth of 8mm is required
44
Q

What are the dimensions of a sublingual bar?

A

Thickness 4mm
Kidney shaped
Thickest cross sectional area sits horizontally

45
Q

What are the dimensions of the pin dam?

A

0.5mm deep to 1mm wide

46
Q

What is the general dimensions of bar connectors? (Maxilla)

A

Width 6mm

Thickness 1.5mm

47
Q

What are the general dimensions of plate/strap connectors?

A

Thickness 0.4mm minimum

48
Q

What are the dimensions of clasps?

A

Length 15mm to engage in 0.25mm undercut

49
Q

What functions do connectors provide?

A

Stability
Indirect Retention
Bracing

50
Q

What properties do you look for in a maxillary connector?

A 
Function - connection, support, retention, indirect retention
Anatomical restraints
Hygiene - open gingival margins
Rigidity
Patient tolerance
51
Q

What are the pros & cons of a palatal plate connector?

A

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
Q

What are the pros and cons of a maxillary ring connector?

A

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
Q

What properties do you look for in mandibular connectors?

A 
Connection
Bracing
Indirect retention
Rigidity
Hygiene
Tolerance
54
Q

What are the pros and cons of a lingual bar connector?

A

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
Q

What are the pros and cons of a sub lingual bar connector?

A

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
Q

What are the pros and cons of a lingual plate connector?

A

Provides bracing and indirect retention
Good rigidity
Good patient tolerance
Poor hygiene - AVOID unless patient has perfect oral hygiene

57
Q

What are the pros and cons of a dental bar connector?

A

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
Q

What are the pros and cons of a labial bar connector?

A

Good hygiene
Used when anterior teeth are lingually inclined preventing any lingual connectors.
? Rigidity
? Tolerance
Doesn’t provide bracing or indirect retention

59
Q

What are the pros and cons of a lingual bar w/ dental bar connector?

A

Good rigidity
Very complex to create
? tolerance
AVOID if there are simpler alternatives

60
Q

What are the key stages in denture design?

A 
Saddles
Support
Retention
Indirect retention
Bracing and reciprocation
Connector
61
Q

What is adhesion?

A

Retentive factor in RPD design.

Adhesion is the bonding of one material to another, usually a substrate to an adhesive.

62
Q

What is an embrasure rest?

A

Rest that sits over two teeth (distal surface of one tooth and mesial surface of other tooth)

63
Q

What are the components of an RPI?

A

Rest - Mesial
Proximal plate - for reciprocation
I Bar Clasp - mesial?

BDS2: Prosthodontics (3 decks)

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