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Removable Partial Dentures > RPD lab session > Flashcards

RPD lab session Flashcards

1
Q

What is an RPD?

A

A removable appliance which replaces one or more missing teeth but not the entire arch
Distinct from a bridge which is fixed

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2
Q

Mucosa borne RPDs

A 
Made primarily from acrylic
Metal components may be included for strength or clasping
Relatively cheap
Can be easily modified or added to
Transitional denture
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3
Q

Tooth borne RPDs

A

Metal Framework
Made from rigid metal (Cobalt Chromium)
Teeth attached with acrylic or composite
Can only be purely tooth borne for bounded saddles
Strong and transmit load well
Complex, expensive, provided where oral health is good and stable
Can not be modified*

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4
Q

Tooth and mucosa borne

A

Metal Framework (CoCr0
Acrylic forms the fitting surface and provides support in the saddle area
Complex, expensive, provided where OH is good and stable
Most challenging RPDs

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5
Q

Classification by support

A

Craddock and Beckett

  • Mucosa borne RPD: support gained from occlusal, cingulum or incisal rests
  • Tooth borne RPD
  • Tooth/ mucosa borne RPD: support gained from occlusal, incisal or cingulum rests and from the mucosa
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6
Q

Requirements of an RPD

A 
Aesthetics
Mastication
Comfort
Distribute occlusal forces to appropriate structures
Retentive
Space maintenance
OVD maintenance
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7
Q

Advantages/ clinical indications of an RPD

A 
Aesthetics
Function
-speech and mastication (SDA)
Tooth movement prevention
Maintenance of OVD
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8
Q

Disadvantages of RPDs

A

Tooth loss greater when RPD is provided rather than other methods of tooth replacement
> plaque accumulation
Caries, gingivitis, periodontal
Tooth movement*
Design dependent?
Damage to tooth tissue
Forces on teeth may impact on supporting structures

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9
Q

Clinical need vs pt demand

A

Aesthetics
RPDs replacing anterior teeth are more likely to be used
Those replacing posterior teeth only are often discarded

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10
Q

Preparing to provide an RPD

A

Medical history: Can the patient handle a RPD?
Presenting complaint: Aesthetic or functional?
Dental history:
-is the patient suitable for an RPD?
-does pt want and need an RPD?
-is the RPD likely to be destructive?
-is there a clinical need to make provision for future treatment?
Study models:
-edentulous areas: Size and position
-undercut: for retention (POD, POI & Clasping)
-occlusion (may need to mount on an articulator, therefore may need registration rims producing)

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11
Q

Components when designing an RPD

A

Saddles: number and extent
Support
-tooth/ tissue borne
-extent of connectors and saddle for mucosa borne
-occlusal rests for tooth borne
Retention
-physical, muscular, mechanical retentive forces
-surveying model for undercut, may be used relative to path of displacement
-path of insertion different to path of displacement?
-design options for clasps
Reciprocation for each clasp
Bracing: resistance to lateral movements
Connectors: design criteria and options for connectors
Indirect retention: for free end saddles

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12
Q

Classification by pattern of tooth loss

A

Kennedy Class I-IV with modifications

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13
Q

Kennedy Class I

A

Bilateral edentulous areas located posterior to the remaining natural teeth

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14
Q

Kennedy Class II

A

Unilateral edentulous area located posterior to remaining natural teeth

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15
Q

Kennedy Class III

A

A unilateral edentulous area with natural teeth remaining both anterior and posterior to it

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16
Q

Kennedy Class IV

A

A single, but bilateral (crossing the midline), edentulous area located anterior to the remaining natural teeth

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17
Q

Designing saddles

A

Which teeth need to be replaced

Can I reduce the occlusal table by using fewer or narrower teeth

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18
Q

Designing support

A

Resistance to movement towards the mucosa

Mucosa, tooth, or mucosa/ tooth borne

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19
Q

Designing support: mucosa borne

A

Make the footprint of the denture large to spread the load over a wide area
The hard palate generally provides adequate support for mucosa borne dentures to be used
Where possible extend the denture base to the maximum denture bearing area even if only a few teeth are being replaced

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20
Q

Designing support: tooth borne

A

Bounded Saddles
Position occlusal rests both sides of the saddle areas
Keep them as close to the saddle area as possible.
This ensures the load is transmitted from the saddle area to the tooth efficiently
Metal framework is rigid
Occlusal,Cingulum and Incisal rests need rest seats.
Occlusion
Direct loading down the long axis of the tooth
Overdenture - prep tooth

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21
Q

Designing support: tooth and mucosa borne

A

Free-end Saddles
Position the occlusal rest distant to the saddle areas
-this ensures load is transmitted down long axis of tooth when denture rotates
-also ensures clasps disengage from undercut under load when denture moves

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22
Q

Designing retention

A

Physical Forces: same as complete dentures
Muscular Forces: Same as complete dentures
Mechanical Forces:
-path of insertion
-clasping

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23
Q

Designing mechanical retention: path of insertion

-question you must ask

A

Can the path of insertion be altered such that it differs to the path of displacement?

