RPD lecture Flashcards
What is an RPD?
A removable appliance which replaces one or more missing teeth but not the entire arch
No 2 RPD’s are the same
What is a mucosa borne RPD?
Made primarily from acrylic Metal components may be included for strength or clasping Relatively cheap Can be easily modified or added to Transitional denture
What is a tooth borne RPD?
Metal framework
CoCr
Teeth attached with acrylic or composite
What is a tooth and mucosa borne RPD?
Metal framework
Acrylic forms the fitting surface and provides support in the saddle area
Where is support gained on tooth borne RPD’s?
From occlusal, cingulum or incisal rests
What are the only tooth borne dentures?
Bounded saddles
What are the properties of a tooth borne denture?
Strong and transmit load well
Complex, expensive, provided where OH is good and stable
What are tooth and mucosa borne RPD’s made from?
CoCr
What is support gained from in tooth and mucosa borne RPD’s
occlusal, incisal or cingulum rests and from the mucosa
What are the properties of tooth and mucosa borne RPD’s
Complex
Expensive
Provided with good OH
What are the requirements of an RPD?
Aesthetics Mastication Comfort Distribute occlusal forces to appropriate structures Retentive Space maintenance OVD maintenance
What are the advantages of an RPD?
Aesthetics
Function - speech and mastication
Tooth movement prevention
maintenance of OVD
What are the disadvantages of an RPD?
Tooth loss is greater with RPD rather than other methods of tooth replacement
Increased plaque accumulation
Caries, gingivitis, periodontal
Tooth movement
Design dependant?
Damage to tooth tissue
Forces on teeth may impact on supporting structures
What needs to be check in the dental history before can provide an RPD
Is the pt suitable
Does the pt want and need an RPD
Is the RPD likely to be destructive
Is there clinical need to make provision for future treatment
When providing an RPD what is the study model used for?
Edentulous areas: size and position
Undercut: for retention (POD, POI and clasping)
Occlusion - may need to mount on an articulator, so need registration rims producing
What needs to be incorporated when designing an RPD?
Saddles - number and extent
Support - tooth or tissue borne, extent of connectors and saddle for mucosa borne. Tooth rests for tooth borne
Retention - Physical muscular and mechanical forces need to be considered, survey the model for undercuts that may be used relative to path of displacement, path of insertion different to path of displacement, design options
Reciprocation for each clasp
Bracing - resistance to lateral movements
Connectors - design criteria and options for connectors
Indirect retention for free end saddles
When designing saddles what needs to be considered?
Which teeth needs to be replaced
Can I reduce occlusal table by using fewer or narrower teeth
What is the support?
What are the different ways of gaining support?
Resistance of vertical forces directed towards the mucosa
Mucosa borne
Tooth borne
Tooth/mucosa borne
How do you gain support in a mucosa borne denture?
Make the footprint of the denture large to spread the load over a large area
The hard palate provides adequate support for mucosa borne dentures to be used
Extend the denture base to the maximum denture bearing area even if only a few teeth being replaced
How can you gain support in a tooth borne denture?
Bounded saddles
Position occlusal rests on 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
What do occlusal, cingulum and incisal rests need?
Rest seats:
Direct load down the long axis of the tooth
Overdenture, prep tooth
Where should the occlusal rests be positioned in a tooth and mucosa borne denture?
Why?
Distant to the saddle areas
- this ensures the load is transmitted down the long axis of the tooth when the denture rotates
- Also ensures that clasps disengage from the undercut under load when the denture moves
Which retentive forces are the same as complete dentures?
Physical and muscular
What are the mechanical forces needed in RPD?
Path of insertion- needs to be different to path of displacement and clasping - need enough undercut to engage
What makes up the model surveyor?
Parallelometer - Holds the tools in one plane
Adjustable table
Analysing rod, pencil lead, chisel, measuring gauges
What does model surveyor show?
The undercut areas relative to the path of displacement
Allows the survey line to be recorded on the study model
Allows assessment of path of insertion
what does model surveying allow you to do?
Block-out undercuts prior to denture construction
How do you create a path of insertion?
Block out relative to path of insertion, adjust the table, tipping it in one direction and block out
Why is planning the position of the clasp arms important?
Engaging in too much undercut may cause trauma to the tooth or cause the cusp to fracture
What are the undercut depths?
CoCr
Au
SS
Cobalt chromium: 0.25mm
Gold: 0.5mm
Stainless steel 0.75mm
What can model surveying also be used for?
Finding areas on the soft tissue that may be used for added retention
To create guide planes on the wax patterns of the crown to co-incide with the path of insertion
Improve the fit of the appliance and aid reciprocation
What is retention?
Resistance to forces away from the mucosa
Why is reciprocation needed?
Clasps put a sideways load on teeth during function, which is bad.
Provision should always be made to oppose this force with a reciprocating component
What is used for reciprocation?
Recipricating plates
How can recipricating arms be more effective?
by using a combination with guide planes
Whatis bracing needed for?
Resistance to lateral movement - cross arch bracing
What are the differences in minor and major connectors?
Major - link saddle areas and create rigidity of denture
Minor - connects small components to the major connector
What do connectors also contribute to?
Support
Bracing
Direct retention
Indirect retention
Where should connectors finish?
3mm from gingival margin or above the survey line, not in between the 2
What are the requirements of connectors?
Comfort strength support retention Hygiene
What are the different mandibular connectors?
Lingual bar Lingual plate Sub-lingual bar Dental bar or continuous clasp Kennedy bar
What does indirect retention apply to?
Free end saddles to aid retention by ensuring the clasps work effectively
How do indirect retainers work?``
Occlusal rests are used to ensure axis of rotation on displacement keeps the clasps moving along the axis of the abutment tooth
Where should the occlusal rest for the indirect retention be?
As far away from fulcrum as possible and perpendicular to the fulcrum line
What is the different preparatory work that can be done?
Rest seats
Guide planes
Creating undercut
Direct and indirect restorations