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24
Q

Designing mechanical retention: clasping

-questions you must ask

A

Are the abutment teeth sound?

Is there enough undercut for the clasp to engage?

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25
Q

Designing retention: model surveyor

A 
Parallelometer
Holds tools in one plane
Adjustable table
Selection of tools
-analysing Rod
-pencil lead
-chisel
-measuring gauges
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26
Q

Designing retention: model surveying function

A

Shows the undercut areas relative to the path of displacement
Allows the survey line to be recorded on the study model
Allows assessment for a path of insertion
Allows planning for the position clasp arms
Engaging too much undercut may cause trauma to the tooth or cause the clasp to fracture
Finding areas on the soft tissue that may be used for added retention
To create guide planes
-on wax patterns of crowns to coincide with the path of insertion
-improve fit of the appliance and aid reciprocation

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27
Q

Mechanical Retention: Creating a Path of Insertion

A

Undercut relative to the path of displacement

  • block-out undercuts relative to path of insertion prior to denture construction
  • path of insertion does not = path of displacement
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28
Q

Undercut depth for clasps

A

Cobalt Chromium: 0.25mm
Gold: 0.5mm
Stainless steel: 0.75mm

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29
Q

Designing reciprocation

A

Clasps will always put a sideways load on teeth during function. This is bad.
Provision should always be made to oppose this force with a reciprocating component
Make reciprocating arms effective by using in combination with guide planes

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30
Q

Designing bracing

A

Resistance to lateral movements
Usually provided by other components
e.g. cross arch bracing

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31
Q

Designing connectors

A

Major and minor
Connectors get blended into components such that there is no ‘junction’
Connectors also contribute to: support, bracing, direct retention, indirect retention
Should finish 3mm from gingival margin or above the survey line, not in between the twoNeed to be robust enough to withstand use
Can be challenging to provide lower lingual connectors of adequate cross sectional area

32
Q

Major connectors

A

link saddle areas and create rigidity of denture

33
Q

Minro connectors

A

connect small components to the major connector

34
Q

Requirements of a connector

A 
Comfort
Strength
Support
Retention
Hygiene
35
Q

Maxillary connectors: ring, skeletal or open design

A 
WEIGH UP
Comfort
Simplicity
Strength
Support
Retention
Hygiene
36
Q

Types of mandibular connector

A 
Lingual bar
Lingual plate
Sub-lingual bar
Dental bar or continuous clasp
Kennedy bar
37
Q

Designing indirect retention

A

This applies to free-end saddles to aid retention by ensuring the clasps work effectively
Occlusal rests are used to ensure ‘axis of rotation’ on displacement keeps the clasps moving along the long axis of the abutment tooth

38
Q

Prep work for an RPD

A

Rest Seats
Guide planes
Creating undercut
Direct and indirect restorations

39
Q

Spoon denture

A

Used as a temporary denture
Can have a modified spoon
Acrylic denture to replace one or two anterior teeth, usually the lateral incisor

40
Q

Every dentures

A

Borders 3mm form margins
Open design at saddle/tooth junction
Point contacts between abutment and artificial
Flanges included to provide bracing
Posterior wire ‘stops’ to prevent posterior drift and loss of contact
Lateral stresses reduced by as much balanced occlusion as possible

41
Q

RPI system components

A

Combination of

  • occlusal rest (R)
  • distal guide plane (P)
  • gingivally approaching I-bar (I)
42
Q

How the RPI system works

A

Used for Free end saddle cases
Minor connector and distal plate together act to provide reciproaction to the I-bar.
The I-bar should be on or anterior to the midpoint of the buccal surface

43
Q

Path of insertion

A

Mechanical retention relative to the path of displacement

-consider creating guide planes to restrict the path of insertion, particularly when providing mucosa borne RPDs

44
Q

Recording a path of insertion

A

Mark on the model

  • 3 marks with lead at fixed height
  • scribe side of model
45
Q

Shortened dental arch

A

A reduced dentition may be adequate for many patients
It is more important to maintain the teeth that remain rather than replacing the missing ones
However, in the context of having a functional occlusion it may be less important than the number of teeth that occlude with each other

46
Q

Shortened dental arch definition WHO

A

20 natural teeth throughout adulthood

47
Q

Why consider SDA?

A

RPDs that replace molar teeth may not provide the patient with any immediate masticatory benefit
RPDs often require the patient to learn new skills to effectively use the appliance
A high standard of oral hygiene is required by the patient if further tooth loss is to be avoided.
Patients may find this harder to achieve with an RPD
Approximately 50% of all free-end saddle RPDs are not worn

48
Q

Disadvantages of SDA

A 
Increased risk of anterior tooth wear
RPD provision in future may be more challenging
-fewer teeth
-tongue space
-controlling a larger denture
49
Q

Flexible dentures

A

Valplast

50
Q

CoCr RPD/ onlay

A

Where space for acrylic teeth is limited.

Where increase in OVD

51
Q

Telescopic crowns

A

Primary crown anchored to tooth made from suitable gold alloy
Telescopic crown attached to denture made from the same alloy

52
Q

RPDs: roles and responsibilities of dentist

A 
Assess pt
Treatment plan
Prep work
Tooth prep
Design partial denture
Prescribe RPD
Monitor denture in Changing oral environment
53
Q

RPDs: roles and responsibilities of technician

A

Treatment plan with dentist
Design RPD with dentist
Construct RPD to prescription

54
Q

RPDs: roles and responsibilities of clinical dental technician

A

Assess pt
Tx plan with dentist
Design RPD with dentist
Construct RPD to prescription
Amend detail but not direction of tx plan/ prescription
Monitor denture in changing oral environment

55
Q

Communication between dentist/ technician/ clinical dental technician

A 
Study models
Written description of design
Drawn prescription on paper or models
Photographs
Use recognised terms and of partially dentate and component parts
56
Q

Steps: provision of RPDs at CCDH

A
  1. Study Casts
  2. Clinical Summary Sheet
  3. Provisional Design with DP/DW
  4. Definitive Design with Clinical Tutor
  5. Book job in with Production Lab
57
Q

Study casts: edentulous areas

A

Size and position
Which are going to be saddle areas?
Is there room for teeth?
Is tooth preparation necessary to enlarge the gap?

58
Q

Study casts: undercut assessment

A

For POI & POD
For clasping
For reciprocation

59
Q

Study casts: occlusion

A

Is there room for the occlusal rest?
What will happen in excursion?
Is the ICP and OVD acceptable/ workable?

60
Q

Study casts: questions to ask

A

Edentulous areas
Undercut assessment
Occlusion
Should study casts be mounted on an articulator in order to tx plan?
Do you need registration rims to do this?
Combination work

61
Q

Study casts: combination work

A

Are any direct or indirect restorations being placed as part of the prep work?
Is a diagnostic wax-up required to plan these?

62
Q

Clinical summary sheet

A

Designed to ensure you consider all the factors relevant to the provision of an RPD
Complete prior to requesting a provisional design

63
Q

Definitive design

A

Transfer your approved provisional design to the Lab Card

Get a Clinical Tutors signature

64
Q

Book in with the lab

A

The whole job gets booked in:

Trays, blocks, framework, try-in etc

65
Q

Writing your prescription: draw your design including

A

Extension of saddles and the number and size of teeth
Position of occlusal rests
Clasp types on which teeth and corresponding reciprocation
Type of connectors and their extension
Colour of the acrylic base where important for aesthetics

66
Q

Metal framework RPDs

A

Most commonly cast Co-Cr
Historically Au
Ti alloy is available
SLM production is rapidly developing

67
Q

Fitting an RPD

A

Check the undercut first.

Remember blocking-out undercut on the model is necessary to provide a useable denture

68
Q

When do we work to centric relation?

A

Complete dentures
Vertical dimension
Unstable ICP

69
Q

Primary imps

A

For very simple acrylic dentures replacing 1 or 2 teeth a good primary impression may be all that you require

70
Q

Tooth prep and secondary imps

A

If rest seats are required make sure these are cut to appropriate dimensions
There needs to be enough space for the rest without it affecting the occlusion
Don’t forget to leave enough space for the minor connectors or clasp arms
Ensure that rest seat preparations are picked up well by the secondary impression

71
Q

Framework try-in

A

First check the metal framework fits well on the cast and is fully seated
Transfer to the mouth and ensure that the framework fully seats. Pay particular attention to the rest seats
Check the occlusion:
-if conforming to current ICP make sure the occlusion is not altered
If required, adjust until the framework seats fully and doesn’t interfere with the occlusion

72
Q

Wax reg stage

A

This will be on a wax, shellac or acrylic base for acrylic dentures
This should be on the metal framework for a cobalt-chrome denture
Confirm:
-occlusal relationship
-tooth position
-incisal plane

73
Q

Wax try in stage

A

Ensure the occlusion is identical to the wax registration

If there are discrepancies make any adjustments at this stage

74
Q

Fit stage

A

Check there have been no changes to the occlusion from the wax try-in stage
Make any adjustments as required
Check record

75
Q

Metal backing

A

Very occasionally you may be providing a co/cr denture with metal backings
If so, you will need to do a tooth try-in at this stage to tell the technician where the denture teeth (and therefore the metal backings need to be)
If so, this adds a further visit to the denture construction process

Removable Partial Dentures (5 decks)

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